Bioactive compounds and antiradical activity in grape pomace flours from different cultivars dehydrated in a freeze dryer and in an oven

Abstract This study aimed to characterize the bioactive compounds and antiradical activity in grape pomace flours from the cultivars Cabernet Sauvignon, Merlot, Sauvignon Blanc and Sangiovese (Vitis vinifera), dehydrated either in an air circulation oven at 45 °C or a vacuum freeze dryer. The total and individual phenolic compounds, monomeric anthocyanins and antiradical activity were analysed by the ABTS and HOCl methods. The total loss of monomeric anthocyanins was higher for the cultivars Cabernet Sauvignon and Sangiovese dehydrated in the air circulation oven. All the freeze dried cultivars preserved a statistically higher index for the total phenolic compounds, the highest being the cultivar Sauvignon Blanc. In the individual analysis of these compounds the freeze dried samples showed higher average levels of all the flavonoids (epicatechin, catechin, quercetin, vanillic acid, rutin), whereas gallic, caffeic and ferulic acids were apparently not influenced by the drying method. All the samples dehydrated in the oven showed less free radical inhibition capacity than the freeze dried samples as determined by both IC50 methods. The ABTS method presented the best results for the freeze dried samples, that is, smaller amounts of the flours were able to inhibit at least 50% of the ABTS and HOCl free radical activities, with emphasis on the Merlot cultivar.