Preparation method of freeze-dried zizania latifolia
By fermenting the white rot fungus on the wild rice bamboo, decomposing lignin, and combining vacuum freeze-drying technology, the problem of long-term storage of the wild rice bamboo is solved, and the quality and flavor are improved.
Patent Information
- Application Number
- CN202510256837.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-05
- Publication Date
- 2025-05-13
AI Technical Summary
Due to its high moisture content and timbering, the water chestnuts are difficult to store for a long time. The existing drying technology has problems such as Maillard reaction, degraded nutritional quality and uneven drying.
The water chestnuts were fermented by chlorophyllium, pinephrine and sub-black tube bacteria, decompose lignin, and then the quality of water chestnuts was maintained by vacuum freeze-drying.
Effectively prevent the lignification of water chestnuts, improve the flavor, reduce the lignin content, and maintain the physical quality and flavor of water chestnuts.
Smart Images
Figure CN119969468A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a preparation method of freeze-dried wild rice stem, belonging to the technical field of food. Background Art
[0002] Zizania latifolia, also known as water bamboo shoots. Zizania latifolia is rich in functional ingredients such as polysaccharides, resistant starch, dietary fiber, vitamins, minerals, flavonoids and phenolic compounds, and exhibits a variety of health benefits such as anti-oxidation, anti-atherosclerosis and relief of alcoholism. Zizania latifolia is a highly seasonal vegetable, which limits its sales time and cannot meet the year-round demand of the consumer market. Despite the vigorous development of vegetable preservation technology, the high moisture content and easy lignification of Zizania latifolia still greatly hinder its long-term storage. Therefore, exploring the long-term storage process of Zizania latifolia has become the key to promoting the industrial development of Zizania latifolia. Among them, the drying process is widely adopted by the food industry because it can extend the shelf life, reduce weight and maintain product quality. Applying it to the long-term storage of Zizania latifolia may solve the problem of long-term storage of Zizania latifolia.
[0003] The development history of drying technology is long. From the early natural drying to the modern multiple efficient drying technologies, it has undergone a long and rich evolution process. Therefore, drying wild rice can be achieved in a variety of ways, including natural air drying, hot air drying and microwave drying. However, the above drying conditions have their own limitations. The high drying temperature of hot air drying can easily cause the Maillard reaction of wild rice; the drying time of natural air drying is long and the nutritional quality is seriously reduced; microwave drying has problems such as uneven drying and difficult to control drying time. Vacuum freeze drying creates a low temperature and vacuum environment for the material, and converts the water in the material directly from solid to gas through sublimation, thereby achieving drying and avoiding the problems existing in the above drying methods. In addition, vacuum freeze drying has the characteristics of protecting the material structure and reducing the loss of nutrients. It is also used in fruit and vegetable products such as Chinese cabbage, wolfberry and mulberry.
[0004] The drying quality of vegetables is an important screening criterion for drying technology. Lignin is one of the components of plant cell walls and has the function of promoting cell connection. Its content is extremely significantly positively correlated with the lignification index of wild rice. The lignification of wild rice is the result of the reverse accumulation of lignin and other substances in the cell wall. The water content of wild rice after harvest is high and the lignin content is also low. With the continuous extension of storage time, the lignin content in wild rice continues to rise. Under normal temperature conditions, within 48 hours after harvesting, wild rice will become "lignified". Therefore, if it cannot be processed in time after harvesting, lignin will accumulate and eventually lead to an increase in the hardness of wild rice tissue, a rough texture, and a poor taste, which seriously affects its edible quality and commercial value. Lignin is a complex organic substance with high thermal stability and resistance to degradation. Some microorganisms, such as some saprophytes, can decompose lignin, thereby delaying the lignification process. However, there is currently no report on how to use microbial treatment to delay the lignification of wild rice. Summary of the invention
[0005] In order to solve at least one of the above problems, the present invention provides a preparation method of freeze-dried Zizania latifolia, which comprises fermenting Zizania latifolia with Phanerochaete chrysosporium, Trametes rigidus and Porioporus nigrosiformis to effectively decompose lignin in Zizania latifolia, and then maintaining the quality of the dried Zizania latifolia through vacuum freeze-drying.
[0006] The first object of the present invention is to provide a method for preparing freeze-dried wild rice stem, comprising the following steps:
[0007] S1. Wash and cut wild rice stem into pieces for later use;
[0008] S2, activating the white rot fungus species to prepare a seed solution;
[0009] S3, adding water to the wild rice stem block in step S1, and then inoculating the seed liquid into the water according to the inoculation content of 10^6~8CFU / mL, and fermenting for 2~5 days;
[0010] S4, after fermentation, removing the fermentation liquid to obtain fermented wild rice stem, pre-freezing the fermented wild rice stem, and then performing vacuum freeze drying to obtain the freeze-dried wild rice stem.
[0011] In one embodiment of the present invention, the white rot fungus is one or more of Phanerochaete chrysosporium, Trametes rigidus and Poriophora nigrosporium.
[0012] In one embodiment of the present invention, the Phanerochaete chrysosporium was purchased from China Industrial Microbiological Culture Collection Center with a serial number of CICC 40299.
[0013] In one embodiment of the present invention, the Trametes rigidus was purchased from the Microbial Strain Query Network with the serial number Bio-85322.
[0014] In one embodiment of the present invention, the sub-melanopore fungus was purchased from the microbial strain query website and is numbered Bio-27528.
[0015] In one embodiment of the present invention, in step S3, the weight ratio of wild rice stem: water is 1:5-15.
[0016] In one embodiment of the present invention, in step S3, the fermentation temperature is 20-30° C., and the stirring speed is 150-250 rpm.
[0017] In one embodiment of the present invention, the pre-freezing temperature is -20 to -15°C.
[0018] In one embodiment of the present invention, the vacuum freeze drying is to reduce the water content of wild rice stem to below 5%.
[0019] The second object of the present invention is to provide a freeze-dried wild rice stem prepared by the preparation method.
[0020] Beneficial Effects
[0021] The invention provides a preparation method of freeze-dried wild rice stem, wherein the wild rice stem is fermented by using Phanerochaete chrysosporium, Trametes rigidus and Porinella sub-melanocephala to effectively decompose the lignin in the wild rice stem, and then the quality of the dried wild rice stem is maintained by vacuum freeze drying. The freeze-dried wild rice stem prepared by the method of the invention can not only prevent the wild rice stem from becoming lignified, but also promote the metabolism of sugars, lipids and proteins into volatile flavor substances, thereby improving the flavor of the wild rice stem. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 The effect of different bacterial strains on the total phenol content of Zizania latifolia;
[0023] Figure 2 The effects of different bacterial species on the microstructure of wild rice stem.
[0024] Figure 3 The effect of different bacterial species on the lignin content of wild rice stem.
[0025] Figure 4 It is the composition of volatile flavor substances;
[0026] Figure 5 The effect of different bacterial strains on the relative content of total volatile flavor substances;
[0027] Figure 6 This is the PCA analysis of volatile flavor compounds in dried wild rice stem;
[0028] Figure 7 PLS-DA analysis of volatile flavor compounds in dried wild rice stem;
[0029] Figure 8 This is the fingerprint analysis of volatile flavor compounds in dried Zizania latifolia. DETAILED DESCRIPTION
[0030] Materials and Methods
[0031] Fresh wild rice stems (purchased from Shanghai Liantang Yelv Wild Rice Co., Ltd., Shanghai, China) were peeled and cleaned, cut into 10 mm × 10 mm × 50 mm cuboids, and randomly divided into 5 groups. The CR group was set as a fresh sample without any treatment. The CK group was not fermented with any strains and was directly freeze-dried in vacuum. The MA group was inoculated with Phanerochaetechrysosporium (CICC 40299) and fermented for 3 days before vacuum freeze-drying, the MB group was inoculated with Trametes rigidus (bio-85322) and fermented for 3 days before vacuum freeze-drying, and the MC group was inoculated with Porifera subglabrata (bio-27528) and fermented for 3 days before vacuum freeze-drying. When fermenting rice stem, the weight of rice stem: sterile water = 1:10, the content of Phanerochaete chrysosporium, Porphyromonas sclerotiorum and Porphyromonas nigra after inoculation is 10^7 CFU / mL, the growth temperature is 25±1℃, the stirring speed is 200rpm, and the shaking fermentation is carried out on a shaking table. Porphyromonas sclerotiorum and Porphyromonas nigra were purchased from the Microbial Strain Query Network. Phanerochaete chrysosporium was purchased from the China Industrial Microbial Strain Collection Management Center. A vacuum freeze dryer ( 8L, Labconco Freeze Dryer Instrument Company, Missouri, US) was used to vacuum freeze-dry the wild rice stems, with the vacuum degree set to 0.005 mPa and the cold trap temperature set to -50°C. The wild rice stems needed to be frozen at -18°C before vacuum freeze-drying. The treatment was terminated when the moisture content of the wild rice stems in each treatment group dropped to 5% (wet basis).
[0032] 1. Determination of moisture content
[0033] Weigh 10 g of the sample and place it in an electric hot air drying oven at 105±2°C for 4 hours. Calculate the wet basis moisture content and dry basis moisture content of wild rice stem using formulas (1) and (2).
[0034]
[0035] In the formula: X is the moisture content on a wet basis, %; Xi is the moisture content on a dry basis at time point i, %; m1 is the initial mass of the sample, g; m2 is the mass of the sample when it is dried to constant weight, g; mi is the mass of the sample when it is dried to time point i, g; m0 is the mass of the sample after it is completely dried, g.
[0036] 2 Color
[0037] The color is measured using a colorimeter, and the color is expressed by L*, a*, and b*. Before the measurement, the colorimeter is calibrated with a standard white plate. In addition, the color difference is expressed by ΔE, and the calculation formula (3) is as follows:
[0038]
[0039] Note: The subscript "0" is the color of the fresh sample of WBS.
[0040] 3. Texture
[0041] The measurement process uses a P / 2E probe with a trigger force of 10g, a deformation of 6mm, and a downward speed of 2mm / s. During the penetration test, the first peak is recorded as the hardness.
[0042] 4 Determination of total phenol content
[0043] Weigh 0.2g of sample and add it to 25mL of methanol solution (80%). Then place in a water bath at 40℃ for 3h, filter and dilute to 50mL with 80% methanol solution. Take 500μL of extract and add 250μL of 50% Folin phenol colorimetric agent, vortex mix for 5min, add 500μL of 5% Na2CO3 solution, shake well, protect from light for 60min, and measure absorbance at 765nm wavelength.
[0044] 5 Microstructure analysis
[0045] Cut the dried wild rice stem into pieces of 0.5×0.5×1cm 3 The cuboid was fixed on the sample stage for metallization. High-resolution images were collected at 200 μm under 15 kV using a scanning electron microscope (TM4000Plus Tabletop Microscope, Hitachi High-Tech (Shanghai) International Trading Co., Ltd., Shanghai, China).
[0046] 6 Determination of lignin
[0047] The lignin content in the sample was measured using a lignin kit (Beijing Box Biotechnology Co., Ltd.). The sample was dried at 80°C to constant weight, crushed, and then passed through a 30-50 mesh sieve. The absorbance was measured at 280 nm according to the instructions of the kit. The lignin content was expressed in mg / g.
[0048] 7 Volatile Organic Compounds
[0049] 3 g of sample was transferred into a headspace vial for HS-GC-IMS ( Dortmund, Germany). The experimental parameters of IMS were set as follows: the sample was incubated at 60 °C for 20 min, the column was FS-SE-54-CB-1 (15 m × 15 m 0.53 mm thickness 1 μm), and the carrier gas (nitrogen with a purity of 99.99%) flow rate was 2 mL / min in the first 2 min, linearly increased to 10 mL / min within 2-10 min, and linearly increased to 100 mL / min within 10-20 min. Finally, IMS data were collected in positive mode and analyzed using VOCal software (v.1.0.7, GAS, Germany). The NIST 23 mass spectral library was used in combination with retention index (RI), IMS database and drift time (Dt) for qualitative analysis of volatile organic compounds. RI was calculated by the retention time of n-ketone C4-C9 (Sinopharm Chemical Reagent Beijing Co., Ltd., China). The content of volatile organic compounds was based on the peak volume of the selected signal.
[0050] 8 Standardized Analysis
[0051] In the experiment, there were 5 parallels in each group, and the results were expressed as mean ± standard deviation. Duncan's variance analysis was performed on the experimental data using one-way analysis of variance in SPSS20 software, and the significance level was set at P < 0.05. Origin2018 software was used to draw bar graphs and line graphs. The PCA and PLS-DA of volatile organic compounds were calculated using the metabolic analysis tool (https: / / www.metaboanalyst.ca / )
[0052] Embodiment 1:
[0053] The method comprises the following steps: activating Phanerochaete chrysosporium to prepare seed liquid; peeling and washing fresh water bamboo shoots, cutting the fresh water bamboo shoots into 10 mm×10 mm×50 mm cuboids, placing the water bamboo shoots in sterile water at a weight ratio of water bamboo shoots: sterile water=1:10, inoculating the seed liquid at a content of 10^7 CFU / mL after inoculation, fermenting the mixture on a shaking table at a temperature of 25±1°C and a rotation speed of 200 rpm for 3 days, filtering out the fermentation liquid after fermentation, freezing the fermented water bamboo shoots at -18°C, and then performing vacuum freeze drying, and the drying is terminated when the moisture content of the water bamboo shoots is reduced to 5% (wet basis).
[0054] Embodiment 2:
[0055] The method comprises the following steps: activating the rigid-haired Trametes fungi to prepare seed liquid; peeling and washing fresh wild rice stems, cutting the fresh stems into rectangular blocks of 10 mm×10 mm×50 mm, placing the stems in sterile water at a weight ratio of 1:10, inoculating the seed liquid at a content of 10^7 CFU / mL after inoculation, and fermenting the mixture on a shaking table at a temperature of 25±1°C and a rotation speed of 200 rpm for 3 days, filtering out the fermentation liquid after fermentation, freezing the fermented stems at -18°C, and then performing vacuum freeze drying, and the drying is terminated when the moisture content of the stems is reduced to 5% (wet basis).
[0056] Embodiment 3:
[0057] The sub-melanopore fungus is activated to prepare seed liquid; fresh wild rice stem is peeled and washed, and then cut into 10 mm×10 mm×50 mm cuboids, and the wild rice stem is placed in sterile water according to a weight ratio of wild rice stem: sterile water=1:10, and then the seed liquid is inoculated according to a content after inoculation of 10^7 CFU / mL, and fermented on a shaking table at a temperature of 25±1°C and a rotation speed of 200 rpm for 3 days, and the fermentation liquid is filtered out after fermentation, and the fermented wild rice stem is placed at -18°C for freezing, and then vacuum freeze-drying is performed, and the process is terminated when the moisture content of the wild rice stem is reduced to 5% (wet basis).
[0058] Comparative Example 1:
[0059] Take fresh wild rice stem, peel and wash it, cut it into 10mm×10mm×50mm cuboids, put the wild rice stem in sterile water according to the weight ratio of wild rice stem: sterile water=1:10, place it on a shaking table at a temperature of 25±1°C and a rotation speed of 200rpm for 3 days, then filter to remove the sterile water, freeze it at -18°C, and then perform vacuum freeze drying until the moisture content of the wild rice stem drops to 5% (wet basis).
[0060] Result test example:
[0061] (1) Effects of different bacterial strains on the texture and color of freeze-dried wild rice stem
[0062] The magnitude of the rupture force reflects the quality of the dried product to a certain extent. The rupture force of the wild rice in the MA and MC groups was significantly lower than that in the other treatment groups (P<0.05), and the lowest rupture force occurred in the MA group. This may be because the decomposition of cellulose and lignin by microorganisms reduced the toughness of the dried wild rice and reduced the difficulty of puncture. The rupture force of the wild rice in the CK group was significantly lower than that in the CR group, which may be caused by the abundant cavities left after the water sublimated.
[0063] The larger the color difference value, the greater the difference from the fresh sample. The change in the surface color of the wild rice in the CK group was mainly caused by the loss of water after freeze-drying, which was consistent with the significant decrease in brightness value (P<0.05). The color difference of the MA, MB and MC groups was significantly higher than that of the CK group (P<0.05), which may be due to the change of the color of the freeze-dried wild rice by the inoculated bacteria.
[0064] Therefore, the MA group was able to impart better texture to wild rice stem, while the CK group had better color of wild rice stem than the CR group.
[0065] Table 1 Effects of different bacterial strains on texture and color of freeze-dried wild rice stem
[0066]
[0067] Note: Different lowercase letters in the table indicate significant differences at the 0.05 level.
[0068] (2) Effects of different bacterial strains on the total phenol content of Zizania latifolia
[0069] Phenolic compounds are an important natural active substance with good antioxidant capacity, but like vitamin C, they are also extremely susceptible to factors such as temperature and oxygen, leading to oxidative degradation. Figure 1 The results showed that the total phenol content of the CK group (2.71 mg / g) was the lowest, while the total phenol content of the MA (3.93 mg / g), MB (3.45 mg / g) and MC (3.23 mg / g) groups was significantly higher than that of the CK group (P<0.05), among which the total phenol content of the MA group was the highest. This may be because the white rot fungi decompose the complex polyphenols in wild rice stems, release bound phenolic substances, and make them exist in a free state, thereby increasing the total phenol content. Therefore, the MA group can effectively increase the content of total phenols.
[0070] (3) Effects of different bacterial strains on the microstructure of Zizania latifolia
[0071] like Figure 2 As shown in the figure, vacuum freeze drying allows the water to sublime, and the material retains a rich porous structure; after inoculation with white rot fungi, the size of the cavity in the dried wild rice stem further expands, as shown in the MA, MB, and MC groups. While retaining a rich porous structure, its pore structure has increased. This may be due to the decomposition of lignin during the fermentation process of white rot fungi, which changes the fiber structure of wild rice stem. In addition, the lower rupture force of the MA, MB, and MC groups is also consistent with the results of their microstructure.
[0072] (4) Effects of different bacterial strains on the lignin content of wild rice stem
[0073] Lignin is an important component of plant cell walls and can enhance the hardness and strength of cell walls, thereby providing structural support for the stems of wild rice stems and enabling them to remain upright. However, the accumulation of lignin in wild rice stems will increase its tissue hardness, affecting its quality and commercial value. Figure 3 As shown. The lignin content of the CK group was significantly higher than that of the other treatment groups (P<0.05), which was 200.53 mg / g. After inoculation with white rot fungi, the lignin content of the MA, MB and MC groups decreased to varying degrees, which was attributed to the good decomposition effect of Phanerochaete chrysosporium, Trametes rigidus and Sub-melanocystis on Zizania latifolia lignin. Among them, the lignin content of the MA group was significantly lower than that of the other treatment groups (P<0.05), which was 80.50 mg / g. Therefore, the MA group inoculated with Phanerochaete chrysosporium can more effectively decompose lignin and improve the texture of dried Zizania latifolia.
[0074] (5) Effects of different bacterial strains on the composition of volatile flavor compounds in Zizania latifolia
[0075] Flavor is one of the important quality indicators of dried wild rice stem, which directly affects consumers' purchasing intention and eating experience. Good flavor can enhance the market competitiveness of dried wild rice stem and make it more attractive. GC-IMS was used to detect the composition of volatile flavor compounds in vacuum freeze-dried wild rice stem. Figure 4 Shown is the composition of volatile flavor species, and the results show that, among other species, aldehydes are the most numerous, followed by alcohols and esters. Figure 5 The results showed the effect of different strains on the relative content of total volatile flavor substances. The total relative content of the MA group was significantly higher than that of other groups (P<0.05), which was 56709.78, followed by the MC group (41996.29). This shows that the dried wild rice in the MA and MC groups has a richer flavor, which mainly comes from the fermentation of the strains.
[0076] Aldehydes are important volatile compounds in dried wild rice stems. Their main metabolic pathways are the oxidation of unsaturated fatty acids and the degradation of amino acids, and they have the characteristics of low flavor threshold. The relative content of n-butyraldehyde in the CK group was the highest, at 3875.01±153.92, which can bring a suffocating aldehyde flavor to dried wild rice stems. The relative content of 5-methyl-2-furfural in the MA group was the highest, at 8065.77±59.36, which can bring a special smell to dried wild rice stems. The volatile flavor substance with the highest relative content in the MB and MC groups was isovaleraldehyde, which can bring an apple aroma to dried wild rice stems.
[0077] Alcohols can bring herbal and fatty aromas to dried wild rice stems, which is mainly due to the oxidation of fats and the degradation of amino acids, which helps to form ideal flavors and aromas. 3-Methyl-1-butanol in the CK and MB groups is the alcohol with the highest relative content, which is 1401.26±46.68 and 771.4±2.97, respectively, which brings a special wine aroma to dried wild rice stems. Ethanol in the MA group is the alcohol with the highest relative content, which can bring aromatic odor to dried wild rice stems. In the MC group, 1-penten-3-ol has the highest relative content among alcohols, which is 1790.12±60.17, which can bring fruity aroma to dried wild rice stems.
[0078] Ketones can provide a special flavor for dried wild rice stems, which mainly come from lipid oxidation, amino acid degradation and microbial metabolism. The relative content of 2-pentanone in the CK group was the highest, at 1719.45±85.35, which can bring an acetone-like smell to dried wild rice stems. The MA group was hydroxyacetone, at 2448.2±84.37, which can bring sweetness and caramel aroma. The MB and MC groups had the highest relative contents of 2-butanone, at 1419.84±53.48 and 1361.14±31.7, respectively, which can also bring an acetone-like smell to dried wild rice stems.
[0079] Lipid oxidation, phospholipid and triglyceride hydrolysis are the main metabolic pathways of acid substances. The study only detected two acids, propionic acid and acetic acid. Among all groups, acetic acid is the acid with the highest relative content and can bring a pungent smell to dried wild rice stem.
[0080] The esterification reaction between acid and alcohol is the main way to form esters, which is related to the esterase activity in microorganisms. γ-Butyrolactone in the CK and MA groups is the ester with the highest relative content, which is 248.15±11.33 and 5891.98±65.27, respectively, which can give the aroma of cream. The ester with the highest relative content in the MB group is methyl acetate, which is 385.25±0.83, which can bring fruity aroma to dried wild rice stems. The MC group is butyl formate, which is 770.74±17.15, showing fruity and plum aroma.
[0081] Among the other 10 volatile flavor substances, methoxybenzene is the volatile flavor substance with the highest relative content in the CK group, MA group and MB group, which can bring a fennel-like sweet aroma to dried wild rice stem.
[0082] Figure 6This is a PCA diagram made based on GC-IMS test data. The differences between PC1 and PC2 are 80.5% and 9.3%, respectively. All groups are scattered in four quadrants, indicating that there are large differences in the types and contents of VOCs between different groups. The MA group is mainly distributed in the first quadrant; the MC group is mainly distributed in the second quadrant; and the MB group and the CK group are mainly distributed in the third quadrant, with small differences between the groups. In the PLS-DA combined with PCA analysis ( Figure 7 ) showed that valeraldehyde, 5-methyl-2-furfural, hexanal, γ-butyrolactone, n-butyraldehyde, (E)-2-heptenal, furfural, ethanol and 2-pentanone were the main sources of differences in volatile flavor compounds among the groups (VIP>1).
[0083] Figure 8 The fingerprint analysis of volatile flavor substances in dried wild rice stem is provided. The higher the brightness of the relevant box in the figure, the higher the relative content of the corresponding volatile flavor substances. Figure 8 Based on the brightness changes of the samples, four regions were identified, marked as AD. Region A contained 19 volatile flavor substances, mainly including valeraldehyde, 1-nonanal and heptanal. The relative contents of these volatile flavor substances showed a significant upward trend in the MC group. Region B included 18 volatile flavor substances, mainly from aldehydes, ketones and esters, such as 5-methyl-2-furfural, hydroxyacetone and methyl acetate. The relative content analysis of volatile flavor substances in this region showed that the measured value of the MA group was significantly higher than that of the other three treatment groups (P<0.05). Region C included 4 volatile flavor substances, mainly from aldehydes, such as 3-methyl-2-butenal, isovaleraldehyde, benzaldehyde and α-tolualdehyde. The relative content analysis of volatile flavor substances in this region showed that the measured value of the MB group was significantly higher than that of the other three treatment groups (P<0.05). The relative contents of volatile flavor substances in the 9 CK groups in area D were significantly higher than those in other treatment groups (P<0.05), such as methoxybenzene, linalool oxide and n-butyraldehyde. The volatile flavor substances in different regions may be used as flavor markers to identify dried wild rice stems fermented by different strains.
[0084] This application explores the decomposition of wild rice lignin by inoculating different white rot fungi, and analyzes the physical quality and flavor changes of dried wild rice after vacuum freeze drying by texture analyzer and GC-IMS. Compared with the CK group, the rupture force of the treatment group inoculated with white rot fungi has a downward trend to varying degrees, and the microstructure results also show larger holes, among which the change trend of the MA group is the most significant. The detection results of lignin show that the treatment group inoculated with white rot fungi can effectively decompose lignin, among which the lignin content of the MA group is the lowest, which reduces the tissue strength of wild rice and can also explain the changes in rupture force and microstructure. At the same time, the dried wild rice made after inoculation with white rot fungi has obvious color changes, which is quite different from the color of fresh wild rice. In addition, after inoculation with white rot fungi, the total phenol content and relative content of volatile flavor substances in dried wild rice are improved. Compared with the CK group, the treatment group inoculated with white rot fungi has a higher total phenol content and relative content of total volatile flavor substances, with the highest measurement result of the MA group. Among the 52 volatile substances detected, aldehydes are the largest flavor type and the main source of the highest relative content of volatile flavor substances in each group. The CK group is n-butyraldehyde, the MA group is 5-methyl-2-furfural, and the MB and MC groups are isovaleraldehyde. In addition, valeraldehyde is the main source of the differences in volatile flavor substances between groups, and its relative content is the highest in the MC group. Fingerprint analysis provides flavor markers for distinguishing fermentation of different strains, including valeraldehyde in the MC group, isovaleraldehyde in the MB group, 5-methyl-2-furfural in the MA group, and n-butyraldehyde in the CK group. Therefore, inoculation with white rot fungi can effectively decompose lignin in Zizania latifolia and improve its physical quality and flavor. Among them, the comprehensive quality of dried Zizania latifolia inoculated with Phanerochaete chrysosporium is the best.
[0085] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.
Claims
1. A method for preparing freeze-dried wild rice stem, characterized in that: The following steps are involved: S1. Wash and cut wild rice stem into pieces for later use; S2, activating the white rot fungus species to prepare a seed solution; S3, adding water to the wild rice stem block in step S1, and then inoculating the seed liquid into the water according to the inoculation content of 10^6~8CFU / mL, and fermenting for 2~5 days; S4, after fermentation, removing the fermentation liquid to obtain fermented wild rice stem, pre-freezing the fermented wild rice stem, and then performing vacuum freeze drying to obtain the freeze-dried wild rice stem.
2. The preparation method according to claim 1, characterized in that: The white rot fungi are one or more of Phanerochaete chrysosporium, Trametes rigidus and Poriophora nigrosporium.
3. The preparation method according to claim 2, characterized in that: The Phanerochaete chrysosporium was purchased from China Industrial Microbiological Culture Collection Center with a serial number of CICC 40299.
4. The preparation method according to claim 2, characterized in that: The Trametes rigidus was purchased from the microbial strain query website and is numbered Bio-85322.
5. The preparation method according to claim 2, characterized in that: The sub-melanopore fungus was purchased from the microbial strain query website and is numbered Bio-27528.
6. The preparation method according to claim 1, characterized in that: In step S3, the weight ratio of wild rice stem: water is 1:5-15.
7. The preparation method according to claim 1, characterized in that: In step S3, the fermentation temperature is 20-30°C, and the stirring speed is 150-250 rpm.
8. The preparation method according to claim 1, characterized in that: The pre-freezing temperature is -20 to -15°C.
9. The preparation method according to claim 1, characterized in that: The vacuum freeze drying is to reduce the water content of wild rice stem to below 5%.
10. Freeze-dried wild rice stem obtained by the preparation method according to any one of claims 1 to 9.