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Variety-specific responses of lettuce grown in. a gravel-film technique closed hydroponic system to N supply on yield, morphology, phytochemicals, mineral 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 Martin M. Maboko Puffy Soundy Dharini Sivakumar phytochemical food network to improve nutritional quality for consumers 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） element is a common practice used to reach profitable yields in horticultural crops and N supply can be used as a tool to manipulate the enhancement of phytochemicals and minerals in vegetable crops to address consumer-oriented quality production. Hence the study was aimed to investigate the effect of N application on leaf morphology, ascorbic acid content, phenolic acids, flavonoids, mineral content, and nitrate residues in three lettuce varieties （two green leafy lettuce, Multigreen 1 and Multigreen 3; one red leafy lettuce, Multired 4） grown in a closed hydroponic system （grave^-film） at harvest. Nitrogen was applied as ammonium nitrate （NH4NO3） at six different concentrations of 0, 60, 90, 120, 150 and 180 mg L^-1. The results obtained during 2015 and 2016 seasons were similar and demonstrated variety dependent responses with respect to different N application rates. Multigreen 3 was more sensitive to N supply and showed higher amount of nitrate residue at harvest. Variety Multired 4 was less sensitive to N supply followed by Multigreen 11 Although N supply at 120 mg L^-1 improved the yield and the number of leaves in Multigreen 3, overall 90 mg L^-1 can be recommended for these lettuce varieties to improve the yield and the accumulation of ascorbic acid content, phenolic acids mainly caffeic, caftaric acids, quercetin （the important flavonoid in lettuce）, and Fe and Mn contents. Furthermore, the concentration of 90 mg L^-1 improved the antioxidant property （FRAP and ABTS^＋） and reduced the nitrate accumulation, ensuring safe food for consumers.

关键词： fertilizer application fresh weight phenolic acids antioxidant property flavonoids Fe Mn 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 Martin Maboko Puffy Soundy Dharini Sivakumar phytochemical 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

Limited information is available on the influence of preharvest N application rates on postharvest quality of different lettuce genotypes. Two green leafy lettuce (Multigreen 1 and Multigreen 3) and red leafy lettuce (Multired 4) were grown in gravel film technique and fertigated with five different N application rates: 60, 90, 120, 150 and 180 mg L^-1. The 120 mg L^-1 N application is commercially recommended for lettuce. After harvest, lettuce samples 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 time affected the leaf colour coordinates, phenolic acids (dicaffeoyltataric acid, caffeoyl tartaric acid, 3-caffeoylquinic acid and 3,4-dihydroxycinnamic acid) and browning enzyme activities (phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD)). Lower rates of N application at preharvest stage showed higher weight loss with the storage time increasing in Multigreen 3. In Multigreen 1, colour coordinate b* value decreased remarkably with N application rates from 60 to 120 mg L^–1 due to the onset of browning during storage. While in Multigreen 3 and N application higher than 60 mg L^–1 influenced the decrease in b* value. Browning occurred due to the increased activity of PAL enzyme and the availability of the substrates caftaric, chlorogenic, caffeic acids, PPO activity and production of browning pigments due to the activity of POD. Higher, N application rates (>120 mg L^–1) influenced the browning mechanism and showed brownish red leaves in Multired 4 during storage. Higher ascorbic acid concentration played a role in reducing the onset of browning in the fresh cuts leaves of Mulitired 4 and Multigreen 3 fertilized with lower preharvest lower N application rates (<120 mg L^–1). Preharvest N application at 90 mg L^–1 retained the colour, ascorbic acid content and the phenolic acid components and extended the shelf life of Multired 4 lettuce up to 6 days.

关键词： Lactuca sativa ascorbic acid phenylalanine ammonia-lyase polyphenol oxidase tissue browning

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