Effects of pre- and postharvest lighting on quality and shelf life of fresh-cut lettuce

The effects of pre- and postharvest lighting on quality and shelf life of fresh-cut lettuce was investigated. Lettuce was grown under different light intensities (120 and 250 mu mol m(-2) s(-1) PAR from fluorescent tubes) and quality at harvest and subsequent postharvest performance of intact leaves and fresh-cut product was monitored. Cultivation under high light prolonged the shelf life (dark storage) of both intact leaves and fresh-cut product (butterhead and iceberg lettuce). The improved shelf life was reflected in improved chlorophyll fluorescence values. Postharvest lighting of the fresh-cut product, at low intensities (7 and 30 mu mol m(-2) s(-1) PAR from fluorescent tubes) considerably prolonged the shelf life of fresh-cut product (butterhead lettuce) compared to storage in darkness. This was reflected in higher overall visual quality values and delayed cut-edge browning. The applied light levels caused an 8 to 10 times increase in carbohydrate levels (sugars and starch) whereas carbohydrates decreased when the fresh-cut product was stored in the dark. Storage in light caused an increase in dark respiration leading to increasingly negative photosynthetic values. The prolonged shelf life of low light-treated samples is presumably related to the higher levels of sugar, counteracting starvation processes. Currently, it is not clear which processes are responsible for the sugar accumulation in lit samples. We hypothesize that, under low light conditions, sugars may be produced through the processing of chloroplast degradation products in the glyoxysome, subsequent production of malate and oxaloacetate and production of glucose through reversal of the glycolysis pathway (gluconeogenesis).