Effect of Nitrogen Source, Crop Maturity Stage and Storage Conditions on Phenolics and Oxalate Contents in Vegetable Amaranth (Amaranthus hypochondriacus
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Date
2012Author
Onyango, Cecilia Moraa
Harbinson, Jeremy
Imungi, Jasper Kathenya
Onwonga, Richard Ndemo
Kooten, Olaf
Type
ArticleLanguage
enMetadata
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This study was designed to assess the effect of Diammonium Phosphate (DAP) fertilizer and cattle manure on the
accumulation of total phenolics, quercetin and oxalates during growth and storage of vegetable amaranth (var.
Amaranthus hypochondriacus L). Field trials were set up at the University of Nairobi Field Station-Upper Kabete
Campus, Kenya during the long (March –May) rains of 2007 and 2008. Trials were laid out in a randomized
complete block design with four fertilization treatments: 20, 40, and 60kg N.ha-1 supplied by DAP (18:46:0),
cattle manure (40 kg Nha-1) and an unfertilized control variant. The vegetables were harvested at 6, 7, and 8
weeks after planting and either refrigerated (4+1oC) or stored at ambient temperature (20+3oC) for a period of 4
days. The vegetables were then analyzed for total phenolic, quercetin, total and soluble oxalates content before
and after storage. The total phenolic content decreased with increasing N, the extent of decrease depended on the
level and source of N. DAP at 20kg Nha-1 had the same effect on the phenolic content as that of cattle manure at
40kg Nha-1. The levels of phenolics and quercetin increased with crop maturity while the converse was true for the
oxalate content. During refrigeration, levels of phenolics increased whereas those of oxalates did not change
appreciably. There was a decrease in phenolics content during storage at ambient temperatures. The vegetable
amaranth accumulates higher levels of total phenolic and quercetin when grown with manure than with DAP for
similar levels of N. Total phenolics and quercetin levels increased, while that of oxalates decreased, with maturity
of the vegetables. The accumulation of oxalates during the periods considered normal for growth are low enough
to maintain their levels within safe limits for human consumption. Storage of the fresh vegetables at 4oC for limited
periods improves their quality by increasing total phenolics and quercetin contents that also fulfill beneficial health
functions in the human body
URI
http://dx.doi.org/10.5539/jas.v4n7p219http://erepository.uonbi.ac.ke:8080/xmlui/handle/123456789/11628
Citation
Journal of Agricultural Science; Vol. 4, No. 7; 2012Publisher
Canadian Center of Science and Education Department of Plant Science and Crop Protection Department of Food Science, Nutrition and Technology Department of land Resource management and Agricultural Technology