MEMBRANE STRUCTURAL LIPID CHANGES IN FRESH-CUT CARROTS: REVISITING THE "WOUNDING AND AGING" PHENOMENON

Abstract

Virtually no quantitative data exist for membrane lipid metabolism of fresh-cut (wound-stressed) vegetables and fruits, despite the inevitable consequences of wounding. One such result is the rupture of cell membranes and activation of membrane lipid catabolic processes. We have evaluated changes in membrane sterols and glycerolipids in shredded carrots, a popular fresh-cut commodity. 'Apache' and 'Caropak' carrots were shredded and stored under conditions similar to those used in retail markets (10°C and 95% RH). Between 0 and 10 days of storage, membrane lipid concentrations in the shredded tissue were determined using HPLC/evaporative light scattering detection. Total phospholipid and acylated sterol glycoside concentrations increase by as much as 31% and 135%, respectively, following 10 days of storage. These increases are indicative of membrane restructuring (repair) processes, are accentuated by Ca 2+ pretreatment, and appear to be cultivar-dependent. During storage, Ca 2+ pretreatment also delays onset of increases in the ratios of free sterols to phospholipids and of free stigmasterol to free sitosterol (both senescence-driven processes); and as expected, Ca 2+ pretreatment reduces cell permeability. However, Ca 2+ pretreatment does not curb the rate of accumulation of phosphatidic acid, a membrane degradation product. Coexistence of membrane degradation and repair processes appears to be a characteristic feature of wounding and long-term storage of carrots. Further, Ca 2+ pretreatment may prove to be a valuable approach for maintaining quality of fresh-cut carrots and possibly other fresh-cut products, owing to its stabilising influence on cell membrane systems.