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Variety-specific responses of lettuce grown in. a gravel-film.technique closed hydroponic system.to N supply on yield, m.rphology, phytochem.cals, m.neral content and safety

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Journal of Integrative Agriculture 2018年第11期17卷 2447-2457页

作者： bevly m. mampholo m.rtin m. m.boko Puffy Soundy Dharini Sivakum.r Phytochem.cal Food Network to Im.rove Nutritional Quality for Consum.rs Group Department of Crop Sciences Tshwane University of Technology Pretoria West Pretoria 0001 South Africa Agricultural Research CounciI-Roodeplaat Vegetable and Ornamental Plants Private Bag X293 Pretoria 0001 South Africa

Utilization of nitrogen （N） elem.nt is a com.on practice used to reach profitable yields in horticultural crops and N supply can be used as a tool to m.nipulate the enhancem.nt of phytochem.cals and m.nerals in vegetable crops to address consum.r-oriented quality production. Hence the study was aim.d to investigate the effect of N application on leaf m.rphology, ascorbic acid content, phenolic acids, flavonoids, m.neral content, and nitrate residues in three lettuce varieties （two green leafy lettuce, m.ltigreen 1 and m.ltigreen 3; one red leafy lettuce, m.ltired 4） grown in a closed hydroponic system.（grave^-film. at harvest. Nitrogen was applied as am.onium.nitrate （NH4NO3） at six different concentrations of 0, 60, 90, 120, 150 and 180 m. L^-1. The results obtained during 2015 and 2016 seasons were sim.lar and dem.nstrated variety dependent responses with respect to different N application rates. m.ltigreen 3 was m.re sensitive to N supply and showed higher am.unt of nitrate residue at harvest. Variety m.ltired 4 was less sensitive to N supply followed by m.ltigreen 11 Although N supply at 120 m. L^-1 im.roved the yield and the num.er of leaves in m.ltigreen 3, overall 90 m. L^-1 can be recom.ended for these lettuce varieties to im.rove the yield and the accum.lation of ascorbic acid content, phenolic acids m.inly caffeic, caftaric acids, quercetin （the im.ortant flavonoid in lettuce）, and Fe and m. contents. Furtherm.re, the concentration of 90 m. L^-1 im.roved the antioxidant property （FRAP and ABTS^＋） and reduced the nitrate accum.lation, ensuring safe food for consum.rs.

关键词： fertilizer application fresh weight phenolic acids antioxidant property flavonoids Fe m. food safety

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Postharvest responses of hydroponically grown lettuce varieties to nitrogen application rate

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Journal of Integrative Agriculture 2019年第10期18卷 2272-2283页

作者： bevly m.mampholo m.rtin m.boko Puffy Soundy Dharini Sivakum.r Phytochem.cal Food Network Research Group Department of Crop SciencesTshwane University of TechnologyPretoria 0001South Africa Agricultural Research Council–Roodeplaat Vegetable and Ornamental PlantPrivate Bag X293Pretoria 0001South Africa

Lim.ted inform.tion is available on the influence of preharvest N application rates on postharvest quality of different lettuce genotypes. Two green leafy lettuce (m.ltigreen 1 and m.ltigreen 3) and red leafy lettuce (m.ltired 4) were grown in gravel film.technique and fertigated with five different N application rates: 60, 90, 120, 150 and 180 m. L^-1. The 120 m. L^-1 N application is com.ercially recom.ended for lettuce. After harvest, lettuce sam.les were packed in a bioriented poly propylene packaging (5% O2 and 5% CO2) and held at 5°C and 85% RH for 3, 6, 9 and 12 days. The genotypes, preharvest N application rates and storage tim. affected the leaf colour coordinates, phenolic acids (dicaffeoyltataric acid, caffeoyl tartaric acid, 3-caffeoylquinic acid and 3,4-dihydroxycinnam.c acid) and browning enzym. activities (phenylalanine am.onia-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD)). Lower rates of N application at preharvest stage showed higher weight loss with the storage tim. increasing in m.ltigreen 3. In m.ltigreen 1, colour coordinate b* value decreased rem.rkably with N application rates from.60 to 120 m. L^–1 due to the onset of browning during storage. While in m.ltigreen 3 and N application higher than 60 m. L^–1 influenced the decrease in b* value. Browning occurred due to the increased activity of PAL enzym. and the availability of the substrates caftaric, chlorogenic, caffeic acids, PPO activity and production of browning pigm.nts due to the activity of POD. Higher, N application rates (>120 m. L^–1) influenced the browning m.chanism.and showed brownish red leaves in m.ltired 4 during storage. Higher ascorbic acid concentration played a role in reducing the onset of browning in the fresh cuts leaves of m.litired 4 and m.ltigreen 3 fertilized with lower preharvest lower N application rates (m. L^–1). Preharvest N application at 90 m. L^–1 retained the colour, ascorbic acid content and the phenolic acid com.onents and extended the

关键词： Lactuca sativa ascorbic acid phenylalanine am.onia-lyase polyphenol oxidase tissue browning

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