Raisin as a Functional Food: Antioxidant and Antiglycation Activity Assessed by Model Systems

Raisin can be used a substitution of artificially sweetened snacks/ingredients, in order to counteract the increasing consumption of sugar-added foods, which is associated to adverse health effects. The aim of this study was to investigate the phenolic content, reducing capacity and antiglycation activities of traditional, sun-dried raisin samples obtained from six Tunisian varieties. Total phenolics were determined by the Folin Ciocalteu assay, proanthocyanidins by depolymerisation with n-butanol/HCl, monomeric and dimeric flavanols, flavonols and anthocyanins by HPLC with diode array and fluorimetric detectors. The reducing capacity was assessed by ferric ion reducing antioxidant power assay (FRAP) and anti-glycation activity by the bovine serum albumin/fructose (BSA/FRU) and BSA/methyglyoxal (BSA/MGO) model systems. Results showed a remarkable biodiversity in phenolic contents and profile among raisin samples. The reducing capacity ranged between 43.8 and 97.8 mmol Fe(II) eq/kg d.w. Raisin samples inhibited protein glycation in the in vitro model systems, which simulate the early and intermediate steps of the formation of advanced-glycation end-products occurring in vivo and leading to cell damage. The anti-glycation effectiveness in the BSA/FRU and BSA/MGO model systems was in the range 48–176 and 9.6–20.5 mmol catechin eq./kg d.w., respectively and was generally comparable or, for some raisin varieties higher than that of well-known antiglycation agents. These results support the promising role of raisin as a functional food/ingredient targeting the inhibition of glycoxidative damage.