Effect Of Combination Pre-treatment On The Quality Of Explosion Puffing Drying Sweet Potato At Variable Temperature And Pressure Difference

Sweet potato is one of the important food crops in China, but it exists a lot of waste every year. Therefore, it’s necessary to study the deep processing sweet potato’s products for reducing the waste of sweet potato’s deterioration and improving it’s added value. In this topic, we explored the effect combination pretreatment on differential puffing drying product quality of sweet potato. So, this study discussed several kinds of combination pretreatment methods on puffing drying quality of sweet potato. Studied sugar permeability and freezing-thawing process. And measured the changes of polyphenol content during combination pretreatment process and the digestive properties of puffed sweet potato. The main results were as follow:With the hardness, color, rehydration, sensory score and its like of puffed sweet potato as index, compared the effects of sugar penetration, freeze-thaw and its combinations pretreatment on the quality of puffed sweet potato. The results showed that the sucrose was better than maltose as penetration solution, the comprehensive score of 95 and 90 respectively. Combination pretreatment could effectively improve the quality of products, make the hardness decreased, rehydration increased. Comprehensive analysis:the "40% sugar boiled(lmin)+freeze-thaw(2 times)+sugar soaked(4h)" was the best combination to achieve the best products.Investigated the changing rules of moisture and quality with time during sugar permeability(sugar blanching and sugar impregnation) process. The results showed that the moisture content was decreasing, and the weight was increasing. The effect of sucrose as osmotic. solution was better than maltose’s, the moisture content was dropped from 72% to 56%. And the quality of puffed sweet potato pre-treated by sucrose solution is better than pre-treated by maltose solution’s.Using LF-NMR and MRI technology, T2 transverse relaxation time as the quota, to explore the mechanism of combination pretreatment on the quality of explosion puffing drying sweet potato’s quality at variable temperature and pressure difference. The results showed:The inner of combination pretreated sweet potato existed three kinds of moisture compounds. It’s T2 relaxation time ranges respectively were T2i(3-7.5ms), T22(20-33ms), T23(75-135ms). Freezing-thawing times could change the inner moisture of samples. The water of T23 relaxation time ranges raised and 722’s declined. Different sugar had different effect on moisture migration. Sweet potato immersed into boiled sucrose solution, the water of T21 relaxation time ranges slightly lessened, and Sweet potato immersed into boiled maltose solution, the water of T21 relaxation time ranges slightly increased. The MRI showed that the internal water of sugar boiled sweet potato spread around with the freeze-thaw times increased, and the moisture diffused along the longitudinal direction was easier than in the lateral direction.Through the simulating intestinal digestion in vitro, to explore the preprocessing of combination pretreated on puffed samples’digestion characteristics. Determination results found that during the enzyme processing, the reducing sugar content increased significantly. Maltose pretreated samples’reducing sugar content increased from 1 Omg/g around to 50mg/g around, sucrose pretreated samples’reducing sugar content increased from 6.5mg/g around to 17mg/g around. Combination pretreatment could improve the samples’digestion. RDS and SDS were increased about 2%-3%. Sugar blanching could decrease the polyphenols content on sweet potato material, it fell to 0.3 from 0.6 after 3min sugar blanched. And polyphenols content decreased by 0.05 or so after freezing-thawing 3 times. Therefore, freezing-thawing and sugar blanching could affect the stability of polyphenols, and sugar blanching effect was more significant.Pretreatment could effectively improve the quality of puffing drying product, but combination pretreated methods, the puffed products would be better. Sugar infiltration and freezing-thawing influenced the external and internal moisture migration of sweet potato, thus affected the quality of puffed products. Combination pretreatment could decrease the final polyphenols content on expanded sweet potato, but improve the digestive characteristics of drying products, so, the products would be more suitable for consumption.