Effects of Vacuum Impregnation with Calcium Ascorbate and Disodium Stannous Citrate on Chinese Red Bayberry

This study aimed to improve the shelf life of Chinese red bayberries using vacuum impregnation. Vacuum pressure of 5 kPa for 15 min, atmospheric pressure for 10 min, an impregnation temperature of 20 A degrees C, alone or in combination with isotonic sucrose solution, 1% food-grade disodium stannous citrate (DSC) and 2% food-grade calcium ascorbate were used for vacuum impregnation. Quality parameters, including firmness, weight loss, decay rate, microbial counts and polyphenol oxidase (PPO) and peroxidase (POD) activities, of red bayberries were studied at 2 A degrees C for 10 days. The monosaccharide components, chemical structures and nanostructure properties of chelate-soluble pectin (CSP) were further studied using high-performance liquid chromatography, Fourier transform infrared spectroscopy and atomic force microscopy (AFM). The results indicated that vacuum impregnation with calcium ascorbate alone or calcium ascorbate combined with DSC showed significant effects on inhibiting the decrease of firmness (4-10 days), the increase of weight loss (2-10 days), decay rate (4-10 days) and microbial growth (2-10 days). In addition, vacuum impregnation with single calcium ascorbate or DSC or their combination significantly inhibited the increase of colour difference from day 6 to day 10 during storage, which was better than atmospheric impregnation. Furthermore, vacuum impregnation with DSC and calcium ascorbate had the best effect on sensory attributes. The nanostructure analysis by AFM showed CSP of large width and length when calcium ascorbate was impregnated, suggesting that vacuum impregnated with 2% calcium ascorbate inhibited the degradation and dissociation of CSP, although these fruits showed more branching of rhamnogalacturonan and a small change in chemical structure.