Consequences of Cool Storage of Broccoli on Physiological and Biochemical Changes and Subsequent Senescence at 20 °C

Abstract

In most broccoli (Brassica oleracea L. var. italica) cultivars studied, the loss of chlorophyll was marginal after 5 weeks cool storage (1 °C) + 2 days at 20 °C, but there was significant loss of chlorophyll from some poor-storing cultivars, particularly after 10 weeks cool storage (+2 days at 20 °C). Soluble sugars were depleted rapidly during cool storage (especially sucrose) and were essentially exhausted after 10 weeks at 1 °C. Losses of total proteins were only 20% after 10 weeks cool storage. There is preferential catabolism of carbohydrates (sucrose, glucose, and fructose) at low temperatures, whereas, at 20 °C, protein and carbohydrate levels decline concomitantly. The patterns of sugar and protein depletion suggest that all soluble sugar is potentially accessible for metabolism, but protein catabolism is targeted to specific tissues or organs. After 5 weeks at 1 °C and placing at 20 °C, ethylene production and respiration increased to steady-state levels. Peak production of wound ethylene usually occurs 4 to 6 hours after harvest at 20 °C. After 5 or 10 weeks cool storage, this peak of production was not detected at 20 °C. After 10 weeks at 1 °C, recovery of ethylene production was delayed and the respiration rate only partially recovered to the steady level. However, chlorophyll loss is the major determinant of marketable life without cool storage, and, after 5 weeks at 1 °C, postharvest decay is the major determinant of marketable life after cool storage, particularly after 10 weeks at 1 °C.