Cysteine Protease Inhibitors Reduce Enzymatic Browning of Potato by Lowering the Accumulation of Free Amino Acids

A combined approach of lauroyl arginine ethyl ester hydrochloride and kojic acid in mitigating fresh-cut potato deterioration

The combinational effects of kojic acid and lauroyl arginine ethyl ester hydrochloride (ELAH) on fresh-cut potatoes were investigated. Kojic acid of 0.6% (w/w) effectively inhibited the browning of fresh-cut potatoes and displayed antimicrobial capacity. The color difference value of samples was decreased from 175 to 26 by kojic acid. In contrast, ELAH could not effectively bind with the active sites of tyrosinase and catechol oxidase at molecular level. Although 0.5% (w/w) of ELAH prominently inhibited the microbial growth, it promoted the browning of samples. However, combining kojic acid and ELAH effectively inhibited the browning of samples and microbial growth during the storage and the color difference value of samples was decreased to 52. This amount of kojic acid inhibited enzyme activities toward phenolic compounds. The results indicated that combination of kojic acid and ELAH could provide a potential strategy to extend the shelf life of fresh-cut products.

Enzymatic browning and polyphenol oxidase control strategies

Significant amounts of fresh and fresh-cut fruits and vegetables are wasted every year due to enzymatic browning. Polyphenol oxidase (PPO) is the key enzyme involved in the enzymatic browning. In the past decades, various methods have been developed to inhibit browning of various fresh produce items. However, for most fresh horticultural produce, ideal measures accepted by industries and consumers are still scarce. This review provides up-to-date knowledge of browning control technologies, including physical methods, chemical methods such as natural inhibitors, molecular biotechnology, and nanotechnology. In addition, we propose some ideas to improve the efficacies of these strategies with fewer side effects. To better inhibit tissue browning, new research directions are also discussed, for example, regulation of PPO substrate techniques.

The stability of cell structure and antioxidant enzymes are essential for fresh-cut potato browning

In this study, the browning degrees of fresh-cut potatoes of different cultivars were investigated. Fresh-cut potatoes of the 'Huangjin' cultivar exhibited a higher browning index and sensory quality deterioration over time compared with 'Minshu' potatoes. 'Huangjin' exhibited a higher activity of browning-related enzymes such as polyphenol oxidase, tyrosinase, peroxidase, phenylalanine ammonia-lyase, phospholipase D (PLD), and lipoxygenase (LOX) than 'Minshu'. Furthermore, 'Minshu' exhibited lower H₂O₂ and malonaldehyde (MDA) contents, lower membrane lipid degradation and peroxidation, and delayed browning, attributable to its low PLD and LOX activities. The ultrastructure of 'Minshu' cells remained intact 7 h after cutting, while that of 'Huangjin' cells was severely damaged, and 'Minshu' cells exhibited more Golgi complexes and black particles than 'Huangjin' cells. Moreover, 'Huangjin' cells exhibited numerous multivesicular bodies, which were nonexistent in 'Minshu' cells. The results show that 'Minshu' potatoes feature a lower browning-related enzyme activity than 'Huangjin', and a tough cell structure to resist post-cut browning.

Multifunctional nanocomposite based on polyvinyl alcohol, cellulose nanocrystals, titanium dioxide, and apple peel extract for food packaging

Although polyvinyl alcohol (PVA) is a potential biodegradable food packaging material, it has several critical limitations: low mechanical strength, poor ultraviolet (UV) and water vapor barrier properties, and lack of antioxidant and antimicrobial properties. Previous studies have used cellulose nanocrystals (CNCs) to improve the mechanical and water vapor barrier properties of the PVA matrix. In this study, a multifunctional nanocomposite for food packaging applications was developed by incorporating titanium dioxide (TiO₂) and apple peel extract (APE) into a PVA/CNC matrix. The combination of TiO₂ and APE in the nanocomposites not only enhanced multifunctionality but also improved mechanical and barrier properties. The mechanical strength and water vapor barrier properties of PVA/CNC/TiO₂/APE (5 wt% TiO₂ and 20 wt% APE in the PVA/CNC matrix containing 5 wt% of CNCs) increased by 49.9 % and 36.6 % compared to PVA. Furthermore, PVA/CNC/TiO₂/APE exhibited an excellent UV barrier (UV-protection factor of 1012.73) and high antioxidant and antimicrobial properties. In food packaging tests with fresh cherry tomatoes and potatoes, PVA/CNC/TiO₂/APE effectively protected samples from external influences and prolonged their self-life, demonstrating the potential use of this nanocomposite as a biodegradable and multifunctional food packaging material.

Browning inhibition of seabuckthorn leaf extract on fresh-cut potato sticks during cold storage

Seabuckthorn extract is rich in bioactive compounds and well known for its health benefits. The study investigated the effect of seabuckthorn leaf extract on browning of fresh-cut potatoes. The results showed that seabuckthorn leaf extract significantly inhibited the browning of fresh-cut potatoes compared with seabuckthorn fruit extract. Catechin, hypericin, gallic acid, casuarinin and isorhamnetin were main components in seabuckthorn leaf extract. Further research revealed that seabuckthorn leaf extract competitively inhibited polyphenol oxidase (PPO) with IC₅₀ value of 0.7 mg/mL. Molecular docking indicated that gallic acid stably bound to the active site of PPO, while isorhamnetin had low affinity on PPO. These results also demonstrated that seabuckthorn leaf extract inhibited browning of fresh-cut potatoes by reducing activities of peroxidase and phenylalanine ammonia-lyase, decreasing contents of phenolics and elevating antioxidant capacity. In addition, synergistic anti-browning effect was found with casuarinin, isorhamnetin, gallic acid and pedunculagin.

Chemical inhibition of polyphenol oxidase and cut surface browning of fresh-cut apples

Fresh-cut apples, which offer consumers health benefits and convenience, have become popular in recent years. One of the main challenges for processing fresh-cut apples is rapid development of cut surface browning, immediately after fruits are cut. Browning, a physiological response that impacts organoleptic properties and deters consumer purchase of fresh-cut fresh produce, is mainly a result of enzymatic reaction of phenolic compounds with oxygen catalyzed by polyphenol oxidase (PPO), a decapper enzyme. Many antibrowning agents have been developed and evaluated to inhibit PPO activities by using reducing agents (antioxidants), chelating agents, acidulants, etc. The present manuscript reviews the diverse characteristics of PPO (such as optimum pH and temperature, and molecular weight) in apples reported in the literature and the enzyme's latency, multiplicity and copper states in the active site. It also summarizes the latest development in the investigation and formulations of antibrowning compounds, and discusses future research needs. This review should stimulate further research to discover more effective, low cost, and natural antibrowning compounds to meet the demand of consumers as well as the food industry for clean label and long shelf-life of fresh-cut apples.

Recent developments in cold plasma-based enzyme activity (browning, cell wall degradation, and antioxidant) in fruits and vegetables

According to the Food and Agriculture Organization of United Nations reports, approximately half of the total harvested fruits and vegetables vanish before they reach the end consumer due to their perishable nature. Enzymatic browning is one of the most common problems faced by fruit and vegetable processing. The perishability of fruits and vegetables is contributed by the various browning enzymes (polyphenol oxidase, peroxidase, and phenylalanine ammonia-lyase) and ripening or cell wall degrading enzyme (pectin methyl-esterase). In contrast, antioxidant enzymes (superoxide dismutase and catalase) assist in reversing the damage caused by reactive oxygen species or free radicals. The cold plasma technique has emerged as a novel, economic, and environmentally friendly approach that reduces the expression of ripening and browning enzymes while increasing the activity of antioxidant enzymes; microorganisms are significantly inhibited, therefore improving the shelf life of fruits and vegetables. This review narrates the mechanism and principle involved in the use of cold plasma technique as a nonthermal agent and its application in impeding the activity of browning and ripening enzymes and increasing the expression of antioxidant enzymes for improving the shelf life and quality of fresh fruits and vegetables and preventing spoilage and pathogenic germs from growing. An overview of hurdles and sustainability advantages of cold plasma technology is presented.

Anti-polyphenol oxidase properties of total flavonoids from young loquat fruits: inhibitory activity and mechanism

This study investigated anti-polyphenol oxidase activity and mechanism of purified total flavonoids (PTF) from young loquat fruits. PTF remarkably inhibited the activity of polyphenol oxidase (PPO) with an IC₅₀ value of 21.03 ± 2.37 μg/mL. Based on enzyme kinetics, PTF was found to be a potent, mixed-type, and reversible inhibitor of PPO. The fluorescence intensity of PPO was quenched by PTF through forming a PTF-PPO complex in a static procedure. Therefore, this study authenticated PTF as an efficient PPO inhibitor, which would contribute to their utilization in food industry.