Abstract
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 freshâcut lettuce during storage. The results indicated a competitive inhibition of lettuce PPO in the presence of GSE. Browning of freshâcut 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 highâperformance liquid chromatography. Protecatechuic acid, chlorogenic acid, ferulic acid, coumaric acid and phloridzin were identified in lettuce. Degradation of phenolic compounds followed firstâorder 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: Freshâcut 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 nonâtoxic 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 freshâcut 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 nonâtoxicity, but further feasibility studies are needed to increase its effect as an antiâbrowning agent in its application in the food industry.
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