Influence of Hot Water Immersion and MAP Pre-treatments on Sterilization and Asparagus Spear Qualities During Cold Storage

The purpose of this study was to determine how asparagus spear qualities are affected by hot water immersion (HWT) and modified atmosphere packaging (MAP) pre-treatments. Asparagus spears were treated either with different durations of HWT or packed with 10,000 cc/m² ㆍdayㆍatm oxygen transmission rate (OTR) film as the MAP treatment, and then stored at 4℃ until the final storage day. Respiration and ethylene production rates in asparagus increased after HWT, with 8 and 16 min treatments having the most effect on these parameters. Fresh weight loss was less than 0.3% with all treatments. Gas composition (i.e., C₂H₄, CO₂, and O₂) within the packaging was not significant among all treatments during storage. The MAP and HWT treatments made no difference not only in fresh weight but also in gas composition. Microbial growth (i.e., total aerobic bacteria, yeast, mold, and E. coli) was lower with the 2 and 4 min treatments than with the other treatments. Electrolyte leakage was less in the control, 2 min, and 4 min treatments compared to the 8 and 16 min treatments. The hue angle and total chlorophyll values, which are associated with yellowing, remained constant at the 2 and 4 min treatments compared to the other treatments, which did not have maintained values. Asparagine content accumulated in the control, 2 and 4 min treatments, whereas the 8 and 16 min treatments showed a decrease in asparagine content. Stem firmness was similar to pre-storage measurements with the 4 min treatment. Stem length for all of the treatments was slightly increased before storage regardless of HWT duration. Asparagus off-odor and visual qualities were the best with 4 min treatment compared to the other treatments. Consequently, HWT for 2-4 min and MAP Pre-treatments were effective in maintaining the measured qualities among the treatment and control groups. In contrast, HWT for more than 8 min offset any beneficial heat-treatment effects for long-term storage; as indicated by tissue softening at the stem tip, which resulted in secondary damages that included microorganism infection and deterioration of visual quality in the vegetables.