| Summary: | There has been considerable interest in using natural polyphenol oxidase (PPO) inhibitors to control browning in fruit and vegetable products. <i>p</i>-Coumaric acid (<i>p</i>CA), a common secondary metabolite of plants, has been studied as an inhibitor of PPOs/tyrosinases from several foods (e.g., mushroom, apple, and potato). However, studies on the use of <i>p</i>CA for the inhibition of PPO-initiated browning in actual food systems are limited. Therefore, a study was carried out to ascertain the efficacy of using <i>p</i>CA to limit PPO-initiated browning in fresh potato juice. The extent of browning inhibition by <i>p</i>CA was shown to be reaction system-dependent. Browning in potato juice was unexpectedly enhanced by the addition of <i>p</i>CA. This was interpreted as <i>p</i>CA acting as an alternative substrate with significantly higher browning efficiency; extent of browning under this condition was higher than that observed in the native potato juice. The addition of <i>p</i>CA to any of the model reaction mixtures (i.e., those containing semi-purified enzymes and substrates) significantly inhibited browning. The discrepancy in <i>p</i>CA effects on browning inhibition in different reaction systems is postulated to be mainly due to non-enzyme and non-substrate components in potato juice that participate in the post-PPO reaction sequences, which ultimately lead to brown color formation.
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