Effect Of Different Drying Methods On Polyphenols And Antioxidant Activity Of Wine Grape Pomace

Wine grape pomace is the major by-product from wine processing.With abundant polyphenols and high antioxidant activity,wine grape pomace has a wide range of applications in the industry of food,chemicals,health care,cosmetics et al.Winemaking is a seasonal activity,which leads to the production of large quantities of grape pomace during a short period.Wine grape pomace is rich in moisture and microbes,which are easy to decay.Accumulation of wine grape pomace is a serious environmental problem and a resource wasting phenomenon.Therefore,the aim of this study was to investigate economically feasible pomace drying methods,and to provide high quality materials for the futher study,and to make good use of pomace.The influence of hot air drying temperature on the extraction of polyphenols and antioxidant activity was investigated in order to find the optimum temperature.Fresh wine grape pomace was respectively squeezed by air bag press,screw press and oil press,which was used to shorten drying time and find an appropriate squeezing method.To explore the best crushed particle size,the dry pomace was processed by superfine grinding and then screened into different meshes.After that,grape pomace were subjected to six different drying methods: hot air drying,sun drying,freeze drying,air drying,infrared drying,microwave drying.Drying qualities,including extraction of polyphenols,antioxidant activity were analysed.After the above study,the best drying method was found.The main results are as follows:1.The influences of different drying temperature on the content of phenolic compounds and antioxidant activity of grape pomace were different.40? drying pomace has the highest content of total phenolic compounds(34.49 mg/g).But the highest content of proanthocyanidins(22.29 mg/g)existed in 30? drying pomace.The DPPH,ABTS,HRSA,MA and FRAP of 40? drying were significantly higher than other drying temperature.Therefore,the best hot air drying temperature of wine grape pomace was 40?.2.Squeezing could quickly reduce the moisture content,shorten the drying time and enhance the extraction yield of soluble dietary fiber.Screw press has the highest extraction yield of soluble dietary(6.35%).Since the phenolic compounds and antioxidant activity of the pomace processed by squeezing were lost seriously,squeezing was not suitable for pre-treatment.3.When the particle size was 80-160 mesh,wine grape pomace achieved the highest extraction yield of phenolic compounds and the highest antioxidant activity.The best particle size was different in different materials,respectively 120 mesh of grape skins,80 mesh of seeds and 160 mesh of pomace.4.Freeze drying led to the highest phenolic compounds content and antioxidant activity,which was superior to infrared drying and hot air drying.Sun drying and air drying required longer time,and their drying qualities were not good.Microwave drying took the shortest drying time and led to the lowest content of polyphenols and antioxidant activity,but it could significantly improve the extraction yield of soluble dietary.Although freeze drying had good drying quality,it required longer time and high cost.Therefore,infrared drying was chose as the suitable drying method.5.Microwave drying had the best sterilizing effects of bacteria,yeast and mold,followed by infrared drying.Freeze drying had a better sterilizing effect only on yeast,while the sterilizing quality of natural drying was poor.6.The correlation between antioxidant activity and different phenolic compounds was diverse.Except for total hydroxycinnamic acids,the other phenolic compounds had significant correlation to antioxidant activity.There were also high correlations among the other antioxidant methods except for metal-chelating ability.