Effect of Hot Calcium Chloride and Acetic Acid Solutions or Hot Water Treatments on Inhibition of Total Microbial Counts and Browning in Lettuce Stem Cut During Cold Storage

Abstract

Heads of iceberg lettuce (Lactuca sativa L. cv. Iceberg) were harvested at the proper stage of maturity from Kaha Experimental Farm, Qalubia Governorate, Egypt, during two successive seasons in 2015 and 2016. Good heads were transported immediately to the laboratory of Handling of Vegetable Crops Department Horticulture Research Institute at Giza. Egypt. All leaves were removed and stems were cut by a sharp knife into round slices (1 cm thickness × 2.5 diameter) then dipped for 1 min in the following solutions, hot CaCl23% or 5% at 50oC, hot acetic acid 1% or 3% at 50oC, CaCl23% or 5% at 20oC, acetic acid 1% or 3% at 20oC, hot water at 50oC and distilled water (control) to study the effect of these treatments on inhibition butt discoloration and microbial count of the stem cut lettuce during storage at 2±1 °C and 95 % relative humidity (RH) for 10 days. Results indicated that all studied treatments reduced browning index, Polyphenol oxidase (PPO) activity, Phenylalanine ammonia-lyase (PAL) activity, had lower level of microbial load and maintaining total phenolic contents of the stem cut lettuce during cold storage comparing with untreated control. Stem cut lettuce dipped in hot Calcium Chloride 5% solution showed a positive effect on enzymes related to color maintenance. It reduced the activity of the browning related enzymes polyphenol oxidase (PPO) and Phenylalanine ammonia-lyase (PAL), maintained of total phenolic content, had the lowest total bacterial counts and inhibited browning on the cut surface of lettuce stem during storage at 2±1 °C and 95 % relative humidity for 10 days.