Inhibition of enzymatic browning in sweet potato (Ipomoea batatas (L.)) with chemical and natural anti-browning agents

Honey, pineapple, chilli pepper, and onion extracts were investigated for their ability to inhibit enzymatic browning in sweet potatoes. Honey had the highest inhibition (41.39%-48.0%), comparable with l-ascorbic acid. Heated onion extract increased polyphenol oxidase (PPO) inhibition by 2.5-fold when 4-methylcatechol was used as substrate. However, percentage inhibition decreased drastically (7.42%-19.67%) when heated pineapple extract was used. Fresh chilli pepper extract showed a higher PPO inhibition (45.97%) than that of heated extract. These natural inhibitors were also compared to synthetic inhibitors that ranked: l-cysteine > l-ascorbic acid > sodium chloride. l-cysteine was the most effective chemical inhibitor which inhibited up to 70.4% PPO activity. It was found that natural inhibitors extracted from common food items are able to control the enzymatic browning of sweet potato. These natural inhibitors extracts are safe to human and would also be potentially replaced chemical inhibitors for the preservation of other fruits as well as vegetables. Fruits and vegetables are prone to enzymatic browning. This is caused by the oxidation reaction of endogenous phenolic compounds, catalyzed by PPO. PPO oxidizes o-diphenols to o-quinones, which will turn into brown pigments as the o-quinones polymerize immediately. Enzymatic browning of fruits and vegetables always take places after harvest, during the post-harvest processing as well as storage. Thus, identification of suitable and acceptable inhibitors is important in order to prevent food browning and to increase the food marketability for food industry. This study indicated that sweet potato PPO was successfully inhibited by extracts from common food items such as honey, chilli pepper, pineapple, and onion which are safe for human consumption. Thus, these natural inhibitors could also be applied to similar food materials such as apples, star-fruit, and normal potatoes. We expect that the inhibitors examined in this study can be isolated and identified as lead molecules for the development of natural anti-browning food additives. Practical applications