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Low intensity postharvest lighting improves quality and shelf life of fresh-cut lettuce

Woltering, E.J. (Wageningen University and Research Centre, Food & Biobased Research, Bornse Weilanden 9, 6708 WG Wageningen, The Netherlands and Wageningen University, Horticulture & Product Physiology, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands)Witkowska, I.M. (Wageningen University, Horticulture & Product Physiology, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands)Schouten, R.(Wageningen University, Horticulture & Product Physiology, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands)Harbinson, J. (Wageningen University, Horticulture & Product Physiology, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands)
Fresh-cut butterhead and iceberg lettuce was stored in darkness and under low light conditions (approximately 5 ┬Ámol m-2 s-1 PAR) provided by either fluorescent tubes, red, blue or green LEDs. Low light conditions considerably improved quality compared to storage in darkness; lighting delayed cut-edge browning and greatly prolonged the shelf life. In dark stored samples a rapid depletion of chlorophyll, carotenoids, ascorbic acid and carbohydrates was observed. In lit samples, chlorophyll and carotenoids decreased in a similar fashion as in dark stored samples but ascorbic acid levels were preserved. In lit butterhead samples total carbohydrates increased over 10 times the initial levels. In iceberg samples, the decrease in total carbohydrates observed in the dark was greatly delayed by light. The applied light levels of approximately 5 ┬Ámol m-2 s-1 PAR are well below the light compensation point of lettuce, indicating that the preservation of carbohydrates is not through photosynthetic sugar production. Measurements of photosynthetic activity confirmed that there was no net photosynthesis in lit samples. The preservation of sugar and ascorbic acid and the prolonged shelf life occurred independent of the applied light source (fluorescence tubes, LEDs). The prolonged shelf life of low light-treated samples is presumably due to the higher levels of sugar and ascorbate that may act as antioxidants, may preserve membrane integrity and may provide sufficient respiratory substrate to prevent ATP depletion. 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). The use of light as a novel sustainable postharvest technology is discussed.

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