Low-GI yoghourt added with quinoa protein and preparation method of low-GI yoghourt

Abstract

The invention relates to the technical field of food processing, and discloses low-GI yoghurt added with quinoa protein and a preparation method of the low-GI yoghurt, the yoghurt comprises the following raw materials: raw milk, xylitol, xylooligosaccharide, erythritol, inulin, konjac polysaccharide, quinoa protein and a leavening agent; the preparation method comprises the following steps: mixing the raw materials, sterilizing, inoculating a leavening agent, fermenting and performing after-ripening to form a yoghourt product. The method disclosed by the invention is feasible in theory and simple to operate, the glycemic index of the obtained product is lower than 30 due to the introduction of the high-nutrition quinoa protein and the compounding of the functional sugar, and the product is rich in nutrition, fine and smooth in taste and good in flavor.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, and in particular to a low GI yogurt added with quinoa protein and a preparation method thereof. Background Art

[0002] Quinoa protein has been shown to have multiple biological activities such as blood pressure regulation, anti-inflammatory, anti-cancer and cholesterol lowering. Compared with other cereal proteins, quinoa protein is a complete protein, comparable to animal protein, rich in essential amino acids for the human body, especially lysine, and has high nutritional value. In addition, quinoa protein has good processing properties, such as emulsification, foaming and gelling properties. It is considered to be one of the most promising animal protein substitutes and has broad application prospects in the field of food processing. Therefore, adding quinoa protein to yogurt can improve the nutritional value of yogurt products and even improve the texture characteristics of yogurt.

[0003] In traditional yogurt, the amount of sucrose added is generally about 7%, which is used for probiotic fermentation to finally form a sweet and sour taste of yogurt. However, sucrose has a high glycemic index, so functional sugars are usually used to improve the glycemic index of yogurt. The ingredients of low GI yogurt have the following characteristics: added dietary fiber and sweeteners, no sucrose or low sucrose addition. The present invention attempts to use quinoa protein and a variety of functional sugars to develop a low GI yogurt with added quinoa protein. Summary of the invention

[0004] The purpose of the present invention is to propose a low GI yogurt with added quinoa protein and a preparation method thereof in response to the current dual demand of people for deliciousness and health. Adding quinoa protein can not only increase the protein content of yogurt and increase its nutritional properties, but also interact with milk protein during the yogurt formation process to improve the texture properties of yogurt, such as viscosity and hardness. The compounding of functional sugars can provide the sweetness of yogurt with a lower glycemic index, and can also promote the proliferation of probiotics, improve the fermentation efficiency of probiotics, and make the flavor of the product more mellow.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing low GI yogurt with added quinoa protein comprises the following steps:

[0007] Step 1: adding quinoa protein, xylitol, xylo-oligosaccharide, erythritol, inulin and konjac polysaccharide into raw milk, stirring evenly to obtain a mixed liquid;

[0008] Step 2: Place the mixed liquid in a constant temperature water bath for sterilization;

[0009] Step 3: When the mixed liquid is cooled to 43°C-46°C, the fermentation agent is inoculated;

[0010] Step 4: After mixing, place in a constant temperature box for fermentation;

[0011] Step 5: After the fermentation is completed, the yogurt that has returned to room temperature is placed in a refrigerator at 4°C for refrigeration and then ripened to obtain the low GI yogurt with added quinoa protein.

[0012] Preferably, in step 1, the protein content of quinoa protein is about 83% and the isoelectric point is about 4.5.

[0013] Preferably, the quinoa protein is prepared by the following method: quinoa powder is defatted, deionized water is added to dissolve the degreased powder, the pH is adjusted to 8.0, the powder is stirred at a constant temperature of 35°C for 3 hours, and then the supernatant is obtained after centrifugation at 10,000 rpm, the pH is adjusted to 4.5, the powder is allowed to stand for 1 hour, the precipitate is obtained after centrifugation at 5,000 rpm, and the quinoa protein is obtained after vacuum freeze-drying.

[0014] Preferably, in step 3, the mixed starter consists of Lactobacillus bulgaricus, Lactobacillus acidophilus, Streptococcus thermophilus and Bifidobacterium.

[0015] Preferably, in step 2, the temperature of the constant temperature water bath is 85°C-90°C, and the sterilization time is 20 minutes.

[0016] Preferably, in step 4, the constant temperature fermentation temperature is 43°C.

[0017] The low GI yogurt with added quinoa protein prepared by the above-mentioned preparation method of the low GI yogurt with added quinoa protein is a low GI yogurt with added quinoa protein.

[0018] The beneficial effects of the present invention are:

[0019] The method of the invention is feasible in theory and simple to operate; the obtained product introduces highly nutritious quinoa protein; the compounding of functional sugars makes the glycemic index of the obtained product lower than 30, and the product is rich in nutrition, delicate in taste and good in flavor. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0021] The present invention provides a method for preparing a low GI yogurt with added quinoa protein, comprising the following steps:

[0022] S1: Preparation of quinoa protein aqueous solution: dissolve 6 g quinoa protein powder in 100 mL deionized water, adjust the solution pH to 8.0, stir to dissolve and adjust the solution pH to 7.0, place at 4°C overnight for hydration to prepare quinoa protein solution.

[0023] S2: Preparation of low GI yogurt: take equal parts of raw milk and add them into a beaker, add 1%-5% xylitol, 2%-4% erythritol, 0.1%-0.5% inulin, 0.1%-0.3% konjac polysaccharide and part of the above-prepared quinoa protein aqueous solution respectively, place in a water bath and heat at 50℃ for 10 minutes, stir evenly and heat to 85℃-90℃ for sterilization for 15-20 minutes, inoculate the starter when cooled to 43℃, mix well, fill, ferment at 43℃ for 3-5 hours, take out, cool to room temperature, and place at 4℃ for post-ripening to finally prepare a low GI yogurt product with added quinoa protein.

[0024] In the present invention, the examples and control examples all use the same mixed fermentation agent, which is composed of Lactobacillus bulgaricus, Lactobacillus acidophilus, Streptococcus thermophilus and Bifidobacterium.

[0025] Example 1: A low GI yogurt with added quinoa protein is prepared according to the following steps:

[0026] Step 1: Prepare a 6% quinoa protein aqueous solution, take 6 g of quinoa protein powder, dissolve it in 100 mL of deionized water, adjust the solution pH to 8.0, stir to dissolve and then adjust the solution pH to 7.0, place at 4°C overnight for hydration to prepare a quinoa protein solution.

[0027] Step 2: Measure 90 mL of raw milk and add it to a container, then add 5 g of xylitol, 2 g of erythritol, 0.1 g of inulin, 0.1 g of konjac polysaccharide, and 10 mL of 6% (w / v) quinoa protein aqueous solution. Place the mixed liquid in a constant temperature water bath at 43°C and stir for 20 minutes to accelerate dissolution.

[0028] Step 3: Place the mixed liquid in a constant temperature water bath at 85°C for 20 minutes for sterilization.

[0029] Step 4: When the mixed liquid is cooled to about 43°C, inoculate the fermentation agent and mix well.

[0030] Step 5: After mixing evenly, place it in a 43℃ constant temperature fermentation box and ferment for 3-5 hours.

[0031] Step 6: Place the fermented yogurt in a 4°C refrigerator to ripen.

[0032] Example 2: A low GI yogurt with added quinoa protein is prepared according to the following steps:

[0033] Step 1: Prepare a 6% quinoa protein aqueous solution, take 6 g of quinoa protein powder, dissolve it in 100 mL of deionized water, adjust the solution pH to 8.0, stir to dissolve and then adjust the solution pH to 7.0, place at 4°C overnight for hydration to prepare a quinoa protein solution.

[0034] Step 2: Measure 90 mL of raw milk and add it to a container, then add 4 g of xylitol, 3 g of erythritol, 0.15 g of inulin, 0.15 g of konjac polysaccharide, and 10 mL of 6% (w / v) quinoa protein aqueous solution. Place the mixed liquid in a constant temperature water bath at 43°C and stir for 20 minutes to accelerate dissolution.

[0035] Step 3: Place the mixed liquid in a constant temperature water bath at 85°C for 20 minutes.

[0036] Step 4: When the mixed liquid is cooled to about 43°C, inoculate the fermentation agent and mix well.

[0037] Step 5: Ferment at a constant temperature of 43°C for 3-5 hours.

[0038] Step 6: Place the fermented yogurt in a 4°C refrigerator to ripen.

[0039] Example 3, a low GI yogurt with added quinoa protein is prepared according to the following steps:

[0040] Step 1: Prepare a 6% quinoa protein aqueous solution, take 6 g of quinoa protein powder, dissolve it in 100 mL of deionized water, adjust the solution pH to 8.0, stir to dissolve and then adjust the solution pH to 7.0, place at 4°C overnight for hydration to prepare a quinoa protein solution.

[0041] Step 2: Measure 90 mL of raw milk and add it to a container, then add 3 g of xylitol, 4 g of erythritol, 0.2 g of inulin, 0.2 g of konjac polysaccharide, and 10 mL of 6% (w / v) quinoa protein aqueous solution. Place the mixed liquid in a constant temperature water bath at 43°C and stir for 20 minutes to accelerate dissolution.

[0042] Step 3: Place the mixed liquid in a constant temperature water bath at 85°C for 20 minutes.

[0043] Step 4: When the mixed liquid is cooled to about 43°C, inoculate the fermentation agent and mix well.

[0044] Step 5: Ferment at a constant temperature of 43°C for 3-5 hours.

[0045] Step 6: Place the fermented yogurt in a 4°C refrigerator to ripen.

[0046] The difference between the control example and examples 1-3 is that 7 g of white sugar is added in step 2, and no functional sugar is added, and the other conditions are not changed.

[0047] The following performance tests were performed on the low GI yogurt containing quinoa protein prepared in Examples 1 to 3:

[0048] 1. Water holding capacity analysis

[0049] Put the fermented yogurt into a centrifuge tube, centrifuge it at 4000 rpm at 4°C for 10 minutes, aspirate the supernatant, and re-weigh the mass of the yogurt.

[0050] Water holding capacity (%) = (m2-m0) / (m1-m0)×100

[0051] Where m0 is the weight of the centrifuge tube, m1 is the total weight of the centrifuge tube and yogurt before centrifugation, and m2 is the total weight of the centrifuge tube and yogurt after removing the supernatant after centrifugation.

[0052] The water holding capacity of yogurt reflects the compactness of the yogurt gel network. The water holding capacity of yogurt is the ability of the protein network to retain water. The higher the water holding capacity, the more stable the gel network structure of the yogurt. The water holding capacities of Examples 1 to 3 are 75.71%, 74.73% and 75.34%, respectively, all higher than 68.92% of the control example. Example 1 has the highest water holding capacity, indicating that its gel structure is uniform and the most stable.

[0053] 2. Analysis of whey precipitation rate

[0054] Tilt the plastic box containing yogurt at room temperature for half an hour, then suck out the supernatant, weigh the total weight before and after, and calculate the whey precipitation rate of the yogurt.

[0055] Whey precipitation rate (%) = (m4-m5) / (m4-m3)×100

[0056] Wherein m3 is the weight of the plastic box, m4 is the total weight of the sauce box and yogurt before tilting, and m5 is the total weight of the sauce box and yogurt after tilting.

[0057] Whey precipitation is an undesirable characteristic, mainly due to the syneresis of fermented milk. The whey precipitation rates of Examples 1 to 3 were 5.53%, 6.46% and 6.59%, respectively, while the control was 8.92%. This is somewhat related to the water holding capacity of yogurt. The amount of whey precipitation generally increases with the extension of storage time.

[0058] 3. Texture characteristics analysis

[0059] The TPA test of fermented yogurt was carried out using a texture analyzer. A cylindrical P2 probe was selected, the test distance was 15 mm, the deformation was 20%, the pre-test speed was 2 mm / s, the test speed was 1 mm / s, and the post-test speed was 2 mm / s. The experimental structure is shown in Table 1:

[0060] Table 1

[0061]

[0062] 4. Chromaticity change analysis

[0063] The colorimeter was used to characterize the color difference of yogurt. The experimental results are shown in Table 2:

[0064] Table 2

[0065] L* a* b* Comparison Example 88.19 -0.61 7.09 Example 1 87.47 -0.5 7.79 Example 2 87.61 -0.24 8.27 Example 3 87.62 -0.39 7.92

[0066] 5. pH analysis after fermentation completion

[0067] The pH of the Examples and Comparative Examples after fermentation was completed was measured using a pH meter.

[0068] After the yogurt was ripened, the pH of the control system decreased to 4.56, while that of Examples 1-3 decreased to 4.45, 4.51 and 4.47 respectively.

[0069] 6. In vitro method for estimating glycemic index

[0070] The glycemic index is estimated by simulating in vitro digestion. First, the hydrolysis rate of the sample is calculated, the corresponding curve is drawn, and the area under the curve is calculated, and then the eGI value of the sample is calculated.

[0071] According to the GI value, food is divided into high GI (>70) food, medium GI (between 55-70) food and low GI (≤55) food. The eGI values ​​of Examples 1-3 were calculated to be 28.13, 27.69 and 29.21, respectively. The estimated glycemic index is lower than 55, and all three yogurts are low GI foods. It can be seen that this type of fermented yogurt can not only improve the nutritional value of food, but also has a lower glycemic index.

[0072] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing low GI yogurt with added quinoa protein, characterized in that: The following steps are involved: Step 1: adding quinoa protein, xylitol, xylo-oligosaccharide, erythritol, inulin and konjac polysaccharide into raw milk, stirring evenly to obtain a mixed liquid; Step 2: Place the mixed liquid in a constant temperature water bath for sterilization; Step 3: When the mixed liquid is cooled to 43°C-46°C, add the fermentation agent; Step 4: After mixing, place in a constant temperature fermentation box for fermentation; Step 5: Place the fermented yogurt in a refrigerator at 4°C for refrigeration and ripening to obtain the low GI yogurt with added quinoa protein.

2. The method for preparing a low GI yogurt with added quinoa protein according to claim 1, characterized in that: In step 1, the purity of quinoa protein is 83% and the isoelectric point is 4.

5.

3. The method for preparing a low GI yogurt with added quinoa protein according to claim 2, characterized in that: The quinoa protein is prepared by the following method: firstly, quinoa powder is defatted, deionized water is added to dissolve after defatting, the pH value is adjusted to 8.0, the mixture is stirred at a constant temperature of 35°C for 3 hours, and then the supernatant is obtained after centrifugation at 10000 rpm, the pH value is adjusted to 4.5, the mixture is allowed to stand for 1 hour, the precipitate is obtained after centrifugation at 5000 rpm, and the quinoa protein is obtained after vacuum freeze-drying.

4. The method for preparing a low GI yogurt with added quinoa protein according to claim 1, characterized in that: In step 3, the mixed starter consists of Lactobacillus bulgaricus, Lactobacillus acidophilus, Streptococcus thermophilus and Bifidobacterium.

5. The method for preparing a low GI yogurt with added quinoa protein according to claim 1, characterized in that: In step 2, the temperature of the constant temperature water bath is 85°C-90°C, and the sterilization time is 15-20 minutes.

6. The method for preparing a low GI yogurt with added quinoa protein according to claim 1, characterized in that: In step 4, the constant temperature fermentation temperature is 43°C.

7. A low GI yogurt with added quinoa protein prepared by the method for preparing a low GI yogurt with added quinoa protein as claimed in any one of claims 1 to 6.

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