Process optimization of rice protein milk drink

 Abstract In order to optimize the production process of rice protein milk drink, rice protein and whey protein were used as the main ingredients, and the final formula was optimized by one-way and orthogonal tests. The results of amino acid analysis showed that the amino acid composition of the protein powder was reasonable after the compounding of rice protein and whey protein in the ratio of 3∶2; the results of one-way stability test showed that rice starch, carrageenan and gellan gum had good stability for rice protein milk drink, and xanthan gum was not effective; the additive amounts of compound stabilizers were determined to be 0.040% for carrageenan, 0.035% for gellan gum and 0.60% for rice starch in the orthogonal test; the additive amounts of stabilizer were determined to be 0.040% for carrageenan, 0.035% for gellan gum, and 0.60% for rice starch. Starch 0.60%; flavor blending results show that the addition of compound protein powder 6.0%, sucrose 5.0%, citric acid 0.04%, fried rice flavoring 0.08%, the amino acid composition of rice protein milk drink produced under this process is reasonable, the product has good stability and good flavor.

 

Rice protein is a by-product of the deep processing of starch, sugar, monosodium glutamate (MSG) and organic acids[1] , which is composed of 75%~90% gluten, 2%~5% albumen, 2%~10% globulin, and 1%~5% alkyd proteins[2] , and has a reasonable amino acid ratio close to the ideal pattern recommended by the FAO/WHO, and a high Protein Efficiency Ratio (PER) and Biovalue (BV)[3] , which is an ideal source of plant protein. Rice protein is an ideal source of plant protein because of its high protein efficiency ratio (PER) and biomass value (BV)[3] .

 

With the rapid development of modern food industry, people's demand for healthy food is also increasing year by year, based on which it is especially necessary to develop a healthy milk drink rich in rice protein. Since more than 75% of rice protein is water-insoluble gluten, the solubility of rice protein is poor, which limits the application of rice protein in the food industry. In order to improve the comprehensive utilization of rice protein, this study screened several stabilizers to improve the suspension stability of rice protein through one-way and orthogonal tests, and on the basis of this study, the taste of the beverage was rationally formulated, and a rice protein milk drink with good taste and high suspension stability was developed, which provides a new way to improve the comprehensive utilization of rice protein.

 

1 Materials and Methods

1.1   makings  

Rice protein powder (300 mesh, protein content 82.54%), rice starch (100 mesh) were from Anhui Shunxin Shengyuan Biofood Co., Ltd; whey powder (food grade), Davylin International Trade (Shanghai) Co.

 

1.2    Instruments and equipment   

S433D Fully Automatic Amino Acid Analyzer (Sykam, Germany); DHR-2 Rheometer (TA, USA); BSA124S-CW Electronic Balance (Sartorius Scientific Instruments Co., Ltd.); DF-101S Magnetic Stirrer (Gongyi Iuhua Instrument Co., Ltd.); L550 Low-speed Centrifuge (Hunan Xiangyi Centrifuge Instrument Co., Ltd.); FJ300-SH Digital Display High-speed Dispersing Homogenizer (Shanghai Standard Model Factory); BPG-9140A Precision Blast Drying Box (Shanghai Yiheng Scientific Instrument Co., Ltd.). SH Digital Display High-speed Dispersing Homogenizer (Shanghai Specimen Model Factory); BPG-9140A Precision Blast Drying Oven (Shanghai Yiheng Scientific Instrument Co., Ltd.).

 

1.3 Experimental design

1.3.1 Process flow for making rice protein milk drink. The process flow is shown in Figure 1.

 

Fig. 1 Process of making rice protein milk beverage

1.3.2 Determination of protein ratios for protein powders

The protein ratios in the main ingredient formulations were determined based on the amino acid score (AAS) and the principle of complementarity, where AAS is the percentage of an essential amino acid in the protein to be measured in relation to the corresponding amino acid in the FAO/WHO scoring model[4-5] .

 

1.3.3 One-way test for stability optimization of rice protein milk drink. In the stability optimization single-factor test, 15 g of rice protein powder and 10 g of whey powder were added into 500 mL of water at 80 ℃, and rice starch (0.2%, 0.4%, 0.6%, 0.8%, 1.0%), carrageenan (0.02%, 0.03%, 0.04%, 0.05%, 0.06%), xanthan (0.01%, 0.02%, 0.03%, 0.04%, 0.05%), condensed gel (0.01%, 0.02%, 0.03%, 0.04%, 0.05%) and rice protein milk drink (0.03%, 0.04%, 0.05%) were added, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%), xanthan gum (0.01%, 0.02%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%), xanthan gum (0.03%, 0.04%, 0.05%), 0.05%, 0.06%), 0.05%, 0.03%, 0.04%, 0.05%, 0.05%), 0.03%, 0.04%, 0.05%), and 0.05%), the solution was stirred by a constant-temperature water bath with a magnetic stirrer for 15 min until the solution was uniform, and then homogenized for 2 min at 11,000 r/min in a high-speed homogenizer to examine the viscosity of solution and the centrifugal precipitation rate, Carrageenan, xanthan gum and gellan gum were used as the indexes of solution viscosity and centrifugal sedimentation rate to examine the effects of rice starch, carrageenan, xanthan gum and gellan gum on the stabilization of the solution.

 

1.3.4 Orthogonal test for stability of rice protein milk beverage

On the basis of one-way test, the amount of carrageenan, gellan gum and rice starch was used as the objects and centrifugal sedimentation rate was used as the index to optimize the amount of stabilizer for rice protein milk beverage by using the orthogonal test of L9 (34), and the levels of the factors are shown in Table 1.

Table 1 Stabilizer optimization orthogonal experimental design

 

1.3.5 Flavor blending tests

The flavor blending test was an orthogonal L9 (34) test based on the one-way test, which was used to determine the optimal additions of protein powder, sucrose, citric acid and edible flavor by sensory evaluation method, and to select the optimal combination. The factor levels of the orthogonal experimental design are shown in Table 2.

 

Table 2 Orthogonal experimental design for flavor blending

 

1.3.6 Indicator measurement methods

1.3.6.1 Determination of amino acid composition of protein powders

The amino acid composition was analyzed with reference to GB/T 5009.124-2016 "Determination of Amino Acids in Food", and the samples were pretreated by hydrochloric acid hydrolysis at 570 nm and 570 nm.

Detection was performed at 440 nm.

 

1.3.6.2 Viscosity determination

The viscosity of the samples was determined using a DHR-2 rheometer with a 40 mm plate fixture at 25 ℃, a shear rate of 100 r/min, a run time of 2,000 s, and a gap of 52 μm. The sample was analyzed by the DHR-2 rheometer.

 

1.3.6.3 Determination of centrifugal sedimentation rate (SR)

The centrifugal sedimentation rate was determined with reference to the method of Zhang Tao[6] with slight modification, and the sample was centrifuged at 3,000 r/min for 10 min in a centrifuge tube, the supernatant of centrifugation was poured out, and the mass of the remaining precipitate was weighed to calculate the centrifugal sedimentation rate (CSR), and the CSR was calculated by taking the average of three parallel tests as the final stability index, the smaller SR is, the better the stability is.

SR = (M1/M2 ) × 100% where M1 and M2 denote the total mass of precipitate after centrifugation and the mass of sample solution before centrifugation (g), respectively.

 

1.3.6.4 Sensory evaluation of flavor blends

The flavor blending adopted the percent sensory evaluation method, and the evaluation team was composed of 10 evaluators, who scored the sensory quality of the rice protein milk drink in four aspects, namely, color, aroma, taste, and stability, and the specific evaluation criteria are shown in Table 3.

 

1.4 Data processing  

The data were analyzed by Microsoft Office Excel 2007 and plotted by Origin 8.0.

 

2 Results and analysis

2.1 Determination of proportions of main and auxiliary ingredients  

The closer the AAS value is to 100, the closer the amino acid composition is to the model, and the higher the nutritional value of the protein is[4] . As shown in Table 4, the AAS score of lysine in the rice protein powder used in the experiment was only 69, which is the first limiting amino acid, and the contents of isoleucine, threonine, methionine and cystine were lower than the recommended model values, while the contents of leucine and valine were close to the recommended values. Comparing the AAS values of the essential amino acids of whey protein, it was found that the contents of these amino acids were higher than the recommended values, among which lysine was the most abundant. The complementary relationship between whey protein powder and rice protein powder in essential amino acids can be utilized to develop a more comprehensive nutritional complex protein powder.

 

The first limiting amino acid lysine in rice protein was used as the index, and the ratio of rice protein to whey protein was finally determined to be 3:2. Table 4 shows that the AAS scores of the blended protein powder were close to the recommended mode, and the limiting amino acid lysine score of rice protein was increased to 109 after the blending.

 

2.2 Results of one-factor test for optimizing the stability of rice protein milk beverage

2.2.1 Effect of rice starch addition on beverage stability

Rice starch has a small particle size[7] and large specific surface area, and has a smooth and delicate texture similar to that of fat. It can be used as a thickener in soups, sauces, and instant rice, and can improve the texture of food products[8-9] , therefore, here, rice starch was added into a rice-based egg white emulsion drink to investigate the effect of starch on the suspension stability of the drink. The effect of rice starch on the suspension stability of the beverage was investigated.

 

Figure 2 shows that the apparent viscosity of the solution system of rice protein milk drink increases with the increase of rice starch addition, and the centrifugal sedimentation rate of the solution decreases with the increase of rice starch addition, that is, the stability of the solution system improves with the increase of rice starch addition. When the addition of rice starch is 0.6%, the centrifugal sedimentation rate of rice protein milk beverage decreased slowly, continue to increase the addition of rice starch, the viscosity of the solution system increases, but the centrifugal sedimentation rate tends to slow down or even a downward trend, which shows that the stability of the solution system and the addition of rice starch is not exactly proportional to the stability of the solution system, and viscosity is not the only factor that determines the stability of the solution system. The viscosity is not the only factor that determines the stability of the solution system. In summary, the addition of rice starch is effective in maintaining the stability of rice protein milk drink solution system, and the optimal amount of rice starch is about 0.6%.

2.2.2 Effect of carrageenan addition on beverage stability

Add 0.02% ~ 0.06% carrageenan, through the determination of sample viscosity, centrifugal sedimentation rate and other comprehensive analysis of the effect of carrageenan on the stability of rice protein milk drink solution system. As can be seen from Figure 3, with the increase of the amount of carrageenan, the precipitation rate of the rice protein milk beverage solution system continues to decline, the stability of the system to improve, and the viscosity gradually increased. At the same time can also be seen that carrageenan has a low concentration of high viscosity characteristics, in the dosage of 0.04%, the system viscosity increase rate is greater, and the system's sedimentation rate changes did not viscosity change trend is obvious, continue to increase the dosage of carrageenan on the stability of the solution system does not play a big role in the system concentration of the system but affect the sensory quality of the finished product. Comprehensive analysis of carrageenan concentration of 0.04% is no longer suitable as a stabilizer of rice protein milk beverage solution system, so the optimal concentration of carrageenan addition is about 0.04%.

 

2.2.3 Effect of xanthan gum addition on beverage stability

In order to understand the effect of different concentrations of xanthan gum on the stability of the solution system of rice protein milk drink, 0.01% ~ 0.05% xanthan gum was added sequentially. As can be seen from Fig. 4, the viscosity of the solution system increased with the increase of xanthan gum concentration, and the centrifugal sedimentation rate of the solution also decreased significantly, when adding 0.01% xanthan gum, it can ensure that the sedimentation rate of the protein powder tends to be stabilized, but it was found that too large an addition of xanthan gum in the test would make the solution of the beverage fluidity is poor, and does not conform to the organoleptic properties of the beverage. It was determined that xanthan gum should not be used as a solution stabilizer for rice protein milk drink.

 

2.2.4 Effect of Gellan gum addition on beverage stability

Gellan gum has good stability, acid resistance, high temperature resistance, thermal reversibility and low dosage[10], a certain amount of gel within the range of the stability of the solution system of rice protein milk beverage has a certain effect, as can be seen from Figure 5, with the increasing amount of gel, the viscosity of the solution system of rice protein milk beverage is constantly rising, centrifugal precipitation rate gradually decreased, the stability of the solution system is constantly improving. However, when the gelatin concentration of 0.03%, the solution system shows viscous characteristics, affecting the sensory quality, the most suitable amount of gelatin control at about 0.03%.

 

2.3 Results of orthogonal test for stability optimization of rice protein milk beverage  

Based on the results of the one-way test, the three factors that had a greater influence on the stability of rice protein milk beverage, namely, the amount of carrageenan added (A), the amount of gellan gum added (B), and the amount of rice starch added (C), were selected to perform the orthogonal test of L9 (34). The centrifugal sedimentation rate was used as the stability evaluation index, and the optimal solution was selected as the stabilizer compounding dosage.

 

From the polar analysis in Table 5, RA >RB >RC, i.e., the three factors on the stability of rice protein milk beverage solution system were carrageenan addition (A) > refrigerant gum addition (B) > rice starch addition (C), and the optimal combination of the factor levels was A2 B3 C2, i.e., the optimal combination of the formulations was 0.040% for carrageenan, 0.035% for refrigerant gum, and 0.60% for rice starch. 0.035%, 0.60% rice starch. According to the test conditions of A2 B3 C2, three parallel verification tests were carried out, and the average sedimentation rate of the three groups was 1.16%, which was better than the results of each group of orthogonal tests, so A2 B3 C2 was the optimal combination, and the taste of rice protein milk drink produced at this time was silky and delicate, not viscous, and the finished product had good stability, and there was no obvious precipitate during the drinking time.

 

2.4 Results of flavor blending  

The rice protein milk drink prepared under the above conditions had proper nutritional ratio and good stability of the solution, but the flavor was poor, and the flavor was optimized by orthogonal test based on the sensory indexes of sweetness, acidity, viscosity, aroma and overall preference. From Table 6, it can be seen that the relationship between the four factors on the flavor of rice protein milk drink is: compound protein powder (B) > sucrose (A) > citric acid (C) > fried rice flavor (D), and the optimal combination of the factors is A2 B2 C3 D1, i.e., 6.0% for protein powder, 5.0% for sucrose, 0.04% for citric acid, and 0.08% for fried rice flavor. According to the test conditions of A2 B2 C3 D1, three replications of validation test were carried out, and the results of the validation group were consistent with those of the orthogonal test, so A2 B2 C3 D1 was the optimal combination of the test. Under the conditions of this formula, the rice protein milk drink was bright in color, showing a characteristic beige color, delicate in taste, moderately sweet and sour, with a mixed aroma of fried rice and whey, and uniform turbidity.

Table 5 Orthogonal test results and analysis

 

We need to increase support, improve relevant laws and regulations, introduce supporting policies and measures, and strive to build a good external environment for the shared agricultural business system. Secondly, we should provide subsidies and support in terms of capital, provide financial services such as finance and loan guarantees, improve rural credit policies, and streamline credit procedures. Finally, in terms of technology, we will implement a talent cultivation program, encourage agricultural technology extension workers and special agents of agricultural science and technology to carry out technology promotion and education and publicity, and provide agricultural technology services to farmers. It also encourages the sharing of agricultural production technologies among business entities and service organizations, and encourages innovation in agricultural science and technology.

 

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