Changes in the phenolic profile of Argentinean fresh grapes during production of sun-dried raisins

Abstract

Changes in the phenolic profile of ‘Arizul’, ‘Sultanina’, ‘Superior’, and ‘Flame’ grapes from the Province of San Juan (Argentina) caused by sun drying were evaluated. Our main goal was to propose that the obtained raisins are a good source of bioactive antioxidants. The ‘Flame’ red variety had the highest amount of total phenols when compared to white raisins (TSP = 201 ± 13 and 154 ± 28 mg gallic acid equivalent/100 g DW raisins, respectively). The sun drying of fresh grapes produced an increased amount of phenolic acids and flavonoids (rutin, kaempferol-hexoside, quercetin and isoquercitrin). Multiple regression analysis (MRA), principal components (PC) and factor analysis (FA) showed a high correlation between the phenolic profile and the antioxidant activity (AA) of raisins (r ≥ 0.90, p < 0.05). The ‘Flame’ variety showed the highest AA, which was linked to the amount of gallic acid, astilbin, quercetin-3-O-glucuronide, isorhamnetin, and isorhamnetin-hexoside present in this variety. On the other hand, the AA in the ‘Arizul’ variety was better correlated with the content of (+)-catechin, caftaric and fertaric acids, whereas the ‘Sultanina’ variety was correlated with resveratrol. Multi-elemental analyses showed that raisins are rich in K (639–883 mg/100 g), Ca (51–121 mg/100 g) and Mg (28–42 mg/100 g). These findings support the potential health properties of raisins as health-promoting food.