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Traditional metal–organic frameworks (MOFs), although have the ability to accumulate some chemicals from solution, are usually electrochemically inert. Here, spherical MIL-53(NiFe) MOFs have been synthesized via a simple solvothermal method. A series of characterization methods including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrophotometry, energy dispersive X-ray spectroscopy (EDS), and element mapping were used to investigate this material. An MIL-53(NiFe)/AB/GCE-modified electrode was constructed using acetylene black (AB) as the conductive substrate, which can make up for the electrochemical inertness of metal in the MOFs to some extent. Moreover, the bimetallic center can coordinate with the azo functional group in Sudan I to some extent, which is beneficial to the binding of the molecules to the electrode. Thus, the sensitive and rapid detection of Sudan I can be realized. The quantitative determination of Sudan I was carried out via the differential pulse voltammetry (DPV) method in a wider linear range (0.005–10 μM) and lower detection limit (0.002 μM, S/N = 3). The developed method can be successfully applied to the detection of Sudan I in chilli powder and tomato paste with satisfactory results.

In this study, chitosan (CH) coating with different number-average molecular weight (MW, ca. 5, 19 and 61 kDa) was electrostatic sprayed on strawberry. The effects of MW on strawberry quality changes were evaluated during 15 days of storage at 4 °C. The qualities of strawberry included mold growth, weight loss, firmness, total soluble solids (TSS), pH, flavonoids content, superoxide dismutase (SOD) activity and malondialdehyde (MDA) content. Results showed that CH coating could significantly maintain the strawberry qualities during storage compared to uncoated treatment. CH coating with 61 kDa was more effective in retarding the increases of pH and MDA, and could better maintain flavonoids content. However, MW had no significant impact on mold growth, weight loss, firmness, SOD activity of coated strawberry. According to evaluation criteria, CH coating with 61 kDa had better performance on strawberry preservation with the highest synthetic value (6.93), and could be used to maintain quality and prolong the shelf life of strawberry during cold storage.

This study used electrostatic spraying (ES) system as an efficient technique for strawberry preservation with chitosan (CH) coating. The effects of CH deacetylation degree (DD, 81.0, 88.1 and 95.2%) on the qualities (weight loss, pH, total soluble solids (TSS), firmness, flavonoids content, malondialdehyde (MDA) content and superoxide dismutase (SOD) activity and mold growth) of strawberry during cold storage were investigated. Results showed that CH coating by ES formed more continuous and uniform protective layer compared with conventional spraying (CS). CH coating effectively enhanced the overall quality and extended shelf life of strawberry at least 2 days. CH coating with 81.0% and 88.1% DD were more effective in reducing weight loss of strawberry, and CH coating with 88.1% DD could better maintain TSS content, while CH coating with 95.2% DD delayed the decline in flavonoids more obviously. However, DD had no significant impact on pH, firmness, SOD activity, MDA and mold growth of coated samples. The evaluation criteria indicated CH coating with 88.1% DD had better preservation performance with the highest synthetic value (6.17) during storage. These findings suggest that CH coating especially with 88.1% DD by ES, as a safe, cheap and efficient technique, has great potential for industrial application of fruit preservation.