Wild strawberry yoghurt with skin and method for preparing the same

Abstract

The present application provides a wild strawberry milk skin yogurt and a preparation method thereof, and relates to the technical field of dairy product preparation.The wild strawberry milk skin yogurt comprises wild strawberry juice, pure milk, light cream, condensed milk, bacterial powder, milk powder and white granulated sugar.The preparation method comprises the following steps: firstly, uniformly mixing the wild strawberry juice, the light cream, the milk powder and the pure milk;then, adding the white granulated sugar and the condensed milk, and sequentially performing filtering, heating and cooling;after cooling to a preset temperature, adding the bacterial powder for inoculation;after fermentation for a preset time, cold storage and post-ripening.The wild strawberry milk skin yogurt provided by the present application retains the natural fruit aroma and sweet and sour flavor of wild strawberries, and improves the organization state and storage stability of the yogurt.

Description

Technical Field

[0001] This invention provides a wild strawberry milk skin yogurt and its preparation method, relating to the field of dairy product preparation technology. Background Technology

[0002] Yogurt is a type of dairy product made primarily from cow's milk, goat's milk, or other milk sources through fermentation with lactic acid bacteria. It is characterized by its smooth texture, mild flavor, and high nutritional value. With increasing consumer health awareness, yogurt products are no longer limited to traditional fermented milk forms but are gradually evolving towards nutritional fortification, flavor diversification, and functionalization. In particular, compound yogurt products with added natural fruits and vegetables, plant extracts, or local specialty ingredients are gaining market attention due to their combination of nutritional value and unique flavor.

[0003] Wild strawberries are a type of natural berry with local characteristics, typically characterized by their sweet and sour taste, rich aroma, and vibrant color. They also contain certain amounts of vitamins, organic acids, polyphenols, and dietary fiber. Incorporating wild strawberries into yogurt products can not only improve the flavor and color of the yogurt but also enrich its nutritional composition and enhance its natural fruity aroma and sensory appeal. However, wild strawberries have a high water content and are relatively rich in fruit acids and polyphenols. Directly adding them to the yogurt system can easily affect the stability of milk proteins, leading to problems such as layering, water separation, sedimentation, a rough texture, or unbalanced flavors. Therefore, how to improve the compatibility of wild strawberries with the yogurt system while maintaining their natural flavor and nutritional characteristics is a crucial technical challenge that needs to be addressed in the development of this type of product. Current research and product development on the synergistic application of wild strawberries and milk skin in yogurt products are relatively limited, especially regarding the harmonious integration of wild strawberry flavor, milk skin aroma, and yogurt fermentation flavor, as well as the control of product stability. Summary of the Invention

[0004] This invention provides wild strawberry milk skin yogurt and its preparation method, which solves the technical problem that there is relatively little research and product development on the synergistic application of wild strawberries and milk skin in the prior art.

[0005] The present invention is implemented as follows: comprising the following components and their mass ratios: 9% wild strawberry juice, 49.8% pure milk, 25% light cream, 6% condensed milk, 0.2% starter culture powder, 6% milk powder and 4% white sugar.

[0006] As a further preferred embodiment, the bacterial powder includes Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus plantarum, and Lactobacillus casei.

[0007] The preparation method of wild strawberry milk skin yogurt includes the following steps: first, mix wild strawberry juice, light cream, milk powder and pure milk evenly according to the preset ratio, then filter white sugar and condensed milk, heat mix and sterilize, cool, add starter culture powder after cooling to the preset temperature, ferment for the preset time, and then refrigerate for ripening.

[0008] As a further preferred option, the heat-mixed sterilization conditions are a 75°C water bath for 15 minutes.

[0009] As a further optimization, the fermentation conditions are: 41℃, 9 h.

[0010] As a further optimization, the post-ripening conditions are: 4℃, 12 h.

[0011] The beneficial effects of this invention are as follows: By rationally combining and optimizing the processes of wild strawberry raw materials, milk skin raw materials, and fermented milk system, the product possesses both the natural fruity aroma and sweet-sour flavor of wild strawberries, as well as the rich milky aroma and mellow taste of milk skin, while simultaneously improving the product's texture and storage stability. This technology can enrich the types of yogurt products, increase the added value of local specialty dairy products, and has good market application prospects. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0013] Figure 1 This is a schematic diagram of the process flow of one embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the effect of the amount of wild strawberry juice added on the sensory score of wild strawberry milk skin yogurt in one embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the effect of the amount of starter culture added on the sensory score of wild strawberry milk skin yogurt in one embodiment of the present invention; Figure 4 This is an embodiment of the invention showing the effect of the amount of light cream added on the sensory score of wild strawberry milk skin yogurt; Figure 5 This is a schematic diagram illustrating the effect of milk powder addition on the sensory score of wild strawberry milk skin yogurt in one embodiment of the present invention; Figure 6 This is a graph showing the ABTS scavenging rate of different wild strawberry yogurt concentrations in Experiment Example 2; Figure 7 This is a graph showing the DPPH scavenging rate of different wild strawberry yogurt concentrations in Experiment Example 2; Figure 8 This represents the hydroxyl radical scavenging rate of different wild strawberry yogurt concentrations in Experiment Example 2. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Wild strawberry milk skin yogurt includes the following components and their weight ratios: wild strawberry juice 9%, pure milk 49.8%, light cream 25%, condensed milk 6%, starter culture powder 0.2%, milk powder 6%, and white sugar 4%.

[0016] Furthermore, the bacterial strains in the bacterial powder include Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus plantarum, and Lactobacillus casei, with a total viable count of 1×10⁻⁶. 10 CFU / g.

[0017] See Figure 1 The preparation method of wild strawberry milk skin yogurt includes the following steps: First, mix wild strawberry juice, light cream, milk powder, and pure milk evenly according to a preset ratio. Then, add white sugar and condensed milk in a preset ratio, stir evenly, and filter to remove wild strawberry seeds to prevent sedimentation. Heat the mixture and continuously shake it to prevent the formation of a milk skin on the surface. Heating promotes the Maillard reaction, causing protein denaturation and coagulation, while simultaneously sterilizing and stabilizing the yogurt system. After sterilization, allow it to cool naturally. After cooling to a preset temperature, add a preset ratio of starter culture for inoculation, and then filter using a strainer to remove foam, resulting in a smoother finished product. The inoculated mixture is then fermented at a constant temperature, and after fermentation, it is refrigerated for further ripening.

[0018] Furthermore, the temperature for heat sterilization was 75℃ water bath for 15 min; the fermentation conditions were 41℃ for 9 h; and the post-ripening conditions were 4℃ for 12 h.

[0019] Furthermore, the wild strawberry juice is obtained by crushing canned wild strawberries using a high-speed blender.

[0020] The technical solution of the present invention will be further described below with reference to the embodiments and accompanying drawings.

[0021] Materials and reagents used in the examples: Wild strawberry preserves (five-leaf strawberry), commercially available; pure milk, Pinwo Food Co., Ltd.; Yili skim milk powder, Tianjin Yili Dairy Co., Ltd.; Anchor animal cream (59% fat content), Fonterra Trading (Shanghai) Co., Ltd.; Chuanxiu probiotic powder (containing Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus plantarum, and Lactobacillus casei, 1×10 10 CFU / g), Beijing Chuanxiu International Trade Co., Ltd.; white sugar, Shanghai Xinglian Biotechnology Co., Ltd.; condensed milk, Nestle Eagle Brand Original Condensed Milk; Coomassie Brilliant Blue Solution G-250, Shanghai Maikun Chemical Co., Ltd.; bovine serum albumin, Sinopharm Chemical Reagent Co., Ltd.

[0022] Instruments and equipment used: pHS-25 pH meter (Shanghai Instrument & Electronics Scientific Instruments Co., Ltd.), SW-LB90T handheld refractometer (Guangzhou Suwei Electronic Technology Co., Ltd.), BSA124S electronic balance (Sartorius Scientific Instruments (Beijing) Co., Ltd.), HSY-26 electric thermostatic water bath (Shanghai Yuejin Medical Instruments Co., Ltd.), SHP-150 biochemical incubator (Shanghai Peiying Experimental Instruments Co., Ltd.). Example 1

[0023] Single-factor experiment and orthogonal experiment Based on the preliminary test results, four factors—the amount of wild strawberry juice added, the amount of light cream added, the amount of starter culture added, and the amount of milk powder added—were selected for single-factor experiments. Five levels were selected for each factor: wild strawberry juice added (3%, 6%, 9%, 12%, 15%), light cream added (5%, 15%, 25%, 35%, 45%), starter culture added (0.1%, 0.15%, 0.2%, 0.25%, 0.3%), and milk powder added (2%, 4%, 6%, 8%, 10%). The effects on sensory scores were investigated. The proportion of added amounts refers to the mass proportion.

[0024] Based on the single-factor experiment, four factors were selected: the amount of wild strawberry juice added, the amount of light cream added, the amount of bacterial powder added, and the amount of milk powder added. An orthogonal experiment with four factors and three levels (L9(34)) was designed. The factor levels are shown in Table 1.

[0025] Table 1. Factor Levels in Orthogonal Experiments Wild strawberry juice addition (A) / % Whipping cream addition (B) / % Microbial powder addition amount (C) / % Milk powder addition amount (D) / % 1 6 5 0.15 4 2 9 15 0.2 6 3 12 25 0.25 8 Yogurt sensory evaluation The evaluation panel consisted of 10 sensory evaluators with experience in food sensory evaluation, who conducted a sensory evaluation of the wild strawberry milk skin yogurt. Referring to the sensory requirements in RHB 103-2004 "Detailed Rules for Sensory Quality Evaluation of Yogurt" and considering the actual conditions of the wild strawberry milk skin yogurt, sensory evaluation standards were developed. Color, flavor and aroma, mouthfeel, and texture were scored, with a total score of 100 points. The results are shown in Table 2.

[0026] Table 2 Sensory Evaluation Criteria for Wild Strawberry Milk Skin Yogurt

[0027] See Figure 2 As the amount of wild strawberry juice added increased, the sensory score initially rose and then fell. The sensory score reached its highest value when the wild strawberry juice content was 9%, indicating the best balance of flavor and texture in the yogurt. Further increases to 12% or more caused the sensory score to decline, as the strawberry flavor became too strong, masking the refreshing taste of the yogurt and resulting in an unbalanced overall flavor. Therefore, the optimal amount of wild strawberry juice added is 9%.

[0028] See Figure 3 As the amount of starter culture added increases, the sensory score initially rises and then falls. The sensory score reaches its highest value when the starter culture content is 0.2%, at which point the yogurt with the milk skin has a harmonious flavor and optimal texture. When the starter culture content is further increased to 0.25% or higher, the sensory score begins to decline. Therefore, the optimal amount of starter culture added is 0.2%.

[0029] See Figure 4 As the amount of heavy cream added increases, the sensory score initially rises and then falls. The sensory score reaches its highest value when the cream content is 15%, at which point the yogurt with cream skin has the best texture. When the cream content continues to increase to 25% or higher, the sensory score begins to decline. Therefore, the optimal amount of heavy cream to add is 15%.

[0030] See Figure 5 As the amount of milk powder added increased, the sensory score showed a trend of first rising and then falling. The sensory score reached its highest value when the milk powder content was 6%. When the milk powder content continued to increase beyond 8%, the sensory score began to decline. Therefore, the optimal milk powder content is 6%.

[0031] Based on the conclusions of the single-factor experiments, an orthogonal experiment was designed with four key factors: the amount of wild strawberry juice added (A), the amount of light cream added (B), the amount of starter culture added (C), and the amount of milk powder added (D). Sensory evaluation was used as the evaluation index to explore the interactions between the factors and determine the optimal formula for wild strawberry milk skin yogurt.

[0032] Table 3. Results of the orthogonal experiment on wild strawberry milk skin yogurt

[0033]

[0034] As shown in Table 3, the order of influence of oat flour gelatinization factors is as follows: milk powder addition (D) > cream addition (B) > starter culture addition (C) > wild strawberry juice addition (A). According to the analysis of the orthogonal experiment results, the wild strawberry milk skin yogurt formula with the highest score is A2B3C2D2, that is, milk powder addition is 6%, cream addition is 25%, starter culture addition is 0.2%, and wild strawberry juice addition is 9%.

[0035] Experimental Example 1 Detection of physicochemical and microbiological indicators of yogurt Referencing GB5009.239—2016, "National Food Safety Standard - Determination of Acidity in Food," weigh 10 g of yogurt sample and titrate it with 0.1 mol / L NaOH standard solution.

[0036] Protein determination: Weigh 100 mg of bovine serum albumin and add it to 100 mL of purified water. Shake well. Transfer 0, 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0 mL of the solution to test tubes, respectively. Add water to 1.0 mL, and then add 4.0 mL of Coomassie brilliant blue staining solution. Shake well and incubate at room temperature in a dark place for 5 min. Take 250 μL of the sample solution and measure its absorbance at 595 nm using an ELISA reader. Plot the protein concentration on the x-axis and the measured absorbance on the y-axis to obtain the regression equation y = 11.7480x + 0.9445, R. 2 =0.9991.

[0037] Determination of total solids content: Weigh the constant weight culture dish (M0). Place a small amount of yogurt in the culture dish and weigh the total weight (M1). Dry at 105℃ until constant weight, and weigh the total weight after drying (M2). Calculate the total solids content according to formula (1).

[0038] Total solids content / % = (M2-M0) / (M1-M0)*100% Formula (1) Determination of whey separation rate: Place an appropriate amount of yogurt in a centrifuge tube, centrifuge at 3000 r / min for 10 min, remove the supernatant, and calculate the whey separation rate of the yogurt according to formula (2).

[0039] In the formula: W0 — mass of the centrifuge tube, g; W1 — total mass of yogurt and centrifuge tube, g; W2 — total mass of yogurt and centrifuge tube after removing the supernatant, g.

[0040] Whey separation rate / % = (W1-W2) / (W1-W0)*100% Formula (2) Determination of water-holding capacity: Pour 10 mL of yogurt into a centrifuge tube, weigh the centrifuge tube as H0, and the total mass after adding yogurt as H1. Centrifuge at 4℃ and 4000 r / min for 15 min, let stand for 10 min, remove the supernatant in the centrifuge tube, and weigh the mass at this time as H2. Calculate the water-holding capacity according to formula (3).

[0041] Water holding capacity / % = (H2-H0) / (H1-H0)*100% Formula (3) pH value was measured using a pH meter.

[0042] Determination of soluble solids: A handheld refractometer was used.

[0043] Table 4 Physicochemical Indicators pH 4.57 Acidity (°T) 90 Water holding capacity (%) 92.3 Total solids content (%) 25.82 Soluble fixed content (%) 20 Protein (g / 100 g) 5.6 Whey separation rate (%) 3.74 The physicochemical indicators of the yogurt produced by the optimized process were tested. As shown in Table 4, the yogurt had a pH of 4.57, an acidity of 90°T, a water holding capacity of 92.3%, a total solids content of 25.82%, a soluble solids content of 20%, a protein content of 5.6 g / 100 g, a whey separation rate of 3.74%, suitable acidity, and a viscous texture.

[0044] Microbiological indicators were determined as follows: Coliform bacteria were detected using the plate count method (Method II) in GB 4789.3—2016 "National Food Safety Standard - Microbiological Examination of Food - Coliform Bacteria Count"; Staphylococcus aureus was detected using the qualitative test method (Method I) in GB 4789.10—2016 "National Food Safety Standard - Microbiological Examination of Food - Staphylococcus aureus Test". Results are shown in Table 5.

[0045] Table 5 Microbiological Indicators Total bacterial count (CFU / mL) ≤100 ＜1 Escherichia coli (MPN / 100mL) ≤3 Not detected Mold and yeast (CFU / mL) ≤20 Not detected Pathogenic bacteria (Salmonella, Shigella, Staphylococcus aureus) Not detectable Not detected Number of lactic acid bacteria / (CFU / mL) <![CDATA[≥1×10 6 ]]> <![CDATA[2.39±0.76×10 7 ]]> As shown in Table 5, the lactic acid bacteria content in wild strawberry yogurt was 2.39 ± 0.76 × 10⁻⁶. 7 CFU / mL, higher than the 10 required by GB19302-2010. 6 CFU / mL. Escherichia coli, molds, yeasts, Salmonella, Shigella, and Staphylococcus aureus were not detected, meeting the microbial limits for fermented milk as required by GB19302-2010. Therefore, the product's microbial safety is reliable.

[0046] Experimental Example 2 Antioxidant capacity test (1) Determination of ABTS free radical scavenging rate: Prepare a 7 mmol / L ABTS stock solution and a 2.45 mmol / L potassium persulfate stock solution, mix them at a 1:1 volume ratio, and place them at room temperature in the dark for 12-16 h. Continuously dilute the above stock solution with deionized water until its absorbance at 734 nm stabilizes at 0.70±0.02, which is the ABTS working solution. Take 0.10 mL of wild strawberry yogurt sample and mix it with 3.90 mL of working solution, react at 25℃ for 6 min, use distilled water as a blank control, measure the absorbance at a wavelength of 734 nm, and record the data.

[0047] ABTS radical scavenging rate (%) = [1-(A1-A2) / A0]x100% Equation (1) In formula (1), A0 is the absorbance of the blank (distilled water instead of the sample), A1 is the absorbance of the wild strawberry yogurt sample, and A2 is the absorbance of the control (distilled water instead of ABTS stock solution).

[0048] (2) Determination of DPPH free radical scavenging rate: A 2 mmol / L DPPH solution was prepared using 95% ethanol. Wild strawberry yogurt was dissolved in distilled water to different concentrations (20%, 40%, 60%, 80%, 100%). 2.0 ml of wild strawberry yogurt and 2.0 ml of DPPH were added to each test tube. The solution was immediately shaken well and stored in the dark at room temperature for 30 minutes. The solution was centrifuged at 4500 r / min for 15 min. Using 95% ethanol as a blank control, the absorbance of the supernatant was measured at 517 nm, and the data were recorded.

[0049] DPPH free radical scavenging rate (%) = [1-(A1-A2) / A0]x100% Equation (2) In formula (2), A0 is the absorbance of the blank (ethanol instead of the sample), A1 is the absorbance of the sample, and A2 is the absorbance of the control (ethanol instead of DPPH).

[0050] (3) Determination of hydroxyl radical scavenging rate: 2.0 mL samples of wild strawberry yogurt at different concentrations (20%, 40%, 60%, 80%, 100%) were mixed with 2.0 mL FeSO4 (9 mmol / L), 2.0 mL salicylic acid-ethanol (9 mmol / L), and 2.0 mL H2O2 (9 mmol / L), respectively. The mixtures were incubated at 37°C for 30 min. Finally, the absorbance of the blank (distilled water instead of the samples and H2O2) was measured at 510 nm, and the data were recorded.

[0051] The scavenging ability against hydroxyl radicals is calculated using the following formula: Hydroxyl radical scavenging rate (%) = [A0 - (A1 - A2)] / A0 x 100% Equation (3) In formula (3), A0 is the absorbance of the blank (distilled water instead of the sample), A1 is the absorbance of the wild strawberry yogurt sample, and A2 is the absorbance of the control (distilled water instead of hydrogen peroxide).

[0052] By diluting the yogurt, different concentrations of wild strawberry yogurt can be obtained. For example, 20% concentration yogurt refers to yogurt containing 20mg of wild strawberry. The sample was obtained by mixing yogurt with 100ml of water. The ABTS scavenging rate, DPPH scavenging rate, and other parameters of different concentrations of wild strawberry yogurt were analyzed. Detection of hydroxyl radical scavenging rate.

[0053] See Figure 6 , Figure 7 and Figure 8 As the concentration of wild strawberry yogurt increased, the ABTS scavenging rate, DPPH scavenging rate, and hydroxyl radical scavenging rate all increased, indicating that wild strawberry yogurt has good antioxidant capacity.

[0054] This invention combines wild strawberry raw materials, milk skin-flavored cream raw materials, and a yogurt fermentation system to create a complex yogurt product that combines natural berry flavor, fermented milk aroma, and the rich texture of milk skin. Existing fruit-flavored yogurts often use ordinary fruit jams, fruit pieces, or flavorings for flavoring, resulting in a relatively simple flavor profile. This invention, however, through the synergistic fusion of wild strawberry and milk skin flavors, gives the yogurt a distinct local character and a high degree of flavor recognition.

[0055] Through single-factor and orthogonal experiments to optimize the addition amounts of wild strawberry juice, light cream, starter culture, and milk powder, the optimal formula combination was determined: 9% wild strawberry juice, 25% light cream, 0.2% starter culture, and 6% milk powder. This formula effectively harmonizes the sweet and sour flavor of wild strawberries, the milky aroma of milk skin, and the fermented flavor of yogurt, resulting in a high sensory score and a harmonious taste.

[0056] The addition of milk powder and light cream improved the texture and mouthfeel of the yogurt system. Milk powder increases milk solids and protein content, strengthens gel structure, improves water retention, and reduces whey separation; light cream imparts a rich, creamy aroma and smooth texture, resulting in a fuller flavor in the finished product.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. Wild strawberry milk skin yogurt, characterized in that, It includes the following components and their mass ratios: wild strawberry juice 9%, pure milk 49.8%, light cream 25%, condensed milk 6%, starter culture powder 0.2%, milk powder 6%, and white sugar 4%.

2. The wild strawberry milk skin yogurt according to claim 1, characterized in that, The bacterial powder includes Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus plantarum, and Lactobacillus casei.

3. The method for preparing wild strawberry milk skin yogurt as described in claim 1, characterized in that, The process includes the following steps: First, mix wild strawberry juice, light cream, milk powder, and pure milk evenly according to the preset ratio. Then, add white sugar and condensed milk, filter, heat-mix and sterilize, and cool. After cooling to the preset temperature, add the starter culture powder for inoculation. After fermentation for the preset time, refrigerate for post-ripening.

4. The preparation method according to claim 3, characterized in that, The conditions for heat sterilization are a 75°C water bath for 15 minutes.

5. The preparation method according to claim 3, characterized in that, Fermentation conditions: 41℃, 9 h.

6. The preparation method according to claim 3, characterized in that, The post-ripening conditions were: 4℃, 12 h.

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