Effect of heat treatment on the quality of onions during long-term tropical storage.

Onion bulbs (cv. Nasik red) were exposed to hot air currents prior to storage to
curtail storage losses. Treatments at 80°C for 30min or 60°C for 1 h resulted in heat
damage while temperatures of 60°C for 30min or 50°C for 3 h or 40°C for 48 h did
not cause any heat damage to the bulbs.
A Commercial lot treated at 47, 50 or 53°C for 3 h and another commercial lot
treated at 47 or 50°C for 2-5 h, were stored for 4 or 5 months in ventilated polyethylene
bags at (1) ambient conditions 20-30”C, RH 50-80’70, and (2) 21 k 1”C,
RH 60-65%. In general the treated lots had more marketable bulbs, with less
incidence of Aspergillus niger infection than untreated controls. Factorial experiments
using temperatures 47, 50, and 53°C with durations of treatment between 2 and 5 h
revealed that the temperature and duration of heat treatment had a significant effect
on the yield of good bulbs and reduction in microbial spoilage during storage.
Treatment at a temperature from 47 and 50°C for a duration between 2 and 4 h gave
best results when stored at 21 2 1°C. The effect of treatment lasted up to 3 months
in storage.