The Research On Explosion Puffing Drying For Sweetpotato At Variable Temperature And Pressure Difference

In this dissertation, sweetpotato, chosen as the raw material, were puffed in the explosion puffing equipment (QDPH10-1) to optimize the puffing process and analyse the affecting factors. The changes of physico-chemical properties and flavor compounds were also discussed. The effect of five drying methods on the physic-chemical properties and flavor compounds of the products were compared, aiming to provide theoretical basis and guidance for the industrial production.Through the comparative investigation on the changes of physic-chemical properties and flavor compounds of sweetpotato products dried by explosion puffing and other four different drying methods, the conclusions can be summarized as follows:1. The appropriate parameter ranges were determined by the single factor experiments: puffing temperature was 110°C, vacuum temperature was 100°C, vacuum time was 2 h, the pressure difference was 0.3 MPa, and the dwell time was 10 min. A central composite rotatable design (CCRD) was adopted to optimize the technology of explosion puffing drying for sweetpotatoes and the effect of puffing temperature, vacuum drying temperature and vacuum drying time on the water content, color and hardness were analyzed. The explosion puffing process parameters were optimized by response surface method and frequency analysis as the optimal puffing temperature of 108°C -113°C, vacuum temperature of 96°C-102°C, vacuum time of 2-2.5 h.2. Through the comparative analysis on the changes of physic-chemical properties and flavor before and after sweetpotato puffing drying, the results indicated that explosion puffing drying treatments induced a reduction in the contents of , crude starch, protein, ascorbic acid,β-carotene and potassium element, and an increase in the contents of reducing sugars , calcium and phosphorus elements. The scanning electron microscope scanning result showed that explosion puffing process formed the inside expanded porous structure, similar to the sponge structure, and important for crispness. Compared to untreated samples, volatile aroma compounds of explosion puffed sweetpotato chips were significantly changed and special volatile aroma appeared.3. Comparative investigation were conducted on the physico-chemical properties (nutrional components, color, hardness and rehydration ratio) and flavor compounds of sweetpotato chips dried by five different methods (hot air drying, microwave drying, explosion puffing drying at variable temperature and pressure difference, vacuum freeze drying and vacuum drying). The results indicated that, vacuum freeze drying treatment induced the lowest loss of nutritional components, less hardness and dramatically changed color; the hot air drying led to poor physical characteristic and nutritional components and harder texture; the vacuum drying caused the similar results as that of hot air drying; the explosion puffing drying method resulted in better color, hardness, lest nutrional component loss and particular inside porous structure.Different drying methods had great effect on the volatile compounds of sweetpotato chips.