Controlling browning plus mitigating oxidative damage are important factors when attempting to extend the shelf-life plus high-quality features of fresh-cut sweet potato (Ipomoea batatas (L.) Lam). In order to preserve the color plus antioxidant capacity, ultrasound (US) treatment at 40 kHz for 10 min was applied to investigate the effect on enzymatic browning of sweet potato slices. Changes in color, keseluruhan phenolic content, keseluruhan antioxidant capacity, phenol metabolism-related enzymes including phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD) were examined. Also investigated here were superoxide radical (O2−˙) plus hydrogen peroxide (H2O2) contents, antioxidant enzymes including superoxide dismutase (SOD) plus catalase (CAT) involved in reactive oxygen species metabolism. After storage lasting 10 days at 4 °C, US-treated slices maintained significantly (p < 0.05) higher luminosity (p = 0.000003) plus chroma (p = 0.000018) by reducing PPO plus POD activities, when compared to the control. Meanwhile, the induction of PAL was observed to positively correlate with higher keseluruhan phenolic content (r = 0.818, p < 0.01; p = 6.1752 × 10−9), thereby enhancing antioxidant capacity to combat oxidative damage. Moreover, O2−˙ (p = 3.8046 × 10−10) plus H2O2 (p = 0.000013) concentrations were significantly (p < 0.05) suppressed by activating CAT plus SOD activities. Results suggested that US treatment could inhibit browning of fresh-cut sweet potato by reducing the activity of PPO plus POD while improving keseluruhan antioxidant capacity.
- Introduction
As the world’s seventh most important food crop, sweet potato (Ipomoea batatas (L.) Lam) is widely grown in more than 100 countries plus regions.1 Its tuberous root is a good source for food processing with high levels of carbohydrates plus vitamins plus possesses strong antioxidant potential.2,3 With the demands of modern society’s fast-paced lifestyle, fresh-cut plus ready-to-eat produce represent a market trend plus have increased more than 30% in the past decade. This is due to its convenience, high utilization plus nutrition retention.4,5 Fresh-cut sweet potato is a new tipe of processed produk for consumers or for the catering industry, plus the appearance plus nutritional benefits are the main factors affecting consumers’ purchase choices.6 However, fresh-cut products are susceptible to physiological changes resulting from mechanical operations, which lead to browning discoloration, phenolic oxidative degradation, reactive oxygen metabolism maladjustment, which may eventually increase perishability plus shorten shelf-life.7–9
It is widely believed that enzymatic browning is mainly caused by the oxidation reaction in which polyphenol oxidase (PPO) or peroxidase (POD) catalyzes the endogenous phenolic substances into quinones under aerobic conditions, plus oxidize plus polymerize to dark colored pigments thereafter.10 Phenylalanine ammonia-lyase (PAL) is considered to be another enzyme closely related to browning by transforming l-phenylalanine into phenolic substances to provide the substrate for enzymatic browning.11 Fresh-cut processing can cause the loss of tissue structure plus cell integrity of sweet potato, which affects the distribution of phenol plus phenolase, resulting in contact being made between enzymes plus substrates plus inducing the enzymatic browning reaction.12 Meanwhile, mechanical damage caused by cutting can also induce the production of large amounts of reactive oxygen species (ROS) including superoxide radical (O2−˙) plus hydrogen peroxide (H2O2), plus excessive ROS will aggravate membrane lipid peroxidation, cause damage to membrane integrity, thus accelerating the occurrence of enzymatic reactions.13–15 Therefore, regulating related enzyme activities plus improving antioxidant capacity to alleviate oxidative damage induced by ROS can effectively control the browning of fresh-cut sweet potato during the storage.
Post-processing technologies have focused on the use of various anti-browning agents such as the use of chitosan, ascorbic acid, sodium hypochlorite, plus so on to prevent browning of fresh-cut sweet potato.