| The main work in this paper includes:establishe a method to evaluate the quality of frozen cooked rice, study on material adaptability for frozen cooked rice, determine the best production technology and research on quality characteristics of the product. Through those study can provide a theoretical reference for the development of frozen cooked rice, and a practical guide for production optimization and the final quality of the product. The main conclusions of this paper are listed as follows:10 kind of rice were selected to be made into frozen cooked rice, and the correlation coefficients between sensory evaluation and instrumental measurement indexes were analyzed. The result showed that hardness measured by TPA mode of Texture Analyser was significantly negatively correlated to total score of sensory evaluation(P<0.01). And adhesiveness was significantly positively correlated to total score(P<0.01). So hardness and adhesiveness measured by TPA mode of Texture Analyser could be used as recommend indexes for evaluating the quality of frozen cooked rice. After analyzing the relationships between the content of amylose and total protein of 10 kind of rice and the qualities of frozen cooked rice, significant positive correlation between amylose content and hardness(P<0.01), significant negative correlation between amylose content and adhesiveness (P<0.01) were found. But the total protein content and the product quality were uncorrelated. At last, it has been found that the rice with about 17% amylose content is adequate for producing frozen cooked rice.The research on the production technology of frozen cooked rice indicated that the water absorption of rice was under the influence of temperature, pH and the ratio between water and rice. The hardness and adhesiveness of frozen cooked rice were both significantly correlated to the soaking temperature and time(P<0.05), and the quality of frozen cooked rice with high temperature socking was better than low temperature. The quality of frozen cooked rice was also affected by different cooking conditions, better product quality was made by electromagnetic induction heating which can distribute heat evenly, and the cooker with good thermal insulation properties. Furthermore, boiling time and holding time were also important factors. The studies on analysing the freezing curves of cooked rice showed that freezing temperature, weight, shape and package had a great influence on freezing rate. And the freezing rate significantly affected on hardness, adhesiveness and retrogradation enthalpy of frozen cooked rice. In order to reduce the possibility of adhereing each other, chosen SSPS, rice bran oil and citric acid as quality improver, and were analyzed by experiment of response surface analysis, found the optimal formula was:SSPS 0.48%, rice bran oil 0.44%, citric acid 0.005%.Under the three different storage temperature -18℃,4℃and 25℃, the qualities of cooked rice were analyzed by evaluating the gelatinization degree, water content, hardness, adhesiveness, whiteness and aerobic bacterial count, found that -18℃was a better storage temperature for keeping the quality of cooked rice from decreasing, and inhibiting microorganism from growth. The quality degradation of cooked rice at 4℃was serious, while less serious at 25℃, but at 25℃the growth trend of total bacteria was obvious. Through analysing the Correlation coefficients between gelatinization degree and hardness and adhesiveness, found that gelatinization degree respectively negatively and positively correlated to hardness and adhesiveness. Other result showed the process of retrogradation had no affect on whiteness of cooked rice, while frozen situation made the whiteness increasing obviously.Temperature profile and moisture immigration of frozen cooked rice through microwave reheating were studied. It showed that microwave power and the weight of frozen cooked rice both had an effect on the temperature rising and moisture immigration. Moreover, the conversion of temperature gradient existed during microwave reheating and that the temperature rising and moisture loss were different among surface and inner.An in vitro digestion method was used to investigate the difference between fresh cooked rice, frozen cooked rice and reheated frozen cooked rice. Results showed that in vitro digestive juice of fresh cooked rice, both the increasing rate and final content of reducing sugar and glucose were more than other two cooked rice. The content of soluble protein in vitro digestive juice of fresh cooked rice was also more than other two cooked rice. Through the determination of free amino acid in vitro digestive juice of fresh cooked rice, frozen cooked rice and reheated cooked rice, found the content of total free amino acid was respectively 1.24mg/g,0.62mg/g and 0.59mg/g, including 15 kind of free amino acid.The volatile aromatic components in cooked rice were extracted by solid-phase micro-extraction(SPME) and were analyzed by GC/MS. The results showed that total 33 different compounds were isolated and identified from fresh cooked rice, and respectively 20 and 18 different compounds were isolated and identified from frozen cooked rice and reheated frozen cooked rice. These compounds were mainly aldehydes, alcohols, ketones, esters etc. |
