Enzymatic browning and its control in fresh-cut produce

Purpose of review: Enzymatic browning of fruits and vegetables during postharvest handling and processing degrades the sensory properties and nutritional value and discourages consumer purchase of fresh-cut products. Consequently, enzymatic browning results in significant economic losses for the fresh produce industry. This paper discusses the biochemistry of enzymatic browning, and focuses on technologies that can be used to prevent browning of fresh-cut fruits and vegetables and maintain good product quality and safety for consumers. Main findings: Enzymatic browning results from oxidation of phenolic compounds catalysed by polyphenol oxidase (PPO) followed by non-enzymatic formation of pigments. PPOs exhibit either mono- or di-phenol oxidase activity, or both types of activities. Peroxidase (POD) and phenylalanine ammonia lyase (PAL) are also found to be closely associated with the browning of fresh-cut fruits and vegetables. A range of physical and chemical treatments that have the potential to be adopted by fresh-cut industry for browning inhibition were reviewed. The effective treatments can be divided into three methods: 1) dipping in anti-browning solutions; 2) modified atmosphere packaging; and 3) heat shock and refrigerated storage. The importance of balancing browning inhibition and pathogen inactivation in fresh-cut produce was particularly emphasised. Directions for future research: Understanding the details of enzymatic browning, which occurs during the processing of fresh-cut products, is necessary for improving browning control. The activities of PPO, POD and PAL, as well as their interactions during browning reactions in fresh-cut produce need more investigation. The relationship between enzymatic browning and the content of total phenolic compounds (or specific phenolic composition) also requires further research. In addition, the development of dual controls to prevent both browning and pathogen contamination in fresh-cut produce is critical to maintaining the quality and safety of fresh-cut produce.