| Paddy is a main foodstuff crop in China . Its yield accounts for 37% of the global paddy yield per year and take a first in the whole world. The yield of rice is too high to overstock in China, but consumption is very slow. United States Department of Agriculture reported that the yield of China rice came up to 67,350,000 ton in the end of 2002. It accounted for 64.2% of that in the world. China is still one of the country which has the most stock rice. The stocks continuous mount up which not only causes large quantity of deterioration and wastage every year but become the burden of farmer and government. About 80% the overstocked rice is Indica. Consumption of processing rice accounts for 1.4% in our country in 2002 and is far from the average level in the world. Rice cultivars Indica is widely planted with its high yield and good quality for producing rice noodles in south of China. Traditional fermented rice noodles are very popular because of its favorite mouth feel and taste. Processing technology of rice noodles is key for solving overstock. The further theoretical research is needed for its industrialized product. The paper reveals the influence of natural fermentation on the physicochemical characteristics of rice and gel mechanism of rice noodle. The main contents and results are as follows.1. Chemical components of rice flour were significantly modified by whole rice granule fermentation. About 33% of total protein, 61% of total lipid and 62% of total ash content were lost during fermentation period. The rice starch content remained almost constant. So, the natural fermentation improved the purity of rice starch.2. The natural fermentation mainly affected the amorphous region of the starch granule structure. The micrography of starch granule showed that the shape of starch granule remained unchanged. Starch damage didn't change. Results by the X-ray diffraction indicated that fermentation had little effects on starch crystal structure, but the ratio of crystal area to amorphous area increased. FTIR indicated that starch have not new chemical bond and structure.3. The structure and form of starch were changed by natural fermentation. It is mainly that Amylopectin starch was broken and debranched. The amylose content had 3.28% increase , the area of larger molecular decreased but smaller molecular increased by fermentation. The number of average molecular polymerization was changed from 12597.6GLU to 12051.0 GLU for the area of larger molecular and from 3061.5 GLU to 3423.1 GLU for the area of smaller molecular after fermentation. The -hydrolysis ratio was increased. RVA peak viscosity decreased. They both showed that starch chain was broken and debranched.4. Lactic acid in metabolites of fermentation play an important role in improving the rheologyical properties of rice starch gel. A large quantity of organic acid were produced by natural fermentation. More than 90%of total acid were lactic acid by Ion Chromatography analysis. The rice noodle for PH 4.0 treatment has similar sensory evaluation score compared with the natural fermentation one. Rice granule treated by trypsin, pectinase and lipase also produced good quality rice noodles. Maltose, glucose and ethanol produced during fermentation had negative effects on gel properties.The paper discusses the influence of natural fermentation on the physicochemical characteristics of rice and gel mechanism of rice noodle. Conclusions are that organic acid and enzymes produced by natural fermentation caused starch modification and purification, and further improved the rheological properties of rice noodles. Lactic acid plays a key role, hydrolyzed the external chains of amylopectin among the amorphous region in starch granule, homogenized the starch molecular distribution, decreased the branching degree of single amylopectin molecule, and weaken its re-crystallization trend. Furthermore, fermentation increased the intermedium and amylose content, and enhanced their retrogradation property. Low PH value condition is also beneficial to...
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