Effects of Vacuum Impregnation with Calcium Lactate and Pectin Methylesterase on Quality Attributes and Chelate-Soluble Pectin Morphology of Fresh-Cut Papayas

Vacuum impregnation was used to improve the quality attributes of fresh-cut papayas. Vacuum pressure of 5 kPa was applied for 5 min, then calcium lactate (1%, w/w) and pectin methylesterase (PME) (15 U/ml), alone and in combinations (calcium lactate plus PME), were vacuum impregnated into fresh-cut papaya cubes. Papaya cubes were stored at 4 A degrees C, and the quality of fresh-cut papaya was studied at intervals for 8 days. The hardness and chewiness levels of fresh-cut papayas that were treated with calcium lactate and PME were 8.02 and 7.83 times of untreated fresh-cut papayas at day 8, respectively. After vacuum impregnation, colour of fresh-cut papayas changed significantly (P < 0.05) and an overall weight loss was observed as well. Chelate-soluble pectin (CSP) was extracted and its content correlated well with texture properties of fresh-cut papayas. Qualitative and quantitative analyses of CSP were conducted using atomic force microscopy. The proportion of chain widths greater than 45 nm had increased 35.0% in fresh-cut papayas vacuum impregnated with calcium lactate and PME at the end of storage. The results indicate that a combination of calcium ions and PME was able to maximally preserve the quality attributes of fresh-cut papayas and extend the shelf life.