Studies On The Quality Holding And Sheif Life Of Cold Distributional Cooked Rice

Cold distributional cooked rice is a new product of instant rice products. It is a rice cooked by using industrial open fire cooking technology and immediately cooled to medium or low temperature. It is distributed to the consumer market in a short period and consumed after minimum reheating. In view of the great development potential of the current domestic instant rice market, studies on the cooling technology of cooked rice, the quality holding of cold distributional cooked rice, and its shelf life quality could provide a theoretical reference for the industrialized production of cold distributional cooked rice, and provide a practical guide for the domestic large-scale applications of vacuum cooling technology. The main contents and conclusions of this paper are listed as follows:Compared with the traditional cooled rice, vacuum cooled rice was cooled faster. It had a higher weight loss, had a uniform temperature and moisture content from the surface and the center, and had a low degree of retrogradation in storage. The exploration on the changes of moisture state of cold cooked rice showed that the combination between moisture and macromolecule become close, and the degree of freedom was reduced. Vacuum cooling could delay the short-term retrogradation of starch effectively, while the effect on long-term retrogradation was not obvious. The force air cooled rice had the highest degree of retrogradation.The increase in vacuum could lead a significant increase in the vacuum cooling rate, while the cooked rice moisture content and the terminal vacuum cooling temperature were positively correlated. In different storage temperature, the retrogradation rate of rice srarch was4℃>25℃>-18℃, and during the first12hours in storage period it changed significantly. The exploration on the changes of moisture state of cold cooked rice under different temperature showed:in storage, the H-bond action between the water of T21and macromolecule generally enhanced, and the water of T21migrated; the water of T22participated in the recrystallization of starch retrogradation, and the starch retrogradation rate could be determined by the T22value; the changes of the water of T23showed that water holding capacity of cooked rice decreased, and it positively correlated with the starch retrogradation rate. The changes of the water of T2*were the cooked rice at4℃>the cooked rice at15℃>the cooked rice at20℃, it showed that avoiding been stored in the retrogradation temperature zone could restrain the short-term retrogradation of starch, and improve the water holding capacity and the water freedom degree. Microwave heating was suit for cold distributional cooked rice, and the reheating technologies were as follows:800W microwave output power,200g microwave quality, and75s-105s microwave time.Through the single-factor experiment, Plackett-Burman experiment, the steepest ascent experiment and Box-Behnken surface design, the compound quality improver formulation of cold distributional cooked rice was optimized as follows:0.55%soluble soybean polysaccharides,0.15%miola and0.02%citric acid.The total bacterial count of cold distributional cooked rice stored below15℃was under standard limit, while it was over standard at25℃. Storing at low temperature, or being in modified atmosphere packaging, could ensure the quality and safety of cold distributional cooked rice.The main volatile components of cold distributional cooked rice were alcohols, aldehydes, ketones and esters, and the most important components were alcohols and aldehydes. After being cooled and stored, the number of the main volatile components of cooked rice reduced from12to3, the number of the main volatile components of optimized cooked rice reduced from11to7. It showed that the compound quality improver could preserve the most of volatile components of fresh cooked rice.The starch granules in fresh cooked rice was ectatic and blurry, and they adhered to each other to form starch amorphous materials. After storage the starch granules turned into shrunken and symmetrical crystal particles with compact structures. Inside of the optimized fresh cooked rice there was an abundant and intact starch network structure, while after storage the starch network structure became cracked. But the water lost rate and degree of crystallinity of the optimized cooked rice were lower then those of cooked rice in storage. It means the compound quality improver could slow down the starch retrogradation of cold distributional cooked rice.The gelatinization endothermic enthalpy(AHg) of optimized rice starch increased from2.40J/g to3.04J/g, which showed that it needed more energy to form the abundant starch network structure. And the retrogradation endothermic enthalpy(△Hr) of optimized rice starch increased from1.67J/g to1.15J/g, which showed that the compound quality improver could decrease the amount of crystalline amyloses, and restrain the short-term retrogradation. During the storage period of72hours, the rice starch was dominated by short-term retrogradation, and the Avrami equation could effectively fit the recrystallization process of starch retrogradation. According to the value of the Avrami parameter n, the nucleation model of amyloses at4℃was primary nucleation, and the nucleation models of amyloses at4℃and at-18℃were constant nucleation. And according to the value of the rate constant k, the retrogradation rate was the starch at4℃ >the starch at25℃>the starch at-18℃. Avoiding been stored in the retrogradation temperature zone and adding the compound quality improver could decrease the amount of starch crystalline amyloses, and restrain the short-term retrogradation.