Impact of preharvest relative air humidity and postharvest modified atmosphere packaging on cucumber fruit quality

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English. The effect of relative air humidity (RH) was tested on the cucumber (Cocktail, Quarto F1 cultivar) plant growth, morphology and fruit quality in controlled growth chambers. The plants were grown at moderate RH (60%) and high RH (90%) with the same temperature, CO2 and irradiance. In addition, another experiment was conducted to test that effect of exogenous application of abscisic acid (ABA) and different packaging materials (modified atmosphere packaging bags and plastic folio) on the quality of commercial produced cucumber fruits stored at low temperature (TC) storage for 14 days and 21 days. Cucumber plants and fruits responded strongly to the different RH conditions. The plant shoot length, number of leaves and fruit diameter was increased at high RH, while average leaf area, relative chlorophyll contents, number of side shoots were increased at moderate RH compared to high RH. Higher antioxidant capacity and total phenolics contents were observed in fruits from moderate RH. Through High Pressure Liquid Chromatography (HPLC) analysis 3 polyphenols (resveratrol, luteolin and apigenin) were identified in cucumber leaf samples and 6 polyphenols (apigenin, luteolin, quercetin 3 glycoside, quercetin, pinoresinol and resveratrol) were found in cucumber fruit samples. Moderate RH increased the resveratrol and luteolin concentration in cucumber leaves and increased the luteolin, quercetin 3 glycoside, quercetin and pinoresinol in cucumber fruit sample. Moderate RH not only affected the polyphenols contents, but it also influenced the sugars concentration in cucumber leaves and specifically in cucumber fruits. Significantly higher starch contents were found in cucumber leaves from high RH, while fructose, glucose and sucrose was not really effected by difference in RH. Stachyose and raffinose contents in leaves were significantly increased at moderate RH. On the other hand, fructose, glucose and starch was significantly higher in cucumber fruits from moderate RH. Furthermore, total nitrogen, potassium and boron contents were higher in cucumber leaves from moderate RH. Higher total nitrogen, total carbon, phosphorous and potassium contents were found in cucumber fruits from moderate RH, while calcium, magnesium, manganese and molybdenum contents in fruits were increased with increased RH. The sensory evaluation of cucumber fruits indicated that RH induced a more bitter taste perception and contained more water. On the other hand, cucumber fruits from moderate RH was perceived more sweet, better in flavour and colour. Through correlation analysis, it was found that better flavour and good colour of cucumber fruits was due to starch contents and bitterness might be the taste of molybdenum. In the second experiment, ABA application and MAP bags reduced the respiration of commercially produced cucumber fruits. Furthermore, the combined treatment of ABA with MAP bags effectively reduced physical weight loss, disease incidence and skin shrivelling of cucumber fruits. The ABA treated-MAP bagged and non ABA treated-MAP bagged fruits showed the lowest percentage of ion leakage, higher anti-oxidant capacity and total phenolics contents. In summary, the cucumber plants grown at moderate RH performed better in terms of vegetative growth and produced good internal and external fruit quality. On the other hand, the cucumber fruits got extended storage life and maintained the better quality under MAP bagged condition.