Effects of calcium and pectin methylesterase on quality attributes and pectin morphology of jujube fruit under vacuum impregnation during storage.

Calcium chloride (1% w/w, CaCl2) and pectin methylesterase (PME) (15 U/mL) were vacuum impregnated (VI) into jujubes to preserve their quality. The nanostructure of jujube pectin was investigated using atomic force microscopy (AFM) to determine the degradation mechanism of pectin. CaCl2 with PME under VI treatment (VI + Ca + PME) maintained jujubes' quality. Weight loss in VI + Ca + PME group at day 56 was only 60.36% of that in control group (CK). Firmness, soluble solids content, and ascorbic acid content of jujubes in VI + Ca + PME group were higher than those in CK. Firmness was highly positively correlated with sodium carbonate-soluble pectin (SSP) content. According to AFM results, frequencies of molecules with a width ≥60 nm of water-soluble pectin (WSP), chelate-soluble pectin (CSP), and SSP were the highest in VI + Ca + PME group at the end of storage. WSP, CSP, and SSP degradation was delayed by VI + Ca + PME treatment. The quality of jujubes was effectively maintained by VI + Ca + PME treatment.