Modified Chinese yam as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of food processing, and discloses modified Chinese yam as well as a preparation method and application thereof. The invention provides a preparation method of modified Chinese yam, which comprises the steps of Chinese yam pretreatment, fermentation substrate preparation, fermentation, solid-liquid separation and the like to obtain the modified Chinese yam. According to the method, lactobacillus plantarum and lactic acid bacillus DU-106 are used for performing fermentation treatment on the Chinese yam, and the microstructure and the material proportion of the Chinese yam are changed, so that the Chinese yam has a crisp taste after being cooked. The modified Chinese yam, the cooked Chinese yam and the modified Chinese yam powder provided by the invention can be used for preparing Chinese yam food, and the prepared Chinese yam noodles are high in boiling fastness, tough and chewy in mouth feel and not easy to become lumps. The method provided by the invention provides an effective path for high-value utilization and deep processing product development of Chinese yam.

Description

Technical Field

[0001] The present invention belongs to the technical field of food processing, and particularly relates to a modified Chinese yam, a preparation method and an application thereof. Background Art

[0002] Chinese yam is one of the food-medicinal homologous substances announced by the National Health Commission of China. Also known as Dioscorea opposita, its prescription names are Chinese yam, raw Chinese yam, Huai Chinese yam, stir-fried Chinese yam, etc. It is the rhizome of the perennial vine herb Dioscorea opposita Thunb. in the Dioscoreaceae family. It is flat in nature, sweet in taste, and belongs to the spleen, lung, and kidney meridians. It is cultivated throughout the country. Due to its rich nutritional value and unique medicinal effects, Chinese yam is widely used in food processing and the pharmaceutical field.

[0003] In food processing, brittleness is a pleasant taste experience. For example, products such as potato chips and crispy lotus roots are favored by consumers because of their unique crispy texture. However, after steaming or stewing in the natural state, the texture of Chinese yam becomes soft and lacks brittleness. This characteristic limits the diversified development of Chinese yam in certain food applications, especially in scenarios where a crispy texture is required.

[0004] Currently, there is no mature technology in the market that can make Chinese yam present a crispy texture after cooking through simple processing. Traditional processing methods of Chinese yam, such as slicing and drying in the sun, quick-freezing, etc., can change the texture of Chinese yam to a certain extent, but cannot achieve the crispy effect after cooking. In addition, although some chemical additives may theoretically improve the texture of Chinese yam, their safety and health are controversial and do not meet the needs of modern consumers for natural and healthy foods. At the same time, the Chinese yam noodles prepared from ordinary Chinese yam have low boiling resistance and are easy to become lumpy, which affects the quality and taste of Chinese yam noodles and restricts the wide application of Chinese yam in noodle products. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a modified Chinese yam, a preparation method and an application thereof. The present invention uses Lactobacillus plantarum ( Lactobacillus plantarum ) and Lactobacillus sporogenes ( Bacillus sp. ) DU-106 to ferment Chinese yam, change the microstructure and the proportion of internal substances of Chinese yam, and obtain a modified Chinese yam different from ordinary Chinese yam. The obtained modified Chinese yam not only has a unique crispy texture after cooking, but also can improve the boiling resistance of Chinese yam noodles and effectively improve the lumping situation of noodles during cooking.

[0006] To achieve the above object, the present invention provides the following technical solutions: In the first aspect, the present invention provides a modified Chinese yam, and the preparation method includes the following steps: S1 Pretreatment of Chinese yam: Select healthy Chinese yam, peel it, cut it, and rinse it with sterile water to obtain pretreated Chinese yam; S2 Preparation of fermentation substrate: Mix the pretreated Chinese yam in S1 with the sterilized edible sugar solution at a mass-volume ratio (g:mL) of 1-2:2 to obtain a fermentation substrate; the edible sugar concentration in the edible sugar solution is 0.01-0.03 g / mL; S3 Fermentation: Inoculate the fermentation substrate in S2 with a mixed strain. Based on the mass of the pretreated Chinese yam, the total inoculation amount is greater than or equal to 1×10 5 CFU / g, and carry out fermentation at 25-37°C. Stop fermentation when at least one of the following conditions is met: i The pH value of the liquid part of the fermentation substrate is less than or equal to 3.74; ii The starch content of the obtained modified Chinese yam after dehydration is greater than or equal to 744.44 mg / g; iii The protein content of the obtained modified Chinese yam after dehydration is less than or equal to 93.93 mg / g; After stopping fermentation, a fermentation product is obtained; the mixed strain includes Lactobacillus plantarum ( Lactobacillus plantarum ) and Bacillus sporolactis ( Bacillus sp. ) DU-106; the viable cell number ratio of Lactobacillus plantarum to Bacillus sporolactis is 600-1200:1; S4 Solid-liquid separation: Remove the liquid part from the fermentation product to obtain modified Chinese yam; The degree of dehydration of the modified Chinese yam is that the water content of the modified Chinese yam after dehydration treatment is ≤5%.

[0007] The present invention adopts a fermentation modification method, using Lactobacillus plantarum and Bacillus sporolactis DU-106 to ferment and modify Chinese yam, changing the original material ratio and internal structure of Chinese yam, reducing the fat content of Chinese yam, increasing the starch and dietary fiber levels, and effectively delaying the softening during the cooking process of Chinese yam. At the same time, the provided fermentation modification method also has the advantages of simple process, wide application range, easy promotion, etc., and is suitable for popularization and application in production environments of various scales.

[0008] The cutting is to process the Chinese yam into a shape suitable for subsequent processing. Specifically, the Chinese yam can be evenly cut into small pieces, strips or slices for easy fermentation treatment.

[0009] Preferably, the cutting in S1 is slicing; the thickness of the pretreated Chinese yam is 0.5-2 cm.

[0010] Preferably, the Chinese yam is Huai yam.

[0011] Preferably, the edible sugar solution in S2 is a white granulated sugar solution, and the concentration of white granulated sugar in the white granulated sugar solution is 0.02 g / mL; the pretreated Chinese yam and the sterilized white granulated sugar solution are mixed at a mass-to-volume ratio (g:mL) of 1:2.

[0012] More preferably, the thickness of the pretreated Chinese yam is 1 cm.

[0013] Preferably, the total inoculum amount in S3 is 3.005×10 5 -6.01×10 5 CFU / g.

[0014] Preferably, in S3, it is fermented at a constant temperature of 28°C, and the fermentation is stopped when the pH of the liquid part of the fermentation substrate is less than or equal to 3.3.

[0015] Preferably, the Lactobacillus plantarum is Lactobacillus plantarum nbk-MA2.

[0016] Preferably, the viable cell count ratio of the Lactobacillus plantarum to the Bacillus sporolactis is 600:1.

[0017] In a second aspect, the present invention also provides a modified Chinese yam prepared by the above preparation method.

[0018] In a third aspect, the present invention also provides a cooked Chinese yam, which is obtained from the modified Chinese yam prepared by the above preparation method or from the above modified Chinese yam after being cooked and processed.

[0019] The core step of the cooking is to cook the modified Chinese yam by heating, and the cooking and processing methods include, but are not limited to, steaming, boiling, roasting, and stir-frying.

[0020] The cooked Chinese yam provided by the present invention has tightly arranged tuber cells, and irregular round aggregates are wrapped in the cell grid. Its hardness can reach 254.1 N, and it has a brittle texture significantly different from traditional cooked Chinese yam.

[0021] Preferably, the cooking and processing method is steaming or boiling.

[0022] In a fourth aspect, the present invention also provides a modified Chinese yam powder, which is obtained from the modified Chinese yam prepared by the above preparation method or from the above modified Chinese yam after being dehydrated and ground into powder.

[0023] By processing the modified Chinese yam into flour, the product diversity of the modified Chinese yam can be expanded, and its application performance can be improved. The modified Chinese yam powder provided by the present invention has good processing characteristics and nutritional characteristics, can be used as a high-quality substitute for wheat flour and other carbohydrate sources, and is widely used in the food processing field, providing more choices for consumers.

[0024] Preferably, the dehydration method is drying, and the modified yam is dried until its water content ≤ 5%.

[0025] A water content below 5% can preferably ensure the quality stability of yam powder during storage and transportation, preventing problems such as caking and mildew due to excessive moisture.

[0026] More preferably, the drying temperature is 45 °C.

[0027] Preferably, the particle size of the modified yam powder is less than or equal to 0.15 mm.

[0028] Controlling the particle size of the modified yam powder to be less than or equal to 0.15 mm (able to pass through a 100-mesh sieve), the obtained modified yam powder has a delicate texture, no obvious granular feeling, and is convenient for further processing and use.

[0029] Fifthly, the present invention also provides the application of the above-mentioned modified yam, the above-mentioned cooked yam, and the above-mentioned modified yam powder in the processing of yam-based foods.

[0030] The provided modified yam, cooked yam, and modified yam powder can be applied to the preparation of yam-based foods. The yam-based foods refer to foods with yam as the main ingredient or ingredient, including but not limited to yam nutritional powder, yam meal replacement porridge, cooked yam, yam crisp, yam cake, yam pudding, yam chips, etc. Optionally, the modified yam can be processed into flour, prefabricated dishes, etc.; the cooked yam can be processed into cold dishes, milk tea ingredients, instant yam chips, etc.; the modified yam powder can be processed into noodles, pastries, and snacks, etc.

[0031] Sixthly, the present invention also provides a kind of yam noodle, and the flour of the yam noodle contains the above-mentioned modified yam powder.

[0032] Compared with ordinary yam noodles, the cooking resistance of the yam noodles prepared by using the modified yam powder is significantly improved, the chewiness is better, and it is not easy to become lumpy after being cooked and placed, which has more advantages in the cooking and eating processes.

[0033] Preferably, the flour of the yam noodle includes 8%-16% of the above-mentioned modified yam powder; the flour of the yam noodle also includes wheat flour.

[0034] More preferably, the flour of the yam noodle is composed of 8%-16% of modified yam powder and 84%-96% of wheat flour.

[0035] More preferably, the flour of the yam noodle is composed of 12% of modified yam powder and 78% of wheat flour.

[0036] Exemplarily, a preparation method of yam noodles is provided, including the following steps: S1: Mix the above-mentioned modified yam powder and wheat flour according to a mass ratio of 4-16:84-96 to obtain a mixed flour; S2: Take the mixed flour and water, stir evenly according to the material-water ratio (g:mL) of 2:0.9 - 1.1, knead into a dough, and after proofing, rolling, and cutting into strips, obtain yam noodles. Description of the Drawings

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0038] Figure 1 It is the hardness of the fermented yam sample in Verification Example 1 of the present invention; Figure 2 It is the cross-sectional morphology diagram of the yam before and after cooking of the unfermented yam sample (A0) and the fermented yam samples (A1 - A3) in Verification Example 1 of the present invention; Figure 3 It is the cross-sectional morphology diagram of the yam before and after cooking of the fermented yam samples (A4 - A7) in Verification Example 1 of the present invention; Figure 4 It is the pH value of the fermentation broth in the verification example of the present invention; Figure 5 It is the starch content in the fermented yam sample in Verification Example 1 of the present invention; Figure 6 It is the protein content in the fermented yam sample in Verification Example 1 of the present invention; Figure 7 It is the cooking time of different yam noodles in Verification Example 2 of the present invention; Figure 8 It is the water absorption rate of different yam noodles in Verification Example 2 of the present invention; Figure 9 It is the turbidity of the noodle soup of different yam noodles in Verification Example 2 of the present invention; Figure 10 It is the apparent change after cooking of the pure wheat noodles in Verification Example 2 of the present invention; Figure 11 It is the apparent change after cooking of the ordinary yam noodles in Verification Example 2 of the present invention; Figure 12 It is the apparent change after cooking of the modified yam noodles in Verification Example 2 of the present invention; Figure 13 It is the hardness of different yam noodles in Verification Example 2 of the present invention; Figure 14 It is the adhesiveness of different yam noodles in Verification Example 2 of the present invention; Figure 15 It is the elasticity of different yam noodles in Verification Example 2 of the present invention; Figure 16 For verifying the cohesiveness of different yam noodles in Verification Example 2 of the present invention; Figure 17 For verifying the chewiness of different yam noodles in Verification Example 2 of the present invention. Detailed implementation manners

[0039] Next, in combination with the implementation manners of the present invention, the technical solutions in the implementation manners of the present invention will be clearly and completely described. Obviously, the described implementation manners are only a part of the implementation manners of the present invention, rather than all the implementation manners. Based on the implementation manners in the present invention, all other implementation manners obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0040] The wheat flour used in the implementation of the present invention is high-gluten wheat flour, purchased from Shanghai Fuze Food Co., Ltd.; the yam used in the implementation of the present invention is Tieguanyin yam, from Wen County, Jiaozuo City, Henan Province.

[0041] The source of the strains used in the embodiments of the present invention: Lactobacillus sporogenes ( Bacillus lactics ) DU-106 was deposited at the Guangdong Provincial Culture Collection Center of Microorganisms on March 29, 2019, with the deposit number GDMCC NO.1.1581. This strain has been disclosed in "Identification and Comparative Genomics Analysis of a High-Yield Lactic Acid-Producing Lactobacillus sporogenes DU-106" (Master's degree thesis, Wu Xueyin).

[0042] Lactobacillus plantarum nbk-MA2 ( Lactobacillus plantarum ) was deposited at the Guangdong Provincial Culture Collection Center of Microorganisms on July 7, 2021, with the deposit number GDMCC NO.1.2685. This strain has been disclosed in "Probiotic-fermented ginger-processed Gastrodia elata BI. Ameliorates AlCl3-induced cognitive dysfunction in an Alzheimer's disease rat model by regulating the gut microbiota and CREB / BDNF pathway" (Junyuan Huang, 2025.4).

[0043] The Lactobacillus sporogenes powder is a freeze-dried powder prepared by enriching and culturing Lactobacillus sporogenes DU-106 and then adding a protective agent through a freeze-drying process. The viable count of Lactobacillus sporogenes DU-106 in this powder is 1×10 8 CFU / g.

[0044] The Lactobacillus plantarum powder is a freeze-dried powder prepared by enriching and culturing Lactobacillus plantarum nbk-MA2 and then adding a protective agent through a freeze-drying process. The viable count of Bacillus lacticus DU-106 in this powder is 1×10 12 CFU / g.

[0045] The detection methods of substances in the embodiments of the present invention are as follows: Determination of protein content: Refer to the national standard GB / T 5009.5-2016 "Determination of Protein in Foods"; Determination of crude fat content: Refer to the national standard GB / T 5009.6-2016 "Determination of Fat in Foods"; Determination of moisture content: Refer to the national standard GB / T 5009.3-2016 "Determination of Moisture in Foods"; Determination of crude fiber content: Refer to the national standard GB / T5009.10-2003 "Determination of Crude Fiber in Plant Foods"; Determination of crude polysaccharide content: Refer to the phenol-sulfuric acid method described in SN / T 4260-2015 "Determination of Crude Polysaccharides in Exported Plant-derived Foods".

[0046] Determination of starch content: Use the box bio starch content detection kit (Beijing Box Bioscience and Technology Co., Ltd., product model: AKSU015M), and detect the starch content by the anthrone colorimetric method.

[0047] Determination of pectin content: Use the box bio total pectin content detection kit (Beijing Box Bioscience and Technology Co., Ltd., product model: AKSU069M), and measure the pectin content by visible spectrophotometry.

[0048] In the embodiments of the present invention, the term "about" means that reasonable technical deviations are allowed for the numerical value, and this deviation range is based on meeting the invention purpose and technical effects, and is specifically defined as ±5% of the nominal value.

[0049] Verification Example 1 1. Preparation of test samples 1.1 Select yams with a root and stem cross-sectional radius of about 2 cm and no obvious wounds and rot. Wash and peel the yams, cut them into slices about 2 cm thick, and rinse them with sterile water to obtain pretreated yams.

[0050] 1.2 Dissolve granulated sugar in pure water to prepare a 0.02 g / mL granulated sugar solution. After autoclaving at 121°C for 30 min, cool it for later use; Put 1 kg of pretreated yams and 2 L of sterilized granulated sugar solution into a sterile fermentation tank and mix to obtain a fermentation substrate.

[0051] 1.3 Preparation of compound powder: Take 12 g of Lactobacillus plantarum powder, 200 g of Bacillus DU-106 powder and 1788 g of glucose, and prepare them into a compound powder.

[0052] 1.4 Add 1 g of the composite bacterial powder (total viable count is 6.01×10 9 CFU / g) to 1 L of physiological saline and activate it at 30 °C for 30 min to obtain the activated bacterial liquid (total viable count is 6.01×10 6 CFU / mL); put 50 mL of the activated bacterial liquid into a sterile fermenter, inoculate it, and ferment it at a constant temperature of 28 °C for 1 - 7 d. At the beginning of fermentation, take the unfermented yam sample (A0) on the ultra-clean workbench, and then take the fermented yam samples (A1 - A7) and the corresponding fermentation broth every 24 h.

[0053] 2. Detection of the taste and hardness of cooked yams Take the unfermented yam sample (A0) and the fermented yam samples (A1 - A7), drain the surface fermentation broth, and put them into a steamer to steam for 20 min to obtain the cooked yam samples (B0 - B7). Take the cooked yam samples (B0 - B7) respectively for hardness detection and crispness sensory evaluation, and conduct crispness grading.

[0054] Crispness sensory evaluation: Form a sensory evaluation panel of 10 people. Each evaluator independently completes the tasting and scores without communication during the process. To avoid the sensory impact of the previous sample on the next sample, the evaluator needs to rinse their mouth with water between tasting each sample to remove the residual sensory stimuli and ensure the objectivity and accuracy of the scoring. Score and evaluate the crispness grade of the cooked yams. To ensure the accuracy of the evaluation results, the maximum and minimum values are removed from each set of data during statistics. The specific scoring criteria for the crispness grade of the cooked yams are shown in Table 1, and the results are shown in Table 2.

[0055] Table 1 Scoring criteria for the crispness of cooked yams

[0056] Hardness detection method: Use the TA / 2 probe of the texture analyzer to measure the hardness of the cooked yam samples (B0 - B7), repeat three times, and take the average value of the results, as Figure 1 shown. The settings of the whole texture measurement parameters: the speed before testing is 2 mm / s, the testing speed is 1 mm / s, the speed after testing is 1 mm / s, the interval time is 5 s, the target mode is displacement, the contact point type is pressure, the experimental type is whole texture test, and the test type is downward pressure test.

[0057] Table 2 Sensory scores for the crispness of cooked yam samples

[0058] It can be seen from the crispness sensory evaluation of the cooked yam samples that the crispness of the cooked yam after 4 days of fermentation is significantly improved, its taste becomes crispy, and the crispness of the cooked yam sample B6 is similar to that of pickled radish.

[0059] Hardness represents the maximum peak value during the first compression of the sample, reflecting the property of the sample's resistance to deformation. There is a highly significant positive correlation between hardness and brittle texture. Therefore, hardness can be used as an important indicator to characterize the brittleness of food. Figure 1 As shown, with the extension of fermentation time, the hardness of the cooked yam samples changed significantly. In the initial stage of fermentation, the change in hardness was relatively slow, but on the 3rd day of fermentation, the hardness began to increase significantly and reached the peak value (251.44 N) on the 6th day of fermentation. This indicates that fermentation significantly improved the crispness of the cooked yam, giving the cooked yam a brittle texture.

[0060] 3. Morphology Observation Take the unfermented yam samples (A0) and the fermented yam samples (A1 - A7), drain the surface fermentation broth, and then put them into a steamer and steam for 20 min to obtain the cooked yam samples (B0 - B7).

[0061] Respectively take the unfermented yam samples (A0), the fermented yam samples (A1 - A7), and the cooked yam samples (B0 - B7) for freeze - drying treatment. Break the freeze - dried yam samples to obtain small pieces with a flat cross - section of about 0.5 cm×0.5 cm. Fix A0 - A7 and B0 - B7 after freeze - drying treatment on the sample stage with conductive glue, conduct gold spraying treatment on them, with a magnification of 200 times, and use an acceleration potential of 10 kV during scanning to obtain the cross - section morphology map of the yam ( Figures 2 - 3 )

[0062] As Figures 2 - 3 can be seen, the starch granules of the unfermented yam sample A0 and the fermented yam samples A1 - A3 are oval or oblate, distributed scattered, in a state of irregular aggregation, and the cell contours of their corresponding cooked yams (B0 - B3) are still messy; the cell contours of the fermented yam samples A4 - A7 are clear, and their starch granules are aggregated in the filled cells, and their corresponding cooked yam samples (B4 - B7) show the characteristics of a compact cell structure and irregular round aggregates wrapped in the cell grid; overall, with the increase of fermentation time, the cell contours of the yam show a gradually clear trend, the arrangement between cells becomes tighter, and finally a dense grid structure is formed.

[0063] This indicates that the fermentation of Lactobacillus plantarum and Bacillus sporolactis DU - 106 on yam can significantly change the microstructure of the yam, regularize the cell structure of the yam tuber, and promote the aggregation of starch granules in the cells. This orderly and tight cell arrangement can make the cooked yam break neatly more easily when stressed, thus giving the cooked yam a brittle texture and changing its edible quality.

[0064] 4. Determination of the pH Value of the Fermentation Broth Fermentation broth at 0 d, 1 d, 2 d, 3 d, 4 d, 5 d, 6 d, and 7 d of yam fermentation was taken respectively. After shaking well, the pH value was measured, and the average value was taken after repeating three times. The results are shown in Figure 4 .

[0065] As can be seen from Figure 4 , from 0 to 3 d, the pH value of the fermentation broth decreased rapidly. From 4 to 6 d, the pH value decreased slowly. At 7 d, it increased slightly. In the early stage, the bacteria grew rapidly and utilized the substrate to produce acid by fermentation. After growing to the stationary phase, the acid production slowed down. At the same time, the fermentation broth from 4 to 6 d had a unique fresh fragrance and a mild fermentation sour taste of yam; the fermentation broth at 7 d had a slight rancid smell, which might be caused by the reproduction of miscellaneous bacteria resulting in spoilage. The increase in the pH value of its fermentation broth was related to bacterial contamination.

[0066] 5. Determination of Component Content Unfermented yam samples (A0) and fermented yam samples (A1 - A7) were taken respectively and dried in a heat pump dryer for 36 h (drying temperature 45°C, moisture content about 5%). The dried yam blocks were ground into powder and passed through a 100-mesh sieve to obtain unfermented yam powder samples (C0) and fermented yam powder samples (C1 - C7). The starch content ( Figure 5 ) and protein content ( Figure 6 ) in the above-mentioned yam powder samples were measured.

[0067] As Figure 5 shown, the change in starch content was not significant during 0 - 1 d of fermentation. It might be that simple substrates such as glucose were preferentially utilized in the early stage of fermentation. During 1 - 6 d of fermentation, the starch content in yam increased significantly. It might be that the bacteria decomposed and utilized some macromolecular substances in yam such as protein, fat, and pectin, thus purifying the yam starch relatively. As Figure 6 shown, as the fermentation days increased, the protein content in yam powder gradually decreased. It might be that the enzymes produced by microorganisms degraded the protein on the surface of the starch. The above results indicate that the fermentation process changed the material composition structure of yam, thus affecting the texture characteristics of yam.

[0068] 6. Correlation Analysis Using the Pearson correlation analysis method, the hardness data of the cooked yam samples (B0 - B7) measured above were correlated with the corresponding pH value of the fermentation broth, starch content, and protein content in the yam powder samples, and the Pearson correlation coefficient r and P were calculated. The results are shown in Table 3.

[0069] Table 3 Correlation Analysis

[0070] Note: "**" represents significant correlation at a confidence level (two-sided) of 0.01 As can be seen from Table 3, the hardness of fermented yam is significantly correlated with the pH value of the fermentation broth (r = -0.728, P < 0.01), starch content (r = 0.900, P < 0.01), and protein content (r = -0.945, P < 0.01). Therefore, at least one of the pH value of the fermentation broth, starch content, and protein content in fermented yam can be selected as the basis for determining the fermentation end point.

[0071] Taking into account taste, hardness, and tuber morphology, at least one of the following is determined as the fermentation end point index: the pH of the fermentation broth is less than or equal to 3.74, the starch content in fermented yam is greater than or equal to 744.44 mg / g, and the protein content in fermented yam is less than or equal to 93.93 mg / g. Considering the fermentation effect, further, at least one of the following is used as the fermentation end point index: the pH value of the fermentation broth is 3.3, the starch content in fermented yam is 767.37 mg / g, and the protein content in fermented yam is 72.81 mg / g. Given that the detection process of the pH value of the fermentation broth is relatively convenient, the pH value of the fermentation broth can be selected as the fermentation end point index.

[0072] Example 1 This example provides a modified yam and a preparation method, and the preparation method consists of the following steps.

[0073] Step 1: Select yams with uniform root and stem thickness, no obvious wounds or rot. Wash and peel the yams, cut them into slices with a thickness of 0.5 - 2.0 cm, and after rinsing with sterile water, obtain pretreated yams.

[0074] Step 2: Dissolve 4 g of glucose in 400 mL of pure water to prepare a 0.01 g / mL glucose solution. Filter and sterilize it with a 0.22 μm pore size filter membrane for later use. Put 150 g of pretreated yams and 200 mL of the sterilized glucose solution into a sterile fermentation tank and mix to obtain a fermentation substrate.

[0075] Step 3: Add Lactobacillus plantarum powder and Lactobacillus sporogenes DU - 106 powder to the glucose solution at a ratio of 1 g:1 L respectively, and activate them at 30°C for 30 min to obtain an activated Lactobacillus plantarum solution and an activated Lactobacillus sporogenes DU - 106 solution. Put the two activated solutions into the sterile fermentation tank. Based on the mass of the pretreated yams, control the inoculation amount of Lactobacillus plantarum nbk - MA2 to be 6×10 5 CFU / g, and the inoculation amount of Lactobacillus sporogenes DU - 106 to be 1×10 3CFU / g, fermentation is carried out at room temperature of 19 - 25°C, and the pH value of the fermentation broth in the fermenter is detected every 1 h. Fermentation is stopped when the pH value is less than or equal to 3.7.

[0076] Step 4: After fermentation is completed, the fermentation broth in the sterile fermenter is drained to obtain modified Chinese yam.

[0077] Cook the obtained modified Chinese yam in boiling water to obtain cooked modified Chinese yam.

[0078] Example 2 This example provides a modified Chinese yam and a preparation method, and its preparation method consists of the following steps.

[0079] Step 1: Select Chinese yam with uniform root and stem thickness, no obvious wounds and rot. Wash and peel the Chinese yam, cut it into pieces about 2 cm × 2 cm, and after rinsing with sterile water, obtain pretreated Chinese yam.

[0080] Step 2: Take sucrose and dissolve it in pure water to prepare a 0.03 g / mL sucrose solution. After filtering and sterilizing with a 0.22 μm pore size filter membrane, it is reserved for use; Put 200 g of pretreated Chinese yam and 200 mL of the sterilized sucrose solution into a sterile fermenter and mix to obtain a fermentation substrate.

[0081] Step 3: Inoculate 0.5 g of Lactobacillus plantarum powder into 250 mL of LB medium, culture at 37°C and 250 rpm for 24 h, then centrifuge to obtain Lactobacillus plantarum bacterial sludge. Obtain Lactobacillus sporogenes DU - 106 bacterial sludge in the same way; Add the Lactobacillus plantarum bacterial sludge and Lactobacillus sporogenes DU - 106 bacterial sludge into sterile physiological saline and suspend to obtain a suspended bacterial liquid (the viable count of Lactobacillus plantarum is 1×10 6 CFU / mL, the viable count of Lactobacillus sporogenes DU - 106 is 1×10 3 CFU / mL).

[0082] Put 20 mL of the activated bacterial liquid into the sterile fermenter and ferment at a constant temperature of 37°C. Detect the pH value of the fermentation broth in the fermenter every 24 h. Fermentation is stopped when the pH value is less than or equal to 3.5.

[0083] Step 4: After fermentation is completed, the fermentation broth in the sterile fermenter is drained to obtain modified Chinese yam.

[0084] Put the obtained modified Chinese yam into an oven at 180°C for 15 min to obtain cooked modified Chinese yam.

[0085] Example 3 This example provides a modified Chinese yam and a preparation method, and its preparation method consists of the following steps.

[0086] Step 1: Select yams with a rhizome cross-sectional radius of about 2 cm and no obvious wounds or rot. Wash and peel the yams, cut them into slices about 1 cm thick, and rinse with sterile water to obtain pretreated yams.

[0087] Step 2: Dissolve granulated sugar in pure water to prepare a 2 g / mL granulated sugar solution. Sterilize it at 121 °C under high pressure for 30 min and then cool for standby. Put the pretreated yams and the sterilized granulated sugar solution into a sterile fermentation tank and mix to obtain a fermentation substrate.

[0088] Step 3: Take 12 g of Lactobacillus plantarum powder, 100 g of Bacillus sp. DU-106 powder, and 1888 g of glucose to prepare a compound bacterial powder. Add 1 g of the compound bacterial powder (total colony count is 6.005×10 9 CFU / g) to 1 L of sterile water and activate it at 30 °C for 30 min to obtain an activated bacterial solution (total colony count is 6.005×10 6 CFU / mL); Put the activated bacterial solution into a sterile fermentation tank. Based on the mass of the pretreated yams, the total inoculation amount is 6.005×10 5 CFU / g; After inoculation, ferment at a constant temperature of 28 °C, and measure the pH value of the fermentation broth in the fermentation tank every 1 h. Stop fermentation when the pH value is less than or equal to 3.3.

[0089] Step 4: After fermentation, drain the fermentation broth in the sterile fermentation tank to obtain modified yams.

[0090] Steam the obtained modified yams until cooked to obtain cooked modified yams.

[0091] Example 4 A modified yam powder in this example is obtained by drying and pulverizing the modified yams provided in Example 3.

[0092] Place the modified yams in a well-ventilated and dry place and naturally dry them until the water content is less than 5%. Grind the dried modified yams into powder and pass through a 100-mesh sieve to obtain modified yam powder.

[0093] Comparative Example 1 An ordinary yam powder in this comparative example is obtained by drying and pulverizing fresh yams.

[0094] Select healthy yams, wash, peel, and slice them, then place them in a well-ventilated and dry place and naturally dry them until the water content is less than 5%. Grind the dried yams into powder and pass through a 100-mesh sieve to obtain ordinary yam powder.

[0095] Measure the contents of starch, protein, fat, crude fiber, and pectin in the modified yam powder provided in Example 3 and the ordinary yam powder provided in Comparative Example 1. The results are shown in Table 4.

[0096] Table 4 Contents of starch, protein, fat, crude fiber and pectin in modified yam powder and common yam powder

[0097] Note: Different lowercase letters indicate significant differences ( P <0.05) Compared with common yam powder, the contents of starch and crude fiber in modified yam powder increase significantly, while the contents of protein, fat and pectin decrease significantly. It is more suitable for people who need to intake high carbohydrates, low fat and high fiber.

[0098] Example 5 A kind of yam noodles in this example is prepared by the following method.

[0099] Step 1: Mix the modified yam powder (provided in Example 4) and wheat flour according to a mass fraction of 16:184 to prepare a mixed powder, and store it at 4°C.

[0100] Step 2: Weigh 200 g of the mixed powder and 110 mL of pure water, stir evenly, knead into a dough, and let it rest for 40 min.

[0101] Step 3: Use a small noodle machine to make the rested dough into noodles. Sheet pressing treatment: Sheet pressing at a 3 mm roller spacing → Sheet combining → Sheet pressing (a total of 5 times), and then adjust to 2 mm and 1 mm in turn, with each sheet pressing 5 times; Noodle cutting treatment: Cut the pressed noodle sheets into slender noodles 1 mm wide.

[0102] Example 6 A kind of yam noodles in this example is prepared by the following method.

[0103] Step 1: Mix the modified yam powder (provided in Example 4), wheat flour and buckwheat flour according to a mass fraction of 32:108:60 to prepare a mixed powder, and store it at 4°C.

[0104] Step 2: Weigh 200 g of the mixed powder and 90 mL of pure water, stir evenly, knead into a dough, and let it rest for 40 min.

[0105] Step 3: Place the rested dough on a floured chopping board, roll out the dough with a rolling pin until it is 0.2 - 0.3 cm thick; Sprinkle some flour on the rolled-out noodle sheet, then fold the noodle sheet and cut it with a knife into wide noodles with a width of 0.5 - 1 cm.

[0106] Verification Example 2 Use common yam powder (provided in Comparative Example 1) and modified yam powder (provided in Example 4) as raw materials to make yam noodles respectively, and compare their properties.

[0107] To prepare pure wheat noodles, weigh 200 g of wheat flour and mix it with 100 mL of water, then knead it into a dough. After the dough is formed, let it rest for 40 min. Use a small noodle machine to make long and thin pure wheat noodles (WN) with a width of 1 mm from the rested dough. The preparation parameters are the same as those in Example 5.

[0108] Prepare mixed powders D4, D8, D12, and D16 with the addition amount of modified yam powder being 4% (8 parts of modified yam powder + 192 parts of wheat flour), 8% (16 parts of modified yam powder + 184 parts of wheat flour), 12% (24 parts of modified yam powder + 176 parts of wheat flour), and 16% (32 parts of modified yam powder + 168 parts of wheat flour), respectively. Weigh 200 g of each mixed powder (D4, D8, D12, and D16), mix and knead it with 100 mL of water into a dough respectively, and then let it rest for 40 min. Use a small noodle machine to make long and thin modified yam noodles (FYN) with a width of 1 mm from the rested dough. The preparation parameters are the same as those in Example 5.

[0109] Prepare mixed powders E4, E8, E12, and E16 with the addition amount of ordinary yam powder being 4% (8 parts of ordinary yam powder + 192 parts of wheat flour), 8% (16 parts of ordinary yam powder + 184 parts of wheat flour), 12% (24 parts of ordinary yam powder + 176 parts of wheat flour), and 16% (32 parts of ordinary yam powder + 168 parts of wheat flour), respectively. Weigh 200 g of each mixed powder (E4, E8, E12, and E16), mix and knead it with 100 mL of water into a dough respectively, and then let it rest for 40 min. Use a small noodle machine to make long and thin ordinary yam noodles (UYN) with a width of 1 mm from the rested dough. The preparation parameters are the same as those in Example 5.

[0110] 1. Cooking resistance Evaluate the cooking resistance of the pure wheat noodles, modified yam noodles, and ordinary yam noodles by measuring their cooking time, noodle breakage rate, noodle water absorption, and noodle soup turbidity.

[0111] 1.1 Cooking time Detect the cooking time of the pure wheat noodles, modified yam noodles, and ordinary yam noodles. The detection results are as Figure 7 shown.

[0112] Measurement method of cooking time: Take 15 noodles with a length of 20 cm. Put 300 mL of distilled water in a beaker. After the water boils, put the noodles in and start timing. After boiling for 2 min, pick up one noodle every 10 s, clamp it between two transparent glass blocks and gently press it. When the white core in the middle of the noodle completely disappears, record the time, which is the cooking time of the noodle.

[0113] It can be seen from the results that as the addition amount of yam powder increases, the steaming time required for cooking yam noodles gradually shortens. However, compared with ordinary yam noodles, the steaming time of modified yam noodles is longer, showing better boil resistance.

[0114] 1.2 Noodle breakage rate The noodle breakage rates of pure wheat noodles, modified yam noodles and ordinary yam noodles were measured, and the measurement results are shown in Table 5.

[0115] Method for measuring noodle breakage rate: Take 40 noodles with a length of 20 cm. There is 800 mL of distilled water in the beaker. After the water boils, put the noodles in and steam them according to the measured steaming time of the noodles. After steaming, immerse the noodles in a beaker containing 400 mL of cold water for 10 s, drain the water, pour the noodles into a container, separate the noodles with a length of more than 10 cm and less than 10 cm, then weigh them, and calculate the breakage rate according to the following formula: Breakage rate (%) = m 1 / ( m 1 + m 2) × 100; In the formula: m 1 represents the mass (g) of the noodles with a length less than 10 cm; m 2 represents the mass (g) of the noodles with a length greater than or equal to 10 cm.

[0116] Table 5 Noodle breakage rate

[0117] Table 5 shows that the higher the addition amount of ordinary yam powder, the greater the noodle breakage rate of ordinary yam noodles. When the addition amount is 16%, the breakage rate reaches 42.83 ± 0.27%. In contrast, when the addition amounts of modified yam powder are 4%, 8% and 12%, the noodle breakage rates of modified yam noodles are all 0. When the addition amount increases to 16%, only slight noodle breakage occurs, indicating that the addition of modified yam powder significantly reduces the noodle breakage rate of yam noodles and effectively improves their boil resistance.

[0118] 1.3 Noodle water absorption The noodle water absorptions of pure wheat noodles, modified yam noodles and ordinary yam noodles were measured, and the measurement results are as Figure 8 shown.

[0119] Method for measuring noodle water absorption: Take 40 noodles with a length of 20 cm, weigh them, and record the weight of the noodles before cooking. There is 800 mL of distilled water in the beaker. After the water boils, put the noodles in and steam them according to the measured steaming time. After steaming, immerse the noodles in a beaker containing 400 mL of cold water for 10 s, drain the water, weigh the wet weight of the cooked noodles, and calculate the water absorption rate according to the following formula: Water absorption rate (%) = ( m 3 - m 4) / m 4 × 100; In the formula: m 3 represents the weight (g) of the noodles before cooking; m 4 represents the wet weight (g) of the cooked noodles.

[0120] It can be seen from the results that with the increase of the addition amount of yam powder, the water absorption rate of yam noodles gradually decreases. However, at the same addition amount, the water absorption rate of modified yam noodles is always higher than that of ordinary yam noodles, and the difference is significant when the addition amounts are 8%, 12% and 16%, indicating that the modified yam powder can improve the water absorption ability of yam noodles during cooking, thereby enhancing the boil resistance of the noodles. At the same time, strong water absorption helps to maintain good taste and texture after long - time boiling or standing.

[0121] 1.4 Turbidity of noodle soup The turbidity of the noodle soup of pure wheat noodles, modified yam noodles and ordinary yam noodles was measured, and the measurement results are as Figure 9 shown.

[0122] Method for measuring the turbidity of noodle soup: Accurately weigh 30 g of noodles. There is 500 mL of distilled water in a beaker. After the water boils, put in the noodles and cook according to the measured cooking time. After cooking, rinse the surface with deionized water and pour the rinsing water into the noodle soup. After the noodle soup cools to room temperature, make up the volume to 500 mL with distilled water, shake well, measure the transmittance of the noodle soup at 720 nm, and calculate the transmittance according to the following formula: T(%) = 10 -A × 100; In the formula: T represents the transmittance of the noodle soup; A represents the absorbance value measured by the noodle soup at a wavelength of 720 nm.

[0123] As Figure 9 shown, with the increase of the addition amount of yam powder, the transmittance of the noodle soup of both types of yam noodles shows a downward trend, indicating that with the addition of yam powder, the turbidity of the noodle soup increases, that is, more substances are released from the yam noodles into the soup, the cooking loss becomes larger, the turbidity of the noodle soup increases, and the boil resistance of the noodles becomes worse.

[0124] With the increase of the addition amount of yam powder, the decline in the transmittance of the noodle soup of modified yam noodles is smaller, and when the addition amount is 8% - 16%, the transmittance of the noodle soup of modified yam noodles is higher than that of ordinary yam noodles, indicating that the modified yam powder can improve the boil resistance of yam noodles.

[0125] 2. Macroscopic evaluation of noodles Macroscopic observation and sensory evaluation were carried out on the appearance and taste of pure wheat noodles, modified yam noodles, and ordinary yam noodles after fresh cooking and after being left for 1 hour.

[0126] 2.1 Evaluation of appearance changes Evaluation method: Weigh 30 g of noodles. Put 500 mL of distilled water in a beaker. After the water boils, put in the noodles and cook them according to the measured cooking time. After cooking, immerse the noodles in a beaker containing 400 mL of cold water for 10 s. Immediately take a photo of them after fishing them out. After standing at room temperature for 1 h, take another photo. Compare the appearance changes of the cooked noodles before and after standing, and check their clumping situation, as Figures 10 - 12 shown.

[0127] Through macroscopic observation, it was found that the pure wheat noodles became grayish-white and dull after being left for 1 h after cooking (as Figure 10 shown), showing obvious adhesion and clumping; in contrast, the color of the ordinary yam noodles after cooking was slightly darker than that of the pure wheat noodles, and the color became lighter and lost its luster after being left for 1 h (as Figure 11 shown), and as the addition amount of ordinary yam powder increased, the noodle adhesion and clumping situation became more serious; compared with the ordinary yam noodles, the cooked modified yam noodles had a lighter color and a smooth surface. Although the color became slightly lighter after being left for 1 h, they still maintained good luster, (as Figure 12 shown), and their adhesion and clumping situation was better than that of the pure wheat noodles, indicating that the addition of modified yam powder could improve the clumping phenomenon of yam noodles. When the addition amount of modified yam powder was 12%, the improvement effect was the most obvious. After being left for 1 h, more moisture was retained on the surface of the noodles, and there was no obvious phenomenon of water absorption, swelling, and whitening.

[0128] 2.2 Sensory evaluation Sensory evaluation method: A 15-person sensory evaluation panel was formed to score and evaluate the color, taste, etc. of the freshly cooked noodles and the noodles after being left for 1 hour. To ensure the accuracy of the evaluation results, the maximum and minimum values were removed when each group of data was statistically analyzed. The specific noodle scoring items and score distributions are shown in the scoring criteria in Table 6. The noodle sensory score results are shown in Table 7 and Table 8.

[0129] Table 6 Noodle scoring standard table

[0130] Table 7 Sensory score results of freshly cooked yam noodles

[0131] Table 8 Sensory score results of cooked yam noodles after being left for 1 h

[0132] As can be seen from Tables 7 and 8, the addition of yam powder can change people's sensory evaluation of cooked noodles. The overall sensory score of modified yam noodles is higher than that of ordinary yam noodles. When the addition amount of modified yam powder is 12%, the color of yam noodles is attractive, the viscosity and elasticity are moderate, and it has a suitable fermented yam flavor, with the highest sensory score.

[0133] Compared with freshly cooked noodles, the sensory scores of pure wheat noodles and yam noodles after being placed at room temperature for 1 h both decreased. This is mainly because during the placement process of the noodles, starch retrogradation and water loss occurred. Starch retrogradation would cause the noodle structure to become more compact, while the loss of water would make the noodle surface dry, which would then lead to the noodles sticking together and becoming lumpy, resulting in a worse taste and overall quality deterioration, and ultimately causing the sensory score to decline.

[0134] For cooked modified yam noodles, the difference in sensory scores before and after placement is small, and the quality change is not obvious. Among them, the modified yam noodles with 12% addition of modified yam powder have the highest sensory score after being cooked and placed for 1 h, and the difference in sensory scores before and after placement is the smallest. This indicates that during the placement process of modified yam noodles, the phenomena of starch retrogradation and water loss are effectively inhibited, the noodles become lumpy less severely, and the taste and quality are better maintained.

[0135] 3. Texture evaluation of noodles Measure and analyze the texture characteristics [hardness, adhesiveness (absolute value), elasticity, cohesiveness, and chewiness] of pure wheat noodles, modified yam noodles, and ordinary yam noodles when they are freshly cooked and after being placed for 1 hour. The results are as Figures 13 - 17 shown.

[0136] Texture measurement method: Accurately weigh 30 g of noodles. There is 500 mL of distilled water in a beaker. After the water boils, put in the noodles and cook according to the measured cooking time. After cooking, immerse the noodles in a beaker containing 400 mL of cold water for 10 s. Immediately take a part of the noodles to measure their texture, and measure the texture of the remaining part of the noodles after being placed at room temperature for 1 h. The TPA experimental parameters are set as follows: pre-test speed 5.0 mm / s, test speed 1.0 mm / s, post-test speed 1.0 mm / s, compression ratio 70%, and minimum sense of force 5 g. When performing texture measurement, each time take 3 noodles and place them horizontally on the stage, and keep the same interval between the noodles. Record the results of hardness, adhesiveness, elasticity, cohesiveness, and chewiness. The experiment is repeated 3 times and the average value is taken.

[0137] The hardness results of different yam noodles are shown in Figure 13 the figure. With the increase of the addition amount of yam powder, the hardness of freshly cooked yam noodles shows an upward trend, but when the addition amount reaches 16%, the hardness decreases; at the same addition amount of yam powder, the hardness of modified yam noodles is higher than that of ordinary yam noodles.

[0138] The change in hardness is an important indicator to measure the quality change of cooked noodles during storage. The hardness difference can reflect the degree of noodle clumping. Generally speaking, a significant increase in hardness means obvious quality deterioration of cooked noodles during storage. As can be seen from the figure, the hardness difference of the modified yam noodles before and after cooking and storage is not large, indicating that during storage, the hardness of the modified yam noodles changes little, the degree of quality deterioration is low, and it can better maintain its initial softness and taste.

[0139] The adhesion results of different yam noodles are shown in Figure 14 the figure. The adhesion of freshly cooked common yam noodles and modified yam noodles ranges from 0.23 to 0.37. The type and addition amount of yam powder have little effect on the adhesion of freshly cooked noodles. When the noodles are cooked and stored for 1 h, the adhesion of both common yam noodles and modified yam noodles increases. In the range of 4%-12% addition amount of yam powder, the adhesion of the modified yam noodles in the freshly cooked state is lower than that of the common yam noodles at the same addition amount, and the change range of adhesion before and after storage is smaller. Among them, the modified yam noodles with an addition amount of 12% have the smallest adhesion and a relatively small change range after storage for 1 h. The change in adhesion is one of the important indicators to measure the texture and taste quality change of cooked noodles. The above research results show that the addition of modified yam powder can significantly improve the adhesion change of yam noodles before and after cooking and storage, making their texture and taste more stable during cooking and storage, and can alleviate the problem of noodle clumping.

[0140] Elasticity refers to the ability of noodles to return to their original state after being compressed and deformed. The elasticity results of different yam noodles are shown in Figure 15 the figure. With the increase in the addition amount of common yam powder, the elasticity of cooked common yam noodles gradually decreases, probably because the addition of common yam powder changes the structure of the noodles, making the yam noodles become looser after cooking and the elasticity weakens. In contrast, with the increase in the addition amount of modified yam powder, the elasticity of cooked modified yam noodles first decreases and then increases. In the range of 8%-16% addition amount, its elasticity is better than that of pure wheat noodles. Therefore, the modified yam noodles are more elastic and have a better taste.

[0141] The cohesiveness results of different yam noodles are shown in Figure 16 the figure. The addition of yam powder can improve the cohesiveness of noodles. In the range of 4%-8% addition amount, the cohesiveness difference between common yam noodles and modified yam noodles is not large. However, when the addition amount of modified yam powder is 12%, the cohesiveness of the modified yam noodles reaches the maximum value, indicating that the internal structure of the noodles is compact. At the same time, the cohesiveness of the modified yam noodles after cooking and storage for 1 h is better than that of pure wheat noodles, and it can still maintain a good chewy texture.

[0142] The chewiness of different yam noodles is shown in Figure 17 the figure. The chewiness of noodles is jointly determined by hardness, elasticity and cohesiveness. The higher the chewiness, the chewier and more resilient the noodle texture, and noodles with high chewiness are generally considered to have better quality. As can be seen from the figure, with the increase in the addition amount of ordinary yam powder, the chewiness of ordinary yam noodles gradually decreases. This may be because the addition of ordinary yam powder changes the internal structure of the noodles, resulting in a decrease in their hardness, elasticity and cohesiveness, thus affecting the overall chewiness of the noodles. However, with the increase in the addition amount of modified yam powder, the chewiness of modified yam noodles increases, and they can still maintain good chewiness after being cooked and left for 1 h.

[0143] From the above texture analysis results, it can be seen that the addition of modified yam powder has a significant improvement effect on the taste and quality stability of yam noodles.

[0144] In summary, the present invention uses Lactobacillus plantarum and Bacillus lacticus DU-106 to ferment yam, changing the microscopic structure of yam and the content of internal starch and protein, and endowing yam with a unique brittle texture after cooking. At the same time, the yam noodles made from modified yam not only have high boiling resistance but also have a chewy texture and are not easy to become lumpy. The preparation method provided by the present invention is simple and safe, suitable for industrial applications, opening up a new way for the development of deep-processed yam products, and having important practical value and broad market prospects.

[0145] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of modified Chinese yam, characterized in that The preparation method includes the following steps: S1 Yam pretreatment: Select healthy yams, peel them, cut them, and after rinsing with sterile water, obtain pretreated yams; S2 Preparation of fermentation substrate: Mix the pretreated yams in S1 with the sterilized edible sugar solution at a mass-to-volume ratio (g:mL) of 1-2:2 to obtain a fermentation substrate; the concentration of edible sugar in the edible sugar solution is 0.01-0.03 g / mL; S3 Fermentation: Inoculate the fermentation substrate described in S2 with a mixed strain. Based on the mass of the pretreated Chinese yam, the total inoculation amount is greater than or equal to 1×10 5 CFU / g, and conduct fermentation at 25-37°C. Stop fermentation when at least one of the following conditions is met: i The pH value of the liquid part of the fermentation substrate is less than or equal to 3.74; ii The starch content of the obtained modified yams after dehydration is greater than or equal to 744.44 mg / g; iii The protein content of the obtained modified yams after dehydration is less than or equal to 93.93 mg / g; After stopping fermentation, a fermentation product is obtained; the mixed strain includes Lactobacillus plantarum ( Lactobacillus plantarum ) and Bacillus sporolactis ( Bacillus sp. ) DU-106; the viable count ratio of Lactobacillus plantarum to Bacillus sporolactis is 600-1200:1; S4 Solid-liquid separation: Remove the liquid part from the fermentation product to obtain modified yams; The degree of dehydration of the modified yams is that the water content of the modified yams after dehydration treatment is ≤5%.

2. The modified Chinese yam according to claim 1, wherein The cutting in S1 is slicing; the thickness of the pretreated yams is 0.5-2 cm; and / or The yam is a Tieguanyin yam; and / or The edible sugar solution in S2 is a white granulated sugar solution, and the concentration of white granulated sugar in the white granulated sugar solution is 0.02 g / mL; the pretreated yams and the sterilized white granulated sugar solution are mixed at a mass-to-volume ratio (g:mL) of 1:

2.

3. The modified Chinese yam according to claim 1, characterized in that, The total inoculum amount described in S3 is 3.005×10 5 -6.01×10 5 CFU / g; and / or In S3, constant temperature fermentation is carried out at 28°C, and fermentation is stopped when the pH of the liquid part of the fermentation substrate is less than or equal to 3.3; and / or The Lactobacillus plantarum is Lactobacillus plantarum nbk-MA2; and / or The viable cell number ratio of the Lactobacillus plantarum to the Bacillus lacticus is 600:

1.

4. Modified yams prepared by the preparation method according to any one of claims 1-3.

5. A cooked Chinese yam, characterized in that, Modified yams prepared by the preparation method according to any one of claims 1-3 or obtained after cooking and processing the modified yams according to claim 4.

6. The cooked yam according to claim 5, wherein The way of the cooking and processing is steaming or boiling.

7. A modified yam powder, characterized in that, Modified yams prepared by the preparation method according to any one of claims 1-3 or ground into powder after dehydration of the modified yams according to claim 4.

8. The modified yam powder according to claim 7, wherein The dehydration method is drying until the water content of the modified yams is ≤5%; and / or The particle size of the modified yam powder is less than or equal to 0.15 mm.

9. Application of the modified yams according to claim 4, the cooked yams according to claim 5 or 6, and the modified yam powder according to claim 7 or 8 in the processing of yam-based foods.

10. A yam noodle, characterized in that, The flour of the yam noodles contains the modified yam powder according to claim 7 or 8.

11. The yam noodles according to claim 10, characterized in that, The flour of the yam noodles includes 8%-16% of the modified yam powder; the flour of the yam noodles also includes wheat flour.

12. The yam noodles according to claim 11, characterized in that, The flour of the yam noodles is composed of 8%-16% of the modified yam powder and 84%-96% of the wheat flour.

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