Properties Of Yinmi Starch And Preliminary Screening Of Fermented Strains During Natural Fermentation

China is the largest rice producer and consumer of the world, in the mean time rice processing is an important part of the grain and oil processing industry in our country. But according to some recent research of relevant department shows, rice processing consumption accounted for only about 6% of the total consumption and rice processing is far behind rice increase production, so it is very important to find some new processing approaches. The object of this paper was a traditional fermented rice product---Yinmi (usually prepared with sticky rice, and then processing by natural fermentation, cooking and drying in the shade), the paper was investigated effects of ferment time on the content of main chemical compositions of the rice and fermented water during fermentation, highlighted the changes of physicochemical properties of rice starch and done a series of researches on the changes of rice and rice starch’s rheological properties after processed in different ways, meanwhile firstly screened preliminarily and identified the main bacterial strains during the natural fermentation, also discussed the optimal fermentation conditions, in order to guide practical production, and establish certain theoretical foundation for making this valuable traditional food becoming industrial production. The major contents and results are as follow:1. The changes of the content of main chemical compositions of rice and fermented water during natural fermentationCompared to the native rice, the contents of crude protein and crude fat were decreased, and the maximum drop was 22.95% and 63.10% respectively. It was observed that the pH in the fermented water initially decreased as time went by, from 6.44 in the first day dropped to 4.44 in the forth day, and then tended to be a equilibrant; titratable acidity (calculated with lactic acid) in fermented water without water changes was increased with the extension of ferment time, from 0.19% in the fifth day up to 0.38% in the fifteenth day; the content of soluble sugar in the fifth day was the highest, at 582.921μg/mL, and the number went down with time went on. The major fatty acids in the rice during fermentation were:palmitic acid, oleic acid and linoleic acid, the sum of the relative content of three fatty acids counted 90% and above of the total fatty acid content in the rice.2. The changes of physicochemical properties of rice starch during natural fermentationThe content of Yinmi starch ranged from 85.91% to 92.22% after fermented different days, and the resistant starch was decreased while time extended. The granular properties and physicochemical properties of rice starches during fermentation have been characterized by the means of chemical methods, scanning electron microscope, X-ray diffraction, differential scanning calorimeter, laser particle size analyzer and other modern analysis methods and technologies, the results were as follows:the solubility and swelling capacity of rice starch after fermentation was increased with temperature raise. As the time of natural fermentation extended, the shape of single starch granular was unobvious, and became an adhesive unity, which in response to the raise of mean diameters of starch granular, but the crystal type was not change during fermentation, still presented typical A-type patterns and 20 were 15.11°、17.00°、18.01°、23.03°, and the degree of crystallization was from 18.4% to 46.3%. In addition, the result of differential scanning calorimeter analysis showed that, the gelatinization parameters of starch paste after fermentation all decreased which compared to native rice starch.3. Preliminary research of the main bacterial strains during natural fermentationThree suspected lactic acid bacteria strains have been separated and selected from fermented water, and named them as Lact.a (rhabditiform), Lact.b (short rhabditiform), Lact.c (hammer shape)on the basis of their different morphology under microscope, besides, the three strains were identified preliminarily as Lactobacillus by some classical physiology and biochemistry methods in microbiology. The capacity of producing acids of these three lactic acid bacteria strains were very strong, the pH of fermented water can be decreased at 4.0 in 24 hours, which same to natural fermentation in 5 days; on the other hand, their growth ability to reproduce reached strongest in 24 hours(Lact.a and Lact.b) or 27 hours (Lact.c), which in response to their capacity of producing acids. Based on the single factor test and orthogonal test, results of optimum conditions of single strain fermentation showed as follows:effects of initial pH (A), ferment temperature (B) and ferment time (C) on the capacity of producing acids of three strains were B>C>A, in terms of the speed of producing acids, the optimum conditions of three strains were all A3B1C1, and the effects of ferment temperature and ferment time on the capacity of producing acids of Lact.a and Lact.b were significant; furthermore, effects of these factors on the growth ability to reproduce of three strains were different, but none of them were significant.4. The changes of rheological behavior of rice and rice starch pastes during fermentationThe rheological properties of rice and rice starch pastes fermented different time were studied by dynamic rheometer, and the results showed as follows:after soaked by lactate-sodium lactate at different pH, different kinds of acids and different strains separated as above, respectively, shear stress of all samples increased while shear rate went up. Under dynamic shear rate, the viscosity of rice pastes processed in different ways and rice starch pastes fermented different time were all decreased while shear rate went up. Rice starch paste presented property of pseudoplastic flow and fitted the non-newtonian fluid rheological characteristics very well, and the rheological behavior can be described by power low function. The storage modulus (G’) and the loss modulus (G") of rice starch pastes fermented different time at different concentrations (4%、6%、8%) increased while shear rate increased; when at the same shear rate, G’and G" increased with the increase of starch pastes concentration, and G’>G". While the scanning temperature went up, G’and G" of rice starch pastes fermented different time presented a pattern of decreased first then increased and decreased at last.