Rice processing developments in China
May 01, 2008
by Meyer Sosland
As the world’s biggest producer and consumer of milled rice, China and its 1.3 billion people are significantly impacted by developments in rice processing technology.
Deep processing of rice using advanced processing technology and making full use of the rice processing byproducts are important to the sustainable development of China, which in 2006-07 produced 127.8 million tonnes of milled rice while consuming approximately the same amount, according to the U.S. Department of Agriculture.
RICE PROCESSING TECHNOLOGY Classified processing technology, which refers to classifying the paddy into several grades according to different characteristics such as size, bulk density and mechanical properties, is used by many Chinese rice processing enterprises. Once classified, the rice is processed using different technologies and technological parameters according to the characteristics of each grade. The process includes pre-cleaning of the raw grain, stone removing and grading before hulling, whitener milling and finished product packing.
Before milling, a conditioning device is used to treat brown rice for 20 to 40 minutes according to the water content, quality and temperature of the rice and the processing demand. Water addition is 0.12% to 0.16%; water content in the upper layer of brown rice is 16% to 17%; and the water gradient between the upper layer and endosperm is 2% to 3%.
High quality rice processing is tied closely to grinding technology, as rational selection of the fine grinding machine and technology is essential. According to the different materials of the whitener mill rollers, the rice milling machines used in Chinese rice processing enterprises can be classified into two kinds: emery roll polishers (45%) and iron roller polishers (55%)
To meet the Chinese National Standard and ensure quality of the finished rice product, rice is graded by separation of the unqualified broken rice and removing rice bran powder and rice tips. The main device for whitened rice grading used in Chinese rice processing enterprises is a rice grading sieve or a grading machine by rice thickness. Rice is generally graded into special grade rice, common rice, big broken rice and small broken rice. In the processing of high quality rice, more than 40% of the Chinese rice processing enterprises use rice grading sieves combined with blasting rice cleaners.
Color sorting — a process in which discolored rice and impurities are removed — is the last quality assurance procedure for head rice. The key performance indicators of color sorters are yield and effect of color sorting. Currently, color sorters are widely used in Chinese rice processing enterprises.
Polishing can effectively remove the rice bran powder and improve the antioxidant capacity of rice, therefore prolonging its shelf life. More than 80% of the Chinese rice processing enterprises use polishers made in China, while the remaining 20% use polishers made primarily by foreign suppliers.
Blended rice refers to putting different kinds of rice together in proper proportion to meet the consumption demands. Blended rice is often of different grades or edible qualities. Blending by gravity and other types of blending equipment are used in processing. Rice blending technology is used in more than 60% of Chinese rice processing enterprises.
RICE PRODUCTS Enriched rice refers to adding nutritional substances. During processing, the upper layer and embryo containing many nutritional substances are removed, which reduces the nutritional value. Years ago, studies on enriched rice were carried out in the United States and Japan, which led to many fortification technologies being developed, many enriched rice products being produced and hygienic standards for the use of nutritional fortification substances in rice being established. In recent years, China has also made some progress in rice nutritional fortification technology.
Germinated rice refers to the kind of polished rice in which the embryo is preserved. In the rice embryo, there are many kinds of vitamins, such as Vitamin E, B1 Vitamin, and B2 Vitamin as well as high-quality proteins and fats. Therefore, the nutritional value of germinated rice is higher than common rice. During the processing of common rice, most of the rice embryos are brushed off during hulling. In the processing of germinated rice, special technologies and equipment are introduced. Before hulling, brown rice is pretreated with chemical solvents or enzymes and then milled under low-pressure by a vertical rice whitener. Some Chinese rice processing enterprises have mastered this technology.
Parboiled rice, also called "half-cooking rice," is also produced in China. The basic parboiled rice process is the same as common rice, but procedures such as soaking, pressure steam cooking and drying prior to hulling are added while processing parboiled rice. This results in improved rice processing quality and a decreased proportion of broken rice. During processing, vitamins and mineral substances in the upper layer soak into the kernels, increasing the nutritional content of the endosperm and the overall nutritional value of the rice.
Parboiled rice has many other positive qualities such as good storage stability, high expansion ratio and excellent digestibility.
Germinated brown rice is brown rice soaked in water until it just begins to bud. The outer bran layer becomes soft and more prone to water absorption, making it easier to cook. Studies show that germinated brown rice may enhance brain functions and reduce levels of lipids or fats in the blood. Studies have found that germinated brown rice contains three times as much y-amino butyric acid as conventional brown rice and five times as much as white rice. Germinated brown rice is known to promote blood flow in the brain, help stabilize blood pressure and reduce lipid levels in the blood. In addition, germinated brown rice contains some substances relating to the brain function that can inhibit the synthesis of prolyl endopeptidase, therefore helping to prevent dementia.
DEEP-PROCESSING RICE PRODUCTS The starch content in rice is high. Besides common rice starch, modified rice starch is another product developed by the Chinese rice processing industry. Rice starch is extracted from low-value rice such as broken rice, early indica rice and aged indica rice using modern bio
logical and chemical technologies, and then transformed into high-value and useful products such as slowly digestible starch, starch substitute for fat, resistant starch and porous starch.
Slowly digestible starch refers to the modified rice product of slow digestibility using heating or enzyme treating technologies. Clinical trials reveal slowly digestible starch can improve the sugar load, which qualifies it as a new kind of food for diabetics. Slowly digestible starch can also be used as the carbohydrate supplement for athletes, especially long-distance runners, since it gives them stable and persistent energy.
Starch substitute for fat is suitable for producing dairy products such as yogurt and cream substitutes. It has the cream-like appearance and taste, which enables it to be applied to the production of non-cream cheese, low-fat ice cream, non-fat butter, sauce and condiments of cold-mixing dishes. There is strong demand for these products in China.
Rice resistant starch is suitable for obese individuals and diabetics, because it can’t be assimilated. Unlike ordinary fiber, resistant starch won’t absorb much water, therefore the taste of low-moisture products won’t be affected after the resistant starch is added.
Porous starch refers to a kind of porous carrier formed after the rice starch is enzymaticly treated. Porous starch has good absorbability because there are many small holes on its surface. Therefore, it can be used as an absorbing carrier for some functionality substances such as medicament, flavor, pigment and activated substances and applied to the medical, chemical and food industries.
Broken rice, indica rice and byproducts of rice starch processing are all good raw materials for rice protein extraction. Rice protein features characteristics such as high nutrition, good digestibility, low hypersusceptibility and good dissolvability, making it especially suitable for children and the elderly. Many processing technologies of rice protein have been developed in China.
UTILIZATION OF RICE BYPRODUCTS In China, the use of rice hull is comprehensive. It can be used to generate electricity and produce furfural. After calcinations, silicon in the rice hull can be transformed into silicon dioxide of large absorption surface and high activity, which can be used as raw materials for many carriers as well as composite materials. In addition, research on silicon to produce raw material of battery silicon sheets are also carried out in China, as there is neither arsenic nor fluorin in rice hull. What’s more, rice hull can be used to produce non-polluted one-off canteens, which is a good prospect in China.
Rice bran oil is used in the health and nutrition sector because it contains various unsaturated fatty acids, sub-oleic acid, oryzanol, vitamins, lecith and phytosprterol. The price of rice bran oil is around five times that of common vegetable oil in China.
Rice germ is also in demand for health and nutrition, as 70% to 80% of the fatty acids in rice germ is unsaturated. The vitamin E content is between 2 to 3 milligrams per gram of rice germ, and there are also special substances such as phytosterol in rice germ. Rice is applied to production of nutrition health food in China, and good economic interest has been received. WG
Liu Zhongdong is a professor at the Henan University of Technology in Henan, China. He can be contacted at firstname.lastname@example.org. This article is supported by National Natural Science Foundation of China (20672029\30270762) and national 863 program of P.R. China (2007AA100401).