Impacts of Different Drying Methods on Mold Viability and Ochratoxin A Content of Grape Pomace

Value added utilization of grape pomace (GP) has been the interest of many food researchers due to its high contents in fiber and polyphenols. However, the contamination of GP by molds and ochratoxin A (OTA) present a serious safety issue to food or feed use of GP. To ensure the safety of direct usage of GP as food ingredient, this study investigated the effects of drying method on mold viability and ochratoxin A (OTA) content of GP. Pomaces of seven grape cultivars were dehydrated by freeze, room temperature and vacuum drying methods. The total population of yeast and mold colonies was enumerated using Dichloran Rose Bengal Chloramphenicol Agar (DRBC) and Dichloran Glycerol 18% (DG18) media. The OTA was extracted by 70% methanol aqueous solution, and then quantified by an ELISA method. Regardless the grape cultivars, vacuum drying most effectively reduced the viability of mold in GP samples, while freeze-drying was the least effective method. OTA was present in all pomace samples tested but the contents of OTA in GP varied with grape variety. Vacuum drying and freeze drying significantly reduced the OTA contents of most of the pomace samples tested whereas room temperature drying increased OTA contents of all GP samples tested compared with OTA contents measured before drying. Overall, vacuum dry and freeze dry methods resulted in safer GP for food and feed use due to the greater reduction of viable molds and OTA content