Soluble Rice Protein Powder Study

Rice protein is a highly nutritious protein. It has a complete composition of essential amino acids, but is relatively deficient in lysine and threonine compared to animal protein. Because plant proteins and animal proteins each have their own characteristics and nutritional effects are different, it is ideal to consume these two types of protein in a balanced ratio. Clinical studies in the United States have shown that less than 1% of highly allergic patients out of about 700 cases of hereditary allergies are allergic to rice protein, and allergies to rice protein are rarely reported in pediatrics [1-2].

It is precisely because of the high nutritional value and hypoallergenicity of rice protein that it has particularly good prospects for development in the food market. However, because the solubility of rice protein extracted using the solvent method is very low, the preparation of soluble rice protein powder generally uses the enzymatic method. However, the relatively expensive price of the enzymes used in the enzymatic preparation of rice protein powder has greatly limited its application [2]. Rice protein is enzymatically hydrolyzed to produce bioactive peptides, which have special physiological activity and can regulate the body's vital activity. Most of these bioactive peptides exist in an inactive state in the long chain of proteins. Their physiological activity only becomes apparent when they are enzymatically hydrolyzed to an appropriate length[3].

Domestic and foreign research on the modification of rice protein has mainly focused on chemical and enzymatic modification, and there has also been research on physical modification.

1 Physical modification

Physical modification refers to the use of methods such as mechanical processing, freezing, extrusion, magnetic fields, electric fields, sound fields, ultrafiltration, low-dose radiation, and the addition of small molecule amphiphilic substances to improve the functional properties of proteins [4]. Yang Huili et al. [5] used ultrasonic circulation technology to treat soy protein isolate. The study showed that with an ultrasonic power of 320 W and an ultrasonic time of 15 min, the emulsifying ability was increased by 17% and the emulsifying stability was increased by 49%.

When the ultrasonic power was 960 or 800 W and the ultrasonic time was 15 min , the foaming ability and foaming stability reached their maximum, respectively, 70% and 7% higher than the protein that had not been treated with ultrasound; when the ultrasonic power was 640 W, the hydrophobicity of the soy protein isolate reached its maximum, an increase of 39% compared to the non-ultrasonic treatment. Kato et al. [6] subjected rice to high pressure treatment. When the pressure reached 100~ 400 MPa, the amount of allergenic protein in the rice dissolved was 0.2–0.5 mg (protein) /g (rice); when the pressure reached 300–400 MPa, the amount dissolved was 0.5 mg protein /g (rice); when the pressure exceeded 500 MPa, the amount dissolved did not increase. Physical modification has the characteristics of minimal toxic side effects, low cost, and short duration of action, but it is rarely used because of its lack of obvious effect.

2 Chemical modification

Chemical modification mainly involves introducing various functional groups into the protein, such as hydrophilic and lipophilic groups, negatively charged groups, disulfide groups, etc., and using the chemical activity of certain groups on the side chain of the protein to improve the structure, hydrophobicity and electrostatic charge of the protein in order to change its properties [4, 7]. At present, commonly used chemical modification methods include: deamidation, acylation, glycosylation, phosphorylation, alkylation and lipophilic modification. Reports on the chemical modification of rice protein mainly focus on deamidation, acylation, glycosylation, phosphorylation and alkylation.

2.1 Deamidation modification

Deamidation modification is a commonly used method in the modification of vegetable proteins. Compared with unmodified protein samples, deamidation-modified proteins have varying degrees of improvement in solubility, emulsification and emulsion stability, foaming and foam stability, and water retention [8]. Yi Cuiping et al. [9] studied the effect of deamidation modification on the solubility of rice protein. The study found that when the degree of deamidation was 0–63.5%, the solubility of rice protein increased linearly with the degree of deamidation to 99.4%; when the degree of deamidation exceeded 63.5% and reached 66.2%, the solubility of rice protein increased slightly. the degree of deamidation increased linearly to 99.4%; when the degree of deamidation exceeded 63.5% and reached 66.2%, the solubility of rice protein decreased slightly. Chen Zhicheng [10] modified rice protein by acid deamidation, and used orthogonal experiments to optimize the conditions for the acid modification of rice protein: 50 g/L rice protein content, 0.3 mol/L hydrochloric acid concentration, 3 h reaction time, and 85 ℃ reaction temperature.

2.2 Glycosylation modification

After the grafting modification of proteins and polysaccharides, their functionality is greatly improved, mainly in terms of water solubility and emulsifying properties [11]. Du Yansu et al. [12] used a dry-method Maillard reaction to glycosylate modified rice bran gluten, and investigated the effect of the mass ratio of gluten and carrageenan and the reaction time on the grafting reaction process and the functional properties of the grafted product. The results showed that at a mass ratio of gluten to carrageenan of 1:2, a relative humidity of 79%, temperature 60 °C, reaction for 24 h, the grafting degree of the product reached 28. 84%; compared to gluten, the solubility, emulsifying properties and emulsion stability of the grafted product were increased by 2. 04 times, 4. 84 times and 0. 63 times, respectively.

2.3 Phosphorylation modification

Phosphorylation modification of proteins is the selective use of protein active groups, such as Ser, Thr -OH and Lye ε-NH2, which are close to a phosphate group, thereby introducing a large number of phosphate groups, The introduction of phosphate groups increases the protein's electronegativity, thereby increasing the electrostatic repulsion between the proteins, making them more dispersed in the protein system, and increasing their solubility and aggregation stability [13-14].

Shen Shiqiang et al. [15] used a low molar ratio of phosphorus oxychloride/protein to phosphorylate soy protein isolate. The results showed that when the optimal process conditions were: soy protein isolate concentration 4%, reaction time 30 min, phosphorus oxychloride volume 0.20 mL, and pH 10.00, the isoelectric point of the phosphorylated soy protein isolate decreased from 4.25 to 3.75. volume 0.20 mL, pH 10.00, the isoelectric point of the phosphorylated soy protein isolate was reduced from 4.25 to 3.75, and its solubility and emulsifying ability were significantly improved. Li Hongju et al. [16] used red pine seeds as a raw material and modified red pine nut isolated protein with sodium tripolyphosphate (STP). The optimal dissolution conditions for the phosphorylated modified red pine nut isolated protein were: The reaction temperature was 45 °C, the pH was 8.5, the mass fraction of STP was 7%, and the reaction time was 75 min. Under these conditions, the solubility of the pine nut protein isolate can reach 80.2%.

3 Enzyme modification

Enzyme modification uses enzymes to change the amino acid residues and polypeptide chains of proteins, causing changes in their structure, thereby improving their functional and nutritional properties. The main methods of enzyme modification are covalent cross-linking, hydrolysis, deamidation and phosphorylation [17]. The use of enzymes to cross-link proteins to improve the functional properties of rice proteins is better than using chemical modification methods because the conditions required for enzymatic methods are milder, they are more specific, they do not produce toxic substances, and consumers feel that enzymatic modification is more “natural” [18].

Enzyme modification mainly involves the specific cleavage of peptide chains by enzymes, so that the hydrophobic amino acid residues that were originally exposed on the outside of the protein's higher structure are cleaved, thereby increasing the solubility of the protein [19]. Ren Wencong et al. [20] used alkaline protease modification, and determined the optimal enzymatic hydrolysis process conditions for high temperature denatured soybean meal using the nitrogen solubility index as an indicator through single factor and response surface experiments. The conditions were as follows: pH 9.0, substrate concentration 8.56 g/100 mL, enzyme amount 13 004. 69 U/g protein, temperature 59. 10 ℃, time 20. 47 min, hydrolysis degree 15. 86%.

 Xueguo Dong et al. [21] used alkaline protease to modify rice dregs protein. The results showed that the optimal enzymatic conditions were enzyme amount [E]/[S] = 1%, pH 8.0, temperature 65°C, solid-liquid ratio 1:5. Under these conditions, the solubility, emulsifying properties, and foaming properties of rice protein were significantly improved. Chen Ji-wang et al. [22] showed that rice peptides obtained by alkaline protease hydrolysis of rice proteins have good solubility and low viscosity, and can be widely used in the food industry. Zheng Mai et al. [23] used a composite protease to hydrolyze cereal protein powder to obtain a soluble cereal protein powder with a degree of hydrolysis of 25% to 30%.

4 Outlook

At present, chemical modification and enzymatic modification are the main methods used to modify rice protein. Chemical modification has the hidden danger of chemical reagent residues, so enzymatic modification has become the focus of research on rice protein modification. The hydrolysis rates of enzymatically modified proteins are not very high, generally at most 30% to 35%, which is a great waste of resources. In order to increase the degree of protein hydrolysis and enable the active ingredients to be used to a greater extent, biological modification methods such as the interaction of several enzymes can be used to hydrolyze the protein of grains and beans, so that the hydrolysis rate of the grain protein can be increased and its active ingredients can be more fully utilized by the body. The protein is hydrolyzed into small molecular peptides, and its solubility is ensured, thereby improving the disadvantage of poor palatability of grain foods.

References:

[1] Zhang Zhaoying, Wang Li, Ge Na, et al. Research and development of compound rice protein powder [J]. Grain and Feed Industry, 2006 (12): 22-23.

[2] Han Xiuli, Zhang Ruyi, Ma Xiaojian, et al. Research progress on rice protein extraction process [J]. Food Research and Development, 2007, 28(22): 161-163.

[3] Yang Zhendong. Research progress on active peptides in rice [J]. Cereals, Oils and Fats, 2009(12): 39-42.

[4] Yin Bo, Li Yiwei, Wang Xiali, et al. Research progress on rice protein modification technology [J]. Food and Machinery, 2011, 27(3): 147-151.

[5] Yang Huili, Ma Haile. Research on physical modification of rice protein separation by ultrasound [J]. Chinese Brewing , 2009 , 206 ( 5): 24-27.

[6] Kato T, Katayama E, Matsubara S, et al. Release of allergic proteins from rice grains induced by high hydrostatic pressure [J]. Journal of Agricultrual and Food Chemistry 2000, 48 ( 8): 3 124-2 136.

[7] Aoki T, Hiidome Y. Improvement of heat stability and emul- sifying activity of albumin by Eonjugation with glueuronie acid though the maillard reaction [J]. Food Research International, 1999, 32: 129-133.

[8] Yi Cuiping, Yao Huiyuan. Study on the deamidation of rice protein concentrate (I) – Comparison of acid deamidation and enzymatic deamidation processes and optimization of parameters [J]. Food Science, 2005, 26(1): 145-149.

[9] Yi Cuiping, Yao Huiyuan. Study on the deamidation of rice protein concentrate (II) ℴℴ The effect of acid deamidation modification on the functional properties and nutritional properties of rice protein [J]. Food Science, 2005, 26(3): 79-83.

[10] Chen Zhicheng. Study on the process of acid deamidation modification of rice protein [J]. Journal of Guangxi Vocational and Technical College, 2009, 6(2): 1-7.

[11] Liu Shuanghui, Elmer C, Lown H, et al. Effect of pH on the functional behaviour of pea protein isolate gum Arabic complexes [J]. Food Research International, 2010, 43 (2): 489-495.

[12] Du Y X, Shi S H, Xiong H, et al. Modification and functional properties of rice bran gluten carrageenan by glycosylation [J]. Food Science, 2011, 32(16): 11-15.

[13] Kito M. Properties of spray dried powder of phosphorylated latecl SPI. Nippon Shokuhin Kogyo Gakkaishi, 1985, 32(9): 629.

[14] Sitohy M. Phosphosylation of β-Lactoglubin under mild conditions [J]. Aqric Food Chem, 1995, 43: 49-52.

[15] Shen Shiqiang, Fu Liang, Xu Kang, et al. Research on the modification of soy protein isolate by phosphorylation [J]. Food Industry Science and Technology, 2010, 31(6): 141-147.

[16] Li Hongju, Wang Zhenyu, Zhao Xin, et al. Optimization of process parameters for the solubility of phosphorylated modified red pine nut isolated protein by response surface methodology [J]. Food Research and Development, 2010, 30(9): 28-33.

[17] Liu Xiao, Wu Jinju, Gao Jinyan, et al. Research on enzymatic modification of food proteins [J]. Food Science, 2010, 31(9): 409-413.

[18] Singh H. Modification of food proteins by covalent cross linking [J]. Trends in Food Sci Technol, 1991, 2: 196-200.

[19] Jens A N. Enzymatic hydrolysis of proteins for increased solubility [J]. J Agric Food Chem, 1976, 24(6): 1090-1093.

[20] Ren Wicong, Cheng Jianjun, Zhang Zhiyu, et al. Effect of enzyme modification on the solubility of high temperature denatured soybean meal [J]. Food Science, 2010, 31(21): 137-141.

[21] Xuan Guodong, He Guoqing, Xiong Haoping, et al. Study on the modification of rice protease and the functional characteristics of the enzymatic hydrolysate [J]. Chinese Journal of Cereals, Oils and Foodstuffs, 2005, 20(3): 1-4.

[22] Chen Ji-wang, Sun Qing-jie, Xia Wen-shui, et al. Study on the preparation process and characteristics of rice peptides by enzymatic method [J]. Journal of Agricultural Engineering, 2006, 22(6): 178-181.

[23] Zheng Mai, Nie Binying, Zheng Weihan. Development of soluble cereal protein powder [J]. Jiangxi Food Industry, 2006(3): 34-35.