engleski

Polyphenolic profile and biological properties of Vitis vinifera leaf extracts

Introduction: Having knowledge of the chemical composition and the properties of plant extracts, regardless of whether it is dealt with only one plant or its part (root, leaf, …), or with complex herbal mixtures, is the basic prerequisite of their further usage in food, pharmaceutical or some other industry. Nowadays a special attention is given to the biological activity of extracts/fractions, especially their antioxidant and antimicrobial properties. There is an intense research activity of their exploitation in: a) process of producing functional food, b) food processing as a replacement of synthetic food additives. For the industrial purposes, apart from effectiveness, accessibility and the price of herbal material are very important. Although vines, Vitis vinifera L., are usually reared with the scope of grape production, preparations of single parts of vines are known to have been used in folk medicine, and the old culinary writings have witnessed the use of fresh vine leaves in food preparation. The aim of this study was to get insight in the phenolic composition and antioxidant potential of leaf extracts of 21 grape varieties with the aim of evaluating the possibilities of their further exploitation in food and pharmaceutical industry. Materials and methods: The plant material, vine leaves of Vitis vinifera L. varieties reared in the Dalmatian area, were collected after the grape harvest. The polyphenolic constituents from grape leaves were extracted using conventional solvent extraction procedure. The phenolic content of leaf extracts was determined using spectrophotometric and chromatographic (HPLC-RP-PAD) methods. The antioxidant potential of all tested extracts was evaluated, in vitro, by the use of four different antioxidant methods (FRAP, DPPH, Briggs-Rauscher, Fe (II) ion chelating ability). Results: The results of this research indicate a rich and very interesting phenolic potential in terms of chemical composition of vine leaves. As expected, the influence of vine variety was confirmed. Despite the relatively mild conditions of extraction, vine leaf extracts of all varieties were rich in phenolic compounds. With a range of different antioxidant methods, used to analyze antioxidant profile of extracts, it was confirmed that all leaf extracts have very promising antioxidant properties determined as: ferric reducing/antioxidant power (FRAP), free radical (DPPH) scavenging ability and metal chelating activity. The capacity of interference with the making/acting of lipid hydroperoxides, determined by the Briggs-Rauscher method is of special interest, since these reactive compounds, apart from food, appear also in biological systems. The results of the HLPC analysis confirmed the presence of some of most popular polyphenolic compounds, e.g. flavonol rutin, well known for its antioxidant effect, and non the less famous resveratrol, phytoalexin of the stilbene family. Conclusions: Vine leaf extracts are very rich in phenolic compounds with extremely good antioxidant properties. This plant material which remains unused after the grape harvest can be a rich, cheap and an easily accessible source of biologically active compounds. Acknowledgments: The authors would like to thank the Ministry of Science, Education and Sports of Republic of Croatia for financing their national project 011-2160547-2226.

phenolics; vine leaf; antioxidant properties

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