EFFECT OF GRAPE SEED EXTRACT ON PHENOLIC PROFILE AND BROWNING OF FRESH-CUT LETTUCE (L. SATIVA)

This study aimed to investigate the effects of grape seed extract (GSE) on the inhibition of lettuce polyphenol oxidase (PPO) and on the loss of phenolic compounds in fresh-cut lettuce during storage. The results indicated a competitive inhibition of lettuce PPO in the presence of GSE. Browning of fresh-cut lettuce was also monitored during storage. Addition of GSE prevented the loss of lightness in lettuce. Loss of phenolic compounds was measured during the enzymatic browning process by high-performance liquid chromatography. Protecatechuic acid, chlorogenic acid, ferulic acid, coumaric acid and phloridzin were identified in lettuce. Degradation of phenolic compounds followed first-order kinetic pattern during storage. Synergistic effects of GSE in combination with ascorbic acid (AA) or citric acid (CA) were also tested for the protection of phenolics. Combination of GSE and AA exhibited a synergistic preservative effect for the protection of lettuce phenolic compounds against PPO catalyzed oxidation. PRACTICAL APPLICATION Fresh-cut produce, especially lettuce, deteriorates faster than intact produce because of internal and external browning of the cut surface. Addition of chemicals, pH adjustment, refrigeration, thermal treatments and exclusion of oxygen are among the most effective methods for the inhibition of browning. Several authors have stated the necessity to evaluate the inhibitory effect of natural and non-toxic compounds on PPO activity and its potential applicability to the food industry. The result of present study revealed that GSE had an inhibitory effect on PPO and effectively prevented enzymatic browning in fresh-cut lettuce. Our results suggest that GSE could potentially be used as a natural inhibitor of PPO, and its utilization is possible due to its wide occurrence, low cost and non-toxicity, but further feasibility studies are needed to increase its effect as an anti-browning agent in its application in the food industry.