Preparation, characterization, and application of composite coating based on jujube leaf cuticular wax, soy protein isolate, and wheat gluten protein for blueberry preservation.

Jujube leaves contain abundant cuticular wax (CW), which is a natural protective layer secreted by plants that serves as a barrier against microbial invasion. At present, jujube leaves are largely discarded as agricultural pruning waste. In this study, a soy protein isolate/wheat gluten-based composite coating film (SG-CW) incorporating CW was developed to extend blueberry shelf life. The optimal extraction conditions were determined to be anhydrous ethanol extraction at 35 °C for 20 s, yielding 15.03 mg/g of wax mainly composed of alkanes, alcohols, esters, and fatty acids, as revealed by gas chromatography-mass spectrometry (GC-MS) analysis. The addition of CW increased the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of SG-CW from 8.37 % to 15.75 % and effectively inhibited the growth of total plate count, molds, and yeasts. When 1.0 % CW was added, the water vapor permeability (WVP) of SG-CW decreased to 4.39 g·m/(h·Pa·m2). The results of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses indicated the formation of a stable and compatible network structure between the CW and the protein matrix. The decay incidences of blueberry fruits at 15 d were 35.75 % in the control group and 16.64 % in the SG-CW treatment group. The ascorbic acid (AsA) and total anthocyanin contents of blueberry in the SG-CW treatment group were 17.63 % and 30.16 % higher than those in the control group, respectively. Overall, this study provides a potential solution to both the underutilization of jujube leaf resources and the high perishability of blueberry.