Research On Anti-browning Technology Of Seedless Green Raisins During Cleaning And Drying

The seedless green raisin is a dry fruit product with competitive advantage in Xinjiang,accounting for more than 70% of the raisins in Xinjiang.Aiming at the problem that the seedless green raisin is prone to browning after cleaning,this paper takes Turpan seedless green raisin as the raw material,understands the substrate that causes enzymatic browning during cleaning,and explores the anti browning technology of ultrasonic cleaning of Seedless green raisin assisted by edible alcohol solution to clarify the anti browning technology of heat pump drying after cleaning the seedless green raisins,so as to provide theoretical basis and reference for enterprises to process the green raisins.1.For the seedless green raisins before and after cleaning,the content of 13 phenols was determined by UPLC-Vion-IMS-QTof,and the ability of these phenols as enzymatic browning substrate was identified by using polyphenol oxidase of Seedless green raisins.The results showed that 11 phenols decreased after cleaning and caffeic acid,p-coumaric acid,quercetin,catechin,kaempferol and chlorogenic acid six phenols reacted with polyphenol oxidase of raisin by enzyme.The activity of these phenols was as follows: caffeic acid > p-coumaric acid > quercetin > catechin > kaempferol > chlorogenic acid.The content of phenols in raisin changed before and after cleaning,and they combined with polyphenol oxidase of green raisin,the order of combining ability was caffeic acid > p-coumaric acid > quercetin > catechin > kaempferol > chlorogenic acid.The correlation analysis of browning degree and enzymatic browning during cleaning showed that caffeic acid,p-coumaric acid,quercetin,catechin and kaempferol had significant effect on the browning of Seedless green raisins.2.Using the characteristics of edible alcohol which can accelerate the subsequent drying process and is safe,the ultrasonic assisted technology was used to clean the seedless green raisins.The best cleaning conditions were determined as follows: the precision of cleaning agent liquor was 44°,the cleaning temperature was 9℃,and the cleaning time was 90 s.Under this condition,the browning index BI value of Seedless green raisins is only 33.43,which is 26.98% lower than that of traditional water spray cleaning.It shows that ultrasonic assisted cleaning method is suitable for the cleaning of Seedless green raisins and can effectively prevent the occurrence of enzymatic browning.3.The heat pump drying technology was used to dry the seedless green raisins after cleaning.The best drying conditions were determined as follows: drying temperature 46℃,relative humidity 7%,moisture removal time 3min.At this time,the browning index BI value of Seedless green raisins was only 25.00,24.56% lower than that of traditional hot air drying,and only 2.38% higher than that of non cleaned seedless green raisins.This method significantly reduced the browning index BI value of Seedless green raisins in the drying process,and was suitable for the artificial drying of Seedless green raisins after cleaning.