Synthesis, anti-browning effect and mechanism research of kojic acid-coumarin derivatives as anti-tyrosinase inhibitors

Thirteen kojic acid-coumarin derivatives were synthesized using the principle of molecular hybridization, and their structures were characterized by 1H NMR, 13C NMR, and HRMS. In vitro enzyme inhibition experiments showed that all newly synthesized derivatives have excellent inhibition of tyrosinase (TYR) activity. As a mixed inhibitor, compound 6f has the strongest activity, with an IC50 value of 0.88 ± 0.10 µM. Multispectral experiments have confirmed that the mode of action of compound 6f on TYR was static quenching. In addition, compound 6f formed a new complex with TYR, which increased the hydrophobicity of the enzyme microenvironment, reduced the content of the α-helix in the enzyme, and changed the secondary structure. The experimental results showed that compound 6f effectively inhibited the browning of lotus root slices and had low cytotoxicity. Therefore, compound 6f is believed to have great development potential as a TYR inhibitor in the food industry.

Biosynthesis of the phycocyanin β-subunit in Escherichia coli BL21 and its antioxidant activity and application in the preservation of fresh-cut apples

In this study, the biosynthesis of phycocyanin β-subunit (CpcB) in Escherichia coli BL21 was investigated, and its antioxidant activity and application in anti-browning of fresh-cut apples was explored. Four genes (cpcB, cpeS, hox1 and pcyA) involved in the biosynthesis of CpcB were cloned and transformed into E. coli BL21 by constructing recombinant plasmid pETDuet-5. The positive transformant was screened by ampicillin resistance. The analysis of SDS-PAGE and zinc fluorescence spectrum showed that CpcB was successfully expressed in E. coli BL21 with a molecular weight of 21 kDa. The purified CpcB had a maximum absorption peak at 615 nm, and its maximum florescence emission wavelength was 640 nm. It exhibited a stronger ability to scavenge four free radicals than Vc. The color change in fresh-cut apples was obviously delayed by the CpcB treatment. These results suggest that CpcB may be used as a potential anti-browning agent for food preservation.

Investigation on the inhibition mechanism and binding behavior of paeonol to tyrosinase and its anti-browning property by multi-spectroscopic and molecular docking methods

Paeonol, as one effective tyrosinase inhibitor, had been used as food preservative and clinical medication for skin disorders. In this study, the inhibition mechanism and binding behavior of paeonol to tyrosinase and its anti-browning property were investigated using multi-spectroscopic and molecular docking methods. Activity assay and kinetic results confirmed paeonol as a reversible mixed-type tyrosinase inhibitor. Results of the mechanistic studies were clarified using fluorescence quenching, synchronous fluorescence, CD spectra and 3D fluorescence, and showed that the binding of paeonol to tyrosinase might change the chromophore microenvironment and conformation of tyrosinase to inhibit enzyme catalytic activity. Molecular docking results revealed the detailed binding between paeonol and tyrosinase. Moreover, paeonol could prevent the browning of fresh-cut apples, as well as inhibiting PPO and POD activities and increasing APX activity. All above findings established a reliable basis for the inhibitory mechanism of paeonol against tyrosinase and therefore contributed to its application in anti-browning.

Synthesis and evaluation of the antioxidant and anti-tyrosinase activities of thiazolyl hydrazone derivatives and their application in the anti-browning of fresh-cut potato

Tyrosinase is a key enzyme in the biosynthesis of melanin, which is responsible for the browning of foods as well as many skin disorders. In order to develop new anti-browning agents with dual antioxidant and anti-tyrosinase capacities, a series of 30 thiazolyl hydrazone derivatives were synthesized. Among the molecules prepared, 6 and 30 were found to be the most potent tyrosinase inhibitors with IC₅₀ values ​​comparable to that of kojic acid. Interestingly, 6 also has the highest radical scavenging activity among the prepared molecules. The inhibition kinetics study indicated that 6 is a non-competitive inhibitor while 30 inhibits tyrosinase competitively. The anti-browning assay of fresh-cut potato slices revealed that 6 and 30 are potent anti-browning agents with a capacity as high as kojic acid. The mechanisms of free radical scavenging and tyrosinase inhibition have been fully investigated in silico using computational kinetics, molecular docking, and molecular dynamics simulations.

Chitosan-based nanocomposites as coatings and packaging materials for the postharvest improvement of agricultural product: A review

The perishability nature of harvested fruits and vegetables, along with the effect of environmental factors, storage conditions, and transportation, reduce the products' quality and shelf-life. Considerable efforts have been allocated to alternate conventional coatings based on new edible biopolymers for packaging. Chitosan is an attractive alternative to synthetic plastic polymers due to its biodegradability, antimicrobial activity, and film-forming properties. However, its conservative properties can be improved by adding active compounds, limiting microbial agents' growth and biochemical and physical damages, and enhancing the stored products' quality, shelf-life, and consumer acceptability. Most of the research on chitosan-based coatings focuses on antimicrobial or antioxidant properties. Along with the advancement of polymer science and nanotechnology, novel chitosan blends with multiple functionalities are required and should be fabricated using numerous strategies, especially for application during storage. This review discusses recent developments in using chitosan as a matrix to fabricate bioactive edible coatings and their positive impacts on increasing the quality and shelf-life of fruits and vegetables.

Anti-browning and antibacterial dual functions of novel hydroxypyranone-thiosemicarbazone derivatives as shrimp preservative agents: Synthesis, bio-evaluation, mechanism, and application

To develop new shrimp preservative agents with dual functions of anti-browning and antibacterial, thirteen hydroxypyranone-thiosemicarbazone derivatives were prepared according to molecular hybridization. Thereinto, compound 7j (IC₅₀ = 1.99 ± 0.19 μM) shown the strongest anti-tyrosinase activity and was about twenty-three folds stronger than kojic acid (45.73 ± 4.03 μM). The anti-tyrosinase mechanism of 7j was illustrated through enzyme kinetic, copper ion chelating ability, fluorescence quenching, ultraviolet spectrum, AFM analysis, and molecular docking study. On the other hand, antibacterial assay and time-kill kinetics analysis confirmed that 7j also had good antibacterial activity against V. parahaemolyticus (MIC = 0.13 mM). PI uptake test, SDS-PAGE, and fluorescence spectrometry analysis proved that 7j can affect the bacterial cell membrane. Finally, the shrimp preservation and safety study indicated that 7j has dual effects of inhibiting bacterial growth and preventing enzyme browning, and can be applied to the preservation of fresh shrimp.

Tyrosinase inhibitory mechanism and anti-browning properties of novel kojic acid derivatives bearing aromatic aldehyde moiety

Kojic acid-aromatic aldehydes 6a-6m were synthesized and screened for their anti-tyrosinase activities. These compounds showed potently anti-tyrosinase activity with IC₅₀ values in the range of 5.32 ± 0.23 to 77.89 ± 3.36 μM compared with kojic acid (IC₅₀ = 48.05 ± 3.28 μM). Thereinto, compound 6j with 3-fluorine and 4-aldehyde substitutions showed the most potent anti-tyrosinase activity (IC₅₀ = 5.32 ± 0.23 μM). Enzyme kinetic study revealed that 6j is a noncompetitive tyrosinase inhibitor (Ki = 2.73 μM). The action mechanism of 6j was evaluated by fluorescence spectrum quenching, molecular docking, ¹H NMR titration, etc. The anti-browning assay showed that 6j could delay the enzymatic browning of fresh-cut apples. Besides, the cell viability assay proved that 6j had a good safety profile as an anti-browning agent. Hence, these results identify a new class of anti-tyrosinase and anti-browning agents for further investigation in the food industry.

A comprehensive study to explore tyrosinase inhibitory medicinal plants and respective phytochemicals for hyperpigmentation; molecular approach and future perspectives

Tyrosinase is acopper-containing key substance in the pigmentation of mammalian hair and skin. Melanin synthesis is influenced by variety of extrinsic and internal variables, including hormone fluctuations, inflammation, ageing, and subsequent ultraviolet light exposure. Melasma, senile lentigines, freckles, and diminished colour are all undesirable side effects of excessive melanin production. The current review provides the pursuit of effective and safe tyrosinase inhibitors derived from medicinal plants, and ascribes an updated inferences on current practices. Commercially available tyrosinase inhibitors provide an even skin tone and are used clinically to treat hyperpigmentation and related disorders. This review focuses on the mechanism of melanogenesis and on experimentally verified potent and natural tyrosinase inhibitors. Bioactive compounds such as phenols, flavonoids, stilbenes, and a few traditional herbal formulations from the Indian system of medicine, have been used since long in India and subcontinents for the effective management of melanogenesis and related problems. Scientific information was gathered from different sources of databases such as PubMed, Google Scholar, Springer, Scopus, and Science Direct, as well as the literature found in medicinal plant books. This critically summarized review ensures to aid researchers and enterprises working on tyrosinase inhibitors and on conditions associated with melanogenesis, to get one-step solutions for identifying more safe and effective natural remedies.

Design and synthesis of novel stilbene-hydroxypyridinone hybrids as tyrosinase inhibitors and their application in the anti-browning of freshly-cut apples

In order to develop the tyrosinase inhibitors with potential application in food industry, a series of stilbene-hydroxypyridinone hybrids were prepared. Among these compounds, 1h was found to possess the most potent tyrosinase inhibitory effect on both monophenolase and diphenolase activities, with IC₅₀ values of 2.72 μM and 15.86 μM, respectively. The inhibitory effect of 1h on monophenolase activity was 4.6 times that of kojic acid. An inhibition kinetic assay indicated that 1h was a mixed-type and reversible inhibitor. The copper-binding and reducing ability assays, molecular docking study, intrinsic and ANS-binding fluorescence assays indicated that copper coordination and reduction is likely to be the causative mechanism for 1h-induced inhibition on tyrosinase. The results of color measurement and browning index determination indicated that treatment with 1h retarded effectively the browning of freshly-cut apples during their storage. Meanwhile, PPO and POD activities in apple slices were found to be effectively inhibited.

Tyrosinase inhibitory mechanism and the anti-browning properties of piceid and its ester

Different mechanisms for inhibiting tyrosinase can be exploited to avoid quality losses caused by the enzymatic browning of fruits and vegetables. Piceid (PI) and piceid 6″-O- azelaic acid ester (PIA) are oxidized by tyrosinase; however, their oxidation products may have inhibitory effects on tyrosinase. This notion is because l-DOPA oxidation was inhibited after the pre-incubation of PI/PIA with tyrosinase, however, l-DOPA oxidation was not affected if this pre-incubation was not performed. Circular dichroism analysis indicated a conformational change in the secondary structure of tyrosinase after pre-incubation. Further, molecular docking and enzyme reaction kinetics assays were employed to reveal the mechanism underlying the effects of PI/PIA on tyrosinase in the absence of pre-incubation with tyrosinase. PI/PIA had anti-browning effects in the potato models. The increased rate of A₄₂₀ in PI/PIA groups at 24 h were 281% and 279%, which were approximately 2.4- and 2.5-fold lower than that of control (668%).

Development of active packaging film from sodium alginate/carboxymethyl cellulose containing shallot waste extracts for anti-browning of fresh-cut produce

Owing to growing concerns about making pollution-free sustainable environment by reducing the dumping of agricultural waste and convert it into valuable product is a key to carry out the present study. The ultimate goal of this study is to convert onion solid wastes (OSWs) into active packaging and evaluating the anti-browning effect due to the OSWs holding rich polyphenols and antioxidants. The active packaging film was fabricated by using sodium alginate (SA) and carboxymethyl cellulose (CMC) along with SOWEs such as peel and stalk at 0.2% and 0.5% concentration. The film made with SA/CMC/SOWEs had good physical, mechanical, optical and barrier property, higher phenolic and antioxidant activity compared to control. In addition, the effect of SA/CMC/SOWEs film packaging on anti-browning and quality of fresh-cut apple and potato stored at 4 °C was studied. The results show the SA/CMC/SOWEs film had better effect on controlling browning index in fresh-cut apple and potato over the storage of 12 days and 5 days. This study concludes that the SA/CMC film developed with shallot stalk extract can be used for wrapping of fresh-cut fruits and vegetables. It also prevents browning and maintains the overall quality than control and shallot peel incorporated film.

Improving the shelf life of fresh-cut 'Royal Delicious' apple with edible coatings and anti-browning agents

The objective of this study was to monitor overall quality and to extend the shelf life of fresh-cut apple wedges. Fresh-cut apple wedges were treated with anti-browning agents and edible coatings alone as well as in combination and packed in polypropylene trays. Packed apple wedges were stored at 5 ± 2 °C and monitored for physical (colour, physiological loss in weight and firmness), bio-chemical (ascorbic acid, total antioxidant, phenol, polyphenol oxidase and peroxidase enzymes) and microbial quality. In general carboxymethyl cellulose and aloe vera coatings along with anti-browning agents helped in preserving quality of apple slices during storage. Microbial load was significantly low for wedges coated with carboxymethyl cellulose and aloe vera. Polyphenol oxidase and peroxidase enzyme activity was also low in the coated samples. Firmness of the uncoated apple wedges declined more rapidly than the coated ones during storage. The results showed that carboxymethyl cellulose and aloe vera coating in combination with anti-browning agents improved the quality of stored apple wedges.

Novel hydroxypyridinone derivatives containing an oxime ether moiety: Synthesis, inhibition on mushroom tyrosinase and application in anti-browning of fresh-cut apples

A range of hydroxypyridinone derivatives were synthesized starting from kojic acid. Among them, 10 and 11 were found to possess the strongest inhibitory effect on monophenolase activity of mushroom tyrosinase, having IC₅₀ values of 2.04 and 1.60μM, respectively. The IC₅₀ values of 10 and 11 for the inhibition of diphenolase activity of mushroom tyrosinase were determined as 13.89 and 7.99μM, respectively. Investigation of the inhibitory mechanism of these two compounds indicated that the inhibition was reversible and of a competitive-uncompetitive mixed type. The K_I and K_IS values of 10 were determined to be 24.84 and 32.54μM, respectively, and the corresponding values for 11 being 18.07 and 21.34μM, respectively. The effect of 11 on the browning process of fresh-cut apples was evaluated by measuring the color change and browning index. The results indicated that 11 had a significant effect on controlling the browning of fresh-cut apple slices.