A prickly pear and Job's tears yogurt and its preparation method

Abstract

This invention provides a prickly pear and Job's tears yogurt and its preparation method, belonging to the field of yogurt preparation technology. The preparation method of the prickly pear and Job's tears yogurt includes the following steps: soaking Job's tears and mixing them with water, then successively pulping, gelatinizing, and then hydrolyzing with α-amylase at high temperature to obtain a Job's tears enzymatic hydrolysate; inoculating the Job's tears enzymatic hydrolysate with probiotic BLH1 seed liquid for fermentation; after fermentation, adding prickly pear juice to the fermentation liquid for further fermentation to obtain a prickly pear and Job's tears fermentation liquid; mixing milk powder, water, and sucrose evenly, homogenizing, sterilizing, cooling, and then mixing evenly with the prickly pear and Job's tears fermentation liquid, inoculating with lactic acid bacteria seed liquid for fermentation, and after fermentation, ripening to obtain the prickly pear and Job's tears yogurt. The prickly pear and Job's tears yogurt provided by this invention has a good taste, high sensory evaluation, significantly retains functional components such as phenols, flavonoids, and vitamin C, and greatly increases GABA content and antioxidant activity.

Description

Technical Field

[0001] This invention relates to the field of yogurt preparation technology, and in particular to a prickly pear and Job's tears yogurt and its preparation method. Background Technology

[0002] Yogurt, a globally popular fermented dairy product, owes its quality essentially to the interaction between microbial metabolic activity and matrix components. Traditional yogurt fermentation primarily focuses on the acidification and gelation of the milk matrix, resulting in relatively simple metabolic pathways and products. With consumers' increasing demands for functional and flavorful foods, developing novel yogurts that combine plant nutrients with the characteristics of fermented dairy products has become an important research direction in the food industry. Prickly pear and Job's tears, as unique medicinal and edible plant resources, offer significant potential for development. Prickly pear is rich in vitamin C, polyphenols, and flavonoid antioxidants, while Job's tears are known for their polysaccharides, phenolamides, and amino acids. Together, they possess immense potential for developing high-value-added functional dairy products.

[0003] However, directly introducing plant-based raw materials into the milk system faces numerous technical challenges. For example, plant components may interfere with the normal metabolism and acid production processes of lactic acid bacteria; their macromolecules such as fiber and starch may disrupt the homogeneity of the protein gel network, leading to texture defects; furthermore, the stability and transformation patterns of plant-derived phenols and other active ingredients in the fermentation environment remain unclear. Therefore, how to coordinate the compatibility of plant components with the milk matrix through process design and guide microbial metabolism in the desired direction is a key scientific issue for successful product development. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a prickly pear and Job's tears yogurt and its preparation method.

[0005] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is a method for preparing prickly pear and Job's tears yogurt, comprising the following steps: (1) Soak the Job's tears and mix them with water, then grind and gelatinize them in sequence, and then hydrolyze them with α-amylase at high temperature to obtain Job's tears hydrolysate; (2) The coix seed hydrolysate was inoculated with probiotic BLH1 seed liquid for fermentation; (3) After fermentation is complete, add prickly pear juice to the fermentation liquid and ferment again to obtain prickly pear and Job's tears fermentation liquid; (4) Mix milk powder, water and sucrose evenly, homogenize, sterilize, cool and mix evenly with the prickly pear and coix seed fermentation liquid, inoculate with lactic acid bacteria seed liquid for fermentation, and after fermentation, ripen to obtain the prickly pear and coix seed yogurt.

[0006] The second technical solution of the present invention is a prickly pear and Job's tears yogurt prepared by the above preparation method.

[0007] The present invention discloses the following technical effects: This invention first pre-ferments prickly pear and Job's tears to obtain a prickly pear and Job's tears fermentation broth, which is then fermented with milk powder and other ingredients to produce yogurt. The pre-fermentation process of this invention is not merely a simple pretreatment of raw materials, but a crucial process driving beneficial biotransformation and physicochemical reconstruction within the system, significantly reducing the astringency of prickly pear. This process effectively coordinates the complex relationships between microbial growth, substrate metabolism, and product synthesis, achieving deep integration of plant components and the milk matrix at the molecular and structural levels. Ultimately, it develops a novel yogurt product with excellent texture, balanced flavor, stable gel structure, and clear functional potential.

[0008] The prickly pear and Job's tears yogurt provided by this invention has a good taste, significantly reduced prickly pear astringency, high sensory evaluation, and significantly retains functional components such as phenols, flavonoids and vitamin C, while greatly increasing GABA content and antioxidant activity. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This invention describes the changes in soluble solids during yogurt fermentation. Figure 2 This invention relates to the changes in γ-aminobutyric acid (GABA) during yogurt fermentation. Figure 3 This invention describes the changes in soluble proteins during yogurt fermentation. Figure 4 This invention relates to the changes in protease activity during yogurt fermentation. Figure 5 This invention relates to the changes in total phenols and total flavonoids in the yogurt. Figure 6 This invention relates to changes in the antioxidant activity of yogurt. Figure 7 This invention relates to changes in organic acids in yogurt. Figure 8 The changes in the water-holding capacity and sensory scores of the yogurt of this invention; Figure 9 The rheological changes of the yogurt of this invention; Figure 10 The infrared spectrum of the yogurt of this invention; Figure 11 The image shows the XRD pattern of the yogurt of this invention. Figure 12 This is a microstructure diagram of the yogurt of the present invention. Detailed Implementation

[0011] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0012] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0013] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0014] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0015] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0016] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0017] This invention provides a method for preparing prickly pear and Job's tears yogurt, characterized by comprising the following steps: (1) Soak the Job's tears and mix them with water, then grind and gelatinize them in sequence, and then hydrolyze them with α-amylase at high temperature to obtain Job's tears hydrolysate; (2) The coix seed hydrolysate was inoculated with probiotic BLH1 seed liquid for fermentation; (3) After fermentation is complete, add prickly pear juice to the fermentation liquid and ferment again to obtain prickly pear and Job's tears fermentation liquid; (4) Mix milk powder, water and sucrose evenly, homogenize, sterilize, cool and mix evenly with the prickly pear and coix seed fermentation liquid, inoculate with lactic acid bacteria seed liquid for fermentation, and after fermentation, ripen to obtain the prickly pear and coix seed yogurt.

[0018] In a preferred embodiment of the present invention, in step (1), the ratio of Job's tears to water is 1:(12-18)w / v; the gelatinization temperature is 85-95 °C and the time is 15-30 min; the amount of high-temperature α-amylase used is 170-230 U / g; and the enzymatic hydrolysis temperature is 85-95 °C and the time is 30-60 min.

[0019] In a preferred embodiment of the present invention, in step (2), the inoculation amount of the probiotic BLH1 seed liquid is 3% v / v-5% v / v; the fermentation conditions are: closed fermentation at 37-39 °C in a carbon dioxide environment for 10-14 h.

[0020] In a preferred embodiment of the present invention, in step (3), the volume ratio of the fermentation liquid to the prickly pear juice is 4:6; the conditions for the second fermentation are: 37-39 °C, 150-200 r / min shaker culture for 28-36 h.

[0021] In a preferred embodiment of the present invention, in step (4), the milk powder is 5%-25% by mass percentage, sucrose is 4%, prickly pear and coix seed fermentation liquid is 15%-35%, and the remainder is water.

[0022] More preferably, in step (4), the milk powder is 5%, 10%, 15%, 20%, or 25% by mass percentage, sucrose is 4%, prickly pear and coix seed fermentation liquid is 15%, 20%, 25%, 30%, or 35%, and the remainder is water.

[0023] In a preferred embodiment of the present invention, in step (4), the sterilization temperature is 90 °C and the time is 10 min; the cooling is to cool to 40 °C.

[0024] In a preferred embodiment of the present invention, in step (4), the concentration of the lactic acid bacteria seed solution is 5 × 10⁻⁶. 8CFU / mL; the inoculation amount of the lactic acid bacteria seed solution is 2% v / v; the lactic acid bacteria seed solution includes Bifidobacterium animalis, Lactobacillus plantarum and Streptococcus thermophilus; the fermentation conditions for inoculating the lactic acid bacteria seed solution are: constant temperature fermentation at 41 °C for 8-12 h; after-ripening at 4 °C for 12 h.

[0025] In a preferred embodiment of the present invention, the ratio of viable counts of Bifidobacterium animalis, Lactobacillus plantarum, and Streptococcus thermophilus is 1:1:2.

[0026] In this invention, Bifidobacterium animalis is subspecies BLH1 (accession number: CCTCC M 20221979), isolated from Guizhou Hongsuantang; Lactobacillus plantarum is Lactobacillus plantarum LB12 (accession number: CCTCC M 2022948), isolated from Guizhou Hongsuantang; and Streptococcus thermophilus is Streptococcus thermophilus Q-1.

[0027] The present invention also provides prickly pear and Job's tears yogurt prepared by the above preparation method.

[0028] The raw materials and strains used in the embodiments of this invention are as follows: Prickly pear (Longli County, Guizhou Province); Job's tears (Guizhou Renxin Agricultural Development Co., Ltd.); milk powder, white sugar (Walmart Supermarket). Bifidobacterium animalis subspecies BLH1 (accession number: CCTCC M 20221979) and Lactobacillus plantarum LB12 (accession number: CCTCC M 2022948) were both isolated from Guizhou Hongsuantang. BLH1 was anaerobically cultured in PTYG liquid medium at 37 °C for 48 h; LB12 was anaerobically cultured in MRS broth medium at 37 °C for 24 h; Q-1 was aerobically cultured in MRS broth medium at 37 °C for 48 h.

[0029] High-temperature α-amylase (Jiangsu Ruiyang Biotechnology Co., Ltd.)

[0030] PTYG medium: 5 g soybean peptone, 5 g tryptone, 10 g glucose, 10 g yeast extract, 1 mL Tween 80, 0.05 g L-cysteine ​​hydrochloride, 4 mL salt solution, 1000 mL distilled water. Salt solution (0.2 g anhydrous calcium chloride, 0.48 g magnesium sulfate heptahydrate, 1 g dipotassium hydrogen phosphate, 1 g potassium dihydrogen phosphate, 10 g sodium carbonate, 2 g sodium chloride, 1000 mL distilled water, refrigerated for later use).

[0031] MRS medium: 10 g peptone, 20 g glucose, 5 g beef meal, 4 g yeast extract, 1 mL Tween 80, 2 g dipotassium hydrogen phosphate heptahydrate, 5 g sodium acetate trihydrate, 2 g triammonium citrate, 0.2 g magnesium sulfate heptahydrate, 0.05 g manganese sulfate tetrahydrate, 1000 mL distilled water.

[0032] Example 1 1. Preparation of Prickly Pear and Job's Tears Yogurt Remove fresh prickly pears from the freezer at -20 °C, thaw them, wash them three times, remove the leaves and stems, juice them using a juicer, strain the juice, and refrigerate in the dark for later use. Wash high-quality Job's tears with clean water and soak them overnight at room temperature, then grind them into a paste at a material-to-water ratio of 1:15 (w / v). Then, place the paste in a 90 °C water bath for gelatinization for 20 minutes, add high-temperature α-amylase (200 U / g) for enzymatic hydrolysis, liquefy at 90 °C for 45 minutes, and refrigerate the resulting Job's tears hydrolysate for later use.

[0033] The prickly pear juice and coix seed enzymatic hydrolysate were sterilized at 90 °C (10 min) and 121 °C (20 min), respectively. After cooling, the coix seed enzymatic hydrolysate was inoculated with 4% probiotic BLH1 seed culture and fermented in a sealed CO2 incubator at 37 °C for 12 h. Then, prickly pear juice was added (the volume ratio of coix seed enzymatic hydrolysate to prickly pear juice was 4:6) and cultured in a shaker at 37 °C and 180 r / min for 32 h to obtain the prickly pear and coix seed fermentation broth, which was then refrigerated for later use.

[0034] After mixing milk powder, water, and sucrose in a certain proportion and homogenizing (6000 r / min, 2 min), sterilize at 90 °C for 10 min, cool to 40 °C, mix with prickly pear and Job's tears fermentation broth, and inoculate with 2% v / v lactic acid bacteria seed culture (5×10⁶). 8 The viable cell ratio of BLH1:LB12:Q-1 in the lactic acid bacteria seed culture was 1:1:2 (CFU / mL). Fermentation was carried out at 41 °C, and after fermentation, it was post-ripened at 4 °C for 12 h.

[0035] 1.1 Single-factor experiment (1) Amount of prickly pear and coix seed fermentation liquid added The following formula was used to evaluate the vitamin C, polysaccharide, and sensory evaluation of prickly pear and coix seed yogurt: milk powder 15%, sucrose 4%, prickly pear and coix seed compound fermentation liquid 15%, 20%, 25%, 30%, 35%, with the remainder being water; lactic acid bacteria seed inoculation amount 2% v / v; viable bacteria ratio of BLH1:LB12:Q-1 in lactic acid bacteria seed liquid 1:1:2; fermentation time 10 h.

[0036] (2) Amount of milk powder added The optimal addition amounts were determined as follows: 25% prickly pear and Job's tears compound fermentation liquid, 4% sucrose, 5%, 10%, 15%, 20%, and 25% milk powder, with the remainder being water. The inoculation amount of lactic acid bacteria seed culture was 2% v / v, and the live bacteria ratio of BLH1:LB12:Q-1 in the lactic acid bacteria seed culture was 1:1:2. The fermentation time was 10 h. The vitamin C, polysaccharide, and sensory scores of the prickly pear and Job's tears yogurt were evaluated.

[0037] (3) Fermentation time The optimal addition amounts were determined as follows: 25% prickly pear and Job's tears compound fermentation liquid, 15% milk powder, 4% sucrose, and the remainder water. The inoculation amount of lactic acid bacteria seed culture was 2% v / v, and the live bacteria ratio of BLH1:LB12:Q-1 in the lactic acid bacteria seed culture was 1:1:2. The fermentation times were 8 h, 9 h, 10 h, 11 h, and 12 h. The vitamin C, polysaccharide, and sensory scores of the prickly pear and Job's tears yogurt were evaluated.

[0038] Table 1 Sensory rating criteria

[0039] 1.2 Response Surface Optimization Using vitamin C, polysaccharides, and sensory scores as response indicators, response surface methodology was designed and analyzed using Design Expert 13.0 data processing software to evaluate the amount of prickly pear and Job's tears fermentation liquid added, the amount of milk powder added, and the fermentation time.

[0040] in conclusion: 1) Conclusions of the single-factor experiment: Table 2 shows the effects of the amount of prickly pear and Job's tears fermented liquid, the amount of milk powder, and the fermentation time on the vitamin C, polysaccharides, and sensory properties of yogurt. When the amount of prickly pear and Job's tears fermented with BLH1, which significantly reduces the astringency of prickly pear, was 25%, the sample did not have the highest vitamin C content, but its sensory score reached the highest of all samples at 84.15 points, while maintaining a high polysaccharide content of 3.11 mg / mL. In contrast, although the 35% addition amount had the highest vitamin C content, the sensory score decreased significantly. This may be because the addition of too much fermented liquid resulted in an excessively strong sour and astringent taste, affecting the mouthfeel; its polysaccharide content also decreased, indicating that excessive addition could actually affect the retention of active ingredients. Therefore, the 25% fermented liquid addition amount achieved the best balance between nutritional value and sensory acceptability.

[0041] Regarding the choice of milk powder addition amount, 15% shows unique advantages. This amount has the highest sensory score among the milk powder addition groups, reaching 82.25 points, indicating that it can effectively improve the product texture and flavor, while not producing an overly strong milky smell like higher addition amounts. This suggests that excessive milk powder addition may mask the unique flavor of fermented products and affect overall acceptability.

[0042] The choice of fermentation time is crucial. A fermentation time of 10 hours yielded excellent results, achieving the highest sensory score of 83.6 points among all samples, a polysaccharide content of 4.14 mg / mL, and maintaining a high level of vitamin C. This result suggests that 10 hours may be the optimal period for microbial metabolism, ensuring sufficient production of active substances and the formation of good flavor. Shorter fermentation times may result in incomplete metabolism, while excessively long fermentation times may lead to over-fermentation or the development of undesirable flavors.

[0043] Table 2 Single-factor optimization experiment

[0044] Note: 1-1 to 1-5 represent the amount of prickly pear and Job's tears compound fermented liquid added (15%, 20%, 25%, 30%, 35%); 2-1 to 2-5 represent the amount of milk powder added (5%, 10%, 15%, 20%, 25%); 3-1 to 3-5 represent the fermentation time (9h, 10h, 11h, 12h, 13h). 2) Conclusions of the response surface optimization experiment Response surface methodology was optimized using vitamin C, polysaccharides, and sensory scores as response indicators. The amount of prickly pear and coix seed fermentation liquid added (A), the amount of milk powder added (B), and the fermentation time (C) were selected for three-factor, three-level response surface analysis. The experimental results are shown in Table 3 below.

[0045] Table 3 Results of Response Surface Design

[0046] The experimental data in Table 3 were analyzed using Design Expert 13 software for multiple regression analysis. Analysis of variance was performed on the three response values: vitamin C, polysaccharides, and sensory scores. Combining these three response values, the optimal response surface methodology was determined as follows: 30.00% prickly pear and coix seed fermentation broth, 17.87% milk powder, and 9.89 h fermentation time. Under these optimized conditions, the predicted value for vitamin C was 183.99 mg / 100g, the predicted value for polysaccharides was 3.11 mg / mL, and the predicted value for sensory scores was 84.24. To facilitate practical experimental operation, the optimized conditions were revised as follows: 30% prickly pear and coix seed fermentation broth, 18% milk powder, and 10 h fermentation time. A verification experiment was conducted using the revised optimized conditions. Under these conditions, the vitamin C content, polysaccharide content, and sensory score of the prickly pear and coix seed yogurt were determined. The results showed that the vitamin C content of the prickly pear and coix seed yogurt was 180.02 mg / 100g, the polysaccharide content was 3.22 mg / mL, and the sensory score was 85.25. The resulting prickly pear yogurt had virtually no astringent prickly pear taste.

[0047] 1.2 Compare the pH, viable cell count, soluble solids, γ-aminobutyric acid (GABA), soluble protein, protease, total phenols, total flavonoids, antioxidant activity, phenols, organic acids, water holding capacity, sensory score, texture, rheology, Fourier transform infrared spectroscopy, XRD, and SEM of regular yogurt (PY), yogurt with only unfermented compound liquid added (RCY), and yogurt with prickly pear and coix seed fermentation liquid added (FRCY).

[0048] Regular yogurt: Yogurt prepared without the addition of prickly pear and Job's tears fermentation liquid; Yogurt with only unfermented compound liquid added: Yogurt prepared by replacing the prickly pear and Job's tears fermentation liquid with a mixture of Job's tears enzymatic hydrolysate and prickly pear juice.

[0049] Regular yogurt, yogurt with only unfermented compound liquid, and yogurt with prickly pear and Job's tears fermentation liquid were all prepared according to the aforementioned optimal parameters.

[0050] in conclusion: (1) Changes in pH and viable cell count Table 4 shows the pH dynamics of the three yogurt samples during fermentation, reflecting the fundamental differences in microbial metabolic activity and the initial buffering capacity of the system. The pH of all three samples decreased slowly in the early stages, but dropped sharply after 6 hours of fermentation due to the increase in the lactic acid bacteria index. This may be attributed to the lactic acid bacteria consuming lactose and producing lactic acid and other metabolites. The initial pH of the RCY and FRCY groups, which added prickly pear and Job's tears compound solution, was lower than that of the PY group. This is attributed to the contribution of various organic acids (such as citric acid, tartaric acid, and malic acid) abundant in prickly pear. The initial pH of the FRCY group was higher than that of the RCY group because some plant acids were consumed during the pre-fermentation process. However, it exhibited a more stable and faster pH decrease trend throughout the fermentation process. This result indicates that the microbial community cultivated by the pre-fermentation process has strong metabolic activity; it can not only rapidly utilize lactose but also efficiently metabolize the plant substrate.

[0051] By dynamically monitoring the viable cell count during fermentation, the significant impact of the pre-fermentation process on the microbial system can be clearly observed. Throughout the fermentation cycle, the viable cell counts of the three groups of samples did not change much in the initial stage (0-4 h), but after entering the logarithmic growth phase, the FRCY group with added pre-fermentation broth showed a significant microbial advantage, with the number of various lactic acid bacteria (LB12, Q-1, BLH1) and the total viable cell count reaching their highest levels at the fermentation endpoint (10 h). This phenomenon may stem from the dual biological effects of the pre-fermentation broth: First, the prickly pear and Job's tears substrate acts as an activation culture medium for the microorganisms during pre-fermentation, allowing the lactic acid bacteria to fully adapt and remain in a highly active state; second, pre-fermentation partially degrades the macromolecules in the plant raw materials into easily usable monosaccharides, peptides, and other nutrients. When this fermentation broth, rich in activated microorganisms and pre-digested nutrients, is inoculated into the milk base, the microbial community can quickly adapt to the environment and initiate efficient metabolism, thereby driving a stronger acid production process, catalyzing the synthesis of functional metabolites such as extracellular polysaccharides and calcium lactate, and further generating richer flavor substances through protein hydrolysis and amino acid conversion pathways.

[0052] Table 4. pH and viable cell count during yogurt fermentation.

[0053] Note: Significant differences exist between different letters in the same row of the table. P< 0.05); (2) Changes in soluble solids Figure 1The SSD% results showed that adding the prickly pear and Job's tears compound liquid significantly increased the soluble solids content of the yogurt system. This was mainly attributed to the sugars, organic acids, soluble polysaccharides, and various small molecule metabolites introduced during the plant raw materials and microbial pre-fermentation process. During the subsequent fermentation process, the soluble solids content of all three groups of samples showed a decreasing trend due to the vigorous metabolism of lactic acid bacteria and the continuous consumption of soluble substrates such as sugars. While the FRCY group showed a more significant decrease due to its strongest microbial activity, it still retained a relatively large amount of soluble matter. The RCY and FRCY groups contained more soluble solids than the PY group, providing direct evidence for their potentially superior viscosity, flavor, and nutritional value.

[0054] (3) Changes in γ-aminobutyric acid (GABA) Throughout the fermentation process, the change in GABA content is a result of microbial synthesis and degradation. For example... Figure 2 As shown, in the early stages of fermentation, the GABA content in all groups generally decreased. This is mainly because lactic acid bacteria are in a rapid proliferation phase, requiring a large amount of nitrogen and energy to build cells. At this time, GABA, whether it is naturally present in the fermented milk or contained in exogenous additives, is preferentially decomposed and metabolized by lactic acid bacteria as an easily utilized and high-quality nitrogen and carbon source, providing a material basis for their growth. Therefore, in the early stages of fermentation, the rate of GABA consumption is greater than its rate of synthesis. However, in the RCY and FRCY groups, we observed a rebound in GABA content in the middle and later stages of fermentation. This may be attributed to the sharp drop in environmental pH caused by acid production by lactic acid bacteria as fermentation continues. This acidic stress activates the acid stress response mechanism of lactic acid bacteria, the most important of which is the activation of the glutamate decarboxylase (GAD) system. GAD can use glutamate as a substrate to convert it into GABA. This reaction consumes one hydrogen ion for every molecule of GABA produced, thus effectively helping the bacteria maintain pH homeostasis within the cell and resisting external acid stress.

[0055] The PY group lacked an additional source of glutamate, and the limited substrate in the milk, after initial consumption, could not support effective GABA resynthesis, thus its content continued to decrease. The RCY group, on the other hand, benefited from the fact that prickly pear and Job's tears are rich in glutamate and various amino acids, providing an abundant material basis for lactic acid bacteria fermentation. This enabled the initiation of the GABA pathway under acidic pressure, resulting in a rebound in GABA content. The FRCY group, during its pre-fermentation stage, likely already contained a small amount of pre-synthesized GABA. More importantly, it was rich in highly active GAD enzymes induced under high acidity. When these fermentation broths were added to the milk, these exogenous GAD enzymes synergistically enhanced the endogenous GAD enzymes induced by the lactic acid bacteria, greatly accelerating the conversion of glutamate substrates into GABA. This resulted in the FRCY group having the highest GABA synthesis efficiency and ultimately a higher content than the other groups.

[0056] (4) Changes in soluble proteins like Figure 3 In the early stages of fermentation, lactic acid bacteria are in a rapid growth phase, requiring large amounts of amino acids and short peptides as nitrogen sources to synthesize their own proteins. Extracellular proteases secreted by lactic acid bacteria begin to hydrolyze large milk proteins such as casein, degrading them into peptides and amino acids. These hydrolysis products have small molecular weights and are soluble in the supernatant, resulting in a high level of soluble protein content measured in the early stages of fermentation. After 8 hours of fermentation, the soluble protein content of all three groups of samples experienced a sharp drop, a crucial turning point. The core driving force was that the pH of the fermentation system dropped to and exceeded the isoelectric point of casein. Because lactic acid bacteria continuously produce acid, the pH of the yogurt system continued to decrease. The isoelectric point of casein is approximately pH 4.6. When the pH of the yogurt drops to 4.6, the net charge on the surface of casein molecules is zero, and the electrostatic repulsion between molecules disappears. The casein micelles, destabilized by their charge, begin to aggregate violently, forming a large, insoluble three-dimensional gel network structure through hydrophobic interactions—a hallmark of yogurt coagulation and texture formation. As the gel network shrinks and matures, a large amount of water and whey is expelled. Proteins originally dissolved within the network (including incompletely degraded casein and some larger peptides from earlier hydrolysis) are also encapsulated, drawn in, or co-precipitated as the gel network shrinks. Consequently, they cannot remain in the supernatant after centrifugation, resulting in a sharp decrease in soluble protein content. Therefore, groups PY, RCY, and FRCY all exhibited the same decreasing trend.

[0057] (5) Changes in protease like Figure 4The protease activity of regular yogurt (PY) was generally low, gradually increasing and stabilizing during fermentation. The RCY and FRCY groups showed significantly higher activity than the PY group. In the RCY group, activity decreased initially (0-4 h) and then gradually increased. In the FRCY group, activity stabilized initially (0-6 h), then increased rapidly, reaching its peak at the end of fermentation. The highest activity in the FRCY group indicates that the prickly pear and Job's tears fermentation liquid was more effective than the unfermented liquid, possibly due to the production of more active substances or probiotics during fermentation. Regular yogurt (PY) had the lowest activity, indicating weaker protease activity in yogurt without prickly pear and Job's tears liquid. In conclusion, the addition of prickly pear and Job's tears liquid (RCY and FRCY) significantly increased the protease activity of yogurt, suggesting that components in prickly pear and Job's tears may promote protease activity or microbial growth and metabolism.

[0058] (6) Total phenols and total flavonoids Figure 5 This study clearly revealed the complex effects of adding prickly pear and coix seed compound liquid and fermentation treatment on the functional components of yogurt. The total phenol and total flavonoid contents of RCY and FRCY were significantly higher than those of PY, indicating that prickly pear and coix seed raw materials themselves are good sources of these bioactive substances. However, it is noteworthy that the total phenol and total flavonoid contents of the sample using prickly pear and coix seed fermentation liquid (FRCY) were lower than those of the sample with unfermented liquid (RCY). This phenomenon may be due to the complex influence of the fermentation process on the active components in the raw materials. During fermentation, microorganisms utilize the nutrients in the culture medium for growth and metabolism. Some polyphenols and flavonoids may be transformed or decomposed by microorganisms as substrates, resulting in a decrease in their absolute content compared to the unfermented raw material liquid. At the same time, enzyme systems (such as glycosidases) produced by microbial metabolism may hydrolyze and transform the glycosidic structures of flavonoids. Although this may improve their bioavailability, it often manifests as a decrease in apparent content in conventional assay methods. This result demonstrates that while fermentation processes impart superior texture, flavor, and new bioactive substances to functional foods, they also lead to a decrease in the retention rate of some heat-sensitive and easily converted components. Nevertheless, the core functional component levels in the FRCY group were still significantly higher than those in the benchmark yogurt, indicating that this fermentation process successfully transformed yogurt into a functional food rich in plant-based bioactive components while improving overall quality.

[0059] (7) Antioxidant activity The antioxidant activity results are closely related to the complex interactions between the retention of plant bioactive components and microbial transformation. For example... Figure 6As shown, both the RCY group (with unfermented broth) and the FRCY group (with fermented broth) exhibited strong DPPH and ABTS free radical scavenging abilities and iron reducing power (FRAP), reflecting the bioactivity of naturally occurring vitamin C and flavonoids in the prickly pear raw material. These substances demonstrate superior in vitro antioxidant properties. However, the antioxidant activity of the FRCY group was slightly lower than that of the RCY group. P The concentrations >0.05 revealed a dual impact of microbial metabolism on the active ingredients: while the enzymatic hydrolysis of glycoside flavonoids by lactic acid bacteria during fermentation may improve their long-term bioavailability, it alters their reactive sites in the short term; simultaneously, the irreversible degradation of vitamin C in the fermentation system and metabolic activities reduces its antioxidant activity. Notably, the antioxidant activity of the FRCY group was still significantly higher than that of the PY group, indicating that while microbial metabolism degrades some native antioxidants, it may also form new antioxidant pathways through protein hydrolysis to generate antioxidant peptides or produce microbial-derived antioxidants, thus partially compensating for the loss of activity. This series of changes reveals that the RCY group maximized the immediate antioxidant potential of plant raw materials, while the FRCY group achieved improved overall product quality and transformed the structure of active ingredients through microbial modification, providing a new direction for research on its long-term health benefits.

[0060] (8) Phenolics Table 5 clearly reveals the effects of adding the prickly pear and coix seed compound liquid and its pre-fermentation treatment on the phenolic composition of yogurt. Regular yogurt (PY) contains almost no characteristic phenolic substances listed in the table, except for trace amounts of gallic acid, confirming that cow's milk itself is not the source of these plant-derived phenolic substances. However, the RCY and FRCY groups, due to the addition of the prickly pear and coix seed compound liquid, showed significantly higher levels of all tested phenolic substances than the PY group, directly proving that prickly pear and coix seed are contributors to these functional components. It is noteworthy that the pre-fermentation treatment produced a complex and crucial two-way effect: on the one hand, it led to a decrease in the content of some phenolic substances compared to the unfermented group (RCY), for example, the levels of gallic acid, catechins, and rutin in the FRCY group were significantly lower than those in the RCY group. This is mainly because, during the pre-fermentation stage, lactic acid bacteria and their secreted enzymes biotransform or degrade these phenolic substances. For example, they hydrolyze complex ellagitannins into ellagic acid, or perform glycoside hydrolysis of flavonoid glycosides (such as rutin), resulting in a reduction of their parent structure. However, on the other hand, the fermentation process also synthesizes or increases specific phenolic substances. The chlorogenic acid content in the FRCY group was significantly higher than that in the RCY group, which is highly likely a result of microbial metabolism converting precursor substances into chlorogenic acid. More importantly, epicatechin, which was not detected in the RCY group, appeared in the FRCY group, strongly demonstrating that microbial fermentation can generate or release new active phenolic components through biotransformation.

[0061] In conclusion, while the pre-fermentation process degrades some phenolic substances, it also synthesizes others and may enhance their bioavailability by converting bound phenolic acids into free forms. Therefore, it cannot be simply assumed that fermentation reduces the total phenolic content; rather, it optimizes and transforms the composition of phenolic substances, which may have a more positive impact on the antioxidant activity and functionality of yogurt.

[0062] Table 5. Phenolic content of yogurt

[0063] Note: Significant differences exist between different letters in the same column of the table. P< 0.05).

[0064] (9) Organic acids like Figure 7 As shown, a comprehensive analysis of the organic acid content in the three yogurt samples clearly reveals that the regular yogurt (PY group) exhibits typical milk-based fermentation characteristics, with relatively simple organic acid composition, primarily lactic acid, reflecting the basal metabolic level of conventional lactic acid bacteria under limited substrate conditions. While the RCY group, which added unfermented prickly pear and Job's tears extract, showed some changes in organic acid composition compared to the PY group, the overall increase was limited. This indicates that although the physical addition of plant materials introduced additional substrates, it failed to fully stimulate the potential of the microbial metabolic network.

[0065] Most notably, the FRCY group, which incorporated pre-fermentation broth, exhibited a comprehensive and significant enrichment of organic acids, particularly in key organic acids such as lactic acid, malic acid, and citric acid. This phenomenon reveals that the pre-fermentation stage significantly optimized the microbial community structure, enriched the enzyme system, and pre-generated a large number of metabolic intermediates. This allowed the microbial community to utilize both milk and plant-derived substrates more efficiently after inoculation onto the milk base, while simultaneously enhancing the flow of glycolysis, the tricarboxylic acid cycle, and multiple secondary metabolic pathways. Consequently, a fermentation system with higher metabolic activity and a richer content of flavor precursors was formed. This distinguishes the FRCY group from the other two groups in terms of taste, flavor, and functional characteristics.

[0066] (10) Water holding capacity like Figure 8As shown, the plain yogurt (PY group) had the lowest water-holding capacity, consistent with its relatively loose and porous casein gel network structure, which cannot effectively retain moisture. The RCY group, with the addition of unfermented prickly pear and barley liquid, showed a significant improvement in water-holding capacity, mainly attributed to the physical filling effect of starch granules and dietary fiber in the plant materials, which can absorb and bind some free water; however, this improvement was relatively limited. The FRCY group, with the addition of pre-fermented liquid, achieved the highest water-holding capacity. This is fundamentally due to the dual biological effects of the pre-fermentation process: the extracellular polysaccharides produced by microbial metabolism have extremely strong hydrophilicity, binding a large number of water molecules through hydrogen bonding; simultaneously, the dense and uniform "protein-polysaccharide" composite gel network formed during fermentation has a finer microporous structure, physically fixing more water through capillary action, thus greatly reducing whey separation. This result functionally confirms that the pre-fermentation process significantly improves the structural stability of the product by optimizing the microstructure and chemical composition of the gel network. The water-holding capacity results are in high agreement with the microstructure and rheological data observed by scanning electron microscopy, clearly revealing the influence of different treatments on the water-holding capacity of the yogurt gel network.

[0067] (11) Sensory rating Sensory evaluation results comprehensively reflect consumers' scientific assessment of the overall acceptability of a product. For example... Figure 8 As shown, the regular yogurt (PY group) received the lowest score, which is related to its relatively simple flavor, basic texture, and lack of unique taste from plant-based ingredients. The RCY group (with added unfermented liquid) saw a significant improvement in sensory scores, mainly due to the natural plant aroma, moderate sweet and sour taste introduced by the prickly pear and barley liquid, as well as the improved texture brought by its solids. However, its flavor complexity and superior texture have not yet been fully explored. The FRCY group (with added fermented liquid) received the highest score, which is the inevitable result of its comprehensive quality optimization: in terms of flavor, the volatile substances such as esters and sulfur compounds produced by pre-fermentation jointly create a rich and harmonious fermented aroma, effectively masking any unpleasant odors that may come from plant-based ingredients; in terms of texture, higher firmness and viscoelasticity give the product a full and solid mouthfeel, while its excellent water-holding capacity ensures a smooth and moist mouthfeel, avoiding a powdery texture; in terms of taste, the rich spectrum of organic acids brings a multi-layered sour experience, and although prickly pear has an astringent taste, this astringency can be significantly reduced through probiotic fermentation. This comprehensive improvement in flavor, texture, taste, and nutritional value brought about by microbial transformation ultimately gained the highest consumer recognition at the sensory level.

[0068] (12) Texture Texture reflects the strength, stability, and mouthfeel characteristics of the yogurt gel network. As shown in Table 6, the FRCY group performed best in most indicators, followed by the RCY group, while the PY group performed the worst. This clearly indicates that the additives (prickly pear and Job's tears compound liquid), especially the pre-fermented compound liquid, have a significant effect on improving the texture of yogurt. The FRCY and RCY groups had higher hardness, indicating that their gel networks were the most robust. This is mainly attributed to the extracellular polysaccharides (EPS) contained in the prickly pear and Job's tears compound liquid. Calcium lactate, as a hard filler particle, works together with EPS, as a hydrophilic colloid, to effectively enhance the supporting structure of the casein network, forming a denser gel structure. Cohesion represents the strength of the bonds within the gel. The FRCY group was higher than the other two groups, indicating that its protein-protein and protein-polysaccharide interactions were the strongest, and its internal gel structure was the most coherent and stable. This is closely related to the deeper proteolysis and the better gel-forming environment brought about by the pre-fermentation liquid. There was no significant difference in cohesion among the three groups of samples, indicating that the addition of plant components and fermentation treatment did not disrupt the uniformity of the gel. The elasticity of the FRCY group was higher than that of the PY and RCY groups. This means that the FRCY gel network has a stronger ability to recover its original shape after the external force is removed. This is usually related to a more flexible and elastic three-dimensional network, which is likely due to the filling and regulating effect of EPS, allowing the gel to maintain its firmness without losing its flexibility. In summary, the FRCY group, through the generation of two key components, calcium lactate crystals and extracellular polysaccharides (EPS), has undergone profound physical and chemical interactions with the casein network, constructing a high-strength, highly cohesive, and elastic composite gel structure. This result fully demonstrates from a textural perspective that the pre-fermentation strategy successfully transforms plant raw materials into an effective tool for improving the physical quality of dairy products, rather than simply adding flavor. This has clear guiding significance for the development of high-quality functional yogurt.

[0069] Table 6 Texture properties of yogurt

[0070] Note: Significant differences exist between different letters in the same column of the table. P< 0.05) (13) Rheology like Figure 9As shown, the storage modulus G' of all three groups of samples is greater than the energy dissipation modulus G'', indicating that the sample system is dominated by elastic gel behavior. The G' and G'' of the FRCY and RCY groups are higher than those of the PY group, mainly due to the modifying effect of the prickly pear and coix seed components on the casein gel network. The FRCY group has the highest G', primarily due to the strengthening effect of active substances produced by the prickly pear and coix seed fermentation broth under the action of lactic acid bacteria on the gel network: extracellular polysaccharides (EPS) produced by microbial metabolism can fill the gaps in the protein network, enhancing the stability of the three-dimensional structure, while small molecule acids (such as lactic acid and acetic acid) generated during fermentation promote the formation of denser hydrophobic crosslinks of casein near the isoelectric point. Furthermore, the molecular weight of polyphenols in prickly pear decreases after fermentation, reducing their steric hindrance effect on protein crosslinking, and may instead protect the gel structure through antioxidant effects. Meanwhile, the starch in coix seed may be partially enzymatically hydrolyzed into short-chain dextrins during fermentation, forming additional hydrogen bond interactions with casein, jointly enhancing gel strength. In contrast, the RCY group, although containing unfermented prickly pear and Job's tears liquid, had a G' value between FRCY and PY. This is because while the natural components in the unfermented liquid (such as Job's tears amylose and prickly pear pectin) can assist the protein network through physical filling and weak gelation effects, the large-molecule polyphenols and undegraded plant cell wall components may partially hinder the complete cross-linking of proteins, resulting in a less effective enhancement than fermented liquids. The PY group, being ordinary yogurt, relies solely on the gelation effect of milk proteins (casein and whey protein) and lacks the synergistic effect of plant components, thus exhibiting the lowest G' value. This result confirms that the addition of prickly pear and Job's tears liquid constructs a highly elastic, low-frequency-dependent, stable gel network, providing a theoretical basis for the development of functional fermented dairy products.

[0071] (14) Fourier transform infrared (FTIR) Fourier transform infrared (FTIR) spectroscopy results show that ( Figure 10 The absorption peaks of different samples were similar, but the differences in transmittance of the three groups of samples in different spectral ranges reflected the effects of adding prickly pear and coix seed compound liquid and microbial fermentation on some characteristic functional groups.

[0072] In the protein characteristic region, the amide I band (1635 cm⁻¹) of RCY (with added unfermented broth) is visible. -1 ) and amide II band (1540cm) -1Compared to PY (regular yogurt), the slight changes in peak shape and baseline can be attributed to the perturbation of the protein hydrogen bond network by the binding of prickly pear polyphenols to milk proteins and the synergistic effect of plant-derived proteins. FRCY (with added fermentation broth) further exhibits a significant increase in peak width or change in absorption intensity in this region, directly confirming the limited hydrolysis of casein by microbial proteases during pre-fermentation, generating more polypeptide segments and thus altering the microscopic chemical environment of amide bonds. A more significant difference is observed in the carbohydrate fingerprint region (1000-1100 cm⁻¹). -1 The complex peak enhancement of FRCY and RCY in this region reflects the superposition of coix seed starch with soluble sugars such as prickly pear fructose and glucose. The peak observed near 1057 cm⁻¹ may be a result of COC stretching vibrations, suggesting the presence of pyranoglycosidic bonds. The sample's RCY and FRCY values ​​are between 3300 and 3500 cm⁻¹. -1 The OH stretching vibration peaks in the region are more pronounced, indicating that the intermolecular hydrogen bond network is enhanced after the addition of the prickly pear and coix seed composite liquid.

[0073] (15) XRD In X-ray diffraction (XRD) patterns, broad, diffuse peaks around 20° are typical characteristics of amorphous substances, and their intensity reflects the relative content of amorphous components (such as proteins, polysaccharides, and amorphous sugars) in the sample. Conversely, weak diffraction peaks around 40° represent crystalline substances present in the sample, and their intensity reflects the amount and degree of crystallinity.

[0074] like Figure 11As shown, the PY group exhibits a higher peak intensity at 20°, attributed to its gel network primarily composed of amorphous casein micelles and highly hydrated amorphous lactose, thus displaying a strong amorphous scattering signal. The weaker 40° diffuse peak indicates a low crystal content in ordinary yogurt; the few crystals present may originate from trace amounts of incompletely dissolved lactose or minerals, resulting in low crystallinity and content. The FRCY group shows a lower 20° peak intensity, possibly due to a large number of tiny calcium lactate crystals acting as filler particles, which, along with amorphous substances such as extracellular polysaccharides produced by lactic acid bacteria, embed and reinforce the casein gel network. This "particle-reinforced composite material" structure makes the amorphous phase network more compact, relatively reducing scattering power, thus flattening the broad amorphous peak. This precisely illustrates that the FRCY sample has the most compact and complex microstructure. In other words, the reinforcement of the crystalline phase inhibits the network expansion of the amorphous phase, relatively reducing its scattering signal. The higher 40° diffuse peak intensity of the FRCY group indicates the highest content and best crystallinity of crystalline substances in the FRCY sample, mainly attributed to the pre-fermentation process. The fermented broth of prickly pear and Job's tears contains lactic acid produced by lactic acid bacteria metabolism. When this lactic acid combines with the abundant calcium ions in the milk matrix, it readily forms calcium lactate crystals. These crystals exhibit a standard diffraction peak around 40°, which is the main reason for the significant enhancement of this peak. The peak intensities at 20° and 40° in the RCY group are between those of the PY and FRCY groups, indicating that the unfermented prickly pear and Job's tears broth introduces sugars and starches, partially promoting lactose crystallization or introducing microcrystalline starch, resulting in a stronger crystal signal (40°) than the PY group. However, due to the lack of calcium lactate and extracellular polysaccharides produced by pre-fermentation, the structural reinforcement of its gel network is not as strong as that of the FRCY group, and therefore the amorphous network remains relatively loose. In summary, the FRCY group produced calcium lactate crystals and extracellular polysaccharides through pre-fermentation. These two components work synergistically to create a dense "crystalline-amorphous composite gel" structure, which is expected to bring better texture and stability.

[0075] (16) SEM A comprehensive analysis of the scanning electron microscopy results clearly reveals fundamental differences in the gel network structures of the three groups of samples. For example... Figure 12As shown, regular yogurt (PY) exhibits a typical loose three-dimensional network of casein with a relatively obvious porous structure, which is the baseline gel morphology formed by pure milk matrix fermentation. The RCY group, with the addition of unfermented prickly pear and Job's tears liquid, shows physical structural filling and interference caused by the embedding of plant particles. This is consistent with its improved texture in terms of hardness and adhesiveness, but it failed to fundamentally reshape its gel strength. The FRCY group, with the addition of pre-fermented liquid, exhibits an exceptionally dense and porous "sponge-like" strong gel network, which is the core of understanding its comprehensive superior performance. This unique microstructure directly corresponds to and perfectly explains its macroscopically exhibited highest hardness, adhesiveness, and viscoelasticity. The formation of this structure stems from a dual biological effect induced by the pre-fermentation process: on the one hand, vigorous microbial metabolism produces abundant organic acids such as lactic acid and malic acid, rapidly driving protein gelation and intense dehydration shrinkage, thus forming a rough and porous framework; on the other hand, the extracellular polysaccharides and calcium lactate microcrystals produced by metabolism act as natural bio-adhesives and cross-linking points, filling and stabilizing the network formed by this intense shrinkage, ultimately constructing a strong and tough three-dimensional composite structure. This microstructural reshaping driven by biotransformation is directly manifested macroscopically in the comprehensive improvement of the hardness, cohesiveness, and other textural parameters of this group of samples, proving that the pre-fermentation process achieves fundamental optimization of product texture by regulating the microstructure.

[0076] In summary, this invention, using vitamin C, polysaccharides, and sensory evaluation scores as the main indicators, determined the optimal fermentation process parameters for prickly pear and Job's tears yogurt through single-factor and response surface methodology: 30% prickly pear and Job's tears fermentation liquid, 18% milk powder, and a fermentation time of 10 h. Under these conditions, the yogurt produced had a vitamin C content of 180.02 mg / 100g, a polysaccharide content of 3.22 mg / mL, and a sensory evaluation score of 85.25. Further in-depth research on the dynamic changes during the fermentation process showed that, compared with ordinary yogurt (PY) and yogurt with only unfermented compound liquid (RCY), yogurt using pre-fermented compound liquid (FRCY) exhibited superior comprehensive fermentation characteristics, with stronger microbial activity, a more rapid pH decrease, and more efficient conversion of soluble solids. Regarding metabolites, the pre-fermentation process significantly activated the glutamate decarboxylase system of microorganisms, achieving the targeted accumulation of γ-aminobutyric acid (GABA); simultaneously, through the action of proteases, soluble protein metabolism reached dynamic equilibrium, providing the molecular basis for the product's texture and nutrition.

[0077] At the chemical composition level, although pre-fermentation led to a decrease in the content of some plant-derived vitamin C and total flavonoids, the microbial transformation enriched the types and contents of organic acids, and the core phenolic substances were retained, allowing FRCY to maintain significant antioxidant activity. In terms of physical structure, Fourier transform infrared spectroscopy and X-ray diffraction analysis jointly showed that a protein-polysaccharide complex gel network was formed in FRCY; scanning electron microscopy further revealed its uniform and dense "sponge-like" microstructure, consistent with its optimal textural properties, highest water-holding capacity, and strongest rheological gel strength, and it received the highest recognition in sensory evaluation.

[0078] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing prickly pear and Job's tears yogurt, characterized in that, Includes the following steps: (1) Soak the Job's tears and mix them with water, then grind and gelatinize them in sequence, and then hydrolyze them with α-amylase at high temperature to obtain Job's tears hydrolysate; (2) The coix seed hydrolysate was inoculated with probiotic BLH1 seed liquid for fermentation; (3) After fermentation, add prickly pear juice to the fermentation liquid and ferment again to obtain prickly pear and Job's tears fermentation liquid; (4) Mix milk powder, water and sucrose evenly, homogenize, sterilize, cool and mix evenly with the prickly pear and coix seed fermentation liquid, inoculate with lactic acid bacteria seed liquid for fermentation, and after fermentation, ripen to obtain the prickly pear and coix seed yogurt.

2. The preparation method according to claim 1, characterized in that, In step (1), the ratio of Job's tears to water is 1:(12-18) w / v; the gelatinization temperature is 85-95 °C and the time is 15-30 min; the amount of high-temperature α-amylase used is 170-230 U / g; and the enzymatic hydrolysis temperature is 85-95 °C and the time is 30-60 min.

3. The preparation method according to claim 1, characterized in that, In step (2), the inoculation amount of the probiotic BLH1 seed liquid is 3% v / v-5% v / v; the fermentation conditions are: closed fermentation at 37-39 °C in a carbon dioxide environment for 10-14 hours.

4. The preparation method according to claim 1, characterized in that, In step (3), the volume ratio of the fermentation broth to the prickly pear juice is 4:6; the conditions for the second fermentation are: 37-39 °C, 150-200 r / min shaker culture for 28-36 h.

5. The preparation method according to claim 1, characterized in that, In step (4), by mass percentage, the milk powder is 5%-25%, sucrose is 4%, prickly pear and coix seed fermentation liquid is 15%-35%, and the remainder is water.

6. The preparation method according to claim 1, characterized in that, In step (4), the sterilization temperature is 90 °C and the time is 10 min; the cooling is to cool to 40 °C.

7. The preparation method according to claim 1, characterized in that, In step (4), the concentration of the lactic acid bacteria seed solution is 5 × 10⁻⁶. 8 CFU / mL; the inoculation amount of the lactic acid bacteria seed solution is 2% v / v; the lactic acid bacteria seed solution includes Bifidobacterium animalis, Lactobacillus plantarum and Streptococcus thermophilus; the fermentation conditions for inoculating the lactic acid bacteria seed solution are: constant temperature fermentation at 41 °C for 8-12 h; after-ripening at 4 °C for 12 h.

8. The preparation method according to claim 7, characterized in that, The ratio of viable counts of Bifidobacterium animalis, Lactobacillus plantarum, and Streptococcus thermophilus is 1:1:

2.

9. The prickly pear and Job's tears yogurt prepared by the preparation method according to any one of claims 1-8.

Images