Heat Treatment for Enhancing Postharvest Quality - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 252

160
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Fig. 11.5 The effect of heating apples in hot air for 4 days at 38 ◦ C before slicing on ethylene production,
respiration, slice browning, and firmness of the slices held at 5.5 ◦ C, compared to unheated sliced control apples.
(Adapted from Bai et al., 2004.)

at 38 ◦ C before slicing respiration, ethylene production and softening were reduced, but
acidity loss was high and aroma volatiles were lower (Bai et al., 2004). The slices from
heated apples also showed less browning (Fig. 11.5). Shelf life at 5.5 ◦ C was 50% longer
than for control apples. In another study, apples were held at 34-42 ◦ C for less than 70 min
before slicing. The treatments prevented cut-surface browning and softening during storage
at 5 ◦ C (Barrancos et al., 2003). A similar study was performed with “Rocha” pears (Abreu
et al., 2003). Heating the fruit from 35 to 45 ◦ C for 40-150 min before processing avoided
cut-surface browning and maintained firmness, pH, and soluble solids content (SSC) during
storage at 2 ◦ C. Two studies on fresh-cut fruit have looked at combining heat with a CaCl 2
dip to maintain firmness during storage. In both fresh-cut cantaloupe and mangoes, a dip
in hot water with 2.5-3.5% CaCl 2 improved firmness of the fruit during storage at 5 ◦ C
(Luna-Guzman et al., 1999; Trindale et al., 2003). Dipping in hot water was more effective
than ambient water with CaCl 2 .
One of the largest commodities marketed as fresh-cut is lettuce. Many studies have
looked at the effect of heat treatments on lettuce from various aspects, including reduc-
tion of plant and human pathogens, and inhibition of senescence processes. Cut iceberg
lettuce washed in chlorinated water at 50 ◦ C found that high temperature reduced the mi-
crobial populations more than at 4 ◦ C (Delaquis et al., 2004). The treatment also delayed
the appearance of tissue browning (Fig. 11.6). A 50 ◦ C treatment with or without chlorine
treatment reduced aerobic mesophiles, psychrotrophs, Enterobacteriaceae, molds, and lac-
tic acid bacteria, and also delayed tissue browning (Li et al., 2001b). A study was performed