Effects of dehydration temperature on physico-chemical, antioxidant and antimicrobial properties of grape pomace powder

This study investigated the impact of dehydration temperature on physicochemical, antioxidant and antimicrobial properties of grape pomace. To this end, grape pomace from Vitis vinifera, a by-product of the wine industry, was dehydrated at 35, 50, and 65 °C in a conventional hot air dryer and subsequently ground into fine powders. The three powders were characterized in terms of microbial contamination, antimicrobial activity, antioxidant properties, condensed tannin content and total phenolic content. Furthermore, particle size distribution, nano-scale structure, thermal properties, and water content of each powder were also determined. The results demonstrated that increasing the dehydration temperature from 35 to 65 °C led to a reduction in microbial contamination and the powders exhibited more pronounced effects against selected microbial and fungal species. Notably, the antioxidant properties of the powders remained largely unchanged up to 65 °C, although a kinetic effect was observed, associated with a slower release of the active components in the more efficiently dehydrated samples. Physicochemical analysis indicated that dehydration temperatures ≥50 °C induced minor alterations in the powder size, nano-scale organization, and composition, while substantially reducing hygroscopicity.