•A novel tyrosinase inhibitor and antimicrobial is studied.•Apply Na7PMo11CuO40 decreased the melanin content in B16 melanoma cells.•Extended the use of polyoxometalates in the fields of food preservation and depigmentation.Keggin-type Cu-substituted phosphomolybdic acid (Na7PMo11CuO40, abbreviated as PMo11Cu) was synthesized and characterized. The inhibitory effects of PMo11Cu on mushroom tyrosinase and melanin formation in B16 melanoma cells were studied. The results showed that PMo11Cu could strongly inhibit the activity of tyrosinase, and it was reversible and competitive inhibitor. The IC50 value was estimated to be 0.48 mM for diphenolase activity. PMo11Cu also exhibited inhibitory effects on cell viability, cellular tyrosinase activity and melanin formation in B16 melanoma cells at concentrations ranging from 0 to 200 μM for 24 h. Furthermore, the antimicrobial activities of PMo11Cu against Sarcina lutea, Staphylococcus aureus, Bacillus subtilis and Escherichia coli were investigated. The results showed that PMo11Cu had an obvious antimicrobial activities, and it was more effective against two kinds of coccus than two kinds of bacillus. This study may provide theoretical basis for designing novel effective mushroom tyrosinase inhibitors and extend the use of polyoxometalates in the fields of food preservation and depigmentation.Graphical abstractElectrophoretic analysis of the inhibitory effect of PMo11Cu on the diphenolase activity of mushroom tyrosinase. Mushroom tyrosinase is a tetrameric glycoprotein copper containing metalloenzyme. Figure A is a gel map of SDS–PAGE for the analysis of the molecular weight of mushroom tyrosinase, figure B showed that the color of the tyrosinase activity staining bands became gradually shallow until they disappeared with the increasing of inhibitor concentration. The figures confirmed that PMo11Cu could potently inhibit the activity of tyrosinase.

A sensitive, simple and rapid CE-ECL method is established for the determination of putrescine and spermidine in aquatic products with a new luminous source material, PMo12–Ru(bpy)32+. This method is based on the electrochemical reaction of putrescine, spermidine and PMo12–Ru(bpy)32+ on a platinum electrode. The experimental conditions for the separation and detection of biogenic amines were optimized. Under optimal conditions, the detection limit (S/N = 3) was 6.5 × 10−3 mg L−1. For spermidine, the detection limit (S/N = 3) was 9.8 × 10−3 mg L−1. No spermidine was detected in the fresh ray samples while the content of putrescine was 0.019 mg L−1 in the samples. The relative standard deviation (RSD) of the peak height and migration time for putrescine was 1.19% and 1.11%, respectively, with a recovery of 90.0–104.0%. The new luminous source could make the CE-ECL method cleaner and more effective on the premise of guaranteeing accuracy.

•A novel method for separation and determination of five BAs is established.•CE-ECL has high sensitivity, good selectivity and wide linear range.•The LODs and linearity concentration range are better than those of previous reports.•Concentration of putrescine is expected to become the freshness indicator of oyster.Changes in the concentrations of putrescine, histamine, tyramine, phenylethylamine and spermidine were studied by the method of capillary electrophoresis coupled with electrochemiluminescence (CE-ECL) during the storage of oysters at two different temperatures (0 °C and 4 °C). The results showed that, with an increase in the storage time, spermidine and putrescine became dominant. When the oysters were stored at 0 °C, the concentration of spermidine increased from 45.6 mg/kg to 68.5 mg/kg, and that of putrescine increased from 18.6 mg/kg to 28.3 mg/kg. When the storage temperature was controlled at 4 °C, the concentration of spermidine increased from 46.7 mg/kg to 119.7 mg/kg and that of putrescine increased from 19.4 mg/kg to 136.8 mg/kg, respectively. In contrast, the histamine, tyramine and phenylethylamine levels increased slightly throughout the storage period for all of the experimental conditions.

•A novel tyrosinase inhibitor from polyoxometalates is studied.•Apply α-Na8SiW11CoO40 decreased the browning degree and polyphenol oxidase activity of apple slices.•High contents of phenolic compounds and ascorbic acid are maintained by α-Na8SiW11CoO40 treatment.•Provided a promising anti-browning agent for controlling the browning of fresh-cut apples.α-Na8SiW11CoO40 was synthesized and characterized. The inhibitory effects of α-Na8SiW11CoO40 on the activity of mushroom tyrosinase and the effects of α-Na8SiW11CoO40 on the browning of fresh-cut apples were studied. The Native-PAGE result showed that α-Na8SiW11CoO40 had a significant inhibitory effect on tyrosinase. Kinetic analyses showed that α-Na8SiW11CoO40 was an irreversible and competitive inhibitor. The inhibitor concentration leading to a 50% reduction in activity (IC50) was estimated to be 0.239 mM. Additionally, the results also showed that α-Na8SiW11CoO40 treatment could significantly decrease the browning process of apple slices and inhibit the polyphenol oxidase (PPO) activity. Moreover, application of α-Na8SiW11CoO40 resulted in higher peroxidase activity and promoted high amounts of phenolic compounds and ascorbic acid. This study may provide a promising method for the use of polyoxometalates to inhibit tyrosinase activity and control the browning of fresh-cut apples.Visual appearance of fresh-cut apples with (a) or without (b) short-term SiW11Co treatment after 2 h. α-Na8SiW11CoO40 (SiW11Co) was synthesized and characterized. The Native-PAGE and the spectrophotometry assay showed that SiW11Co had a significant inhibitory effect on tyrosinase dose-dependently (IC50 = 0.239 mM, KI = 0.164 mM). In addition, the assay on the browning of apple slices indicated that SiW11Co treatment could significantly decrease the browning degree of apples slices and the activity of polyphenol oxidase (PPO), and controlled the oxidation of fresh-cut fruits and vegetables. As shown in figure, visual appearance of apple slices in treatment group was apparently lighter than that of the control group, which also suggested that SiW11Co could inhibit the browning process of apple slices distinctly.

•A novel inorganic tyrosinase inhibitor is investigated.•Applied this Na6PMo11FeO40 for preserving the lotus root.•Na6PMo11FeO40 treated lotus root slices significantly slow the browning rate and PPO activity.The inhibitory effects of iron-substituted phosphomolybdic acid (Na6PMo11FeO40, abbreviated as PMo11Fe) on mushroom tyrosinase were investigated. The Native-PAGE results show that PMo11Fe has an inhibitory effect on tyrosinase. A spectrophotometric analysis shows that PMo11Fe is a reversible and noncompetitive inhibitor with KI = KIS = 0.47 mmol L−1. The effects of PMo11Fe on the preservation of lotus root slices were studied. The results show that PMo11Fe can significantly slow the browning rate of lotus root slices, inhibit the activity of polyphenol oxidase (PPO), enhance the activity of peroxidase (POD) and superoxide dismutase (SOD), maintain high levels of glutathione (GSH), ascorbic acid (ASA) and sucrose and control the peroxidation degree of fresh-cut fruits and vegetables. This study may help to elucidate the design of mushroom tyrosinase inhibitors of polyoxometalates (abbreviated as POMs) and a theoretical basis for the use of POMs to inhibit fruit spoilage.Graphical abstractThe Native-PAGE analysis of inhibitory effect of PMo11Fe on the diphenolase activity of mushroom tyrosinase.Tyrosinase is encoded by multi-gene family (Richter et al., 2012), the molecular weight are usually 30–34 kDa (Bernan et al., 1985), 42–46 kDa (Gerdemann et al., 2002; Wichers et al., 2003), 64–68 kDa (Wichers et al., 2003). Figure A is the electrophoresis analysis of protein molecular weight and species of mushroom tyrosinase, figure B is the inhibitory spectrum of Native-PAGE of PMo11Fe on mushroom tyrosinase. The figures confirm that three kinds of molecular weight of tyrosinase are all existed in the sample and with activity.

A general strategy for the preparation of polyoxometalate coordination polymer modified electrodes via an ionic liquid route was proposed. A polyoxometalate (POMs) coordination polymer 1, [H2bpy]2[{Cu(bpy)2}Mo5P2O23]⋅4H2O (bpy = 4,4′-bpyridine) was successfully reconstructed by electrolyzing in its ionic liquid solution on conducting glasses electrode coated with indium tin oxide (ITO). Polymer 1 is soluble in the an ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), not soluble in water and common organic solvents such as DMF, ether. The reconstructed polyoxometalate coordination polymer on the ITO electrode was characterized by XPS and XRD. XPS spectrums and the XRD patterns of the deposited POMs on ITO electrode show the deposited POMs had the same structure as the polyoxometalate coordination polymer 1, which imply that the structure of the deposited POMs on ITO electrode keeps the same as the original the polyoxometalate coordination polymer 1. Cyclic voltammetry technique was used to study the electrochemical properties of the as-prepared POM modified ITO electrode. The results implied that it had not only a good electrocatalytic activity toward the reduction of iodide, but also a high stability in aqueous solution. The proposed strategy for the construction of POMs coordination polymer modified electrode shows remarkable advantages, which should be important for practical applications.