The postharvest senescence of broccoli (Brassica oleracea L. Italica group) was studied immediately after harvest until senescence was essentially completed at 20C. Changes in respiration, ethylene production, and color were determined for florets, branchlets, and heads of three cultivars of field-harvested `Green Beauty', `Dominator', and `Shogun' broccoli. Changes in respiration and ethylene production were also determined for 3 hours of preharvest and 24 hours of postharvest storage using broccoli grown in containers. Carbon dioxide produced from heads of container-grown broccoli and from heads, branchlets, and florets of field-harvested broccoli decreased markedly during the first 12 hours of postharvest storage before stabilizing. The respiratory quotient shifted toward a more oxidative metabolism in parallel with the respiratory decline. Ethylene production during storage showed no consistent relationship to yellowing. However, time until onset of yellowing was broadly related to the basal levels of ethylene production. The maximum storage life at 20C is ≈72 hours. Branchlets are useful model systems for investigating broccoli senescence.
Graeme A. King and Stephen C. Morris
Barry J. Pogson and Stephen C. Morris
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.
Graeme A. King and Stephen C. Morris
Compositional changes during the postharvest senescence of broccoli branchlets held at 20C in the dark were investigated, particularly during the first 24 hours. Major losses of sugars, organic acids, and proteins from floral, middle, and base sections of branchlets were detected during the first 6 hours. Between 12 and 96 hours, free amino acid pools increased (especially the amides glutamine and asparagine) for all sections of branchlets, while ammonia accumulated only in floral sections. Results are discussed in relation to the nature of the processes that set the tissues on the pathways leading to postharvest senescence.
Margaret Landrigan, Stephen C. Morris, and Barry W. McGlasson
Rambutan (Nephelium lappaceum L.) rapidly lose their attractive appearance after harvest due to a superficial pericarp browning. Storage at high humidity minimizes fruit desiccation and may, therefore, delay browning onset. This paper examines the effect of reduced water loss rate on browning that may occur with time. Rambutan fruit pericarp browning beyond a commercially saleable level occurred at a weight loss of 25% to 40%. This depended on duration and storage relative humidity (RH). Skin browning was 50% greater on the red (R 134) than the yellow (R 156) cultivar at 60% RH. There was a storage time × RH interaction in the development of browning such that browning was observed earlier at lower RHs. Skin browning and spintern (soft spine) browning developed independently. Cracks appeared on the surface of fruit with increased weight loss. Browning occurrence was consistent with increased total phenolic compound levels in the pericarp. Water loss precedes browning occurrence and, over time, water loss is related to browning. Water stress appeared to affect rambutan pericarp tissue in much the same manner as senescence.