Corn starch products are produced from corn grains by the steps of soaking in sulfurous acid, crushing and screening, separating and washing, dehydrating and drying. In addition to direct use in fields of food, paper making, textile, medicine and so on, corn starch is mostly used in deep processing. In China, corn is consumed in a large amount in starch industry. The output of corn starch in China is increasing gradually from 1999 to 2011, which amounted to 21,700,000 tons in 2009, ranking the second in the world. Starch sugar, as a high-end product prepared from corn starch, possesses high economic value and edible value, and is widely used in fields of food, medicine, chemical industry, fermentation and so on. Starch sugar prepared from corn starch includes glucose, fructose, maltose, etc. Corn syrup prepared from corn starch, which is easily assimilated by human body, is a good sweetener for making candies, cakes, beverages and cans. Sorbitol, which is a derivative of starch sugar, is mainly used for producing vitamin C, and there has been high domestic demand for it in recent years. Modified starch is modified on the basis of starch, which is a widely used new product developed in recent years. Over 3000 varieties of modified starch have been developed by foreign countries, but only 50 varieties by China. Modified starch is widely used in fields of paper making, textile, food, feedstuff, medicine, chemical industry, petroleum and so on, with the largest consumption in the fields of paper making, food and textile, and it has promising application prospects. Consequently, the demand of corn starch has been increasing at home and abroad in recent years.
Besides, in addition to the major product of corn starch, four co-products can be obtained in corn starch processing, namely, corn oil, corn fiber, corn gluten meal and corn steep liquor. The corn oil has a content of unsaturated fatty acids over 85%, which mainly includes oleic acid and linoleic acid with an absorption rate over 97% by human body; the corn oil contains sitosterol which could inhibit the increase of cholesterol; and the corn oil is rich in vitamin E which can play a role in cells division in human body and slow down the ageing process. Corn dietary fiber is composed of cellulose and hemicelluloses, which can decrease blood pressure and prevent Heart-Cerebrovascular diseases. The corn gluten meal, as an important co-product in the wet processing of corn, has a content of protein from 50% to 70% and is main material for producing high protein feedstuff and for producing gliadin and other industrial products. The corn steep liquor has a total content of protein from 44% to 48% (dry basis). As a feed formula, the corn steep liquor is a kind of nutriment with high energy and high protein, and is rich in vitamin B and minerals.
Currently, corn starch is commonly processed by wet process in the world. The starch, protein, embryo and fiber in the corn are separated, condensed and dried by mechanical methods such as crushing, screening, centrifugation, squeezing and filtrating and so on. And various methods are adopted by those skilled in the art to improve the processing technology of the corn starch, e.g., a method for shortening the soaking time of corn in corn starch processing was disclosed in Chinese patent publication No. 101372702A, which shortens the soaking time of the corn by soaking the corm under high pressure in combination with complex enzyme. But this method by means of soaking the corn under high pressure goes especially against its application in industrial production, because the process of this method is complex, the cost for the equipment and for the processing is high, and the power consumption is considerable, thus the method for shortening the soaking time of the corn has little practicality in reality. What's more, another method of producing corn starch by means of soaking the corn by enzymatic process was disclosed in Chinese patent publication No. CN1831013A. According to the method, in the first step of soaking, lactobacillus cultivated by fermenting is added to the soaking solution of the corn, and in the third step, proteinase from plant is added to the soaking solution of the crushed corn to degrade proteinaceous matrix so as to release starch, which further shortens the soaking time. In both of the methods disclosed in the patents above, proteinase is added to the soaking solution, but the proteinase will cause some proteins in the corn starch hydrolyzed, finally will result in a loss of the most valuable protein in the corn starch processing. What's more, the soluble protein dissolved in the water will pollute the process water discharged, which is not good for environmental protection. So the separating effect and the purity of the substance separated in the corn starch processing are limited, and the cost for deep processing is high. What's more, power consumptions (water power, electric power and steam power) in the separating process for the substances separated are high, with low efficiency.
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