Progress in the comprehensive utilization of rice protein

 Abstract：Rice protein is hypoallergenic, high in nutritional value, widely available, high in yield, low in cost, strong in functionality, and has great application prospects. This paper gives an overview of the composition of rice protein, separation and extraction technology, comprehensive utilization, and industrialization development at home and abroad, and also looks forward to its market prospects.

 

Rice is one of the most important food crops in the world and an important source of protein for human beings. China is the largest rice producer in the world. Rice is not only the staple food of southern residents, but also an important raw material for the food industry, such as sugar, monosodium glutamate (MSG), dextrose, brewing, and maltodextrin. However, only the use of rice, broken rice, rice embryo, rice bran, rice husk and other processing by-products, there are still about 80% of high-quality rice protein can not be effectively developed and utilized, resulting in a great waste of protein resources. With the progress of food science and technology, rice protein's high nutritional, hypoallergenic, multifunctional and other characteristics are recognized by the industry, the development of rice protein has become a new research hot spot in the industry.

 

1 Introduction to rice protein

According to the classical Osborne classification method, rice proteins are classified into four categories based on solubility: glutelin (alkali-soluble), pro-lamin (alcohol-soluble), albumin (water-soluble) and globulin (salt-soluble)[1] . Among them, the content of albumin and globulin as physiologically active components is relatively low, accounting for 2%~5% and 2%~10% of the total amount, respectively; gluten and alcohol soluble proteins as storage proteins are the main components, and gluten can account for up to 80% of the total amount of storage proteins, while the alcohol soluble proteins usually range from 1%~5% to a maximum of 20%~30% [2]. The storage proteins in rice endosperm are synthesized initially at the endoplasmic reticulum membrane and transported to the endoplasmic reticulum lumen. The rice alcohol soluble proteins are encoded by a complex multigene family, each haploid genome contains 80-100 copies, and their molecular weight ranges from 12-17 kDa. They are type II alcohol soluble proteins and lack the repeat domains rich in proline or glutamylamine. Alcohol-soluble proteins assemble in the lumen of the rough endoplasmic reticulum and accumulate to form protein aggregates PB-I. Each haploid genome encodes about 15 rice glutenin genes, which can be categorized into four subfamilies, A, B, C, and D. Glutenin is first synthesized at 57 kDa, and is then synthesized into a protein of the same size. Glutenin is first synthesized as a 57 kDa precursor, then sheared into an acidic subunit of 37-39 kDa and a basic subunit of 22-23 kDa, and synthesized in the endoplasmic reticulum. After synthesized, glutenin is transported through the Golgi apparatus or vesicles directly from the rough endoplasmic reticulum to the protein storage vesicles to form protein aggregates, PB-II [3].

 

Although the content of rice protein is low compared with other cereals, its essential amino acid composition is more complete, and it is the best quality protein in cereal grains [4]. Among the eight essential amino acids, the content of phenylalanine, lysine, tryptophan, methionine, valine and other five amino acids in rice protein is higher than that of other cereals, and its composition is reasonably balanced and close to the ideal model recommended by the WHO [5]. In addition, rice protein has a raw material value of 77, which is the first among various food crops, comparable to white fish (raw material value of 76), and its nutritional value is irreplaceable [6]. Common sources of plant proteins such as soybeans and peanuts contain harmful anti-nutritional factors (such as trypsin inhibiting factor and lectins, etc.), common sources of animal proteins such as milk and eggs contain β-lactoglobulin, egg mucin, etc., allergic to the human body or poisonous, restricting the development and application of its production [7]. Traditionally, rice is the only hypoallergenic grain that can be exempted from allergy testing [8]. In recent years, the allergenicity of rice proteins has been further studied[9] , but in comparison, rice proteins have the characteristics of low antigenic activity, high digestibility and absorption rate, and are convenient for infants and children as well as special populations, so their superiority is irreplaceable.

 

2 Progress of rice protein isolation and extraction

Rice protein extraction is to obtain high purity rice protein products, generally divided into rice protein concentrate (RPC, rice protein concentrate) and rice protein isolate (RPI, rice protein isolate). Traditional rice processing by-products such as broken rice, rice bran, rice waste and other raw materials can be used to prepare rice protein. Rice protein extraction methods mainly include alkaline extraction, enzymatic extraction, solvent extraction, physical separation method and composite extraction method (Table 1). At present, the common extraction methods have some advantages and shortcomings. The cost of alkaline extraction is relatively low, has been industrialized, but the nutritional value is easy to be damaged, and excessive use of alkali caused by environmental pollution; enzyme extraction conditions are relatively mild, but the cost is high, the extraction time is long, the extraction rate is low, not conducive to the realization of the industrialization; composite extraction method to improve the extraction rate, but the operation is more complex, can not be realized industrially; solvent extraction has a higher recovery rate, but the solvent is not easy to remove, easy to cause safety problems, and so on (Table 1). Solvent extraction method has a high recovery rate, but the solvent is not easy to remove, easily cause safety problems, resulting in high cost; physical separation method is currently a more ideal method of separation and preparation, but the country has not mastered and developed the corresponding mature extraction technology. In summary, the study of a low-cost, high-efficiency, high-activity extraction method is one of the new trends in the future research of rice protein [10]. Studies have shown that the use of subcritical water (subcr-itical water) hydrolysis can effectively extract rice proteins and amino acids[11] , and its protein yield is higher than that of traditional alkaline hydrolysis, but there are problems such as high cost, complex process, and inability to achieve industrialization.

 

3 Comprehensive utilization of rice protein

3.1 Functional peptide development

The small molecule peptides produced by enzymatic hydrolysis of rice proteins are diverse and functional, and are easier to be digested and absorbed by the human body than free amino acids. The active peptide oryzatensin isolated and purified from the trypsin hydrolysate of rice clear protein has opioid-like antagonistic peptide activity and can be used to regulate immune activity [12]. Rice proteolytic products have the effects of chelating metal iron ions, scavenging H2O2, hydroxyl radicals, DPPH free radicals and inhibiting the natural oxidation of linoleic acid, etc. The antioxidant peptide sequences are mainly Met-Pro-Pro-Ser-Ser-Pro-His (376.68u), Leu-Ala-Gly-Pro-Lys-Phe-Ala-Leu (408.75u), and Leu-Ala-Gly-Pro-Lys-Ala-Leu (408.75u), and the peptide is mainly used to regulate the immune activity [12]. (408.75u) and Met-Pro-Arg-His-Asp-Pro - Gln (440.70u), among others [13]. Rice protein active peptides can reduce cholesterol levels and regulate cholesterol metabolism by inhibiting the activity of lipase, hindering intestinal cholesterol absorption, promoting cholesterol conversion and excretion, lowering serum LDL concentration, inhibiting the expression of the ACAT2 gene, and increasing the expression of the CYP7A1 gene [14]. Rice protein active peptide can also activate 5-hydroxytryptamine-N-acetyltransferase activity, enhance glutathione synthesis, thereby improving sleep disorders [15].

 

3.2 Protein supplements

Rice protein is hypoallergenic and highly nutritious, making it the plant protein of choice for supplementation in special populations. Rice protein formulas are effective in improving allergic diarrhea in infants and young children; people with wheat intolerance, allergies, or celiac disease are also better suited to consume gluten-free rice protein. Feed-grade rice protein powder as a by-product of the current rice starch industry, a wide range of sources, large production, rich in nutrients, alternative feed ingredients can not only solve the problem of raw material tensions, while saving feeding costs, improve economic efficiency, is the animal husbandry and the feed industry is an excellent additive [16]. Enzymatic digestion of rice protein produces flavor peptides to replace monosodium glutamate, on the one hand, it can be developed as a flavor modifier for human food, on the other hand, it can be used in animal feed and food to effectively mask the bitter taste, enhance the viscosity and improve the palatability of feed, and improve the feed intake of animals. Rice protein powder has also been widely studied as a substitute for fish meal in aquafeeds, and can be applied to shrimp and other economic fish such as pomfrets, blackhead seabreams, rainbow trout and so on [17].

 

3.3 Edible films

Rice edible protein film is a green packaging film with good freshness retention, gas barrier, oil barrier, and moisture barrier properties, which meets the demand for high quality and safe food as well as being suitable for dealing with the environmental problems of non-renewable packaging materials, and is a new approach to renewable agriculture. In addition, rice edible protein films have great potential to carry active ingredients such as anti-browning agents, colorants, flavors, nutrients, fragrances, and antimicrobial compounds, which can extend shelf life and reduce the risk of pathogens growing on the surface of food. By optimizing the concentration of rice protein and glycerol, as well as the ratio of phenolic extracts and minerals, edible films that are resistant to tensile strength and water vapor were produced and can be directly used as packaging materials for vegetables and fruits [18].

 

3.4 Food additives

Although the solubility of rice protein is poor, but after hydrolysis can increase with the solubility to show better foam, emulsification, etc., and the water loss rate is low, can be effectively developed and utilized in the food industry [19]. Enzymatically hydrolyzed or modified rice protein is widely used in food, can play a foaming role in baked goods and confectionery, and play a stabilizing and thickening role in liquid or semi-solid food (such as meat products). Rice protein is hydrolyzed by proteases alcalase and flavourzyme, and the hydrolysate is subjected to the Maillard reaction to prepare meat flavouring, which can be widely used in instant noodles, puffed food, meat processing and condiments [20].

 

4 Current status of domestic and foreign industrialization development

Overseas research on rice protein is more and has achieved good results. The development of rice protein in the United States tends to be used in daily life of common food, has formed a number of industrial brands, widely used in children's nutritional powder, baking, soup, protein shakes, beverages and other products. Japan in recent years more tend to the depth of the development of rice protein, such as rice protein hydrolysis extracted active peptide, with angiotensin converting enzyme inhibitory components, can play an auxiliary therapeutic role in hypertension; another active peptide can be activated through the activation of 5-hydroxytryptamine-N-acetyltransferase activity, improve sleep disorders and so on. In contrast, there is a certain gap between the domestic and foreign countries in both extraction technology research and application development depth research. With the gradual development of the multifunctionality of rice protein and the attention of countries to rice protein, rice protein in recent years in the research and development of cereal proteins stand out, has become a hot spot in the industry. China's R & D and application of rice protein has also made some breakthroughs. 2011 May, the National Development and Reform Commission approved the establishment of the National Engineering Laboratory of Grain Fermentation Processes and Technology, relying on scientific research results and through the transformation of technological achievements, in the past two years, the successful development of branded products, such as rice protein solid drinks. Two rice protein producers in Jiangxi and Liaoning realized the development of international markets such as the United States and Switzerland in 2016 and 2017, respectively [21].

 

5 Outlook

Rice protein is hypoallergenic, with reasonable amino acid composition, high biological efficiency and high nutritional value. With wide sources, large production and low cost, rice protein has great application prospects in the development of functional peptides, protein nutritional supplements, edible films and food additives. The development and utilization of rice protein, the comprehensive utilization of low value-added by-products generated by rice processing, and its transformation into high value-added products, both in line with China's national conditions, but also the trend of research and development of the domestic market of rice protein, and can provide a new point of growth for China's agricultural economy, has a broad market outlook.

 

References.

[1] SHIH F F. An update on the processing of high-protein rice products[J].Die Nahrung ,2003 ,47(6):420-424.

[2] CHEN Y ,WANG M ,OUWERKERK P B F.Molecular and environmental factors determining grain quality in rice[J].Food & Energy Security ,2013 ,1(2):111 -132.

[3] PEDRAZZINI E ,MAINIERI D ,MARRANO C A ,et al. Where do protein bodies of cereal seeds come from?[J].Frontiers in Plant Science ,2016 (7):1139.

[4] Chen Yuan ,Zhang Zhiguo. Progress of rice protein research[J]. Grain and Fats ,2017 ,30(7):13-16.

[5] M. Li ,E. G. Li ,H. Yan Gao. Overview of rice protein research[J]. Grain and Fats ,2006(8): 3-5.

[6] FINANCE , ZHAO Nian , CHEN Shasha , et al. Research and utilization of rice protein[J]. Food Industry Science and Technology , 2007(1):231-234.

[7] CHEN Datu, LI Rui, HU Guanbo, et al. Nutritional value and utilization of rice protein[J]. China Feed ,2013(10):37-40.

[8] CRAWFORD LV ,HERROD H G.Allergy diets for infants and children[J].Current Problems in Pediatrics ,1989 ,11(12):4-43.

[9] WANG Yi-Man,LU Lu,XU Shanshan,et al. Research progress of rice allergy[J]. Journal of Food Safety and Quality Inspection ,2017,(4):1093-1098.

[10] LI Chao-Nan, LU Bao-Xin, ZHOU Yi, et al. Research progress of rice protein extraction and separation[J]. Agricultural Product Processing ,2017(4):63-64.

[11] SEREEWATTHANAWUT I ,PRAPINTIP S ,WATCHIRARUJI K ,et al.Extraction of protein and amino acids from deoiled rice bran by subcritical water hydrolysis[J].Bioresource Technology,2008 ,99(3):555-561.

[12] TAKAHASHI M ,MORIGUCHI S ,YOSHIKAWA M ,et al.Isolation and characterization of oryzatensin: a novel bioactive peptide with ileum contracting and immunomodulating activities derived from rice albumin[J].Biochem Mol BiolInt , 1994 ,33(6):1151-1158.

[13] LI Jianan,WANG Jing,ZHANG Huijuan,et al. Identification and characterization of antioxidant peptide activity and composition of rice protein[J]. Food Industry Science and Technology ,2013 ,34(23):53-57.

[14] Luan Hui ,Yang Lin . Research progress of rice protein in regulating cholesterol metabolism[J]. Food Industry Science and Technology ,2012 ,33(5):421-424.

[15] TADASHI H. Expectation for improvement of sleep disorder by using rice-derived protein hydrolysate[J].Journal of the brewing society of japan ,. 2016 ,111(7):431-436.

[16] PAN Dizi,HU Guili,WANG Yushi,et al. Application of rice and its processing by-products in broiler production[J]. Feed Research ,2017(1):48-52.

[17] FU Jinghua,DANG Ming,WEN Xinkai,et al. Study on the replacement of fish meal with rice protein meal in the feed of shrimp Penaeus vannamei[J]. China Feed ,2017(19):36-39.

[18] SCHMIDT C G ,CERQUEIRA M A ,VICENTE A A ,et al.Rice bran protein-based films enriched by phenolic extract of fermented rice bran and montmorillonite clay[J].CyTA-Journal of Food ,2015 ,13(2):204 - 212.

[19] HU Zhongze. Enzymatic hydrolysis of rice protein foaming powder[J]. Grain and Feed Industry ,2002,(9):45-46.

[20] LIU Hong-Fu,DONG Bei-Lei,LU Xiao-Bin. Study on the improvement of rice protein hydrolysis by secondary enzyme addition[J]. Food Science and Technology ,2008 ,33(6):26-28.

[21] Ding Zhengwei . Liaoning rice protein powder exported to Switzerland for the first time[J]. China Inspection and Quarantine ,2017(10):8.