Effects of fluctuating temperatures on quality of kiwifruit in modified atmosphere packages

In order to evaluate the effect of changing temperature on maturation control of kiwifruit (var. Hayward) stored in modified atmosphere packages, storage tests were carried out. Two kiwifruits and a 10g sachet of ethylene absorbent (KMn04) were packed in 0.03mm thick low-density polyethylene bags and initially stored at 1degC for 3 weeks. The fruits were then removed and stored at different temperatures until the 8th week. The conditions of storage were: (a) weekly temperature changing between 1degC and 10degC; (b) weekly temperature changing between 1degC and 15degC; (c) weekly stepwise temperature increase of 1degC; (d) constant temperature of 5degC; (e) constant temperature of 10degC; (f) constant temperature of 15 degC; and (g) constant temperature of 1degC, which is ordinary storage condition for comparison with changing temperatures. Due to variations in quality indexes of test samples, such as total soluble solids (TSS), titratable acidity (TA), firmness, weight loss, etc., at each sampling time after the 3rd week, the range of quality values at the end of storage were compared with the values of ripened kiwifruit on retail. As a comparison of inner quality indexes of test samples and fruits ripened for retail, the respective values at storage temperatures of 1degC and 10degC, respectively, at 8 weeks ranged from 12.0%Brix and 14.2%Brix. These values were lower than 15.7%Brix for fruit on retail. On the other hand, the TA values of fruits stored at changing temperatures between 1degC and 15degC and between 1degC and 10degC at 6 and 8 weeks, respectively, were 0.9 and 1.0 citricacid g/100ml. Compared with TA value of 0.71 citric acid g/100 ml for ripened fruit on retail, test sample were higher in TA content. The results show that fruits stored at changing temperatures ripened less than fruits on retail. Moreover, the respective firmness values of fruits at storage temperatures of weekly increase of 1degC and constant temperature of 5degC were 10.8 and 16.8 N/mm, respectively. These values were higher than firmness value of 4.8 N/mm for kiwifruit on retail. This confirmed that test samples were firmer after storage due to scrubbing of ethylene gas in the polyethylene bags. Weight losses at storage temperatures of 1degC and changingt emperature between 1degC and 10degC at 8 weeks ranged from 0.5% to 2.0%. These values were lower than the upper limit of about 5% in fruits usually acceptable to consumers.