Non-freezing points below zero induce low-temperature breakdown of kiwifruit at harvest

To induce low-temperature breakdown (LTB) at harvest, a post-storage disorder of kiwifruit, kiwifruit were exposed to -2 degrees C (a temperature determined to be above the freezing point), for 0 (control), 6, 12, 18, 24, 30, 36 and 42h, followed by 5 days at 20 degrees C. Kiwifruit were also stored at -0.5 degrees C for 16 and 24 weeks plus 5 days at 20 degrees C. LTB incidence and severity were measured on the cut surfaces following slicing at the upper, middle and lower parts of each fruit subjected to -2 degrees C, whereas in stored fruit LTB incidence was measured following slicing at the middle part. Electrolyte leakage (ELL) was also determined. Exposure of fruit to -2 degrees C resulted in induction of LTB incidence and severity, which increased with the duration of exposure, particularly, on the upper fruit part. Maximum ELL during exposure at -2 degrees C for 36 h or during storage at -0.5 degrees C for 16 weeks was as high as 50% of that of the frozen fruit. Fruit exposed to -2 degrees C or stored at -0.5 degrees C had similar LTB symptoms but both differed from those observed in frozen fruit. LTB of fruit stored at - 0. 5 degrees C for 24 weeks was 2 7% and corresponded to LTB induced at harvest by exposure at -2 degrees C for 24h. The results of this study confirm that LTB is inducible by low but not freezing temperatures at harvest and therefore it might be considered as the physiological basis towards the development of an LTB incidence index for harvested kiwifruit. (c) 2006 Society of Chemical Industry.