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The effect of cold storage on the phenolic composition and antioxidant capacity of table grapes of cv. Vittoria

Increased consumption of fresh fruits and vegetables has been associated with protection against various diseases including cancers and cardiovascular diseases. Even the exact mechanism has not yet been fully elucidated, physiological benefits of plant food consumption are often associated with the intake of a plethora of biologically-active compounds, especially those with good antioxidant properties. In recent years great attention has been directed to the polyphenolic compounds. In this study, phenolic composition and antioxidant capacity of white table grapes of cv. Vittoria was investigated, including the stability of phenolics and antioxidant properties during cold storage. Table grapes was sampled from vineyard Sokoluša (Middle Dalmatia, Croatia) and stored at 4 ºC. Total phenols in grape skin extracts (GSE) were determined using Folin-Ciocalteu method. The content of individual polyphenolic compounds was analyzed using HPLC-RP-PDA technique. The antioxidant properties of GSEs were determined as ferric reducing/antioxidant potential (FRAP) and 2, 2-diphenyl-1-pycrilhydrazyl free radical scavenging ability (DPPH). GSEs of fresh grapes were rich in phenolics and had good antioxidant capacity determined as FRAP and DPPH. The average concentration of TP in GSE of fresh grapes was 883±19 mg GAE/L. The presence of quercetin, kaempferol, rutin and trans-resveratrol was confirmed in all GSEs. The dominant flavonoid compound was quercetin-4-glucoside. No obvious changes in total phenol content and FRAP were observed during cold storage. The quercetin, rutin and quercetin-4 glucoside levels declined during the first two weeks of cold storage, while those of resveratrol remained constant and did not differ from fresh grapes. The decrease of DPPH radical scavenging efficiency was also noticed. The results indicate that during the cold storage changes occur in the phenolic composition of table grapes cv. Vittoria. The decrease in flavonols could be responsible for the changes observed in DPPH radical scavenging efficiency of GSEs.

table grapes; cold storage; polyphenols; antioxidant capacity

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