Preparation method of walnut protein ice cream

Abstract

The invention discloses a preparation method of walnut protein ice cream, and belongs to the technical field of frozen food processing, and the preparation method comprises the following steps: adding walnuts into water, adjusting pH and temperature, and extracting to obtain a walnut protein extraction stock solution; adjusting the pH value of the walnut protein extraction stock solution, and performing spray drying to obtain walnut protein powder; weighing whey protein powder, walnut protein powder, isomaltulose, coconut oil, sodium carboxymethyl cellulose, a stabilizer and water; the preparation method comprises the following steps: uniformly mixing the raw materials, standing, refrigerating and aging, congealing by using an automatic ice cream machine, and freezing and hardening the congealed ice cream to obtain the walnut protein ice cream. According to the ice cream, walnut protein powder is used for replacing part of whey protein powder, the cost is reduced, the composition of ice cream protein is enriched, meanwhile, isomaltulose is used for replacing traditional cane sugar, and the energy of the ice cream is effectively reduced. The addition of the walnut protein can significantly increase the apparent viscosity of the ice cream and reduce the melting rate.

Description

Technical Field

[0001] The invention relates to the technical field of frozen food processing, in particular to a method for preparing walnut protein ice cream. Background Art

[0002] China is both a major walnut producer and consumer, and occupies a dominant position in the international walnut industry. According to FAO data, the global walnut planting area reached 18.7191 million mu and the output reached 3.874 million tons. China's walnut planting area and output accounted for 28.58% and 36.14% of the world respectively, ranking first in the world. With the country's attention to woody plant oils, the use of protein has become one of the hot spots for various products. Diet is an important factor in many chronic diseases, premature death, and healthy aging. In recent years, many studies have found that eating plant-based foods can promote the intake of essential nutrients and reduce the risk of chronic diseases. In February 2024, Nature Food reported that plant protein foods can replace red meat, processed meat, and dairy products, which can reduce the risk of chronic diseases and thus prolong life. When 50% of red meat, processed meat, and dairy products are replaced with plant protein foods, life expectancy is extended by 8.7 months and 7.6 months, respectively. In addition, it can also reduce carbon dioxide emissions and has a good environmental effect.

[0003] The quality of ice cream is related to the size of its ice crystals, which can determine the quality of the product to a certain extent. The final size of ice crystals in the product depends largely on the formation of ice crystals during the first freezing and solidification process. Therefore, the first freezing process is the most critical stage in ice cream production. Since ice cream slurry is opaque, the formation of ice crystals during its production process is difficult to observe. Ice cream is a complex mixed system, and its final structure and sensory properties are the result of the interaction of a variety of different processing methods and recipes. It usually requires the interaction of multiple substances to produce ice cream with excellent texture and flavor. Most ice creams on the market have the characteristics of high sugar content and high fat, which are not suitable for people with three highs and certain specific groups. Walnut protein can replace animal cream, non-dairy creamer, etc. in ice cream, reducing the ice crystals in China during the freezing process of ice cream, and effectively reducing the amount of sugar added in the ice cream production process and reducing the use of animal protein.

[0004] As a frozen dessert, ice cream has always been loved by consumers. In recent years, the market size of China's ice cream industry has continued to expand. By 2023, there will be 28,800 ice cream-related companies in my country. According to the overall development trend of ice cream, consumers' demand for ice cream products has shifted from taste to nutrition and functionality, pursuing nutrition, health, naturalness and simplicity of ice cream raw materials and ingredients.

[0005] Therefore, providing a method for preparing walnut protein ice cream with low cost, low energy, low melting rate and high apparent viscosity is a technical problem that technicians in this field urgently need to solve. Summary of the invention

[0006] In view of this, the present invention provides a method for preparing walnut protein ice cream.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] A method for preparing walnut protein ice cream comprises the following steps:

[0009] (1) preparing a walnut protein extraction stock solution: preliminarily removing walnut oil from walnuts by hydraulic cold pressing, then extracting with No. 6 solvent to control the oil content in the walnut kernel to less than 10%, crushing the defatted walnuts into 20-40 meshes, adding the walnuts to water, adjusting the pH and temperature for extraction, and obtaining a walnut protein extraction stock solution;

[0010] (2) preparing walnut protein powder: adjusting the pH value of the walnut protein extraction solution to 6.00-7.00, and spray drying to obtain walnut protein powder;

[0011] (3) Preparation of walnut protein ice cream: weigh the following by mass: 7.4-9.8 parts of whey protein powder, 2.4-4.8 parts of walnut protein powder, 10-14 parts of isomaltulose, 6-10 parts of coconut oil, 0.3-0.5 parts of sodium carboxymethyl cellulose, 0.3-0.5 parts of stabilizer, and 65-70 parts of water;

[0012] (4) preparing ice cream: the raw materials weighed in step (3) are mixed evenly, left to stand for aging in cold storage, and then frozen in an automatic ice cream machine, and the frozen ice cream is frozen and hardened to increase the expansion rate of the ice cream, thereby obtaining walnut protein ice cream.

[0013] Furthermore, in step (1), the pH is adjusted to 10.5-11.5 and the temperature is adjusted to 52-58°C.

[0014] Furthermore, the material-liquid ratio of walnut to water in step (1) is 1 g:18-22 mL.

[0015] Furthermore, in step (2), the spray drying inlet temperature is 165-175° C., the solid content is 30-40%, and the feed flow rate is 3.5-6.5 mL / min.

[0016] In the above scheme of the present invention, a walnut protein powder with a powder collection rate of 86.6±3.8% and a moisture content of 4.67±0.82% can be obtained.

[0017] Furthermore, the refrigeration temperature in step (4) is 3.5-4.5° C., and the refrigeration aging time is 11.5-12.5 h.

[0018] Furthermore, the freezing time of the automatic ice cream machine in step (4) is 19.5 to 20.5 minutes.

[0019] Furthermore, the freezing and hardening temperature of step (4) is -19 to -17°C, and the freezing and hardening time is 23.45 to 24.55 hours.

[0020] The beneficial effects of the present invention are as follows: the ice cream of the present invention uses walnut protein powder to replace part of the whey protein powder, which not only reduces the cost, but also enriches the composition of the ice cream protein. At the same time, isomaltulose is used to replace the traditional sucrose, which effectively reduces the energy of the ice cream. The addition of walnut protein can significantly increase the apparent viscosity of the ice cream and reduce the melting rate. Walnut protein has good solubility and water holding capacity, but its emulsification and foaming properties have low stability. The walnut protein isolate is modified by pH shift and ultrasonic treatment to unfold its compact structure. The modified protein is applied to ice cream, which not only improves the expansion rate of the emulsion, but also promotes the formation of the fat network structure and improves the melting resistance of the ice cream. The present invention provides a vegan yogurt ice cream using walnut protein as a raw material and isomaltulose as a prebiotic. The results show that the walnut protein ice cream not only ensures the prebiotic activity, but also has good melting resistance and palatable hardness. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The effect of different pH values ​​on the extraction rate of walnut protein in the present invention;

[0022] Figure 2 The effect of different temperatures on the extraction rate of walnut protein in the present invention;

[0023] Figure 3 The effects of different material-liquid ratios on the extraction rate of walnut protein in the present invention;

[0024] Figure 4 It is the contour line and response surface diagram of the walnut protein extraction method in the present invention; wherein, A1A2: the interaction between pH and temperature, B1B2: the interaction between pH and material-liquid ratio, C1C2: the interaction between temperature and material-liquid ratio;

[0025] Figure 5 The effect of different walnut protein replacement amounts on the expansion rate of ice cream in the present invention;

[0026] Figure 6 The figure shows the influence of different walnut protein replacement amounts on the ice cream stability index in the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example 1 A method for preparing walnut protein ice cream

[0029] (1) preparing a walnut protein extraction stock solution: preliminarily removing walnut oil from walnuts by hydraulic cold pressing, then extracting with No. 6 solvent to control the oil content in the walnut kernel to less than 10%, crushing the defatted walnuts into 20-40 meshes, adding the walnuts to water, the solid-liquid ratio of walnuts to water being 1 g:20 mL, adjusting the pH to 11 and the temperature to 55° C. to extract, and obtaining a walnut protein extraction stock solution;

[0030] (2) Preparation of walnut protein powder: After adjusting the pH value of the walnut protein extract solution to 6.5, spray drying was performed, the spray drying inlet temperature was 170° C., the solid content was 35%, and the feed flow rate was 5 mL / min to obtain walnut protein powder;

[0031] (3) Preparation of walnut protein ice cream: weigh: whey protein powder, walnut protein powder, isomaltulose, coconut oil, sodium carboxymethyl cellulose, stabilizer, and water;

[0032] (4) preparing ice cream: the raw materials weighed in step (3) were mixed evenly and refrigerated at 4° C. for aging for 12 h, then frozen in an automatic ice cream machine for 20 min, and the frozen ice cream was frozen and hardened at -18° C. for 24 h to obtain walnut protein ice cream.

[0033] Example 2

[0034] According to the method of Example 1, walnut protein ice cream was prepared using the raw material ratios shown in Table 1.

[0035] Table 1

[0036]

[0037] Test Example 1 Determination of amino acid content in walnut protein

[0038] The sample was pretreated and walnut protein powder was weighed in a hydrolysis tube. 10 mL of analytical pure hydrochloric acid was added at a ratio of 1:1, nitrogen was injected into the tube for 30 seconds and then sealed, and the sealed tube containing the hydrolyzate was placed in an oil bath at 110 ° C for 22 hours for hydrolysis, then taken out and cooled to room temperature. The solution was filtered into a 50 mL volumetric flask through a 0.45 μm microfiltration membrane and fixed to volume. 2 mL of the sample solution after fixed volume was transferred to a 50 mm weighing flask, heated to 85 ° C, deacidified twice until no small solid spots or traces were left at the bottom of the flask, 1 mL of sodium citrate buffer was added to completely dissolve it, and filtered through a 0.22 μm filter as an amino acid sample, and the amino acid content of walnut protein was determined using an amino acid automatic analyzer.

[0039] As shown in Table 2, the glutamic acid content in the three walnut protein samples was the highest, followed by arginine and aspartic acid, and the contents of lysine, cysteine ​​and methionine were relatively low, among which methionine was the lowest; the total amino acid content of Shaanxi Green Ridge was significantly different from that of Hebei Green Ridge and Shanxi Qingxiang, indicating that differences in origin and variety would affect the total amino acid content of walnut protein. The average content of acidic amino acids in walnut protein was 32.51%, and the average content of basic amino acids was 18.66%, indicating that most of the walnut protein was acidic amino acids, so the solubility of walnut protein in alkaline environment was higher than that in acidic environment; Hebei Green Ridge had a high content of hydrophobic amino acids and a large hydrophobic interaction, so its protein solubility was poor. There were significant differences in the content of essential amino acids, acidic amino acids, basic amino acids, hydrophilic amino acids and hydrophobic amino acids between Hebei Green Ridge and Shaanxi Green Ridge and Shanxi Qingxiang. The essential amino acid content of Hebei Green Ridge was significantly higher than that of the other two, at 28.53%, so the Hebei Green Ridge walnut variety was selected for the subsequent process optimization test and application in ice cream.

[0040] Table 2 Amino acid composition of three walnut proteins

[0041]

[0042] Note: Different letters indicate significant differences in the amino acid content of Shaanxi Green Ridge, Hebei Green Ridge, and Shanxi Qingxiang walnut proteins (P < 0.05).

[0043] Table 3 Distribution of essential amino acids and amino acid residues of three walnut proteins

[0044]

[0045]

[0046] Note: Different letters indicate that the characteristic amino acid content of Shaanxi Green Ridge, Hebei Green Ridge, and Shanxi Qingxiang walnut protein is significantly different (P < 0.05).

[0047] Experimental Example 2 Optimization of walnut protein extraction process

[0048] 2.1 Single factor experiment

[0049] 1) Effect of pH on protein extraction rate

[0050] Weigh 2.0 g defatted walnut powder, add 40 mL distilled water, adjust the pH value of the solution to 9, 9.5, 10, 10.5, 11, 11.5, extract at 55 ° C for 60 min, centrifuge at 5000 r / min for 15 min, sample the supernatant, and use the Coomassie method to determine the protein content in the extract to determine the optimal pH value. Calculate the protein extraction rate according to formula (1):

[0051]

[0052] Protein is an amphoteric substance, and pH affects its solubility. The isoelectric point of walnut protein is at pH 4. The preparation of walnut protein isolate should be under alkaline conditions, such as Figure 1 As shown in the figure, when the temperature and liquid-to-solid ratio remain unchanged, with the increase of pH, the walnut protein extraction rate shows a trend of increasing first and then decreasing. When the pH is 11, the protein extraction rate reaches the highest, which is 77.52%. Then, as the pH continues to increase, the protein extraction rate drops to 71.58%. This is because as the pH increases, the content of gluten in walnut protein is the highest and is soluble in alkali, which is easier to dissolve in an alkaline environment. Soluble protein will exist in the solution in the form of ions. When the pH continues to increase, other non-protein substances will increase. Therefore, the optimal pH value for walnut protein extraction is 11, and three pH values ​​of 10.5, 11, and 11.5 are selected for subsequent experiments.

[0053] 2) Effect of temperature on protein extraction rate

[0054] Weigh 2.0 g defatted walnut powder, add 40 mL distilled water, adjust the pH value of the solution to 11, extract at 35, 40, 45, 50, 55, 60 ° C for 60 min, centrifuge at 5000 r / min for 15 min, sample the supernatant, and use the Coomassie method to determine the protein content in the extract to determine the optimal temperature. Calculate the protein extraction rate according to formula (1).

[0055] Temperature is an important factor affecting whether protein denaturation occurs. The denaturation temperature of walnut protein is 55°C. Figure 2As shown in the figure, when the pH and liquid-to-solid ratio remain unchanged, the walnut protein extraction rate increases from 62.35% to a maximum of 86.27% when the temperature rises from 35°C to 55°C, showing a significant upward trend. When the extraction temperature continues to rise, the protein extraction rate decreases. This is because the continued increase in temperature causes some proteins to denature, the protein structure is destroyed, and the extraction rate decreases. Therefore, the optimal temperature for walnut protein extraction is 55°C, and three temperatures of 50, 55, and 60°C are selected for subsequent experiments.

[0056] 3) Effect of material-liquid ratio on protein extraction rate

[0057] Weigh 2.0 g defatted walnut powder, add distilled water at a solid-liquid ratio of 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, adjust the pH value of the solution to 11, extract at 55 ° C for 60 minutes, centrifuge at 5000 r / min for 15 minutes, sample the supernatant, and use the Coomassie method to determine the protein content in the extract to determine the optimal solid-liquid ratio. Calculate the protein extraction rate according to formula (1).

[0058] The solid-liquid ratio refers to the ratio of solid to liquid. Figure 3 As shown in the figure, when the pH and extraction temperature remain unchanged, when the solid-liquid ratio is 1:10 (g / mL), the extraction rate is only 25.80%, which may be because the protein is not fully dissolved in the solution, so the extraction rate is low; with the increase of the solid-liquid ratio, the protein extraction rate increases sharply. When the solid-liquid ratio is 1:20 (g / mL), the protein extraction rate is as high as 75.44%. When the solid-liquid ratio increases to 1:25 (g / mL), the protein extraction rate drops to 64.44%, which may be due to the adjustment of pH so that the actual solid-liquid ratio is greater than the set value, and the extraction rate begins to decrease. Therefore, the optimal solid-liquid ratio for walnut protein extraction is 1:20 (g / mL), and three solid-liquid ratios of 1:15, 1:20, and 1:25 are selected for subsequent experiments.

[0059] 2.2 Response surface optimization experiment

[0060] According to the results of single factor test, three influencing factors, pH value, temperature and solid-liquid ratio, were selected, and the extraction conditions were analyzed by three-factor three-level response surface analysis method to determine the optimal extraction conditions with protein extraction rate as the response value. The factors and levels are shown in Table 3.

[0061] Table 4 Response surface analysis factors and levels

[0062]

[0063]

[0064] According to the central composite experimental design principle of Design-Expert13, three factors, pH, temperature and solid-liquid ratio, were selected to design the response surface optimization experiment. A total of 17 groups of experiments were designed, and the results are shown in Table 5.

[0065] By fitting the data with a quadratic multivariate regression equation, the multivariate quadratic regression equation of the independent variables A: pH, B: extraction temperature (°C), C: liquid-to-solid ratio (g / mL) and the dependent variable extraction rate Y (%) can be obtained as follows:

[0066] Y=86.58+4.79A-1.87B-1.13C+0.2675AB+2.98AC+0.5525BC-6.51A2-3.58B2-4.73C2, where R 2 =0.9745, R 2 Adj =0.9418. The model was subjected to variance analysis. From Table 4-5, it can be seen that the P value of the model is <0.0001, indicating that the model is extremely significant. The lack of fit term P = 0.3403> 0.05, indicating that the lack of fit term is not significant, the experimental error is small, and the feasibility is good, proving that the model can be used to analyze and predict the walnut protein extraction rate.

[0067] As shown in Table 5, the significance of the three factors on the model is A (pH) > B (temperature) > C (solid-liquid ratio). It can be seen from the table that A < 0.01, B < 0.05, C > 0.05, indicating that pH has a very significant effect on the model, temperature has a significant effect on the model, and the solid-liquid ratio has no significant effect on the model; the interaction between pH and solid-liquid ratio in the interaction term has a very significant effect on the model, and the effects of pH and temperature, temperature and solid-liquid ratio on the model are not significant. The quadratic term A2B2C2 has a very significant effect on the model.

[0068] like Figure 4 As shown in the figure, with the increase of the three factors in each interval, the walnut protein extraction rate showed a trend of first rising and then falling, and the highest point of the response surface was the point with the maximum protein extraction rate. Whether the interaction of each factor was significant was judged based on whether the contour line graph was elliptical and whether the response surface was steep. The two factors A (pH) and B (temperature) had a significant interaction and had a greater impact on the walnut protein extraction rate; the pH surface was steeper than the temperature, and the temperature surface was steeper than the solid-liquid ratio. The order of the three factors on the protein extraction rate was A (pH) > B (temperature) > C (solid-liquid ratio), which was consistent with the results of variance analysis.

[0069] According to the response surface analysis, the optimal process conditions for walnut protein extraction were obtained as follows: pH 11.179, temperature 53.749℃, and solid-liquid ratio 1:19.898 g / mL. The predicted value of protein extraction rate was 87.685%. Due to the feasibility of the experimental operating conditions, the process conditions were finally adjusted to pH 11, temperature 55℃, and solid-liquid ratio 1:20 g / mL. Five repeated verification tests were carried out under this process condition. The actual average value of walnut meal protein extraction rate was 87.16±0.95%, which was basically consistent with the predicted value, with a relative error of 0.53±0.95%, indicating that the optimal extraction process parameters obtained from the experiment are accurate and reliable.

[0070] Table 5 Response surface design scheme and experimental results

[0071]

[0072] Table 6 Analysis of variance of regression model

[0073]

[0074]

[0075] Test Example 3 Determination of the overrun rate of walnut protein ice cream

[0076] Using the same volume-to-mass method, pour the ice cream before and after freezing into a 25 mL beaker, scrape the surface, record the mass of the sample before and after freezing in three repeated tests, and calculate the expansion rate according to formula (2):

[0077]

[0078] Where: M6: mass of ice cream slurry before freezing, g; M7: mass of finished ice cream after freezing, g.

[0079] Overrun is an important characteristic of ice cream and an important parameter for evaluating the physical and chemical indicators of ice cream. It affects the melting properties, texture characteristics and sensory characteristics of ice cream. An appropriate overrun can improve the taste of ice cream and make it more delicate. The typical overrun of ice cream is generally 50-140%, and the solid content is at least 30%. If the overrun is not appropriate, the ice cream will not have a good solid taste and may decompose. Figure 1As shown in the figure, the expansion rate of ice cream first increased and then decreased with the addition of walnut protein powder. When the walnut protein powder replacement amount was 10%, 20%, 30%, 40%, and 50%, the expansion rate was 42.76%, 44.88%, 43.72%, 40.31%, and 37.34%, respectively, which were all higher than the blank group; when the replacement amount was 20%, the expansion rate was the highest, and there were significant differences in the expansion rates between the other groups. This may be due to the fact that after adding a certain amount of walnut protein, the viscosity of the ice cream gradually increased, which was not conducive to the mixing of air during the freezing process, hindered the violent stirring of the slurry, and reduced the expansion rate. Wu Xingyu et al. also stated that the protein content increased and the expansion rate of ice cream decreased. When the flaxseed protein content in the ice cream slurry was greater than 3%, the expansion rate of ice cream decreased by 12%.

[0080] Test Example 4 Determination of the Melting Resistance of Walnut Protein Ice Cream

[0081] Place the ice cream hardened for 48 hours in a 100 mL beaker and invert it on a sieve with a mesh size of 5 mm. Place a glass dish under the sieve and keep it at a constant temperature of 30°C for 30 minutes. Observe the dripping of the ice cream and record the time when the ice cream starts to drip. Calculate the melting rate according to formula (3):

[0082]

[0083] Where: M8: mass of ice cream before melting, g; M9: mass of ice cream after melting, g.

[0084] Melt resistance and melting rate are reciprocals of each other. Melt resistance is calculated according to formula (4):

[0085] Melt resistance = 1 / melt rate formula (4)

[0086] The melting rate of ice cream is very important for transportation and storage. If the melting rate is too fast, it is not suitable for transportation; if the melting rate is too slow, it is not suitable for the flavor of ice cream to release its taste, affecting its sensory quality. As shown in Table 7, the melting rate of the blank group was 56.65%, and the melting rates of 10%, 20%, 30%, 40% and 50% walnut protein were 41.65%, 13.80%, 12.56%, 14.48% and 9.94%, respectively, which were lower than the blank group. The reason for the decrease in melting rate may be that the addition of walnut protein increased the viscosity, solid content and emulsification of the liquid, thereby reducing the melting rate. There is a negative correlation between the melting rate and the resistance to melting. The smaller the melting rate, the greater the resistance to melting, which will affect the release of flavor substances. The initial drop time of ice cream shows a downward trend with the increase of the amount of walnut protein added. When the replacement amount is 40%, the dripping time is less than one minute. This may be because the ice crystals produced by the ice cream under this formula ratio are too large, the internal network structure of the ice cream is unstable, and the viscosity is too small, so the melting rate is fast and the dripping time is short.

[0087] Table 7 Effect of different walnut protein replacement amounts on ice cream melting characteristics

[0088] Walnut protein replacement amount / % Melting rate / % Melt resistance Start dripping time 0 <![CDATA[56.65±4.26 a ]]> <![CDATA[1.77±0.14 c ]]> <![CDATA[15.23±0.25 a ]]> 10 <![CDATA[41.65±1.05 b ]]> <![CDATA[2.40±0.06 c ]]> <![CDATA[15.29±0.28 a ]]> 20 <![CDATA[13.80±2.84 cd ]]> <![CDATA[7.45±1.54 b ]]> <![CDATA[11.29±1.19 b ]]> 30 <![CDATA[12.56±0.98 cd ]]> <![CDATA[7.99±0.61 b ]]> <![CDATA[13.89±1.91 a ]]> 40 <![CDATA[14.48±1.47 c ]]> <![CDATA[6.95±0.67 b ]]> <![CDATA[0.24±0.07 c ]]> 50 <![CDATA[9.94±0.28 d ]]> <![CDATA[10.07±0.28 a ]]> <![CDATA[1.78±0.43 c ]]>

[0089] Note: Different letters indicate that the melting characteristics of ice cream with different walnut protein replacement amounts are significantly different (P<0.05)

[0090] Test Example 5 Determination of texture characteristics of walnut protein ice cream

[0091] The conditions and parameters of the texture analyzer were set as follows: P / 5 probe, trigger force 20g, pre-test speed 5mm / s, test speed 2mm / s, post-test speed 5mm / s, and penetration depth 20mm. According to the texture curve analysis, the hardness, crispness, adhesion (adhesion / stickiness) and resilience of the ice cream can be obtained.

[0092] The texture of ice cream has a direct impact on its taste. A large number of studies have shown that the hardness of ice cream is affected by many factors, including solid content, viscosity of ice cream suspension and expansion rate. There is a correlation between the various texture indicators. Generally speaking, the relevant indicators of ice cream include hardness, viscosity, etc. The higher the expansion rate of ice cream, the lower the hardness; hardness is the force generated when ice cream is compressed by external force to maintain its shape, which can be used to evaluate the structural characteristics of ice cream. Excessive hardness of ice cream will affect the expansion rate and sensory evaluation of the product. The texture test results of ice cream are shown in Table 8. In the blank group, the hardness, brittleness, viscosity and resilience of ice cream are 8.42, 4.38, -0.53 and 1.34, respectively. With the increase of protein substitution, the hardness increases, the brittleness increases first and then decreases, the viscosity decreases first and then increases, and the resilience decreases. The proportion of walnut protein powder in the slurry is different, and the texture characteristics of the ice cream system formed are also different. When the hardness increases, the ice cream becomes less soft and has a rougher taste. When the replacement amount is 20% and 30%, the expansion rate is almost the same. The melting rate of the 30% replacement amount is 1.24% lower than that of the 20% replacement amount, and the difference is not significant. The hardness of the 30% replacement amount is 7.14 higher than that of the 20% replacement amount, and the viscosity is 1.27 lower. There is a correlation between the three, indicating the accuracy and reliability of the results.

[0093] Table 8 Effect of different walnut protein replacement amounts on ice cream texture characteristics

[0094]

[0095] Note: Different letters indicate that the texture characteristics of ice cream with different walnut protein replacement amounts are significantly different (P<0.05)

[0096] Test Example 6 Determination of the stability of walnut protein ice cream

[0097] The ice cream suspension was diluted to an appropriate multiple, centrifuged at 3500 rpm for 15 min at 4°C, and the absorbance before and after centrifugation was measured at a wavelength of 785 nm. The stability index (R) was calculated according to formula (5):

[0098]

[0099] Formula (5)

[0100] Where: A1: absorbance before centrifugation; A2: absorbance after centrifugation.

[0101] The stability index of ice cream can reflect the quality of ice cream slurry. Figure 2 As shown in the figure, the stability index of the blank group is 0.511. As the substitution rate of walnut protein increases, the stability index first increases and then decreases. When the substitution rate is 10%, the stability index value increases slightly, only increasing by 15.07%; when the substitution rate is 20%, the stability index value increases significantly, with a maximum value of 0.668, an increase of 30.72% compared with the blank group. Generally speaking, the closer the stability index value is to 1, the better and more stable the ice cream suspension is. The farther the stability index value is from 1, the greater the internal structure of the protein molecules in the ice cream, the more hydrophobic groups are exposed, and the hydrophobic interaction increases, so the solubility of the emulsion decreases and the emulsification stability weakens.

[0102] Test Example 7 Determination of color difference of walnut protein ice cream

[0103] Measure with a colorimeter. Place the ice cream slurry in the same container and measure at room temperature. The L*, a*, b* and △E values ​​can be read directly.

[0104] The parameters of the walnut protein ice cream formula color with different substitution amounts were analyzed by using the L*, a*, b* and △E values ​​shown in the colorimeter. As shown in Table 9, when the walnut protein powder substitution rate was 10%, the L* value, a* value and b* value were 31.57, 9.34 and 12.01 respectively, which were significantly different from the blank group. This may be because the color of the walnut protein powder itself was darker, and the color difference with the whey protein powder was large; when the substitution amount was 20%, the L* value decreased by 1.81, the a* value decreased by 3.29, and the b* value decreased by 0.07, which was also significantly different from the blank group; after that, the L* value, a* value and b* value all showed a decreasing trend with the increase of the walnut protein substitution amount, and the color of the ice cream slurry became darker and darker. The reason for the darker color may be that the higher protein content leads to more amine compounds and aldehydes to form dark pigments, thereby forming a darker color in the reaction, but the color difference measurement results will also be greatly affected by the environment, such as ambient brightness, distance, etc., and there is a certain error. According to the △E results, the addition of walnut protein resulted in a significant difference in the color of the ice cream slurry.

[0105] Table 9 Effect of different walnut protein replacement amounts on ice cream color difference

[0106]

[0107] Note: Different letters indicate significant differences in color difference between ice creams with different walnut protein replacement amounts (P < 0.05)

[0108] Test Example 8 Sensory Evaluation of Walnut Protein Ice Cream

[0109] Fifteen students majoring in food were randomly selected to participate in the sensory evaluation test part of this experiment. The sensory scores of these 15 students were recorded and the final scores were calculated.

[0110] Table 10 Walnut protein ice cream sensory evaluation rules

[0111]

[0112] Sensory evaluation is an important indicator of overall product evaluation and can reflect the public's acceptance. The sensory evaluation results of walnut protein ice cream are shown in Table 11. As the amount of walnut protein replacement increases, the sensory evaluation shows a trend of first rising and then falling. The ice cream with 20% walnut protein added has the highest sensory score (84.50), and the ice cream quality is the best; the color and morphology of the ice cream with 10% and 20% walnut protein added are close to the original flavor group, with no significant difference; the overall score of 30% and 40% walnut protein replacement ice cream is not significantly different from that of the blank group.

[0113] Table 11 Effects of different walnut protein replacement amounts on sensory evaluation of ice cream

[0114]

[0115] Note: Different letters indicate significant differences in sensory evaluation scores of ice creams with different walnut protein replacement amounts (P<0.05)

[0116] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing walnut protein ice cream, characterized in that: The following steps are involved: (1) preparing a walnut protein extraction stock solution: preliminarily removing walnut oil from walnuts by hydraulic cold pressing, then extracting with No. 6 solvent to control the oil content in the walnut kernel to less than 10%, crushing the defatted walnuts into 20-40 meshes, adding the walnuts to water, adjusting the pH and temperature for extraction, and obtaining a walnut protein extraction stock solution; (2) preparing walnut protein powder: adjusting the pH value of the walnut protein extraction solution to 6.00-7.00, and spray drying to obtain walnut protein powder; (3) Preparation of walnut protein ice cream: weigh the following by mass: 7.4-9.8 parts of whey protein powder, 2.4-4.8 parts of walnut protein powder, 10-14 parts of isomaltulose, 6-10 parts of coconut oil, 0.3-0.5 parts of sodium carboxymethyl cellulose, 0.3-0.5 parts of stabilizer, and 65-70 parts of water; (4) preparing ice cream: the raw materials weighed in step (3) are mixed evenly, left to stand in cold storage for aging, and then frozen in an automatic ice cream machine, and the frozen ice cream is frozen and hardened to obtain walnut protein ice cream.

2. The method for preparing walnut protein ice cream according to claim 1, characterized in that: In step (1), the pH is adjusted to 10.5-11.5, and the temperature is adjusted to 52-58°C.

3. The method for preparing walnut protein ice cream according to claim 1 or 2, characterized in that: The solid-liquid ratio of walnut to water in step (1) is 1 g:18-22 mL.

4. The method for preparing walnut protein ice cream according to claim 1, characterized in that: The spray drying inlet temperature in step (2) is 165-175° C., the solid content is 30-40%, and the feed flow rate is 3.5-6.5 mL / min.

5. The method for preparing walnut protein ice cream according to claim 1, characterized in that: The refrigeration temperature in step (4) is 3.5-4.5° C., and the refrigeration aging time is 11.5-12.5 hours.

6. The method for preparing walnut protein ice cream according to claim 5, characterized in that: The freezing time of the automatic ice cream machine in step (4) is 19.5 to 20.5 minutes.

7. The method for preparing walnut protein ice cream according to claim 6, characterized in that: The freezing and hardening temperature of step (4) is -19 to -17°C, and the freezing and hardening time is 23.45 to 24.55 hours.

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