阅读说明：本技术 含有挤压乳清蛋白-菊粉复合物的发酵乳及其制备方法 (Fermented milk containing extruded whey protein-inulin complex and method for producing the same ) 是由 侯俊财 姜瞻梅 李金鹏 付润箫 何彦婷 于 2021-07-08 设计创作，主要内容包括：本发明公开了一种含有挤压乳清蛋白-菊粉复合物的发酵乳,属于生物技术领域。所述发酵乳是采用向原料乳中添加挤压乳清蛋白-菊粉复合物进行制备。本发明通过在发酵乳中添加挤压乳清蛋白-菊粉复合物,可改善和提高常规发酵乳的硬度、粘附性、保水性和粘稠度等品质特性,以及提高发酵乳的感官接受度,并可促进乳酸菌的生长代谢,使发酵后的挤压乳清蛋白与菊粉复合发酵乳乳酸菌活菌数维持在较高水平；另外,本发明还利用主成分分析的方法确定了能最大程度改善挤压乳清蛋白与菊粉复合发酵乳综合品质的最优菊粉添加比例,制备得到的挤压乳清蛋白与菊粉复合发酵乳可以满足广大消费者的需求,具有广阔的市场前景。(The invention discloses fermented milk containing an extruded whey protein-inulin complex, and belongs to the technical field of biology. The fermented milk is prepared by adding extruded whey protein-inulin complex into raw milk. According to the invention, the extruded whey protein-inulin complex is added into the fermented milk, so that the quality characteristics such as hardness, adhesion, water retention and viscosity of the conventional fermented milk can be improved and improved, the sensory acceptability of the fermented milk is improved, the growth and metabolism of lactic acid bacteria can be promoted, and the viable count of the lactic acid bacteria in the fermented milk compounded by the extruded whey protein and the inulin is maintained at a high level; in addition, the invention also determines the optimal inulin adding proportion capable of improving the comprehensive quality of the extruded whey protein and the inulin composite fermented milk to the maximum extent by utilizing a method for analyzing the main components, and the prepared extruded whey protein and inulin composite fermented milk can meet the requirements of consumers and has wide market prospect.)

1. A fermented milk containing an extruded whey protein-inulin complex, characterized in that the fermented milk is produced by adding the extruded whey protein-inulin complex to a raw milk.

2. Fermented milk containing extruded whey protein-inulin complex according to claim 1, wherein the mass to volume ratio of extruded whey protein-inulin complex to the starting milk is (1.0-3.5): 100.

3. a fermented milk containing an extruded whey protein-inulin complex according to claim 1, wherein the inulin is present in the extruded whey protein-inulin complex in an amount of 5-15% by weight of the total amount.

4. A method for the production of fermented milk containing extruded whey protein-inulin complex as claimed in any of claims 1-3, comprising the steps of:

step 1: extruding the whey protein at low temperature, and mixing the whey protein with inulin to prepare an extruded whey protein-inulin complex;

step 2: adding the extruded whey protein-inulin complex and sucrose into raw milk, and uniformly mixing and stirring to obtain a material A;

and step 3: preheating, homogenizing, sterilizing and cooling the material A to obtain a fermentation substrate;

and 4, step 4: adding a leaven into the fermentation substrate, filling, preserving heat for fermentation, and stopping fermentation to obtain a material B;

and 5: and cooling the material B, and refrigerating to obtain the fermented milk.

5. The method of claim 4, wherein the step 1 of preparing the extruded whey protein-inulin complex comprises the steps of:

s1: carrying out extrusion pretreatment on whey protein at an extrusion temperature of 45-55 ℃ to obtain extruded whey protein, and then freeze-drying and grinding into powder;

s2: dissolving powdered whey protein and inulin in deionized water at room temperature, mixing, stirring, freeze drying the composite solution, and grinding into powder to obtain the extruded whey protein-inulin composite.

6. The method according to claim 5, wherein the inulin in S2 is added in an amount of 5 to 20% by mass based on the total mass of the inulin and the extruded whey protein.

7. The method according to claim 4, wherein in step 2, the mass-to-volume ratio of the extruded whey protein-inulin complex to the raw milk is (1.0-3.5): 100;

the mass volume ratio of the sucrose to the raw milk is (3-9) to 100;

the stirring time is 15-30 min.

8. The method according to claim 4, wherein in step 3, the preheating temperature is 50-65 ℃ and the preheating time is 5-10 min;

homogenizing under 15-25 MPa;

pasteurizing at 90-95 deg.C for 10-15 min;

cooling the fermentation substrate to 40-42 deg.C.

9. The preparation method according to claim 4, wherein in step 4, 0.35 to 0.45 per thousand mass percent of leavening agent is added to the fermentation substrate;

the temperature of the heat preservation fermentation is 40-42 ℃, and the fermentation time is 4.5-6.0 h.

10. The method of claim 4, wherein in step 5, material B is cooled to 20-35 ℃; refrigerating at 4 deg.C for 24 hr.

Technical Field

The invention relates to the technical field of biology, in particular to fermented milk containing extruded whey protein-inulin complex and a preparation method thereof.

Background

Fermented milk is widely popular with consumers worldwide as a fermented product with high nutritional value. Its texture is an important factor affecting consumer acceptance. Among them, properties such as hardness, water retentivity and viscosity play an important role in texture. When whey separation occurs in fermented milk, its texture is affected. The addition of components such as whey protein, inulin and the like can form firmer fermented milk texture, and is a preferred technology for reducing the whey precipitation in the fermented milk.

Whey protein has various functional properties, and is widely used in food processing as an emulsifier, thickener, gelling agent, and the like. And the secondary and tertiary structures of the whey protein subjected to extrusion pretreatment are changed, so that the development of protein molecules is promoted, and the functional characteristics of water retention, viscosity and the like of the whey protein are improved. Inulin, a functional plant polysaccharide, is often used as a prebiotic, a sugar and fat substitute, a thickener, etc. due to its various physiological functions, such as lowering blood glucose, regulating intestinal microbial flora, etc. Although whey protein and/or inulin are/is used in fermented milk in the prior art, both of the whey protein and/or inulin have the functions of improving viscosity and water retention or regulating intestinal tracts, and have no obvious effect on overall change of properties such as hardness, water retention and viscosity of fermented milk, and at present, no relevant report is provided on whether the whey protein and the inulin are mutually influenced or not, and whether the whey protein and the inulin are compounded and added to influence the viscosity, the water retention and other qualities of the fermented milk.

Disclosure of Invention

The invention aims to provide fermented milk containing extruded whey protein-inulin complex and a preparation method thereof, which aim to solve the problems in the prior art, and the extruded whey protein and inulin complex are added into the fermented milk, so that the quality characteristics of the conventional fermented milk, such as hardness, adhesiveness, water retention, viscosity and the like, are obviously improved, the sensory acceptance of the fermented milk is improved, the growth and metabolism of lactic acid bacteria can be promoted, the viable count of the fermented milk containing the extruded whey protein and the inulin complex is maintained at a high level, the requirements of consumers can be met, and the fermented milk has a wide market prospect.

In order to achieve the purpose, the invention provides the following scheme:

the invention provides fermented milk containing an extruded whey protein-inulin complex, which is prepared by adding the extruded whey protein-inulin complex to raw milk.

Preferably, the mass-to-volume ratio of the extruded whey protein-inulin complex to the raw milk is (1.0-3.5): 100.

preferably, the inulin is present in the extruded whey protein-inulin complex in an amount of 5% to 15% of the total amount.

The invention also provides a preparation method of the fermented milk containing the extruded whey protein-inulin complex, which comprises the following steps:

step 1: extruding the whey protein at low temperature, and mixing the whey protein with inulin to prepare an extruded whey protein-inulin complex;

step 2: adding the extruded whey protein-inulin complex and sucrose into raw milk, and uniformly mixing and stirring to obtain a material A;

and step 3: preheating, homogenizing, sterilizing and cooling the material A to obtain a fermentation substrate;

and 4, step 4: adding a leaven into the fermentation substrate, filling, preserving heat for fermentation, and stopping fermentation to obtain a material B;

and 5: and cooling the material B, and refrigerating to obtain the fermented milk.

Preferably, in step 1, the preparation of the extruded whey protein-inulin complex comprises in particular the following steps:

s1: carrying out extrusion pretreatment on whey protein at the extrusion temperature of 45-55 ℃ to obtain extruded whey protein, and then freeze-drying and grinding the extruded whey protein into powder;

s2: dissolving powdered whey protein and inulin in deionized water at room temperature, mixing, stirring, freeze drying the composite solution, and grinding into powder to obtain the extruded whey protein-inulin composite.

Preferably, the inulin of S2 is added in an amount of 5% to 20% by weight of the total mass of the inulin and the extruded whey protein.

Preferably, in step 2, the mass-to-volume ratio of the extruded whey protein-inulin complex to the raw milk is (1.0-3.5): 100;

the mass volume ratio of the sucrose to the raw milk is (3-9) to 100;

the stirring time is 15-30 min.

Preferably, in the step 3, the preheating temperature is 50-65 ℃, and the preheating time is 5-10 min;

homogenizing under 15-25 MPa;

pasteurizing at 90-95 deg.C for 10-15 min;

cooling the fermentation substrate to 40-42 deg.C.

Preferably, in the step 4, 0.41 per mill of leaven is added into the fermentation substrate according to the mass volume;

the temperature of the heat preservation fermentation is 40-42 ℃, and the fermentation time is 4.5-6.0 h.

Preferably, in the step 5, the material B is cooled to 20-35 ℃; refrigerating at 4 deg.C for 24 hr.

The invention discloses the following technical effects:

(1) the added whey protein is subjected to extrusion pretreatment, the extrusion pretreatment improves the functional characteristics of the protein such as water retention, viscosity and the like, and the added whey protein is compounded with inulin and added into the fermented milk, so that the characteristics of the extruded whey protein and inulin compounded fermented milk such as hardness, adhesion, water retention, viscosity and the like are greatly improved. The concrete points are as follows: compared with the fermented milk which is not treated by the technology, the hardness value of the fermented milk containing the extruded whey protein-inulin complex prepared by the invention is improved by about 3.6 times, namely the hardness value is increased from 16.44g to 59.37 g; the absolute value of the adhesion is improved by about 4.0 times, namely, the absolute value is increased from-78.07 to-310.96; the water retention is improved from 50.16% to 69.34%, and is increased by about 1.4 times; the consistency index increased from 0.92 Pa-sn to 42.60 Pa-sn, an increase of about 46.3 times.

(2) The fermented milk containing the extruded whey protein-inulin complex prepared by the invention has good stability, high quality, fine and smooth mouthfeel, moderate sour and sweet taste and better tissue state and fermented milk flavor from the aspect of sensory quality, and the fact that the inulin and the extruded whey protein are added into the fermented milk in a compounding way is a good choice for developing functional fermented milk. Compared with fermented milk which is not treated by the technology of the invention, the viable count of the lactobacillus in the fermented milk containing the extruded whey protein-inulin compound is increased by 71.43 percent, and the viable count of the lactobacillus is still maintained at a higher level (more than or equal to 10) along with the prolonging of the storage time⁷). Therefore, the fermented milk prepared by the invention can meet the requirements of consumers and has wide market prospect.

Drawings

FIG. 1 is a graph of the effect of different inulin addition ratios on the surface hydrophobicity of extrusion pretreated WPI;

FIG. 2 is a graph of the effect of different inulin addition ratios on the emulsifying activity of extrusion pretreated WPI;

FIG. 3 is a graph of the effect of different inulin addition ratios on the emulsion stability of extrusion pretreated WPI;

FIG. 4 is a graph of the effect of different inulin addition ratios on the foaming capacity of extrusion pretreated WPI;

FIG. 5 is a graph of the effect of different inulin addition ratios on extrusion pretreated WPI foam stability;

FIG. 6 is a graph of the effect of different inulin addition ratios on the hardness of extrusion pretreated WPI gels;

figure 7 is a graph of the effect of different inulin addition ratios on water retention of extrusion pretreated WPI gels;

FIG. 8 is a graph of the effect of different inulin addition ratios on the apparent viscosity of extrusion pretreated WPI;

FIG. 9 is a graph of the effect of different inulin addition ratios on WPI shear stress of extrusion pretreatment;

FIG. 10 is a microstructure diagram of a 5000 fold magnification of WPI without extrusion pre-treatment with 0% inulin added;

FIG. 11 is a microstructure diagram of a 5% inulin-added WPI without extrusion pre-treatment at 5000-fold magnification;

FIG. 12 is a microstructure diagram of a WPI magnification of 5000 fold without extrusion pre-treatment with 10% inulin added;

FIG. 13 is a microstructure diagram of a WPI magnification of 5000 fold without extrusion pre-treatment with 15% inulin added;

FIG. 14 is a microstructure diagram of a WPI magnification of 5000 fold with extrusion pre-treatment with 0% inulin added;

FIG. 15 is a microstructure diagram of a WPI magnification of 5000 fold with extrusion pre-treatment with 5% inulin added;

FIG. 16 is a microstructure diagram of a WPI magnification of 5000 fold with extrusion pre-treatment with 10% inulin added;

FIG. 17 is a microstructure diagram of a WPI magnification of 5000 fold with extrusion pre-treatment with 15% inulin added;

FIG. 18 is the change in apparent viscosity of fermented milk with different proportions of inulin added with squeezed/non-squeezed WPI complex on day 1 of storage;

FIG. 19 is the change in apparent viscosity of fermented milk with different ratios of inulin added with squeezed/non-squeezed WPI complex on day 7 of storage;

FIG. 20 is the change in apparent viscosity of fermented milk with different proportions of inulin added with squeezed/non-squeezed WPI complex on day 14 of storage;

FIG. 21 is a graph of the change in shear stress of fermented milk with different ratios of inulin added to the squeezed/non-squeezed WPI composite on day 1 of storage;

FIG. 22 is a graph of the change in shear stress of fermented milk with different ratios of inulin added to the squeezed/non-squeezed WPI composite on day 7 of storage;

figure 23 is the variation of shear stress of fermented milk with different proportions of inulin added with squeezed/non-squeezed WPI complexes on day 14 of storage;

FIG. 24 is a graph of the principal component loading and scoring for fermented milks PC1 and PC2 with different ratios of inulin added to squeezed/non-squeezed WPI complexes;

figure 25 is a graph of scores and overall score trends for fermented milks PC1, PC2 with different ratios of inulin added to squeezed/non-squeezed WPI complexes.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

Example 1

A method for producing fermented milk containing an extruded whey protein-inulin complex, comprising the steps of:

(1) preparation of extruded whey protein-inulin complex: carrying out extrusion pretreatment on whey protein at an extrusion temperature of 45 ℃, carrying out freeze drying on the obtained extruded whey protein, grinding the obtained extruded whey protein into powder, dissolving inulin with an addition ratio of 5% (g/g, ratio of inulin/inulin to total solid mass of the extruded whey protein) in deionized water at room temperature for compounding, carrying out magnetic stirring for 2 hours, carrying out freeze drying on the composite solution, and grinding the composite solution into powder to obtain an extruded whey protein-inulin composite;

(2) adding 1% by mass of extruded whey protein-inulin complex (namely the mass-volume ratio of the extruded whey protein-inulin complex to the raw material milk is 1 mg: 100mL) and 3% by mass of sucrose (namely the mass-volume ratio of the sucrose to the raw material milk is 1 mg: 100mL) into the raw material milk, and uniformly mixing and stirring for 15 minutes to obtain a material A;

(3) preheating the material A at 50 ℃ for 5 minutes, homogenizing under 15MPa, pasteurizing at 90 ℃ for 10 minutes, and cooling to 40 ℃ to obtain a fermentation substrate;

(4) adding 0.35 per mill (w/v) of a starter (namely, the mass-volume ratio of the starter to the fermentation substrate is 0.35 mg: 1000mL), filling, carrying out heat preservation fermentation at 40 ℃ for 1.5 hours, and stopping fermentation to obtain a material B;

(5) and cooling the material B to 20 ℃, and refrigerating the material B at 4 ℃ for 24 hours to obtain the fermented milk containing the extruded whey protein-inulin complex.

Example 2

A method for producing fermented milk containing an extruded whey protein-inulin complex, comprising the steps of:

(1) preparation of extruded whey protein-inulin complex: carrying out extrusion pretreatment on whey protein at the extrusion temperature of 50 ℃, carrying out freeze drying on the obtained extruded whey protein, grinding the obtained extruded whey protein into powder, dissolving the powder and 15% of inulin in an addition ratio (g/g, the ratio of the inulin to the total solid mass of the inulin and the extruded whey protein) in deionized water at room temperature for compounding, magnetically stirring for 2 hours, freeze drying the composite solution, and grinding the composite solution into powder to obtain an extruded whey protein-inulin composite;

(2) adding 2% of extruded whey protein-inulin complex (namely the mass-volume ratio of the extruded whey protein-inulin complex to the raw material milk is 2 mg: 100mL) and 7% of sucrose (namely the mass-volume ratio of the sucrose to the raw material milk is 7 mg: 100mL) into the raw material milk, and uniformly mixing and stirring for 20 minutes to obtain a material A;

(3) preheating the material A at 55 ℃ for 5 minutes, homogenizing under 20MPa, pasteurizing at 93 ℃ for 12 minutes, and cooling to 42 ℃ to obtain a fermentation substrate;

(4) adding 0.41 per mill (w/v) of a starter (namely, the mass-volume ratio of the starter to the fermentation substrate is 0.41 mg: 1000mL), filling, carrying out heat preservation fermentation at 42 ℃ for 5.5 hours, and terminating fermentation to obtain a material B;

(5) and cooling the material B to 30 ℃, and refrigerating at 4 ℃ for 24 hours to obtain the extruded whey protein and inulin composite fermented milk.

Example 3

A method for producing fermented milk containing an extruded whey protein-inulin complex, comprising the steps of:

(1) preparation of extruded whey protein-inulin complex: carrying out extrusion pretreatment on whey protein at an extrusion temperature of 55 ℃, carrying out freeze drying on the obtained extruded whey protein, grinding the obtained extruded whey protein into powder, dissolving the powder and 20% of inulin in an addition ratio (g/g, the ratio of the inulin to the total solid mass of the inulin and the extruded whey protein) in deionized water at room temperature for compounding, carrying out magnetic stirring for 2 hours, carrying out freeze drying on the compound solution, and grinding the compound solution into powder to obtain an extruded whey protein-inulin compound;

(2) adding 3.5% of extruded whey protein-inulin complex (namely the mass-volume ratio of the extruded whey protein-inulin complex to the raw material milk is 3.5 mg: 100mL) and 9% of cane sugar (namely the mass-volume ratio of the cane sugar to the raw material milk is 9 mg: 100mL) into the raw material milk, and uniformly mixing and stirring for 20 minutes to obtain a material A;

(3) preheating the material A at 65 ℃ for 10 minutes, homogenizing under 25MPa, pasteurizing at 95 ℃ for 15 minutes, and cooling to 42 ℃ to obtain a fermentation substrate;

(4) adding 0.45 per mill (w/v) of a starter (namely, the mass-volume ratio of the starter to the fermentation substrate is 0.45 mg: 1000mL) into the fermentation substrate, filling, carrying out heat preservation fermentation at 42 ℃ for 6 hours, and stopping fermentation to obtain a material B;

(5) and cooling the material B to 35 ℃, and refrigerating the material B at 4 ℃ for 24 hours to obtain the extruded whey protein and inulin composite fermented milk.

Example 4

1) The preparation method of example 2 was followed to compare the effect of different inulin addition ratios on the hydrophobicity of the surface of extrusion-pretreated Whey Protein (WPI)

2) Determination of surface hydrophobicity

The protein sample was diluted to 0.2-1.0mg/mL with phosphate buffer (pH7.0, concentration 0.01mol/L), 20. mu.L of ANS solution (concentration 8mmol/L) was added to 4mL of the diluted protein sample, mixed with shaking and reacted in the dark for 15 min. The excitation wavelength was set at 390nm, the emission wavelength at 470nm, and the slit width at 5 nm. And performing linear regression analysis by taking the measured fluorescence intensity as a vertical coordinate and the protein concentration as a horizontal coordinate, and taking the obtained initial slope as the surface hydrophobicity of the protein sample.

Inulin was added to WPI subjected to extrusion pretreatment at 50 ℃, and the influence of different inulin addition ratios (0%, 5%, 10%, 15%, g/g, ratio of inulin/total solid mass of inulin and extrusion WPI) on the surface hydrophobicity of WPI subjected to extrusion pretreatment and WPI of the control group was investigated.

As shown in fig. 1, when 5% inulin was added, the surface hydrophobicity of both extruded WPI and WPI increased, and increased by 17.48%, 23.48%, respectively, compared to that without the addition; but gradually decreased as the inulin addition ratio (5-15%) increased. WPI subjected to extrusion pretreatment has higher surface hydrophobicity as a whole. This is because, during the extrusion process, under the action of high pressure and high shear force, the hydrophobic amino acids in the interior of the protein are exposed, resulting in increased hydrophobicity of the surface of the protein.

Example 5

1) The influence of different inulin addition ratios on the emulsification properties of extrusion pretreatment WPI was compared according to the preparation method of example 2

2) Determination of the emulsification Properties

The emulsification properties of the protein samples were determined according to Pearce and Kinsella's turbidimetry. First, 3mL of 0.5mg/mL protein sample solution and 1mL of soybean oil were mixed together, followed by homogeneous emulsification at 10000rpm for 2min using a high-speed emulsifier. Then, 50. mu.L of the emulsion was aspirated from the bottom of the tube, left for 0min and 10min, respectively, and immediately mixed with 5mL of a 0.1% SDS solution, and the absorbance was recorded at 500 nm. 0.1% SDS solution was used as a reagent blank. The emulsifying activity (EAI, m2/g) and the emulsifying stability (ESI,%) were calculated using the following formulas:

wherein A is₀The absorbance measured after the emulsion was left for 0min was indicated, D was the dilution factor of 100,. phi.is the oil phase volume fraction of the emulsion of 0.25, C is the concentration of the protein solution before emulsification (mg/mL), and T is the turbidity of 2.303.

Wherein A is₀Denotes the absorbance, A, measured after the emulsion has been left to stand for 0min₁₀The absorbance measured after the emulsion was left for 10min is shown.

The effects of different inulin addition ratios (0%, 5%, 10%, 15%, g/g, ratio of inulin/total solid mass of inulin and extrusion WPI) on the emulsifying activity and the emulsifying stability of the extrusion-pretreated WPI and the control WPI were investigated by adding inulin to the extrusion-pretreated WPI at 50 ℃ as shown in fig. 2 and 3, respectively.

As can be seen from fig. 2, the effect of low concentration of inulin on the emulsifying activity of whey protein was not significant, and the emulsifying activity of whey protein increased with the increase of the inulin addition ratio, but the emulsifying activity of whey protein with the addition of 10% and 15% of inulin was not significantly different (P > 0.05). The emulsifying activity of the extruded protein with 15% inulin added was increased by 4.57% compared to extruded protein without inulin added. The addition of inulin is shown to improve the emulsifying activity of the protein. On the whole, the emulsifying activity of the whey protein subjected to extrusion pretreatment is remarkably higher than that of the non-extruded whey protein with the increase of the adding proportion of the inulin.

Figure 3 shows the effect of inulin on the emulsion stability of extrusion pretreated WPI/non-extruded WPI. Similar to the emulsification activity results, the emulsification stability of whey protein increased with increasing inulin addition rate, especially when the inulin addition rate was 15%, the emulsification stability of whey protein pre-treated by extrusion increased by 8.98%. This may be an increase in inulin content, which increases the viscosity of the solution, thus inhibiting the fluidity of the protein in favor of stability.

Example 6

1) Comparison of the Effect of different inulin addition ratios on the foaming Properties of extrusion Pre-treatment WPI according to the preparation method of example 2

2) Determination of foaming Properties

Protein samples were tested for foaming capacity and foam stability with appropriate modifications according to the method of Jiang et al. 15mL of the sample solution (V) having a concentration of 10mg/mL was added to a 100 mL-volume measuring cylinder, followed by homogenization using a high-speed emulsifier (homogenization at 10000rpm for 2 min). Immediately after homogenization, the volume of foam (V) was recorded at 0min₀). After allowing the mixture to stand for 30min, the volume of foam (V) was recorded₃₀). Foaming capacity and foam stability were calculated using the following formulas:

the effects of different inulin addition ratios (0%, 5%, 10%, 15%, g/g, ratio of inulin/total solid mass of inulin and extruded WPI) on the foaming ability and foam stability of the extrusion-pretreated WPI and the control WPI were investigated as shown in fig. 4 and 5, respectively, by adding inulin to the extrusion-pretreated WPI at 50 ℃.

As can be seen from FIGS. 4 and 5, as the inulin addition ratio increases, both the foaming power and the foam stability of the protein show a tendency to increase. When the inulin addition ratio is 15%, the WPI foaming capacity and the foam stability of the extrusion pretreatment are the maximum, namely 126.57% and 76.17%, respectively; foaming capacity and foam stability increased 8.39%, 15.69% respectively compared to extruded WPI without inulin. It is shown that the addition of inulin is advantageous for improving the foaming properties of the protein. In addition, the protein pre-treated with extrusion had higher foaming capacity and foam stability than the non-extruded protein without the addition of inulin, increasing 137.79% and 22.15%, respectively. The extruded protein molecules can be diffused and adsorbed to a gas-liquid interface more quickly, can be stretched and rearranged quickly after reaching the interface, and form an adsorption film with strong cohesive force and viscoelasticity through the interaction between the molecules, thereby improving the foaming property of the protein.

Example 7

1) According to the preparation method of example 2, the influence of different inulin addition ratios on the gel characteristics of the extrusion pretreatment WPI is compared

2) Determination of gel Properties

Gel strength: preparing a sample into a solution with a protein concentration of 80mg/mL by using deionized water, heating the solution in a water bath at 95 ℃ for 30min, quickly cooling the solution to room temperature after heating, and finally storing the solution at 4 ℃ for 24h to obtain the gel.

The hardness of the gel of the samples was determined using a ta.xt.plus texture analyser, using a P/0.5S probe, with each sample tested three times.

The test parameters are set as: the speed before, after and after the test is respectively 2mm/s, 1mm/s and 1mm/s, the test distance is 5mm, the trigger force is 5g, and the time interval between two times of compression is 5 s.

Gel water retention: place the small sample gel in a 50mL centrifuge tube (M)₁) To average and weigh the total weight (M)₂) The gel was then centrifuged at 4000g for 15min and the supernatant discarded. The total weight of centrifuge tube and residual material was recorded as M3. Therefore, the water retention of the gel is calculated by the following formula:

inulin was added to WPI subjected to extrusion pretreatment at 50 ℃, and the effects of different inulin addition ratios (0%, 5%, 10%, 15%, g/g, ratio of inulin/total solid mass of inulin and extruded WPI) on gel texture and gel water retention of WPI subjected to extrusion pretreatment and WPI of control group were investigated as shown in fig. 6 and fig. 7, respectively.

As can be seen from FIG. 6, the WPI gel hardness after the squeeze pretreatment was reduced from 36.95g to 30.46g as the inulin addition ratio was increased from 0% to 15%. This indicates that inulin hinders the connection of the internal structure of the mixed gel and that the interaction in the mixed gel is easily broken. When the inulin addition ratio is the same, the WPI subjected to the extrusion pretreatment has a lower hardness. In addition, as can be seen from fig. 7, the water retentivity of the gel is opposite to the hardness of the gel. When the inulin addition ratio was increased from 0% to 15%, the water retention of the WPI gel subjected to the extrusion pretreatment was increased from 51.61% to 55.16%. This indicates that the addition of inulin resulted in an increase in water retention but a decrease in hardness of the gel, similar to a "hydrogel", whereas the WPI "hydrogel" effect after extrusion pretreatment was more pronounced. In addition, the inulin adhered to the surface of the protein can be combined with water through hydrogen bonds and filled in the gaps of the network, so that the water retention of the gel is improved.

Example 8

1) The preparation method of example 2 was followed to compare the effect of different inulin addition ratios on the static rheology of extrusion pretreatment WPI

2) Determination of static rheology

Dissolving the protein complexes with different inulin addition ratios in deionized water to obtain a sample solution with the protein concentration of 40mg/mL, and performing rheological measurement by using a RST rheometer. The temperature is controlled at 25 ℃ in the measuring process, and the shear rate is in the range of 0.1-100s^-1The values for shear stress and apparent viscosity were recorded. The flow behavior of the sample was represented using the Power Law model. The logarithmic shear stress versus logarithmic shear rate is plotted and a linear fit is made, and then the flow behavior index n and the consistency index K are obtained according to the following power law equation, which are used as verification parameters for the viscosity change of the sample.

logτ＝log K+n logγ

Wherein τ represents the shear stress (Pa) and K represents the consistency index (Pa · s)ⁿ) And gamma denotes shear rate(s)^-1) And n represents a flow behavior index.

Inulin was added to the WPI subjected to extrusion pre-treatment at 50 ℃ and the effect of different inulin addition ratios (0%, 5%, 10%, 15%, g/g, ratio of inulin/total solid mass of inulin and extruded WPI) on the static rheology of the WPI subjected to extrusion pre-treatment and the WPI of the control group was investigated. The specific test results are shown in fig. 8, fig. 9 and table 1.

As can be seen from fig. 8, the apparent viscosity of all samples decreased with increasing shear rate. This indicates that the sample is shear diluted and is a pseudoplastic fluid. The increase in shear rate causes the destruction of the network structure of the sample, thereby reducing the viscosity. After addition of inulin, the samples showed higher apparent viscosity and increased with increasing proportion of addition. WPI pretreated by extrusion had the highest apparent viscosity when 15% inulin was added. This is probably because the complex formed by the interaction between inulin and protein influences the apparent viscosity of the protein.

The change in the consistency index K and the flow behavior index n obtained by fitting according to the power law model (fig. 9) are shown in table 1. As can be seen from Table 1, all samples had n values less than 1, demonstrating that the samples were pseudoplastic fluids. In addition, the larger the value of the consistency index K is, the smaller the value of the flow behavior index n is, the poorer the fluidity of the sample is, and the higher the viscosity is. Therefore, the consistency index K value is obviously increased (P <0.05) along with the increase of the adding proportion of the inulin, which indicates that the addition of the inulin leads to the increase of the viscosity of the protein. The consistency index shows a similar trend to the apparent viscosity. Also, the consistency factor K value of the WPI after the extrusion pretreatment was significantly higher than that of the non-extruded WPI, indicating that the extrusion pretreatment also increased the viscosity of the protein.

TABLE 1 Effect of different inulin addition ratios on the consistency index and flow behavior index of extrusion pretreated WPI

Note: in the table, the same lower case letters in the same column represent no significant difference (P >0.05), and different represent significant difference (P < 0.05).

Example 9

1) The effect of different inulin addition ratios on the extrusion pretreatment of WPI microstructure was compared according to the preparation method of example 2

2) Determination of microstructure

The microstructure change of the 2000-fold protein sample was observed using a tungsten filament scanning electron microscope at an accelerating voltage of 5 kV. Prior to observation, the protein samples were gold plated using an ion sputter. The specific test results are shown in fig. 10-17.

As can be seen, the WPI without extrusion treatment is mainly spherical structure (FIG. 10), while the protein after extrusion pretreatment is mainly massive structure (FIG. 14). In addition, as the adding proportion of the inulin is increased, the proteins subjected to extrusion pretreatment are connected with each other to form a reticular structure similar to a honeycomb shape and containing a plurality of pores; the protein without extrusion treatment forms a reticular structure similar to a sheet layer. When 10% and 15% inulin was added, there was no significant difference in the microstructure of the protein. The protein and inulin are connected by hydrogen bonds at the boundary of the connecting region and hydrophobic interactions occur, resulting in the formation of a gel network with a high degree of crosslinking.

Example 10 Effect of extrusion of whey protein-inulin Complex on titrated acidity and pH during storage of fermented milks

And measuring the titrated acidity of the squeezed whey protein and inulin composite fermented milk by referring to GB 5009.239-2016 (national food safety standard for measuring the acidity of food).

The method for measuring the pH of the extruded whey protein and inulin composite fermented milk comprises the following steps:

the pH of the fermented milk was measured using a pH meter. The pH meter was calibrated with phosphate buffer before the measurement, the probe was immersed in the sample during the measurement and the value was recorded after it stabilized. Each sample was repeated 3 times.

On the basis of example 2, the influence of the resulting extruded whey protein-inulin complex on the titrated acidity and pH during storage of the fermented milk was varied by varying the inulin addition ratio at 0, 5, 10, 15% (g/g, ratio of inulin/total solid mass of inulin and extruded whey protein), and the results of the specific tests are shown in tables 2 and 3.

TABLE 2 Effect of inulin addition ratio in the extruded whey protein-inulin complex on the titrated acidity during storage of the fermented milk

Note: in the table, the same column (or row) lower case (or upper case) letters represent no significant difference (P >0.05), and the same letters represent significant difference (P < 0.05).

TABLE 3 Effect of inulin addition ratio in the extruded whey protein-inulin complex on pH during storage of fermented milks

Note: in the table, the same column (or row) lower case (or upper case) letters represent no significant difference (P >0.05), and the same letters represent significant difference (P < 0.05).

As can be seen from tables 2 and 3, the titer acidity of each fermented milk sample gradually increased (P <0.05) with the increase of the storage period and the pH value tended to decrease (P <0.05) during the storage period. And the acidity of the fermented milk compounded with inulin added with the extrusion pre-treatment WPI was significantly increased (P <0.05) compared with the fermented milk compounded with inulin added with non-extrusion treated WPI. In addition, fermented milk with 15% inulin added with squeezed WPI compound has the maximum titrated acidity and the minimum pH value during the same storage period. In particular, on day 1 of storage, the titrated acidity of fermented milk with 15% inulin added with squeezed WPI compound increased by 23.27% compared to the blank control (without any addition).

Example 11 Effect of extruded whey protein-inulin Complex on Water Retention during storage of fermented milk

The method for measuring the water retention of the squeezed whey protein and inulin composite fermented milk comprises the following steps:

20g of the sample to be tested was aspirated into a 50mL centrifuge tube (the weight of the centrifuge tube is M1) and the total weight is recorded as M2. After subsequent centrifugation at 2795g for 20 minutes at 4 ℃, the supernatant was removed and the total weight of the residue and centrifuge tube, M3, was recorded and the water retention of the fermented milk was calculated according to the following formula:

on the basis of example 2, the influence of the resulting extruded whey protein-inulin complex on the water retention during storage of the fermented milk was varied by varying the inulin addition ratio at 0, 5, 10, 15% (g/g, ratio of inulin/total solid mass of inulin and extruded whey protein), and the results of the specific tests are shown in table 4.

TABLE 4 Effect of inulin addition ratio in the extruded whey protein-inulin complex on the Water Retention during storage of fermented milks

Note: in the table, the same column (or row) lower case (or upper case) letters represent no significant difference (P >0.05), and the same letters represent significant difference (P < 0.05).

As is clear from Table 4, on day 1 of storage, the water retentivity of the fermented milk gradually increased with the increase in the inulin addition ratio (P < 0.05). The water retention of the fermented milk was highest when 15% inulin was added with the squeezed WPI complex, and increased 38.24% and 3.77% respectively over the blank group and the fermented milk with 15% inulin and non-squeezed WPI complex. And the water retention property of the fermented milk added with the WPI subjected to extrusion pretreatment is higher than that of the fermented milk added with the WPI subjected to non-extrusion treatment and compounded with inulin.

The water retention of all fermented milk samples showed a decreasing trend with increasing storage time, and by day 14, the water retention of the fermented milk samples with the complex added was not significantly different (P >0.05), but was all larger than the blank control fermented milk.

Example 12 Effect of extruded whey protein-inulin Complex on the texture of fermented milk

The method for measuring the texture of the extruded whey protein and inulin composite fermented milk comprises the following steps:

the firmness and adhesiveness of the fermented milk were determined using a ta.xt.plus texture analyser, using an a/BE-d35 probe, each sample tested three times.

The test parameters are set as: the speed before, after and after the test is respectively 2mm/s, 1mm/s and 2mm/s, the test distance is 10mm, the trigger force is 5g, and the time interval between two times of compression is 5 s.

On the basis of example 2, the influence of the resulting extruded whey protein-inulin complex on the texture of fermented milk was varied by varying the inulin addition ratio at 0, 5, 10, 15% (g/g, ratio of inulin/total solid mass of inulin and extruded whey protein), and the results of the specific tests are shown in table 5.

TABLE 5 influence of inulin addition ratio in extruded whey protein-inulin complex on the texture of fermented milk

Note: in the table, the same lower case letters in the same column represent no significant difference (P >0.05), and different represent significant difference (P < 0.05).

The texture of the fermented milk is also one of the important indicators for measuring the quality of the fermented milk, where the stickiness represents the work done to overcome the attraction between the surface of the fermented milk and the surface of the texture probe, and a negative force value indicates the adherence of the fermented milk to the texture probe, i.e. the greater the absolute value of the force, the more viscous the fermented milk, and the more viscous the fermented milk that sticks to the texture probe when pulled up, the more viscous the fermented milk.

As can be seen from Table 5, the absolute values of hardness and stickiness exhibited a tendency to gradually increase (P <0.05) in all the fermented milk samples as the inulin addition ratio increased. The fermented milk with the added 15% inulin and the squeezed WPI compound has the maximum hardness and adhesiveness of 59.37g and-310.96 g.s, which are respectively increased by 261.13% and 298.31% compared with the blank control, the squeezed WPI only added, the added 15% inulin and the non-squeezed WPI compound fermented milk; 52.74%, 31.30%; 2.50 percent and 13.77 percent.

Example 13 Effect of extruded whey protein-inulin Complex on sensory evaluation of fermented milks

The method for measuring the sensory evaluation of the extruded whey protein and inulin composite fermented milk comprises the following steps:

referring to the requirements on the sensory characteristics of the fermented milk in GB 19302-. And 5 persons are randomly selected for carrying out sensory evaluation training, and besides theoretical training of a system, intensive training is also needed to be carried out on the sensory sensitivity and language description of evaluators, so that the sensory stimulation sensing and describing capabilities of the evaluators are improved. After tasting, the mouth was rinsed immediately with clear water and tasted again at 15 minute intervals. Each member of the assessment is scored individually and does not communicate with each other for discussion. Specific sensory scores are shown in table 6.

TABLE 6 sensory evaluation criteria for fermented milks

On the basis of example 2, the impact of the resulting extruded whey protein-inulin complex on the sensory evaluation of fermented milk was varied by varying the inulin addition ratio at 0, 5, 10, 15% (g/g, ratio of inulin/total solid mass of inulin and extruded whey protein), and the results of the specific tests are shown in table 7.

TABLE 7 influence of inulin addition ratio in the extruded whey protein-inulin complex on sensory evaluation of fermented milks

Note: in the table, the same lower case letters in the same column represent no significant difference (P >0.05), and different represent significant difference (P < 0.05).

As can be seen from Table 7, the addition of the extruded WPI and inulin complex significantly affected the smell, taste, mouthfeel, texture and total score of the fermented milk (P <0.05), while it did not significantly affect the color (P > 0.05). From an odor perspective, the addition of inulin and protein imparted a strong fermented milk odor and milk flavor to the fermented milk, resulting in a score higher than that of the blank group. From the aspects of taste and mouthfeel, when 5% of inulin is added and the WPI compound is extruded, the fermented milk is fine and smooth, is moderate in sour and sweet, tastes smooth, has good sensory quality and has the highest sensory score; when the addition proportion of the inulin is gradually increased, the viscosity and the hardness of the fermented milk are increased, the fermented milk has granular feel, the fermented milk is too thick, the palatability is poor, and the taste and the mouthfeel score of the fermented milk are reduced. From the texture, the blank control fermented milk had whey separation and a small amount of coagulum, while the fermented milk with the addition of the squeezed WPI and inulin complex had a uniform texture, a smooth surface, and slight whey separation. And the tissue state score of the fermented milk added with the squeezed WPI and the inulin complex is obviously higher than that of the fermented milk added with the non-squeezed WPI and the inulin complex, which shows that the WPI subjected to squeezing treatment can form a gel network system with a three-dimensional structure and improve the tissue state of the fermented milk. Taken together, the addition of 5% inulin resulted in the highest total score for fermented milk with the WPI complex squeezed.

Example 14 Effect of the extrusion of whey protein-inulin Complex on the viable count of lactic acid bacteria during storage of fermented milks

The method for measuring the viable count of the lactic acid bacteria in the extruded whey protein and inulin composite fermented milk comprises the following steps:

the number of viable bacteria of Lactobacillus bulgaricus and Streptococcus thermophilus is determined by reference to GB 4789.35-2016 (lactic acid bacteria test for food safety national standard food microbiology).

On the basis of example 2, the influence of the obtained extruded whey protein-inulin complex on the viable count of lactic acid bacteria during storage of the fermented milk was determined by varying the inulin addition ratio at 0, 5, 10, 15% (g/g, ratio of inulin/total solid mass of inulin and extruded whey protein), and the specific test results are shown in Table 8.

TABLE 8 influence of inulin addition ratio on viable count of lactic acid bacteria during storage of fermented milk

Note: in the table, the same column (or row) lower case (or upper case) letters represent no significant difference (P >0.05), and the same letters represent significant difference (P < 0.05).

As can be seen from Table 8, the total viable count of Streptococcus thermophilus and Lactobacillus bulgaricus in all the fermented milk samples was consistently higher than the viable count of fermented milk (greater than 1X 10) specified in the national Standard (GB 19302-⁶CFU/mL) and all decreased gradually with increasing storage time, but there was no significant difference in viable count between day 1 and day 7 (P)>0.05). The viable count of Streptococcus thermophilus and Lactobacillus bulgaricus added with non-squeezed WPI and squeezed pretreated WPI fermented milk is higher than that of blank control group (P)<0.05) and the addition of extrusion pre-treatment WPI favours the proliferation of streptococcus thermophilus and lactobacillus bulgaricus. When 15% inulin was added with the extruded WPI complex, the number of viable Streptococcus thermophilus and Lactobacillus bulgaricus survived in the fermented milk was the highest.

Example 15 Effect of the extruded whey protein-inulin Complex on the static rheology of fermented milks during storage

The method for measuring the static rheological property of the extruded whey protein and inulin composite fermented milk comprises the following steps:

the protein complex fermented milk with different inulin addition ratios was measured according to the measurement method of example 8.

The effect of the resulting extruded whey protein-inulin complex on the static rheology of the fermented milk during storage was obtained by varying the inulin addition ratio of 0, 5, 10, 15% (g/g, ratio of inulin/total solid mass of inulin and extruded whey protein) on the basis of example 2, and the results of the specific tests are shown in fig. 18-fig. 23 and table 9-table 11.

The rheological property of the fermented milk refers to the property of the fermented milk showing fluidity and deformation under the action of external force along with the changes of shear rate and shear stress, and mainly relates to the relation between shear rate and apparent viscosity and between shear rate and shear stress. And thus can be used for determining the type of fluid of the fermented milk and evaluating the viscosity of the fermented milk, etc.

As shown in fig. 18-20, all samples showed shear thinning results with decreasing apparent viscosity as the shear rate increased. Samples exhibiting this negative correlation are considered pseudoplastic fluids, as can be seen by the concave orientation of the curves of FIGS. 21-23. With the increase of the inulin addition ratio, the apparent viscosity tends to increase. And the fermented milk with the addition of 15% inulin with the squeezed WPI complex had a higher apparent viscosity. The samples all showed the same trend for different storage times. However, the apparent viscosity of all samples decreased with increasing storage time.

The changes in the consistency index K and the flow behavior index n obtained were fitted according to the power law model (FIG. 21-FIG. 23) as shown in tables 9-11. First, all samples had n values less than 1, indicating that the samples were pseudoplastic fluids. With the increase of the inulin addition ratio, the consistency index K value gradually increases (P <0.05), which indicates that the viscosity of the fermented milk increases. Compared with the fermented milk added with the non-squeezed WPI, the fermented milk added with the squeezed WPI has no significant difference in the thickness coefficient K value (P >0.05) at the 1 st day of storage, but has a low degree of reduction of the thickness coefficient K value with the increase of the storage time and retains higher viscosity. The fermented milk added with 15% inulin and the extruded WPI compound has the largest thickness coefficient K value in each storage period, which indicates that the fermented milk has the highest viscosity and the worst flowability.

TABLE 9 Effect of inulin addition ratio on the consistency index and flow behavior index on day 1 of storage of fermented milks

Note: in the table, the same lower case letters in the same column represent no significant difference (P >0.05), and different represent significant difference (P < 0.05).

TABLE 10 influence of inulin addition ratio on the body index and flow behavior index of fermented milks at day 7 of storage

Note: in the table, the same lower case letters in the same column represent no significant difference (P >0.05), and different represent significant difference (P < 0.05).

TABLE 11 Effect of inulin addition ratio on consistency index and flow behavior index at day 14 of storage of fermented milks

Note: in the table, the same lower case letters in the same column represent no significant difference (P >0.05), and different represent significant difference (P < 0.05).

Example 16

And determining the optimal inulin addition proportion capable of improving the comprehensive quality of the extruded whey protein and the inulin composite fermented milk to the maximum extent by utilizing a main component analysis method.

The principal component analysis method specifically comprises the following steps:

the fermented milk on day 1 of storage was subjected to a main component analysis for organoleptic evaluation, acidity, pH, water retention, texture, viable count, rheology (consistency index) and the like using Origin 2017(Origin lab Corporation, north ampton, MA, USA).

Principal component analysis refers to a multivariate dimension reduction analysis method that uses linear transformation of multiple parameters to select a few (usually two principal components) important parameters. Through research, the variance contribution rates of the first two principal components are 77.88% and 13.81% respectively, and the cumulative variance contribution rate reaches 91.69%, which shows that the two principal components of PC1 (first principal component) and PC2 (second principal component) can reflect all information of the original variables. The specific test results are shown in fig. 24 and fig. 25.

As can be seen from fig. 24, the indices associated with PC1 are: color, smell, tissue state, acidity, water retention, viable count, hardness and consistency index; the indices associated with PC2 are: taste, mouthfeel and pH. The fermented milk with 10% inulin-WPI complex added and the fermented milk with 5% inulin-squeezed WPI complex added to the samples in the first quadrant were characterized by taste, odor, acidity, adhesiveness, water retention and viable count; the samples in the second quadrant were characterized by mouthfeel and pH with fermented milk with added non-squeeze-treated WPI alone, fermented milk with added 5% inulin and WPI complex, and fermented milk with added squeeze-treated WPI alone; the blank control sample is divided into a third quadrant without any attribute characteristics; the fermented milk with added 15% inulin and WPI complex, the fermented milk with added 10% inulin and squeezed WPI complex and the fermented milk with added 15% inulin and squeezed WPI complex of the samples in the fourth quadrant were characterized by firmness, consistency index, texture state and color. Thus, it can be seen that different samples are associated with different characteristic indicators.

As can be seen from FIG. 25, the fermented milk with 15% inulin and squeezed WPI complex had the highest score in PC1, indicating that the fermented milk with 15% inulin and squeezed WPI complex could effectively improve the indexes related to PC1, especially hardness, body index, texture and color; the fermented milk added with 5% of inulin and WPI compound has the highest fraction in PC2, which shows that the fermented milk added with 5% of inulin and WPI compound can effectively improve indexes related to PC2, especially indexes such as mouthfeel and pH. As can be seen from the trend of the total score, the fermented milk with the addition of 15% inulin with the squeezed WPI complex had the highest score. It is shown that the addition of 15% inulin with the extrusion of the WPI complex maximizes the overall quality of the fermented milk as a whole.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.