Optimization Of Processing Air-dried Chestnut And Physicochem Ical Properties And In Vitro Digestibility Of Its Starch

Chestnut is an important woody grain in China and is rich in nutrients such as starch,protein,etc.Chestnut waste too much every year because of its difficulty to be stored.Naturally air-drying is a traditional processing method for chestnut in northern China.The method is simple,however,there are still few studies focused on the quality characteristics and industrial production naturally air-dried chestnut.In this paper,the processing conditions of air-dried chestnut were optimized,and the carbohydrate content and activity of endogenous amylase in the air-dried chestnut,as well as the physicalchemical properties and in vitro digestibility of the starch were studied.The results are as follows:(1)During the air-drying of chestnut,the sweetness increased continuously;the chestnut kernel was shrunk and the color was deepen,and the hardness decreased first and then increased due to the moisture reduction.The optimal conditions were determined to be:50%relative humidity at room temperature for 7 days,70%relative humidity at room temperature for 14 days,14%relative humidity at 40? for 24 h,10%relative humidity at 50? for 8 h,respectively.(2)Compared with fresh chestnut,the air-dried chestnut had a decrease in total starch content,an increase in amylose and total water-soluble sugar content,and a decrease in the content of high molecular weight components.The activity of endogenous amylase of the chestnut increased during the air-drying.The endogenous amylase decomposed the starch into small molecules such as oligosaccharides and dextrin,thereby increasing the sweetness of the chestnut.(3)The starch of air-dried chestnut belongs to C-type crystal,but the relative crystallinity decreased.The transform temperature of starch was measured by differential scanning calorimetry,the absorption rate of 1047/1022 cm-1 in Fourier transform infrared spectrum,and the relative area and full width at half maximum(FWHM)of 480 cm-1 in Raman.These changes also illustrated the reduction of relative crystallinity of chestnut starch after air-drying.The air-dried chestnut starch had an increased swelling power and a reduced solubility.(4)The in vitro digestion and hydrolysis rate,resistant starch(RS),estimated glycemic index(eGI)of fresh and air-dried chestnut starches were not significantly different(P>0.05),but far lower than those of cooked chestnut starch.The starch of air-dried chestnut maintained low digestibility of raw starch.Air-dried chestnut is a medium-glycemic food,which is not easy to cause severe response in postprandial blood glucose,and is good for the diabetics.(5)Based on the comprehensive evaluation of the quality of air-dried chestnut,two optimal conditions for the air-drying process were determined to be 50%relative humidity naturally air-dried at room temperature for 7 days(C-50%-7d)and 14%relative humidity fast air-dried at 40? for 24 h(C-40?-24h).In the C-50%-7d group,the sweetness and chewiness were the highest,and the eGI was low.In the C-40?-24h group,the air-drying time was short,the scores of color and taste were high,and the eGI was also low.The results indicated that the air-dried chestnut not only retains the fresh and delicious taste of the fresh chestnut,but also increases the sweetness.At the same time,the eGI is much less than the cooked chestnut.The air-dried chestnut is a new kind of chestnut product worthy of industrial development.