Microbial Bacteria Groups And Quality Variation Characteristics Of Vacuum-packaged Rice Cake In Storage

Rice cake is a traditional southern China seasonal food. Due to its high water content, and richnutrition, it easily leads to microbial growth and reproduction, and its properties usually changes indifferent level in the process of storage, transportation and sales in the late. The vast majority of microbescould easily be killed in the heat treatment in the producing process of rice cake, but spores of thesebacteria are hard to be killed. Besides, because of the limitation of production technology, the secondarypollution is easily caused in the later cooling, bagging process of producing rice cake. Simultaneously, hightemperature sterilization was not suitable for finished product of rice cake, so pasteurization was mostlyused, but the number and type of microorganisms were difficult to control.The number and type of microorganisms were determined and identified in vacuum-packaged ricecake, and the sensory indicators, physical and chemical indicators, microbial indicators were studied duringlater storage, and the characteristics of variation was explored. Theoretical guidance will be provided aboutcontrolling microorganism, improving quality in the production of vacuum-packaged rice cake inenterprise.Its conclusions are as follows:1. Through the analysis and identification of microbial flora, the bacteria, molds, yeasts and others wasfound in vacuum-packaged rice cake products, and11kinds of strains were detected which was calciumacetate acinetobacter, brevibacterium acetylium, bacillus subtilis, bacillus cereus, bacillus megaterium,bacillus brevis, rhizopus oryzae, aspergillus nidulans, aspergillus oryzae, candida albicans andtrichosporon pullulans respectively. Microorganisms on the surface of the rice cake were more than inside,and inside bacteria were all bacillus subtilis. The corruption of rice cake was always caused by microbialpollution in the environment in the later drying process. With the extension of storage time, the growingtend was shown by total number of colonies of microorganisms in vacuum-packaged rice cake underdifferent storage conditions, and the growing tend was larger while the storage temperature was higher. Theinfluence storage temperature making on the total number of colonies of microorganisms invacuum-packaged rice cake were significant. Therefore, outside microbial pollution control in rice cakesproduction process was a key factor to improve rice cakes shelf life.2. Surface brightness of rice cake decreased, color darkened, and the higher the storage temperature,the greater decline in brightness. With fresh samples for reference,△E*as the dependent variable, storagetemperature (T) as independent variable, the optimized linear regression equation was:△E*=6.760-0.230T（P=0.003，R2=0.472）, which showed the equation was statistically significant very much.Flavor components of rice cake were from the decomposition and oxidation of macromolecules, or somemicrobial activities. With the storage time increasing, alcohols and esters had larger magnitude of reducingwhich was related to its volatile, especially under high temperature the performance was more obvious,downward trend of the percentage content of other volatile components increased with increasing temperature.3. Fresh vacuum-packaged rice cake had moisture content as high as44.5%, pH value of6.78,hardness substantially318g, under different storage conditions and after the specified time stored, pH value,moisture content and hardness of vacuum-packaged rice cake had falling, falling and rising trendrespectively, and the trend was larger while the storage temperature was higher. With hardness (H) as thedependent variable, storage temperature (T) and time(D) as the independent variables, a linear regressionmodel was established: H=3303.86+96.23d-123.68T（P=0.001，R2=0.777）. In the model, T and D revealeda significant correlation with H（P=0.001）.The decaying process of vacuum-packaged rice cake was more complex. Microbial growth traits andstarch aging might be the main effecting factors of the shelf life of rice cake. the quality characteristic ofrice cake storage at different temperatures in different time were studied, its studies have shown that thestorage quality under10℃for30d changed little, the optimal storage temperature was4℃or so.