Compound bacteria leavening agent and application thereof in improving quality of fresh waxy corn food

Abstract

The invention provides a compound bacteria leavening agent and application thereof in improving the quality of fresh waxy corn food, and belongs to the technical field of food processing. The compound bacteria leavening agent consists of lactic acid bacteria, sweet distiller's yeast and saccharomycetes; wherein the lactic acid bacteria are lactococcus lactis and lactobacillus fermentum. The growth conditions of lactobacillus fermentum and lactococcus lactis in the fresh waxy corn paste are superior to those of other groups, further, lactic acid bacteria, sweet distiller's yeast and saccharomycetes are used for constructing a compound bacteria leavening agent, the influence of the compound bacteria leavening agent on the fresh waxy corn paste and the fresh waxy corn pastry is explored, and it is found that the compound bacteria leavening agent is a compound bacteria leavening agent for the fresh waxy corn paste and the fresh waxy corn pastry. The compound bacteria leavening agent not only has favorable influence on physicochemical properties of fresh waxy corn paste, but also can remarkably improve the quality and flavor of fresh waxy corn pastries, and can realize a multi-bacteria synergistic effect, so that the fermentation efficiency, the product quality and the functionality are improved to a certain extent; and a certain theoretical basis is provided for innovative research and development of new products such as fresh waxy corn cakes.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, and in particular to a compound microbial fermentation agent and its application in improving the quality of fresh glutinous corn. Background Technology

[0002] Fresh corn refers to fresh ears of corn harvested during the milk stage. It is divided into three main categories: sweet corn, waxy corn, and sweet waxy corn. It can be used for food or processing and has a unique flavor and nutritional value. It is rich in protein, fat, and other nutrients and has various effects such as anti-oxidation and improving immunity. However, research on the processing and market development of fresh corn is relatively lagging behind, and there are few product categories. Deep processing plays an important role in the entire industrial chain, and deep-processed products of fresh corn need to be further developed.

[0003] Pastries have always been popular with consumers. Making pastries from fresh glutinous corn not only offers a rich texture but also high nutritional value. However, most of these products on the market are either non-fermented or made using a single strain of bacteria. Single-strain fermentation often doesn't ideally improve product quality; for example, Wu Zhenhua's steamed cake made with a single yeast had a low volume, poor sensory evaluation, and mediocre quality. While lactic acid bacteria fermentation can produce large amounts of lactic acid and extracellular polysaccharides, effectively enhancing the volume and nutritional quality of pastries, single-strain fermentation often suffers from poor stability and uncertain fermentation cycles. Therefore, using a compound bacteria synergistic fermentation method can compensate for the shortcomings of single-strain fermentation.

[0004] The aim is to provide a compound microbial fermentation agent that can be used in fresh glutinous corn staple food products. Summary of the Invention

[0005] The purpose of this invention is to provide a compound microbial fermentation agent to improve the fermentation stability of fresh glutinous corn products during the fermentation process and improve product quality.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a compound microbial fermentation agent, which is composed of lactic acid bacteria, sweet wine koji, and yeast; wherein the lactic acid bacteria are Lactococcus lactis and Lactobacillus fermentum.

[0008] Preferably, the compound microbial fermentation agent is composed of lactic acid bacteria, sweet wine koji, and yeast in a mass ratio of 1:1:1 to 3.

[0009] Preferably, the lactococcus lactis is Lactococcus lactis JYLL-60;

[0010] The Lactobacillus fermentum is Lactobacillus fermentum CGMCC1.1880;

[0011] The method for preparing the lactic acid bacteria is as follows: Lactococcus lactis JYLL-60 and Lactobacillus fermentum CGMCC1.1880 are activated and prepared into bacterial suspensions, then mixed at a volume ratio of 0.8-1.2:0.8-1.2, and inoculated into fresh glutinous corn paste at an inoculation amount of 0.8-1.2%. After fermentation at 30-35℃ for 16-20 hours, the bacteria are dried to obtain the final product.

[0012] The concentration of the bacterial suspension is (0.8–1.2) × 10⁻⁶. 9 cfu / mL;

[0013] The number of viable lactic acid bacteria after drying is (2-4) × 10⁻⁶. 9 cfu / g.

[0014] Preferably, the yeast is a highly active dry yeast with a fermentation capacity ≥450mL / h.

[0015] This invention also provides the application of the above-mentioned compound microbial fermentation agent in improving the quality of fresh glutinous corn products.

[0016] Preferably, the amount of the compound microbial fermentation agent added is 0.8-1.2% (w / w), the fermentation temperature is 30-35℃, the relative humidity during fermentation is 70-75%, and the fermentation time is 1-3h.

[0017] Preferably, microwave cooking is used when preparing fresh glutinous corn products, wherein the rated power of the microwave cooking is 1300-1500W and the microwave time is 85-95s.

[0018] This invention uses three types of lactic acid bacteria—Lactobacillus plantarum, Lactobacillus fermentum, and Lactococcus lactis—in single and paired combinations, which are then inoculated into fresh glutinous corn paste. All six groups of lactic acid bacteria showed good growth in the fresh glutinous corn paste, indicating that the nutrient matrix in the paste is rich and suitable for lactic acid bacteria reproduction. The combination of Lactobacillus fermentum + Lactococcus lactis Lf + Ll (volume ratio 1:1) showed the most outstanding performance, exhibiting a synergistic effect. This invention also utilizes a compound fermentation agent constructed from lactic acid bacteria, sweet wine koji, and yeast to explore the effects of compound fermentation on fresh glutinous corn paste and fresh glutinous corn pastries. The results showed that, compared with the unfermented group (Uf), fermentation with a lactic acid bacteria:sweet wine koji:yeast mass ratio of 1:1:1 lowered the pH of the fresh glutinous corn paste, increased α-amylase and protease activities, increased reducing sugar by 199.21%, decreased amylose content by 1.57%, reduced short-range molecular order of starch, stabilized protein secondary structure, significantly increased peak viscosity, and showed minimal changes in thermodynamic characteristics, with decreased G′ and G″ values. The resulting corn cakes not only had a significantly increased specific volume but also exhibited reduced hardness, increased elasticity, and improved taste, achieving a sensory score as high as 86.67. This indicates that the fermenting agent described in this invention not only has a beneficial effect on the physicochemical properties of fresh glutinous corn paste but also significantly improves the quality and flavor of fresh glutinous corn cakes. The synergistic effect of multiple microorganisms enhances fermentation efficiency, product quality, and functionality, providing a theoretical basis for the innovative development of new fresh glutinous corn cake products.

[0019] The present invention also found that microwave heating increases the dietary fiber content and free amino acid content of fresh glutinous corn cake, and microwave heating has little effect on the color of fresh glutinous corn cake. It has lower hardness and chewiness, higher elasticity, and rich volatile flavor substances, resulting in a rich flavor. Attached Figure Description

[0020] Figure 1 The growth curve of lactic acid bacteria in fermented fresh glutinous corn paste;

[0021] Figure 2 The pH (A) and TTA (B) changes of fresh glutinous corn paste containing lactic acid bacteria;

[0022] Figure 3 Changes in α-amylase activity (A) and protease activity (B) of fresh glutinous corn paste containing lactic acid bacteria;

[0023] Figure 4 The changes in reducing sugar content in fresh glutinous corn paste containing lactic acid bacteria;

[0024] Figure 5 The changes in lactic acid (A) and acetic acid (B) content in fresh glutinous corn paste containing lactic acid bacteria;

[0025] Figure 6The effect of compound microbial fermentation on the content of reducing sugar (left) and amylose (right) in fresh glutinous corn paste;

[0026] Figure 7 Fourier transform infrared spectra of fresh glutinous corn paste before and after fermentation with compound bacteria;

[0027] Figure 8 The effect of compound microbial fermentation on the gelatinization characteristics of fresh glutinous corn paste;

[0028] Figure 9 The effect of compound microbial fermentation on the thermodynamic properties of fresh glutinous corn paste;

[0029] Figure 10 Dynamic rheological diagrams G′ (left) and G″ (right) of fresh glutinous corn paste fermented by compound bacteria;

[0030] Figure 11 The dynamic rheological diagram tanδ of fresh glutinous corn paste fermented by compound bacteria;

[0031] Figure 12 Image of fresh glutinous corn cake product;

[0032] Figure 13 Sensory evaluation and comparability of fresh glutinous corn cakes;

[0033] Figure 14 Electron micrographs of fresh glutinous corn cakes processed using different ripening techniques. Detailed Implementation

[0034] In this invention, the yeast is Angel high-activity dry yeast (fermentation power ≥450mL / h, product number 80000055) and the sweet wine starter is Angel sweet wine starter (sweet type, product number 83500003), both purchased from Angel Yeast Co., Ltd.

[0035] Lactococcus lactis JYLL-60 (10 billion / g) and Lactobacillus plantarum JYLP-002 (10 billion / g) were purchased from Shandong Zhongke Jiayi Bioengineering Co., Ltd.

[0036] Lactobacillus fermentum CGMCC1.1880 (10 billion / g) was purchased from the China General Microbiological Culture Collection Center.

[0037] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0038] Example 1: Screening of lactic acid bacteria strains

[0039] Single colonies of *Lactobacillus plantarum* Lp (JYLP-002), *Lactobacillus fermentum* Lf (CGMCC1.1880), and *Lactococcus lactis* Ll (JYLL-60) were picked and inoculated into sterile MRS liquid medium. The culture was then anaerobically cultured at 32℃ for 24 h to activate the bacteria. 1 mL of the culture solution was transferred to 9 mL of sterile physiological saline and serially diluted. The precipitate was collected by centrifugation at 3500 r / min for 5 min, yielding three types of bacterial sludge. After washing twice with sterile distilled water, a bacterial suspension (concentration 1×10⁻⁶) was obtained. 9 (cfu / mL) Fresh glutinous corn was crushed into a paste, with a ratio of 1g fresh glutinous corn to 3ml sterile water. The crushed fresh glutinous corn paste was sterilized at 121℃ for 15min and then cooled to room temperature for 10min. Activated Lactobacillus plantarum (Lp), Lactobacillus fermentum (Lf), and Lactococcus lactis (Ll) were inoculated into the sterilized fresh glutinous corn paste according to the ratio in Table 1, with an inoculation amount of 1%. The paste was incubated at a constant temperature of 32℃ for 18h, and the indicators were measured every 2h.

[0040] Table 1. Proportion of Lactic Acid Bacteria Strains

[0041]

[0042] (1) The total number of lactic acid bacteria in fresh glutinous corn paste was determined according to the method specified in GB 4789.2-2022 "National Food Safety Standard for Microbiological Examination of Food - Determination of Total Colony Count".

[0043] like Figure 1 As shown, the total bacterial count in the six groups of fermented fresh glutinous corn paste increased significantly after 18 hours of fermentation, indicating that the fresh glutinous corn paste was nutrient-rich and suitable for the growth and reproduction of lactic acid bacteria. The six groups of lactic acid bacteria exhibited slow growth rates during the lag phase from 0 to 2 hours, gradually entering the logarithmic growth phase after 2 hours. The Lf, Lp+Lf, and Lf+Ll groups entered the logarithmic growth phase first from 2 to 12 hours. The Lf+Ll group reached a bacterial count of 9.22 lg (CFU / mL) at 12 hours, while the Lp+Ll and Lf+Ll groups reached 9.44 lg (CFU / mL) and 9.46 lg (CFU / mL) respectively at 16 hours. After reaching the stationary phase, the total bacterial count of the six groups showed a slight decreasing trend, possibly due to the continuous consumption of nutrients in the fresh glutinous corn paste during the later stages of fermentation, leading to competition for carbon sources among the bacterial strains, thus affecting the growth of lactic acid bacteria and resulting in a slowdown in growth.

[0044] (2) Determination of pH and titratable acidity (TTA)

[0045] Mix 1g of fresh glutinous corn flour paste with 9mL of distilled water, stir with a magnetic stirrer for 30min, let stand for 10min, and then measure the pH of the suspension using a pH meter. Titrate the suspension with 0.1mol / L NaOH to a final pH of 8.5. TTA is expressed as the volume of NaOH consumed (mL).

[0046] Depend on Figure 2 It was found that all six groups of lactic acid bacteria could acidify fresh glutinous corn paste. After 18 hours of fermentation, the pH of the fresh glutinous corn paste reached 3.19–3.65, and the TTA was between 0.45 and 0.53 mL. Figure 2 A indicates that all six groups of lactic acid bacteria-infused fresh glutinous corn pastes were acidified, with a decrease in pH. The pH of the six groups gradually stabilized within 12–16 hours, with the Lf+Ll group reaching a pH of 3.19 at 16 hours. Figure 2 As shown in B, the titratable total acid content of the six groups of lactic acid bacteria-fed fresh glutinous corn paste all showed an increasing trend. At 2 hours of fermentation, the Ll group and the Lp+Ll group reached 0.2 mL and 0.18 mL, respectively. After 18 hours of fermentation, the Lp group, Lf group, Ll group, Lp+Lf group, Lp+Ll group, and Lf+Ll group reached 0.48 mL, 0.45 mL, 0.52 mL, 0.5 mL, 0.48 mL, and 0.53 mL, respectively. This corresponds to the pH measurement results. The pH and TTA measurements show that the Lf+Ll group had the strongest acid-producing capacity, with a pH value reaching 3.19 and a TTA value of 0.53 mL.

[0047] (3) Determination of α-amylase activity and protease activity

[0048] α-Amylase activity was determined using an α-amylase activity kit according to the instructions; protease activity was determined according to the methods in GB / T23527.1-2023 "Quality Requirements for Enzyme Preparations Part 1: Protease Preparations".

[0049] like Figure 3 As shown in Figure A, with the progress of fermentation, the α-amylase activity of the lactic acid bacteria fresh glutinous corn paste in each group showed a trend of first increasing and then decreasing, eventually increasing compared to the initial state. The α-amylase activity of each group of lactic acid bacteria fresh glutinous corn paste reached its maximum value within 12–14 hours, with the Ll group reaching 1153.49 U / dl, followed by the Lp group at 831.01 U / dl. After 18 hours of fermentation, the group with the largest increase in α-amylase activity compared to the initial state was the Ll group at 626.36 U / dl, while the group with the smallest increase was the Lp group at 210.85 U / dl.

[0050] like Figure 3As shown in Figure B, the protease activity increased and then decreased, reaching its maximum value between 10 and 16 hours. At 12 hours, the Lf+Ll group reached 329.56 U / g, followed by the Lf group at 264.11 U / g, and the smallest group, the Lp+Ll group, at 117.02 U / g. After 18 hours of fermentation, the Lf+Ll group reached 192.85 U / g, followed by the Lp group at 140.29 U / g, and the Lf group at 86.97 U / g. The protease activity of the Ll, Lp+Lf, and Lp+Ll groups of the lactic acid bacteria fresh glutinous corn paste decreased compared to the initial state.

[0051] During fermentation, lactic acid bacteria can produce organic acids such as lactic acid and acetic acid through carbohydrate metabolism, which helps to activate the activity of enzymes such as proteases and amylases, thereby promoting the decomposition of macromolecules.

[0052] (4) Determination of reducing sugar content

[0053] Preparation of the standard curve: Accurately weigh 1.000 g of dried glucose, dissolve it in distilled water, and dilute to 1000 mL to prepare a 1 mg / mL glucose standard solution. Add 0, 0.1, 0.2, 0.3, 0.4, and 0.5 mL of glucose standard solution and 0.5, 0.4, 0.3, 0.2, 0.1, and 0 mL of distilled water to six test tubes, respectively. Add 1.5 mL of DNS reagent (6.5 g / L) to each test tube, mix thoroughly, and heat in a boiling water bath for 5 min. After cooling under running water, add 4 mL of distilled water to each test tube and mix well. Use the test tube with 0 mL of glucose standard solution as a blank control. Measure the absorbance of each tube at 540 nm. Plot the absorbance-glucose concentration curve to obtain the standard curve equation: y = 1.0386x - 0.0075, R0 2 =0.9979.

[0054] Mix 2g of fresh glutinous corn paste with 50mL of distilled water, incubate at 50℃ for 20min, transfer to a 100mL volumetric flask and dilute to volume. Take 0.25mL of the diluted solution, mix with 0.25mL of distilled water, add 1.5mL of DNS reagent (6.5g / L), incubate in a boiling water bath for 5min, immediately cool with running water, add 4mL of distilled water, and measure the absorbance at 540nm.

[0055] Reducing sugars are one of the energy sources required for microbial growth and metabolism; therefore, the reducing sugar content can, to some extent, indicate the degree of fermentation of fresh glutinous corn paste. According to... Figure 4It can be seen that the reducing sugar content of all six groups of lactic acid bacteria fermentation paste showed a decreasing trend during fermentation. The sharp decrease in reducing sugar content from 0 to 2 hours was mainly due to the large number of microorganisms using reducing sugar as a carbon source for growth and reproduction in the early stage, which caused the reducing sugar content to drop rapidly in a short period of time. At 2 hours, the reducing sugar content of the Lf+Ll group decreased to 0.37 mg / g, followed by the Lp+Lf group to 0.50 mg / g. From 2 to 18 hours, the reducing sugar content of each group decreased slowly. At 18 hours of fermentation, the L1 group decreased to 0.22 mg / g, followed by the Lf+Ll group to 0.23 mg / g.

[0056] (5) Determination of organic acids

[0057] Organic acids were determined by HPLC. The HPLC conditions were as follows: column: VP-ODS column (150 mm × 4.6 mm I, d, 5 μm); mobile phase: 20 mmol / L KH2PO4 solution (pH 2.8); flow rate: 0.8 mL / min; column temperature: 30 ℃; injection volume: 20 μL; isocratic elution for 10 min.

[0058] Preparation of standard solutions: Prepare stock solutions of 1 mg / mL each for lactic acid and acetic acid, dilute 10-fold, and filter through a 0.45 μm nylon microfilter. The standard curves of the measured organic acids are shown in Table 2.

[0059] Table 2 Standard Curves for Organic Acids

[0060] organic acids Regression equation Correlation coefficient lactic acid y = 513.97x + 0.4943 <![CDATA[R 2 =1.0000]]> Acetic acid y = 663.88x + 1.2119 <![CDATA[R 2 =0.9999]]>

[0061] During fermentation, microorganisms metabolize sugars and produce organic acids, primarily lactic acid and acetic acid. The increase in lactic acid and acetic acid content during fermentation can lower the pH of the batter, creating an acidic environment that affects the activity of proteases and protein degradation in the fermentation substrate, ultimately impacting the flavor characteristics of the final product. For example... Figure 5 As shown, the lactic acid yield in the fermented fresh glutinous corn paste was higher than that in the lactic acid bacteria fermentation group, and the yields of both lactic acid and acetic acid in each group showed a trend of first increasing and then decreasing. As fermentation progressed, the yields of organic acids varied considerably among the groups. Figure 5 It can be seen from the left that the lactic acid content in fresh glutinous corn paste reaches its maximum value after 10-16 hours of fermentation, and the lactic acid content in the compound group is higher than that in the single-strain group. Among them, the Lf+Ll group reaches as high as 6.40 mg / g at 12 hours. Figure 5 As shown on the right, the maximum acetic acid content of the fresh glutinous corn paste containing lactic acid bacteria in each group reached over 3 mg / g. Since the lactic acid content was significantly higher than the acetic acid content, the acidification ability of the Lf+Ll group was significantly higher than that of the other lactic acid bacteria groups (p<0.05).

[0062] In summary, all groups of lactic acid bacteria grew well in fresh glutinous corn paste, with the compound group showing better performance than the single-strain group. Among them, the Lf+Ll group performed exceptionally well, with a total bacterial count of 9.461g (CFU / mL) after 16h, lactic acid and acetic acid reaching 4.36mg / g and 2.91mg / g respectively after 16h, protease activity reaching 641.58U / dl, and α-amylase activity reaching 195.85U / dl. It also exhibited strong acidification ability, resulting in paste prepared with it having high enzyme activity and high organic acid content.

[0063] Example 2

[0064] Lactococcus lactis JYLL-60 and Lactobacillus fermentum CGMCC1.1880 were activated separately in MRS liquid medium. After centrifugation and discarding the supernatant, the bacterial cells were obtained and washed twice with sterile physiological saline to prepare bacterial suspensions (bacterial concentration of 1×10⁻⁶ for both suspensions). 9 The mixture (cfu / mL) was prepared at a volume ratio of 1:1 and inoculated into fresh glutinous corn paste at a 1% inoculum. Fermentation was carried out at 32℃ for 18 hours, followed by vacuum freeze-drying (-50℃, 10Pa vacuum) for 38 hours to obtain lactic acid bacteria fermentation powder (3×10⁻⁶ cfu / mL). 9 cfu / g).

[0065] Fresh glutinous corn was blended with water (material-to-liquid ratio 3g:1ml). Based on 75g of fresh corn pulp and 25g of low-gluten flour, 10g of egg and 10g of white sugar were added. Eight groups of batter samples were prepared under fermentation conditions of 32℃ and 75% relative humidity. The acid production performance, enzyme activity, reducing sugar, and amylose content of each group of batter samples were measured (the methods for measuring acid production performance, enzyme activity, and reducing sugar are the same as in Example 1). The secondary structure of proteins and the gelatinization characteristics, thermodynamic characteristics, and dynamic rheological characteristics of the batter were analyzed.

[0066] 1. Unfermented group (Uf): Fermentation time 0h, no starter culture added;

[0067] 2. Natural fermentation group (Nf): Natural fermentation for 2 hours, without the addition of starter culture;

[0068] 3. Lactic acid bacteria: yeast mass ratio 1:4 (L-y4): Fermentation for 2 hours, starter culture addition was 1%, lactic acid bacteria: yeast mass ratio was 1:4;

[0069] 4. Lactic acid bacteria: yeast mass ratio 1:8 (L-y8): Fermentation for 2 hours, starter culture addition was 1%, lactic acid bacteria: yeast mass ratio was 1:8;

[0070] 5. Lactic acid bacteria: sweet wine starter mass ratio 1:1 group (L-s1): fermentation for 2 hours, the amount of starter added is 1%, and the mass ratio of lactic acid bacteria: sweet wine starter is 1:1;

[0071] 6. Lactic acid bacteria: sweet wine starter mass ratio 1:3 group (L-s3): fermentation for 2 hours, the amount of starter added is 1%, and the mass ratio of lactic acid bacteria: sweet wine starter is 1:3;

[0072] 7. Lactic acid bacteria: sweet wine starter: yeast mass ratio 1:1:1 group (Ls-y1): fermentation for 2 hours, the amount of starter added is 1%, and the mass ratio of lactic acid bacteria: sweet wine starter: yeast is 1:1:1;

[0073] 8. Lactic acid bacteria: sweet wine starter: yeast mass ratio 1:1:3 group (Ls-y3): fermentation for 2 hours, the amount of starter added is 1%, and the mass ratio of lactic acid bacteria: sweet wine starter: yeast is 1:1:3.

[0074] (1) Determination of acid production performance and enzyme activity

[0075] Table 3. Effects of compound microbial fermentation on the acid production and enzyme activity of fresh glutinous corn paste.

[0076] sample pH TTA / mL α-Amylase activity U / dl Protease activity U / g Uf group <![CDATA[6.97±0.01 a ]]> <![CDATA[0.13±0.01 f ]]> <![CDATA[785.05±18.69 e ]]> <![CDATA[14.32±0 d ]]> Nf group <![CDATA[6.93±0.01 b ]]> <![CDATA[0.15±0.01 f ]]> <![CDATA[769.47±19.45 c ]]> <![CDATA[16.15±2.43 d <!-- 5 -->]]> L-y4 group <![CDATA[5.99±0.01 f ]]> <![CDATA[0.33±0.01 b ]]> <![CDATA[420.56±9.35 f ]]> <![CDATA[35.81±0 b ]]> L-y8 group <![CDATA[5.92±0.018 g ]]> <![CDATA[0.35±0.01 a ]]> <![CDATA[638.63±23.52 d ]]> <![CDATA[40.23±2.36 a ]]> L-s1 group <![CDATA[6.70±0.01 c ]]> <![CDATA[0.18±0.01 c ]]> <![CDATA[1074.77±28.04 a ]]> <![CDATA[34.07±2.41 b ]]> L-s3 group <![CDATA[6.70±0.01 c ]]> <![CDATA[0.18±0.01 c ]]> <![CDATA[987.54±23.52 b ]]> <![CDATA[29.04±2.34 c ]]> Ls-y1 group <![CDATA[6.23±0.01 d ]]> <![CDATA[0.26±0.01 d ]]> <![CDATA[464.17±14.28 c ]]> <![CDATA[39.63±0 a ]]> Ls-y3 group <![CDATA[6.09±0.01 c ]]> <![CDATA[0.28±0.02 c ]]> <![CDATA[638.63±10.79 d ]]> <![CDATA[34.75±2.46 b ]]>

[0077] Note: Different letters in the same column indicate significant differences (p<0.05), and the same applies below.

[0078] As shown in Table 3, compared with the unfermented group Uf, the acid production performance and titratable acidity of the compound bacteria fermented fresh glutinous corn paste, from largest to smallest, are: L-y8 group, L-y4 group, Ls-y3 group, Ls-y1 group, L-s1 group, L-s3 group, and Nf group. The acid production capacity of the compound bacteria fermentation group is significantly higher than that of the Uf group (P<0.05). This is because after the compound bacteria fermentation, substances such as lactic acid and acetic acid are produced, which acidify the fresh glutinous corn paste to different degrees. Compared with the unfermented group (Uf), the α-amylase activity of fresh glutinous corn paste fermented with different compound bacteria showed differences. The α-amylase activity of the Ls fermentation group was significantly increased (P<0.05), while the α-amylase activity of the Ly and Lsy groups was significantly decreased (P<0.05). This is mainly because the mold in the sweet wine starter has strong starch hydrolysis activity, thus leading to a significant increase in α-amylase activity in the Ls fermentation group (P<0.05). The protease activity of the fresh glutinous corn paste fermented with compound bacteria was significantly higher than that of the Uf group (P<0.05). Lactic acid bacteria have a strong acid-producing ability, and the fresh glutinous corn paste fermented with compound bacteria has a certain acidic environment, which promotes or increases protease activation. Protease can promote protein decomposition to produce abundant volatile flavor substances, which has a positive effect on the processed product. The experimental results indicate that compound bacteria can promote the improvement of acid production performance and enzyme activity in the finished fresh glutinous corn paste.

[0079] (2) Determination of reducing sugar content

[0080] Depend on Figure 6As can be seen from the left, compared with the unfermented Uf group, the reducing sugar content in the fresh glutinous corn paste of different fermentation groups increased to varying degrees. Among them, the reducing sugar content in the Ly and Lsy fermentation groups with added yeast was significantly increased (P<0.05). Starch is hydrolyzed into reducing sugars such as glucose under the action of a small amount of organic acids and amylase generated in the fermentation substrate. Due to the addition of yeast, it can fully utilize the added sugars in the raw materials, converting them into fructose and glucose through glycosyltransferases. At this time, the amount of reducing sugar generated is greater than the amount utilized. During the fermentation process, the starch in the Ls fermentation group was decomposed into glucose by the saccharifying bacteria in the yeast starter, and then the glucose was finally converted into alcohol through glycolysis. Therefore, the increase in reducing sugar in the fresh glutinous corn paste of the Ly and Lsy fermentation groups with added yeast was greater than that in the Ls fermentation group without added yeast. The glucose content produced by the Ls-y1 and Ls-y3 groups differed due to the different amounts of each strain added. The reducing sugar content of the Ls-y1 group reached 20.34 mg / g, which was 199.21% higher than that of the unfermented group Uf, significantly higher than the other groups (P<0.05).

[0081] (3) Determination of amylose content

[0082] The content of amylose was determined using a dual-wavelength method. The results are as follows: Figure 6 As shown on the right, compared with the unfermented group Uf, the amylose content in the fermented fresh glutinous corn paste was significantly reduced (P<0.05). This may be due to the action of organic acids or enzymes produced by the strain's metabolism on the amorphous regions of the relatively loose starch structure, leading to the dissolution of amylose. In addition, amylose is degraded into smaller molecules, such as dextrin and monosaccharides, by α-amylase produced by metabolism, thus reducing the amylose content. The degree of amylose reduction varied among the different fermentation groups, possibly due to the different proportions of lactic acid bacteria, sweet wine koji, and yeast. The degree of reduction in amylose content, from largest to smallest, was: L-y8 group, L-y4 group, L-s3 group, L-s1 group, Ls-y3 group, and Ls-y1 group. Among them, the Ls-y1 group showed the smallest reduction, with a reduction rate of 1.57%.

[0083] (4) Determination of short-range ordered structure of starch

[0084] Take 1 mg of sample and mix it with potassium bromide at a ratio of 1:100 to compress it into a tablet. The scanning range is 4000–400 cm⁻¹. -1 32 scans, 4cm resolution -1 Infrared spectral scanning analysis was performed. The infrared spectrum was deconvolved using the infrared software OMNIC 9.0 to improve resolution, with a resolution of 1047 cm⁻¹. -1 1022cm -1Absorbance values ​​were calculated, and their ratios were determined. Fourier transform near-infrared chromatography was used to determine the short-range order of starch molecules in fresh glutinous corn paste before and after fermentation. Results are as follows: Figure 7 And Table 4.

[0085] Table 4. Effects of compound microbial fermentation on the short-range molecular order of starch in fresh glutinous corn paste.

[0086]

[0087] Depend on Figure 7 It can be seen that, compared with the unfermented Uf group, the absorption peak position of starch molecules in the fermented fresh glutinous corn paste did not change significantly, indicating that fermentation by different strains did not alter the position of functional groups. The absorption peak areas of the Ly, Ls, and Lsy fermentation groups showed varying degrees of change, indicating that the absorption intensity changed among the different fermentation groups. (1047cm) -1 With 1022cm -1 The ratio of absorbance at different locations can reflect the short-range order of starch molecules; the lower the ratio, the lower the degree of short-range order in starch crystallinity.

[0088] As shown in Table 4, compared with the Uf group, the absorbance ratio of the Ls fermentation group did not change significantly, while the Nf, Ly, and Lsy fermentation groups all showed a significant decreasing trend (P<0.05). This may be because the addition of yeast consumes a large amount of oxygen, creating more hypoxic or anaerobic environments, which is conducive to the large-scale reproduction of lactic acid bacteria, leading to the production of more amylase. Therefore, the dissociation of starch structure is greater, producing short-chain starch molecules with reduced short-range order.

[0089] (5) Determination of protein secondary structure

[0090] based on Figure 7 The obtained infrared data results were analyzed using PeakFit software at a depth of 1600–1700 cm. -1 Baseline correction was performed on the region, and second-order derivative fitting was performed after convolution. The peak area of ​​each sub-peak was calculated, and the content of each secondary structure was calculated. The calculation method is as follows: Secondary structure content (%) = Area of ​​secondary structure in sub-peak / 1600~1700cm² -1 Total area of ​​the region × 100%.

[0091] Table 5. Relative content of protein secondary structure in fermented fresh corn paste.

[0092]

[0093] α-helices and β-sheets are ordered structures in the secondary structure of proteins, enhancing protein polymerization and forming a more ordered network structure. β-turns and random coils, on the other hand, are considered disordered structures. As shown in Table 5, compared to the unfermented Uf group, the α-helices in the fermented fresh glutinous corn paste from the compound bacteria showed an overall decreasing trend. This may be due to increased endogenous protease activity in the fermented fresh glutinous corn paste, which disrupts the structure and thus reduces the α-helix content. Compared to the unfermented Uf group, the β-sheet content varied among the different fermentation groups, mainly due to changes in gluten proteins, which are primarily related to the acidic environment. The acid production performance of the paste showed that the Ly fermentation group was in a highly acidic environment, followed by the Lsy and Ls fermentation groups. When proteins are in a highly acidic environment, the hydrogen ion concentration increases, leading to the breakage of hydrogen bonds and ionic bonds, thereby altering the protein's original structure. Compared with the Ls-y3 group, the pH of the Ls-y1 group was significantly higher than that of the Ls-y3 group (P<0.05), resulting in a significantly higher β-sheet content in the Ls-y1 group (P<0.05). The β-sheet content of the Ls-y1 group reached 43.63%, indicating that the Ls-y1 group has better aggregation and spatial order, and the fresh glutinous corn paste prepared from it has a more stable and ordered gluten structure.

[0094] (6) Analysis of gelatinization characteristics

[0095] The gelatinization properties of starch are highly correlated with the quality of starchy foods and are a key indicator for evaluating the processing quality of starchy foods. A 3g sample was mixed thoroughly with 25mL of water and measured using an RVA rapid viscosity analyzer. The measurement procedure was as follows: hold at 50℃ for 60s, then heat to 95℃ within 450s and hold for 300s. Finally, cool to 50℃ within 390s and hold for 120s. During the test, the gelatinization temperature, peak viscosity, trough viscosity, final viscosity, disintegration value, and recovery value of the sample were recorded.

[0096] Table 6. Effects of compound microbial fermentation on the gelatinization characteristic parameters of fresh glutinous corn paste.

[0097]

[0098] according to Figure 8As shown in Table 6, there was no significant difference in the gelatinization temperature of fresh glutinous corn paste under different fermentation conditions. Other indicators showed different performances depending on the combination of microorganisms, which may be related to the differences in metabolic intensity produced by different strain combinations. Compared with the unfermented Uf group, all indicators of the fresh glutinous corn paste in the Ly fermentation group decreased. The peak viscosity, trough viscosity, final viscosity, and recovery value of the fresh glutinous corn paste in the Ls fermentation group increased significantly (P<0.05). This may be because the molds in the yeast have strong starch hydrolysis and protease activity, degrading proteins and lipids. The high protein degradation rate gradually exposes starch granules to the surface, promoting water absorption and swelling, thus increasing the peak viscosity. The Lsy fermentation group showed differences in indicators due to different yeast proportions. Among them, the peak viscosity (1511.40 cP), disintegration value (523.44 cP), and recovery value (1017.00 cP) of the Ls-y1 group were significantly higher than those of the unfermented Uf group and the Ls-y3 group (P<0.05). The increase in disintegration value may be due to partially hydrolyzed starch in the paste, which has poor thermal stability and is not resistant to shear after gelatinization. Peak viscosity affects the quality of flour products. Generally, peak viscosity is directly proportional to the quality of flour products; the higher the viscosity, the better the quality. This indicates that the Ls-y1 group has a positive effect on fresh glutinous corn paste and its finished products.

[0099] (7) Thermodynamic property analysis

[0100] Accurately weigh 3.0 ± 0.02 mg of sample and 6 μL of distilled water into an aluminum crucible, mix thoroughly, immediately seal the crucible, and let stand at room temperature for 24 hours. Use an empty crucible as a control. Set the parameters: test temperature range 30–100 °C, with a heating rate of 10 °C / min. Measure the initial gelatinization temperature T0 and peak gelatinization temperature T using a differential scanning calorimeter. p Termination gelatinization temperature T c Enthalpy value ΔH.

[0101] Table 7. Effects of compound microbial fermentation on thermodynamic parameters of fresh glutinous corn paste.

[0102] sample <![CDATA[T0(℃)]]> <![CDATA[T p (℃)]]> <![CDATA[T c (℃)]]> ΔH(J / g) Uf group 61.53±1.54 <![CDATA[68.37±1.64 ab ]]> <![CDATA[83.28±2.11 a ]]> <![CDATA[1.85±0.05 a ]]> Nf group <![CDATA[61.92±1.67 a ]]> <![CDATA[67.57±1.59 ab ]]> <![CDATA[76.48±1.89 bcd ]]> <![CDATA[0.66±0.02 d ]]> L-y4 group <![CDATA[62.18±1.88 a ]]> <![CDATA[66.71±1.43 ab ]]> <![CDATA[73.30±1.99 d ]]> <![CDATA[0.51±0.02 f ]]> L-y8 group <![CDATA[60.39±1.66 a ]]> <![CDATA[65.35±1.74 b ]]> <![CDATA[74.43±2.03 cd ]]> <![CDATA[0.44±0.01 g ]]> L-s1 group <![CDATA[62.44±1.34 a ]]> <![CDATA[68.31±1.68 ab ]]> <![CDATA[77.74±2.42 bc ]]> <![CDATA[0.62±0.02 d ]]> L-s3 group <![CDATA[62.77±1.29 a ]]> <![CDATA[68.54±1.69 a ]]> <![CDATA[77.71±2.16 bc ]]> <![CDATA[0.57±0.02 e ]]> Ls-y1 group <![CDATA[61.90±1.78 a ]]> <![CDATA[67.33±1.49 ab ]]> <![CDATA[78.67±1.77 b ]]> <![CDATA[0.97±0.03 b ]]> Ls-y3 group <![CDATA[60.86±1.85 a ]]> <![CDATA[67.50±1.61 ab ]]> <![CDATA[77.04±1.97 bcd ]]> <![CDATA[0.74±0.03 c ]]>

[0103] Depend on Figure 9 As shown in Table 7, compared with the unfermented group Uf group, the initial gelatinization temperature T0 and peak temperature T of fresh glutinous corn paste fermented by different compound bacteria groups were significantly different. p No significant change, while the termination temperature T cThe gelation enthalpy (ΔH) decreased significantly (P<0.05), indicating that the fermentation by the compound microorganisms had a certain impact on the thermodynamic properties of fresh glutinous corn paste. The fermented fresh glutinous corn paste was less prone to crystallization and had reduced thermal stability. The organic acids and other substances produced during fermentation degraded gluten protein, disrupting the aggregates formed by starch and gluten networks, making starch molecules more easily bound to water, thus reducing starch thermal stability. The significantly decreased gelation enthalpy (ΔH) of the fermented fresh glutinous corn paste (P<0.05) may be due to the fermentation metabolites reducing the density of the starch structure, thus reducing the energy required to open the double helix structure of starch during gelatinization, leading to a decrease in gelation enthalpy. It is generally believed that higher amylose content makes gelatinization more difficult, while amylose has a certain binding force on amylopectin. A decrease in amylose content reduces this binding force, making gelatinization easier and thus lowering ΔH. This corresponds to the above results regarding amylose content determination. The ΔH values ​​of each group, from smallest to largest, are: L-y8, L-y4, L-s3, L-s1, Ls-y3, and Ls-y1. Among them, the Ls-y1 group showed the smallest decrease in gelation enthalpy, with a decrease rate of 47.56%.

[0104] (8) Dynamic rheological property analysis

[0105] A suitable amount of fresh glutinous corn paste was placed on a parallel plate with a diameter of 25 mm for testing. Excess paste around the plate was scraped off. Parameters were set as follows: strain 1% (within the linear viscoelastic region), oscillation frequency within 0.1–10 Hz, and temperature 25℃. The relationship curves between storage modulus (G') and loss modulus (G″) and strain were observed. The loss coefficient tanδ was obtained from the ratio of G' to G″. The storage modulus G' reflects the elastic properties of the fresh glutinous corn paste, while the loss modulus G″ reflects the viscous properties. The ratio of G″ to G' is the loss coefficient tanδ.

[0106] according to Figure 10 It can be seen that both G' (left figure) and G" (right figure) of the fresh glutinous corn paste fermented by compound bacteria increase with increasing frequency, and the G' value is higher than the G" value, indicating that the enhanced fermented glutinous corn paste is a typical weak gel dynamic rheological system. The loss coefficient tanδ of the fresh glutinous corn paste fermented by compound bacteria is less than 1. Figure 11 The results indicate that elasticity is the dominant property of fresh glutinous corn paste. This suggests that the fermentation by the compound microorganisms has a certain impact on the stability and viscoelasticity of the fresh glutinous corn paste. Compared with the unfermented group Uf, the G′ and G″ values ​​of the Ly and Ls fermented groups increased, while the G′ and G″ values ​​of the Lsy fermented group decreased, indicating that the compound microorganisms of lactic acid bacteria, sweet wine koji, and yeast have a certain influence on the hardness and toughness of the dough. Among them, the decrease in G′ and G″ values ​​in the Ls-y1 group was relatively small, and appropriate degradation is beneficial to the plasticity of the dough.

[0107] Example 2: Production and Quality Evaluation of Fresh Glutinous Corn Cakes

[0108] The fermented batter prepared in each group in Example 1 was slowly beaten for 1 minute. 25g of batter was placed in a 5cm×6cm×4.5cm muffin cup, and the air was evenly shaken out. The sample with the air removed was placed in an oven, and the oven temperature was set to 175℃ for 14 minutes to make fresh glutinous corn cake (finished product as shown). Figure 12 (As shown).

[0109] (1) Determination of specific volume of fresh glutinous corn cake

[0110] Specific volume is one of the important indicators for evaluating the quality of fermented flour products, and it is affected by the gas production effect of yeast. The specific volume of fresh glutinous corn cake depends on the amount of gas retained in the dough structure during the cooking process. Generally, the higher the gas holding rate, the greater the specific volume, which reduces the hardness of the cake and increases its softness. The millet displacement method was used, and the experimental results were taken as the average of three measurements. A beaker was filled with millet and the mouth was leveled. The leveled millet was then transferred to another beaker for later use. The fresh glutinous corn cake to be measured was weighed and placed in the same beaker, which was then filled with millet and the mouth was leveled. Finally, the overflowing millet was transferred to a graduated cylinder to measure the volume (mL).

[0111] The calculation formula is as follows:

[0112]

[0113] The volume of the overflowing millet is the volume of the fresh glutinous corn cake, in mL, and the mass is the mass of the fresh glutinous corn cake, in g.

[0114] (2) Sensory evaluation method for fresh glutinous corn cake

[0115] Five male and five female experts, aged 35-55, with extensive experience in sensory evaluation, were invited to develop sensory evaluation standards based on the requirements of GB 7099-2015 "National Food Safety Standard for Pastries and Bread". The aroma, taste, appearance and color, and integrity of the fresh glutinous corn cake were scored according to the standards in Table 8, with a maximum score of 100 points.

[0116] Table 8 Sensory Evaluation Criteria

[0117]

[0118] like Figure 13As shown, the specific volume of fresh glutinous corn cakes fermented in the Ly and Lsy groups was significantly increased (P<0.05). This is partly because the addition of yeast allows for the full utilization of glucose metabolism to produce acetaldehyde, which in turn generates CO2. Additionally, lactic acid bacteria synergistically enhance yeast activity, increasing gas production and resulting in a better appearance of the final product. Sensory evaluation can reflect consumer acceptance of the product to some extent. The sensory scores of the fresh glutinous corn cakes fermented in the Ly and Lsy groups were significantly better than other groups (P<0.05). The specific volume of the fresh glutinous corn cakes fermented in the Ls-y1 group reached 1.27 mL / g. The sensory score was 86.67, with a delicate and soft texture, good chewiness, non-sticky texture, uniform surface color, and a rich aroma. The results indicate that the fresh glutinous corn cakes prepared in the Ls-y1 group had the best quality and appearance.

[0119] (3) Determination of the textural properties of fresh glutinous corn cakes

[0120] Elasticity, hardness, and chewiness are important indicators for evaluating the quality of pastries. Hardness, chewiness, and adhesiveness are negatively correlated with the overall quality of pastry products, while elasticity is positively correlated. Fresh glutinous corn cakes were cut into uniform cubes from their center. The chewiness, hardness, elasticity, and adhesiveness of the samples were measured using the TPA test mode of a TMS-Pro texture analyzer. Specific test conditions were as follows: P36R probe, TPA-50N mode, deformation 30%, 3-second interval between two deformation measurements, and the average of three measurements was taken.

[0121] Table 9 Texture characteristics of fresh glutinous corn cakes

[0122] sample Hardness (N) Elasticity (mm) Adhesiveness (N) Chewing (mj) Uf group <![CDATA[9.73±0.05 a ]]> <![CDATA[5.46±0.22 c ]]> <![CDATA[6.58±0.18 a ]]> <![CDATA[36.29±1.18 a ]]> Nf group <![CDATA[8.13±0.34 b ]]> <![CDATA[4.58±0.17 d ]]> <![CDATA[4.55±0.18 c ]]> <![CDATA[20.77±0.26 c ]]> L-y4 group <![CDATA[3.80±0.18 c ]]> <![CDATA[7.40±0.19 a ]]> <![CDATA[2.64±0.06 d ]]> <![CDATA[19.62±0.81 c ]]> L-y8 group <![CDATA[3.42±0.14 cd ]]> <![CDATA[6.80±0.32 b ]]> <![CDATA[1.73±0.09 e ]]> <![CDATA[11.80±0.49 d ]]> L-s1 group <![CDATA[9.47±0.30 a ]]> <![CDATA[4.09±0.12 c ]]> <![CDATA[5.63±0.23 b ]]> <![CDATA[23.02±0.38 b ]]> L-s3 group <![CDATA[8.37±0.31 b ]]> <![CDATA[4.31±0.07 dc ]]> <![CDATA[4.75±0.24 c ]]> <![CDATA[20.45±0.94 c ]]> Ls-y1 group <![CDATA[2.85±0.13 c ]]> <![CDATA[7.45±0.06 a ]]> <![CDATA[1.56±0.04 c ]]> <![CDATA[11.09±0.54 d ]]> Ls-y3 group <![CDATA[3.01±0.07 dc ]]> <![CDATA[6.83±0.20 a ]]> <![CDATA[1.60±0.07 c ]]> <![CDATA[11.28±0.25 d ]]>

[0123] As shown in Table 9, compared with the unfermented group Uf, the hardness, chewiness, and adhesiveness of the fresh glutinous corn cakes fermented with the compound bacteria all showed a decreasing trend. The elasticity of the Ly and Lsy fermentation groups increased, while the elasticity of the Ls fermentation group decreased. This phenomenon may be due to the lower yeast content in the Ls fermentation group, resulting in less gas production during fermentation and thus lower elasticity in the prepared fresh glutinous corn cakes. From the texture results, the hardness (2.85 N), chewiness (11.09 mj), and adhesiveness (1.56 N) of the fresh glutinous corn cakes prepared by the Ls-y1 group were significantly lower than other groups (P<0.05), while the elasticity (7.45 mm) was significantly higher than other groups (P<0.05). This indicates that a 1:1:1 mass ratio of lactic acid bacteria, sweet wine koji, and yeast in the preparation of fresh glutinous corn batter can form a stable internal network structure, resulting in better taste in the baked fresh glutinous corn cakes, consistent with the sensory evaluation results mentioned above.

[0124] (4) Determination of volatile flavor compounds

[0125] Weigh 1g of the chopped center portion of fresh glutinous corn cake and place it in a 10mL headspace vial. Insert the extraction head (DVB / CAR / PDMS-50 / 30μm) and perform SPME extraction for 30min. Before extraction, age the extraction head at 240℃ for 60min at the GC-MS inlet.

[0126] Gas chromatography conditions: Column: HP-5MS (5% phenyl)methylsiloxane capillary column (30m×0.25mm, ID×0.25μm; Restek; Bellefonte, PA); Carrier gas: High-purity helium (99.999%); Flow rate: 1mL / min; Splitless injection, injection port temperature 250℃, resolution time 5min; Temperature conditions: Initial column oven temperature 40℃, hold for 2min, increase to 50℃ at 2℃ / min, then increase to 110℃ at 5℃ / min, and finally increase to 250℃ at 3℃ / min.

[0127] Mass spectrometry conditions: ionization mode was electron impact ion source, transfer line temperature was 280℃, ion source temperature was 230℃, voltage was 70eV, mass spectrometry scan amplitude was 25~550am, and scan rate was 0.2s / scan.

[0128] Table 10-1 Results of volatile component determination (alkanes) of different fresh glutinous corn cakes

[0129]

[0130] Table 10-2 Results of volatile component determination (aldehydes) of different fresh glutinous corn cakes

[0131]

[0132] Table 10-3 Results of volatile component determination (alcohols) of different fresh glutinous corn cakes

[0133]

[0134] Table 10-4 Results of volatile component determination (ketones and acids) of different fresh glutinous corn cakes

[0135]

[0136]

[0137] Table 10-5 Results of volatile component determination (esters and others) of different fresh glutinous corn cakes

[0138]

[0139]

[0140] As shown in Table 10, a total of 145 components were detected in the 8 groups of samples. Alkanes, aldehydes, alcohols, and acids were detected in all groups of fresh glutinous corn cakes. Small amounts of esters were detected in the control group, L-y4 group, and Ls-y3 group; small amounts of ketones were detected in L-y4 group, L-y8 group, L-s3 group, and Ls-y1 group. After fermentation, alcohols, alkanes, and acids were the main components in L-y4 and L-y8 groups; alkanes, acids, and aldehydes were the main components in L-s1 and L-s3 groups; aldehydes and acids were the main components in Ls-y1 group; and alkanes and acids were the main components in Ls-y3 group. Compared with the control group, the relative content of alcohols increased in all fermentation groups. Alcohols impart a unique rice and fruity aroma to the fresh glutinous corn cakes. Phenylene alcohol is the most important flavor compound in pastry foods; it has a sweet rose fragrance. Except for the Ls fermentation group, phenylethanol was detected in both the Ly and Lsy fermentation groups. This is because the yeast content in the Ls fermentation group was extremely low, resulting in no alcohol production during fermentation and thus fewer alcohol compounds. Regarding aldehydes, nonanal and 3-furfural were detectable in all six fermentation groups. Nonanal has a pleasant citrus and floral aroma, while 3-furfural has a nutty aroma. These contribute to the rich aroma of the fresh glutinous corn cake. Alkane compounds are volatile substances that have little impact on the flavor of the fresh glutinous corn cake. The results show that the alkane content in the Ls-y1 group was significantly lower than in other groups (p<0.05), while the total content of other compounds that contribute to the rich aroma of the fresh glutinous corn cake increased, indicating that the fresh glutinous corn cake prepared with the Ls-y1 group has a richer flavor.

[0141] In summary, when the mass ratio of lactic acid bacteria, sweet wine yeast, and yeast is 1:1:1 for compound fermentation, the physicochemical properties and structure of fresh glutinous corn paste can be altered, and the quality of fresh glutinous corn cakes can be significantly improved.

[0142] Example 3: Effects of different ripening processes on the quality of fresh glutinous corn cakes

[0143] Fresh glutinous corn is blended with water (material-to-liquid ratio 3:1). Using 75g of fresh corn puree and 25g of low-gluten flour as a base, 10g of egg, 10g of sugar, 1g of milk powder, 0.7g of salt, and 1g of compound leavening agent (lactic acid bacteria: sweet wine koji: yeast in a 1:1:1 mass ratio) are added. The mixture is then stirred for 5 minutes. The resulting corn paste is fermented for 2 hours in a proofing box at 32℃ and 75% humidity. The prepared corn paste is then poured into molds for maturation under the following conditions:

[0144] Both No. 1 natural fermentation and No. 2 inoculation fermentation adopt the steaming and cooking process (after the water boils, the mold is put into the pot and steamed for 20 minutes). They are No. 1 natural steaming group and No. 2 inoculation steaming group.

[0145] Both No. 3 natural fermentation and No. 4 inoculated fermentation adopted the baking and ripening process (175℃ for 14 minutes with both top and bottom heat), which are No. 3 natural baking group and No. 4 inoculated baking group.

[0146] Both No. 5 natural fermentation and No. 6 inoculation fermentation adopted microwave ripening process (rated power 1400W, microwave time 90s), which are No. 5 natural microwave group and No. 6 inoculation microwave group;

[0147] The fermentation conditions for natural fermentation were the same as those for group Nf in Example 2, and the fermentation conditions for inoculation fermentation were the same as those for group Ls-y1 in Example 2.

[0148] (1) Reducing sugar content

[0149] Table 11 Effects of different cooking processes on the reducing sugar content of fresh glutinous corn cake (mg / g)

[0150] sample No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 content <![CDATA[2.55±0.02 c ]]> <![CDATA[5.91±0.28 b ]]> <![CDATA[2.54±0.03 c ]]> <![CDATA[6.44±0.32 a ]]> <![CDATA[2.91±0.08 d ]]> <![CDATA[5.25±0.21 c ]]>

[0151] As shown in Table 11, compared with the naturally fermented group, the reducing sugar content of fresh glutinous corn cakes after inoculation increased. This is because the microorganisms in the starter secreted α-amylase and saccharifying enzyme, which decomposed the macromolecular starch in the raw materials into reducing sugars such as glucose. At this time, the enzymatic hydrolysis rate was greater than the microbial consumption rate, thus leading to a significant increase in reducing sugar content.

[0152] (2) Dietary fiber

[0153] The dietary fiber content of fresh glutinous corn cake was determined according to GB / T 5009.88-2023, "National Food Safety Standard - Determination of Dietary Fiber in Food". The determination was repeated three times, and the average value was taken.

[0154] Table 12 Effects of different cooking methods on the dietary fiber content of fresh glutinous corn cake

[0155] sample Total dietary fiber (g / 100g) Soluble dietary fiber g / 100g Insoluble dietary fiber g / 100g No. 1 <![CDATA[2.67±0.11 a ]]> <![CDATA[1.04±0.03 a ]]> <![CDATA[1.63±0.07 a ]]> No. 2 <![CDATA[1.72±0.06 c ]]> <![CDATA[0.45±0.01 d ]]> <![CDATA[1.27±0.05 b ]]> No. 3 <![CDATA[2.17±0.08 b ]]> <![CDATA[1.00±0.04 a ]]> <![CDATA[1.17±0.05 c ]]> No. 4 <![CDATA[1.52±0.04 d ]]> <![CDATA[0.64±0.02 b ]]> <![CDATA[0.88±0.03 c ]]> No. 5 <![CDATA[1.57±0.04 d ]]> <![CDATA[0.55±0.01 c ]]> <![CDATA[1.03±0.03 d ]]> No. 6 <![CDATA[1.63±0.05 cd ]]> <![CDATA[0.52±0.02 c ]]> <![CDATA[1.11±0.04 cd ]]>

[0156] Dietary fiber is an indigestible carbohydrate with three or more monomeric units, and can be divided into soluble and insoluble dietary fiber. Table 12 shows that different cooking methods significantly affect the dietary fiber content of fresh glutinous corn cakes. Compared with the naturally cooked group, the total dietary fiber content of fresh glutinous corn cakes prepared by steaming with inoculum No. 2 and baking with inoculum No. 4 was significantly reduced (p<0.05), decreasing by 35.58% and 29.95% respectively. However, the total dietary fiber content of fresh glutinous corn cakes prepared by inoculum No. 6 was increased compared to the naturally microwaved group (No. 5). This indicates that microwave cooking with inoculum No. 6 can better preserve the dietary fiber content of fresh glutinous corn cakes.

[0157] (3) Free amino acids

[0158] Liquid chromatography was used. 1.0 g of sample was accurately weighed into a 50 mL centrifuge tube, 10 mL of 50% ethanol was added, and the mixture was sonicated for 30 min. The filtrate was evaporated to dryness at 80 °C, reconstituted with distilled water, and brought to a final volume of 1 mL. 200 μL of the sample solution was transferred to a 2 mL centrifuge tube, and 100 μL each of a 1:4 (V:V) triethylamine-acetonitrile solution and a 1:80 (V:V) phenyl isothiocyanate (PITC)-acetonitrile solution were added. The mixture was shaken well and allowed to stand at room temperature for 1 h. 400 μL of n-hexane was added, and the mixture was shaken thoroughly and allowed to stand for 10 min to allow for layering. The lower layer was collected, filtered through a 0.22 μm filter membrane, and then analyzed.

[0159] Chromatographic column: Acclaim™ 120C18 column (4.6 mm × 250 mm, 5 μm); mobile phase: ammonium acetate (A) and acetonitrile (B); flow rate: 1.0 mL / min; column temperature: 40 °C; injection volume: 2 μL; gradient elution: 56 min; wavelength: 254 nm.

[0160] Table 13 Effects of different cooking methods on the free amino acid content of fresh glutinous corn cake

[0161]

[0162] Free amino acids are precursors to flavor compounds and significantly influence the flavor, nutritional value, and sensory quality of the final product. Table 13 shows that the free amino acid content of fresh glutinous corn cakes varied significantly under different cooking methods (p<0.05). Compared to natural fermentation, under the same heat treatment method, the total free amino acid content of fresh glutinous corn cakes prepared with inoculum type 2 (steaming) and type 5 (baking) was significantly reduced (p<0.05), decreasing by 28.32% and 47.61% respectively. The total free amino acid content of fresh glutinous corn cakes prepared with inoculum type 6 increased by 58.49%. Under inoculum conditions, the free amino acid content of fresh glutinous corn cakes, ranked from highest to lowest, was: type 6 (microwave) > type 4 (baking) > type 2 (steaming). This phenomenon is partly due to the fact that steaming with type 2 and baking with type 5 inoculum partially disrupted the three-dimensional structure of endogenous proteases in the fresh glutinous corn cakes, leading to proteolytic inactivation and thus inhibiting the release of free amino acids. On the other hand, the amino acids underwent the Maillard reaction during heating, with lysine and glutamic acid preferentially participating in the reaction, leading to a significant decrease in the content of free amino acids. Alanine is the main sweet amino acid in fresh corn, with a low threshold (60 mg / 100 mL), enhancing the natural sweetness of fresh glutinous corn cakes. Glutamic acid and aspartic acid are the main umami amino acids in fresh corn. The alanine content of microwave-cooked cakes prepared with inoculum No. 6 reached 99.78 μg / g, while the glutamic acid and aspartic acid contents were significantly higher than those in other groups (p<0.05), reaching 77.54 μg / g and 32.40 μg / g, respectively. Therefore, fresh glutinous corn cakes prepared by microwave cooking with inoculum No. 6 have a richer flavor.

[0163] (4) Color difference characteristics

[0164] The CIE color parameters (luminance L) of the surface of fresh glutinous corn cake were determined using a colorimeter. * Red-green value a * And the yellow-blue value b * ) to perform the measurement. L * The value represents the brightness value. In color difference analysis, a reddish tint is represented by 'a'. * It is a positive number, and its color is greenish. * It is a negative number, and its yellowish color is represented by b. * It's a positive number, and the color is bluish. * It is a negative number.

[0165] Table 14. Effects of different cooking methods on color difference of fresh glutinous corn cake.

[0166] sample L* a* b* No. 1 Natural Steaming <![CDATA[62.32±2.74 c ]]> <![CDATA[-0.30±0.01 c ]]> <![CDATA[14.42±0.71 c ]]> No. 2 inoculum cooking <![CDATA[69.81±0.14 a ]]> <![CDATA[-0.81±0.03 d ]]> <![CDATA[20.01±0.59 a ]]> No. 3 Natural Baking <![CDATA[62.68±0.96 c ]]> <![CDATA[-0.31±0.02 c ]]> <![CDATA[13.84±0.57 cd ]]> No. 4 inoculated baking <![CDATA[71.49±0.96 a ]]> <![CDATA[0.41±0.02 a ]]> <![CDATA[19.14±0.25 a ]]> No. 5 Natural Microwave <![CDATA[65.46±0.87 b ]]> <![CDATA[0.40±0.02 a ]]> <![CDATA[12.88±0.60 d ]]> Microwave inoculation of No. 6 bacteria <![CDATA[65.82±0.09 b ]]> <![CDATA[0.31±0.01 b ]]> <![CDATA[16.05±0.48 b ]]>

[0167] As shown in Table 14, compared with the naturally fermented group, the fresh glutinous corn cakes L* and b prepared after inoculation... * The value is significantly improved. Comparing the three baking methods, from L... *In terms of brightness values, from largest to smallest, the order is: baking > steaming > microwaving; from a * In terms of color, fresh glutinous corn cake prepared by steaming or boiling is more greenish, while that prepared by baking or microwaving is more reddish; from b * In terms of color variation, the fresh glutinous corn cakes prepared by steaming, baking, and microwaving showed a yellowish tint, with the order from largest to smallest being steaming > baking > microwaving. From a comprehensive perspective, microwave cooking with inoculum type 6 had the least impact on the color difference of the fresh glutinous corn cakes.

[0168] (5) The moisture content of fresh corn cake was determined by direct drying method according to GB 5009.3-2016 National Food Safety Standard Determination of Moisture in Food. The results are shown in Table 15.

[0169] Table 15 Effects of different cooking processes on the moisture content of fresh glutinous corn cake

[0170]

[0171] Moisture content is a key indicator affecting the quality of fresh glutinous corn cake. Excessive moisture content accelerates mold growth and shortens shelf life. Table 15 shows that the moisture content of the six samples, ranked from lowest to highest, is: No. 3 Natural Baking < No. 5 Natural Microwave < No. 4 Inoculated Baking < No. 1 Natural Steaming < No. 6 Inoculated Microwave < No. 2 Inoculated Steaming. Compared to naturally fermented fresh glutinous corn cake, the moisture content of inoculated fermented fresh glutinous corn cake was significantly higher (p<0.05). This is because the yeast added during fermentation produces CO2 and water through aerobic respiration. Under inoculated fermentation conditions, the moisture content of the three cooking methods, ranked from lowest to highest, is: No. 4 Inoculated Baking < No. 6 Inoculated Microwave < No. 2 Inoculated Steaming. The moisture content of the steamed fresh glutinous corn cake reached 45.10%, significantly higher than the other groups (p<0.05). This is because water vapor penetrates into the fresh glutinous corn cake during steaming, resulting in higher moisture content. The fresh glutinous corn cake cooked in microwave with inoculum No. 6 has a moderate moisture content of 39.95%.

[0172] (6) Specific volume and sensory evaluation (testing methods are the same as in Example 2)

[0173] Table 16 Effects of different cooking methods on the specific volume and sensory score of fresh glutinous corn cake

[0174]

[0175] As shown in Table 16, under the same heat treatment method, the specific volume and sensory score of the fresh glutinous corn cake after inoculation fermentation were significantly higher than those after natural fermentation (p<0.05). The specific volumes of the cakes prepared by inoculation No. 2 (steaming), No. 4 (baking), and No. 6 (microwave cooking) increased by 129.78%, 165.51%, and 224.49%, respectively. This is because the gas produced by the yeast causes the volume of the fresh glutinous corn cake to expand, thus increasing the specific volume. Under the inoculation fermentation conditions, compared with the three cooking methods, the fresh glutinous corn cake prepared by microwave cooking showed the greatest increase in specific volume. This is because the instantaneous high temperature of microwave heating causes starch gelatinization and protein denaturation to occur simultaneously, and the gas expansion rate is fast, thus rapidly increasing the specific volume. The fresh glutinous corn cake prepared by microwave cooking with inoculation No. 6 achieved a sensory score and specific volume as high as 89.50 points and 1.59 mL / g, respectively. It has a rich flavor, delicate texture, and intact appearance.

[0176] (7) Texture characteristics (detection method is the same as in Example 2)

[0177] Table 17 Effects of different cooking processes on the textural characteristics of fresh glutinous corn cake

[0178] sample Hardness / N Elasticity / mm Adhesiveness / N Chewing / mj No. 1 Natural steaming <![CDATA[8.12±0.27 b ]]> <![CDATA[5.36±0.23 d ]]> <![CDATA[4.84±0.12 c ]]> <![CDATA[29.35±1.42 b ]]> No. 2 inoculum steaming <![CDATA[3.61±0.05 c ]]> <![CDATA[7.94±0.09 a ]]> <![CDATA[2.32±0.06 d ]]> <![CDATA[18.39±0.28 d ]]> No. 3 Natural Baking <![CDATA[10.86±0.13 a ]]> <![CDATA[4.88±0.06 c ]]> <![CDATA[7.35±0.17 a ]]> <![CDATA[35.85±0.61 a ]]> No. 4 inoculated baking <![CDATA[3.81±0.16 c ]]> <![CDATA[6.45±0.14 c ]]> <![CDATA[1.99±0.06 c ]]> <![CDATA[13.30±0.5 c ]]> No. 5 Natural Microwave <![CDATA[7.88±0.02 b ]]> <![CDATA[4.18±0.20 f ]]> <![CDATA[5.63±0.23 b ]]> <![CDATA[24.87±0.99 c ]]> Microwave inoculation of No. 6 bacteria <![CDATA[3.31±0.15 d ]]> <![CDATA[6.83±0.31 b ]]> <![CDATA[2.02±0.10 c ]]> <![CDATA[12.80±0.17 c ]]>

[0179] As shown in Table 17, the three cooking methods were compared under the inoculation conditions. The fresh glutinous corn cake cooked by microwave with inoculation No. 6 showed a significant decrease in hardness, chewiness, and adhesiveness (p<0.05), while its elasticity reached 6.83 mm. The textural results indicate that the fresh glutinous corn cake cooked by microwave with inoculation No. 6 has higher quality and taste.

[0180] (8) Microscopic morphological observation

[0181] The center of a fresh glutinous corn cake was sprayed with a layer of gold under vacuum to increase conductivity. The sample was then scanned by electron microscopy at an accelerating voltage of 15kV, and the microstructure of the sample was observed using different magnifications.

[0182] The results are as follows Figure 14 As shown, the morphology of fresh glutinous corn cakes prepared under the six maturation processes differed significantly. Comparing the naturally fermented group and the inoculated fermentation group, groups 2, 4, and 6, which underwent inoculation fermentation, exhibited a certain degree of porosity. The inoculated glutinous corn cakes, due to the introduction of yeast, produced more gas, thus possessing a porous structure. Under inoculation conditions, comparing the three maturation processes, the microwave process resulted in a smooth surface with a complete honeycomb structure. In contrast, the steaming process resulted in a higher moisture content, higher viscosity, and a tendency to collapse. This indicates that the microwave-prepared fresh glutinous corn cake using group 6, with inoculation, had a more fluffy structure and more uniformly distributed pores.

[0183] (10) Determination of volatile flavor compounds

[0184] Table 18 Effects of different cooking processes on volatile flavor compounds in fresh glutinous corn cake

[0185]

[0186] Table 18 shows that a total of 205 volatile components were detected in fresh glutinous corn cakes prepared under different cooking processes. Alkane, alcohol, aldehyde, ester, ketone, and a small amount of acid were detected in all six cooking processes. Alkane contributed little to the flavor of fresh glutinous corn cakes, while alcohol, aldehyde, and ester contributed significantly. The alkyl content of the fresh glutinous corn cake prepared by microwave inoculation No. 6 was significantly lower than that of the other groups (p<0.05), while the total content of alcohol, aldehyde, and ester was significantly higher. Regarding esters, ethyl acetate was detected in all six samples. Ethyl acetate imparts a unique fruity and floral aroma to fresh glutinous corn cakes. Regarding aldehydes, all six samples—hexanal, heptanal, octanal, nonanal, and decanal—were detected. Hexanal has a grassy and apple-like aroma, octanal has a fruity aroma, nonanal has a floral aroma, and decanal has a sweet and floral aroma. These substances all contribute to the rich aroma of the prepared fresh glutinous corn cakes. The experimental results show that the fresh glutinous corn cakes inoculated with strain #6 and microwaved had an even richer aroma.

[0187] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A compound microbial fermentation agent, characterized in that, The compound microbial fermentation agent is composed of lactic acid bacteria, sweet wine koji, and yeast. The lactic acid bacteria are Lactococcus lactis and Lactobacillus fermentum.

2. The compound microbial fermentation agent as described in claim 1, characterized in that, The compound microbial fermentation agent is composed of lactic acid bacteria, sweet wine koji, and yeast in a mass ratio of 1:1:1 to 3.

3. The compound microbial fermentation agent as described in claim 2, characterized in that, The lactococcus lactis is Lactococcus lactis JYLL-60; The Lactobacillus fermentum is Lactobacillus fermentum CGMCC1.1880.

4. The compound microbial fermentation agent as described in claim 3, characterized in that, The method for preparing the lactic acid bacteria is as follows: Lactococcus lactis JYLL-60 and Lactobacillus fermentum CGMCC1.1880 are activated and prepared into bacterial suspensions, then mixed at a volume ratio of 0.8-1.2:0.8-1.2, and inoculated into fresh glutinous corn paste at an inoculation amount of 0.8-1.2%. After fermentation at 30-35℃ for 16-20 hours, the bacteria are dried to obtain the final product. The concentration of the bacterial suspension is (0.8–1.2) × 10⁻⁶. 9 cfu / mL; The number of viable lactic acid bacteria after drying is (2-4) × 10⁻⁶. 9 cfu / g.

5. The compound microbial fermentation agent as described in claim 4, characterized in that, The yeast strain is a highly active dry yeast with a fermentation capacity of ≥450mL / h.

6. The application of the compound microbial fermentation agent according to any one of claims 1 to 5 in improving the quality of fresh glutinous corn food.

7. The application as described in claim 6, characterized in that, The amount of the compound microbial fermentation agent added is 0.8-1.2% (w / w), the fermentation temperature is 30-35℃, the relative humidity during fermentation is 70-75%, and the fermentation time is 1-3h.

8. The application as described in claim 7, characterized in that, Microwave cooking is used when preparing fresh glutinous corn products. The rated power of the microwave cooking is 1300-1500W and the microwave time is 85-95s.

Images