Research On Oyster Drying Technology And Sdorage Of Dried Oyster

On food drying, we "have always hoped to obtain the dried products of highest quality and longest shelf-life with the lowest cost and in shortest time. Microwave drying, duo to its characteristics of high efficiency of drying, low energy consumption and high-quality product, has become a very promising method of food drying. This thesis, taking fresh oysters as raw material, studied the quality change in the process of hot air dying, microwave drying and hot air-microwave drying in order to find out the best technique suitable for oyster drying, and carried out a deep research on the water sorption isotherm and glass transition temperature, based on which, determined the better storage condition of dried oyster to prolong the shelf life and to test the shelf life in different temperatures.On the research of oyster drying technology, the impact of different temperatures of hot air (50℃,60℃,70℃,80℃,90℃) and different microwave intensities (2,3,4,5,6,8,10w/g) on rehydration rate, shrinkage rate and surface color were studied respectively. The experimental results showed that:the best temperature of hot air drying was70℃; the best microwave intensity of microwave drying was4w/g; in hot air-microwave drying, microwave after hot air drying model was significantly better than hot air after microwave drying model. Through the comparison of these methods, it was found finally that microwave drying with the intensity of4w/g was the best.This thesis studied the water sorption isotherm of dried oyster at25℃. The results showed that BET and GAB equation were better to simulate the water sorption of dried oyster. Differential scanning calorimeter was used to test the glass transition temperature of dried oyster thus to obtain the relationship between the moisture content of dried oyster and its glass transition temperature, and Gordon-Taylor model was used to simulate the relation. When the water activity was less than0.6, the microorganisms were difficult to grow and chemical reactions which made the food go bad were inhibited. Using GAB model equation to calculate, the moisture content (dry water) of dried oysters with microwave drying was19.4%, which could be as the basis for controlling the final content (dry water) of products with microwave drying, aiming to prolong the shelf life.Finally, the thesis studied the changes of aerobic bacterial count, pH value and volatile basic nitrogen (TVB-N) of microwave dried oyster products under different temperature (25,35,45and55℃) and temperature fluctuations (25℃/45℃). Taking volatile basic nitrogen (TVB-N) as the key indicator, the first order kinetic model was used to predict shelf-life.