EFFECT OF DIFFERENT PRE-COOLING, PACKAGING AND TRANSPORTATION METHODS ON QUALITY OF LETTUCE

摘要

The effect of pressure cooling (PC) and room cooling (RC) packaged with the plastic box (PB) and carton (CN), four different packaging treatments which were expanded polystyrene cases (EPS) with and without cold accumulator in the temperature of 20.8～23.5°C, cartons with and without 0.06mm polyethylene (PE) at 0±0.5°C during the transportation on the quality of lettuce were studied. The results showed that the cooling times of lettuces by PC+PB from 21.1°C down to 2.8°C, PC+CN from 19.8°C down to 2.8°C, RC+PB from 23°C down to 2.6°C, and RC+CN 20.5°C from down to 2.8°C were 180, 210, 300, and 390 minutes, respectively. The weight losses of lettuces with PC+PB, PC+CN, RC+PB, and RC+CN were 0.82, 0.88, 0.98, and 1.04%, respectively. The cooling rate with pressure cooling was faster than that with room cooling, and its weight losses were lower. The core temperatures of cooled lettuces packaged by expanded polystyrene cases with and without cold accumulators were increased from 0°C to 7.3°C and 21.2°C, 21.1°C and 22.3°C,respectively after 1 day and 2 days in the temperature of 20.8～23.5°C. 2 days later, the soluble sugar contents decreased to 2.00 and 1.87%, ascorbic acid contents decreased to 38.51 and 34.64 mg/100g, the weight losses were 0.84 and 1.10%, respectively. The lettuces packaged by cartons with and without 0.06mm PE at 0±0.5°C, the soluble sugar contents decreased to 1.73 and 1.50%, ascorbic acid contents decreased to 32.94 and 28.63 mg/100g, the weight losses were 1.17 and 4.88%, respectively after 9 days. The sensory evaluation of lettuces packaged carton without 0.06mm PE were grade 3.5 and 2.9 after 7 and 9 days, while the sensory evaluation of lettuces packaged carton with 0.06mm PE was grade 4.4 and 4.2 after 7 and 9 days.