What Is the Nutrition Fact of 1 Kg Rice Protein？

As China's largest grain variety, rice has had an annual output of more than 180 million tons since 2007, accounting for 42% of the country's total grain output and about 34% of the world's total rice output (Wang Kaili et al., 2012; Shen Hongyuan, 2011). Rice protein, produced after crushing rice to make sugar, is a feed protein resource with great development value. This article provides a review of the composition, nutritional value, preparation methods and application of rice protein in livestock and poultry production, to provide a reference for the development and utilization of rice protein resources.

1 Composition and structure of rice protein

As a major source of plant protein in the human diet, rice protein accounts for about 8% of the rice (Mar-shall and Wadsworth, 1994). According to the Osborne classification, rice protein is divided into water-soluble clear protein (albumin), globulin that dissolves in 0.5 mol/L NaCl solution, prolamin that dissolves in 70% to 80% ethanol, and glutelin that dissolves in dilute acid or alkali (Chen Jingjing and Sun Zhigao, 2008; Deng Xiao et al., 2007). Each of these four types accounts for 2% to 5%, 2% to 10%, 1% to 5%, and ≥80% of the total protein, respectively. Among them, glutenin and alcohol-soluble proteins are storage proteins that are the main components of rice proteins, while the lower content of albumin and globulin is the physiologically active protein in rice.

Rice proteins mainly exist in the form of two protein bodies: PB-I and PB-II. Electron microscopy shows that PB-I has a lamellar structure with dense particles measuring 0.5–2 μm in diameter. The structural components are stable and this is the site where alcohol-soluble proteins exist. PB-II is shape, no stratification, uniform texture, particle diameter about 4 μm, its outer membrane is not obvious, the result of the composition is not stable, gluten and globulin in it (Collier et al., 1998). The content of the four types of protein is shown in Table 1. As can be seen from Table 1, the content of gluten in rice is relatively high, which to some extent reflects the instability of the structure of rice protein (Li Ming et al., 2006).

2. Rice protein nutritional value

2.1  Low antigenicity

Proteins are the material basis for life activities and play an important regulatory role in the physiological metabolism of the animal body. Their sources include plant proteins and animal proteins (Ye Jingjing et al., 2011). Low antigenicity activity is a prerequisite for the efficient utilization of protein nutrients in the animal body. It is well known that many plant proteins contain anti-nutritional factors, such as trypsin inhibitors in soybeans, flatulence factors, and lectins in peanuts, which greatly limit their use in production (Yin Xihai et al., 2012; Jiang Qianqian et al., 2012).

However, related research shows that rice protein is highly nutritious, gentle and non-irritating, has low antigenic activity, and does not cause allergic reactions (Guo Yanhe and Zeng Li, 2010; Hettiarachchy and Rath, 2001). It is a plant protein resource with great development potential. In addition some animal protein raw materials contain anti-nutritional factors, such as lactoferrin and some egg albumin, which may cause allergic or toxic reactions in the animal body, while rice protein does not contain similar allergenic factors and is safe and reliable to use (Wang Zhangcun et al., 2004).

2. 2.2 Balanced amino acid composition

Rice protein has a high protein content of 40% to 70%, and is highly absorbable and bioavailable in the body. Its biological value is as high as 77, and its nutritional value is much higher than that of plant proteins such as corn and wheat (Li Ming et al., 2006). Rice has a balanced amino acid composition and is rich in all the essential amino acids the body needs, which is very close to the ideal model recommended by WHO/FAO (1973). Analysis of its component analysis found that rice protein has a high lysine content and contains more than 80% alkali-soluble glutenin (Yi Cuiping and Yao Huiyuan, 2003). Table 2 lists the amino acid composition of rice protein, wheat protein and corn protein, as well as the WHO-recommended optimal protein amino acid pattern (Guo Yanhe and Zeng Li, 2010). As can be seen from Table 2, it can be seen that the lysine, cystine and threonine content in rice protein is slightly lower than that of ideal protein, and compared with corn protein, lysine and threonine are slightly lower. Compared with wheat protein, all kinds of essential amino acids in rice protein are higher, and it is a protein with relatively good amino acid nutritional value.

In addition , combined with Table 3, it can be seen that under the same conditions of crude protein level in the feed, compared with the standard requirements, except for lysine, which is slightly lower, the other three amino acids can meet the growth needs of pigs at all stages. Compared with soybean meal, lysine and threonine are lower in content, while methionine + cystine and isoleucine are higher in content. It can be seen that rice protein is a relatively ideal protein feed for pigs.

3 Preparation method of rice protein 

The purpose of extracting rice protein is to obtain a high-purity rice protein product, which is generally divided into rice protein concentrate (RPC, protein content 50% to 89%) and rice protein isolate (RPI, protein content above 90%). Broken rice , rice lees, rice bran, etc. can all be used as raw materials for preparing rice protein. At present, the main methods of extracting rice protein in China are the alkali method, the enzyme method, and the composite extraction method (Table 4). As can be seen from Table 4, it can be seen that there are significant differences in the extraction rates of rice protein for different extraction methods. The extraction rate of the composite extraction method is higher, the enzyme extraction method is relatively lower, and the extraction rates of other methods fluctuate greatly.

4 Application of Application of rice protein in livestock and poultry production

As a plant protein, rice protein is rich in a variety of amino acids and has a balanced composition, similar to Peruvian fish meal. Nutrient analysis of rice protein has found that it contains ≥60% crude protein, 8% to 9.5% crude fat, 56% digestible protein, and is extremely rich in lysine, ranking first among cereal foods. In addition rice protein contains a variety of trace elements, bioactive substances and microbial enzyme systems, which give it physiological regulatory capabilities (Luan Hui, 2011; Yang Lin et al., 2010). Related studies have shown that adding rice protein products to feed can improve the growth performance and immunity of livestock and poultry, and improve the environment of livestock and poultry houses. It is a protein feed resource with broad application prospects.

4.1 Application in pig production

Wu Xin et al. (2008) used rice protein powder to replace whey protein concentrate in the weaning piglet diet. The results showed that there were no significant differences in ADFI, ADG and F/G among the experimental groups (P > 0.05). The experiment was conducted for 8 to 14 days, and the experimental groups tended to increase the ADG and decrease the F/G of the piglets (P > 0.05). (P>0.05); blood routine tests found that there were no significant differences in the red blood cells, white blood cells, platelets, etc. in the blood of piglets in each group (P>0.05); organ index tests also showed that there were no significant differences in immune function in each group (P>0.05), which indicates that rice protein powder can be used to replace a certain proportion of whey protein powder in early weaned piglets.

Liu Wei Dong et al. (2011) showed that providing a diet containing 1.5% to 2% rice protein peptide to 35-day-old piglets significantly increased the average daily gain, energy metabolic rate, protein metabolic rate and feed efficiency of the pigs ( (P<0.05), and the total protein, blood glucose and alanine aminotransferase levels in the blood were all increased to some extent (P>0.05), while the diarrhea rate, blood urea nitrogen and lactate dehydrogenase concentration were significantly reduced (P<0.05). Hu Yi et al. (2010) found that the apparent and true digestibility of lysine-transgenic rice protein was not significantly different from that of the parent rice (P>0.05), and the digestion effect was good.

4. 2. Application in chicken production

Liu Weidong et al. (2010) found that adding 1.5% to 2% rice protein peptides to the feed of Gushi chickens can significantly improve their productive performance and the deposition of endogenous proteins (P < 0.05), and the content of growth hormone (GH) ), triiodothyronine (T3) and insulin-like growth factor-I in the serum significantly increased (P < 0.05), and the triiodothyronine (T3)/tetraiodothyronine (T4) value significantly increased (P < 0.05). Liu Weidong et al. (2012b) showed in a study on laying hens that under heat stress conditions, the addition of 1.5% to 2% rice protein peptide can significantly increase the egg production rate, feed intake, and total protein , total lipid and thyroxine concentrations (P<0.05), significantly reduced the feed-to-egg ratio, blood glucose, aldosterone and cortisol concentrations (P<0.05), and also reduced the mortality rate to a certain extent. Liu Weidong et al. (2012a) found in a study on the effects of rice protein peptides on harmful gas concentrations and production performance in winter chicken coops that the addition of 1.5% to 2% rice protein peptides to the feed can significantly reduce the concentration of ammonia and hydrogen sulfide in the chicken coop (P<0.05), and significantly improve egg production rate and feed efficiency (P<0.05).

5 Summary

In summary, rice protein has a reasonable amino acid composition, high biological efficacy, low allergenicity and high nutritional value. China is a major rice-producing country with abundant rice resources, which provides a basis for the development and utilization of rice protein. As a plant protein resource with great development potential, rice protein provides a viable way to solve the problem of insufficient feed protein resources in China.

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