No abstract

Electrical impedance spectroscopy was used to follow ripening and chilling injury development in persimmon fruit (Dyospyros kaki L. 'Fuyu'). Tissue resistance and reactance were measured at frequencies between 50 Hz and 1 MHz, and then fitted to an electrical model. Fruit responses to both ripening at 20°C and storage in modified atmosphere at 7°C were distinct and easily detected using electrical impedance spectroscopy. Plots of reactance against resistance at each series of frequencies traced a semicircular arc. During ripening, the arcs dilated between Days 1 and 21, then contracted, until at Day 35 they were smaller than at Day 1. Electrical modelling indicated that the dilation occurred as a result of a 43, 115, and 17% increase in resistance R\ (cell wall resistance), R 2 (cytoplasm resistance), and R 4 (vacuole resistance), respectively. After 35 days of ripening, R 1 was 39% lower and C 3 (membrane capacitance) was 19% higher than at Day 1. Chilling injury developed with increasing time at 7°C in modified atmosphere storage (MA), until severe symptoms were observed after 5 weeks. Chill-injured fruit differed from other fruit in that R2 was significantly lower upon removal from storage, although it rapidly increased when fruit were transferred to 20°C for ripening. These results are discussed in relation to the physiological changes that occur during ripening and development of chilling injury in persimmon.

Postharvest rots and internal disorders of 'Hass' avocado (Persea americana) fruit develop during the latter stages of fruit ripening, with symptoms first appearing when fruit are minimally ripe but often becoming quite severe before the fruit are oversoft. Fruit ripened at 20°C and assessed at the same stage of ripeness, just before the flesh becomes oversoft, had fewer postharvest rots if they had been previously stored at 4 or 6°C, than if they had been stored at either lower or higher temperatures. Postharvest disorders increased with increased length of storage. Fruit failed to ripen properly at 30°C. Even at 25°C (a temperature typically experienced by fruit exported from New Zealand), the level of postharvest disorders was greater than in fruit ripened at 20°C. Best final quality was obtained with fruit coolstored at 6°C and then ripened at 15 °C. However, if fruit are to be ripened at c. 25°C, then final quality was better if the fruit were not coolstored but held at a temperature closer to the final ripening temperature. Fruit from a single orchard block, harvested, coolstored, and ripened together, individually reached minimum eating ripeness over an 8-day period. Fruit which ripened earliest had the fewest disorders, with later ripening fruit typically having high levels of postharvest rots and internal browning.

No abstract

Development of chilling injury in individual persimmon fruit was monitored over a 7week period using nuclear magnetic resonance (NMR) imaging. At commercial harvest, fruit of the non-astringent cultivar, 'Fuyu', were divided into two treatments-one in which samples were sealed in individual polyethylene bags, and another without bags (control). Storage conditions were 0°C for 6 weeks. Proton NMR images (0.39 mm resolution) of trans verse and longitudinal sections were obtained weekly using a standard Hahn spin-echo pulse sequence (T^ = 30 ms, T R = 500 ms) on a 0.5 Tesla whole-body scanner. There was limited NMR evidence to support development of chilling injury in fruit from either treatment during cold storage. After removal to ambient temperatures however, injury developed rapidly causing fruit to be inedible within 1 week. Changes observed non-invasively during the period of degradation were consistent with visual observations describing the development of the disorder in this crop.