Effect of postharvest water loss on ‘Hayward’ kiwifruit water status

Abstract

To investigate the effect of postharvest water loss on ‘Hayward’ kiwifruit (Actinidia deliciosa C.F. Liang and A.R. Ferguson var. deliciosa) water status, fruit were observed over 14 days after harvest while being subjected to dehydrating conditions in chambers ventilated at 1 l min−1 with dry air (∼10% relative humidity, 20°C). Techniques for monitoring the change in internal aqueous characteristics involved serial magnetic resonance (MR) imaging and traditional measures of fruit water status: water content, relative water content (RWC), tissue water potential, and juice osmotic potential. Fruit fresh weight decreased by 8–10% of the initial weight over the trial period. This was accompanied by decreased water content, RWC and water potential. The rate of decrease in fresh weight, water content and RWC slowed with time. Measurements from serial MR images revealed fruit volume also decreased. This was attributable to shrinkage along the stem–calyx axis (6–9% reduction) rather than across the fruit diameter (1–3% reduction). Relaxation measurements (spin–lattice (T1) and spin–spin (T2)) indicated that there were significant differences between the localised aqueous environments of the core, inner pericarp and outer pericarp, and that the water content (proton density) differed across the fruit. However, despite the marked changes in the fruit's tissue water content, RWC, water potential and juice osmotic potential during dehydration, no significant change was observed in any of the MR measurements during the course of this study. Comparison of the relaxation measurements with those from other imaging studies suggested this observation was not unusual.