THE EFFECT OF pH ON THE EFFICIENCY OF VINIFICATION BY‐PRODUCT EXTRACTS TO INHIBIT LIPID PEROXIDATION IN A LECITHIN LIPOSOME MODEL MATRIX

Abstract

ABSTRACTA series of extracts from vinification by‐products, generated under specified, optimal conditions, were tested for their efficiency to inhibit lipid peroxidation in lecithin liposomes at various pH values. Lipid peroxidation was assessed by measuring the kinetics of CDV onset, which over a period of 6 days was found to obey zero‐order kinetics. As positive control samples the synthetic antioxidant, butylated hydroxytoluene and the natural quercetin were also considered. The results obtained showed that the most distinct inhibition as compared with control sample (no antioxidant added) was found upon addition of grape stem extract from the variety Vitis vinifera var. Moschofilero at pH 8, with the kinetics constant (k) being 6.6 × 10−2 CDV/d. By contrast, seed extract from the same variety at pH 2 was prominently prooxidant, with k = 50.7 × 10−2 CDV/d. Extracts from both stems and seeds exhibited large variations as a function of pH, with stem extracts being in general more efficient than seed extracts, but no consistent trend in response to pH was observed. This outcome clearly pointed to efficiency dependence upon both the composition of the extracts and pH.PRACTICAL APPLICATIONSBecause the use of antioxidants in food industry is indispensable, the study of the efficiency of certain widely used plant extracts possessing antioxidant properties becomes imminent. This is because the deployment of natural antioxidants in food matrices has often been accompanied by major discrepancies concerning their efficiency to shield against rancidity. Thus, revealing details on the antioxidant behavior of natural extracts with regard to significant food characteristics, such as pH, is of undisputed importance in utilizing these extracts in a technologically rational way. The results from this study showed that extracts from vinification by‐products, and presumably other extracts from various plant sources, might have variable behavior with regard to inhibiting and/or promoting lipid peroxidation. As this might depend on the pH of the matrix used or other intrinsic factors, the antioxidant potency of a particular extract can be reliably assessed only by case experimentation.