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Rodrigues A.S.,Escola Superior Agraria de Ponte de Lima | Perez-Gregorio M.R.,Nutrition and Bromatology Group | Garcia-Falcon M.S.,Nutrition and Bromatology Group | Simal-Gandara J.,Nutrition and Bromatology Group | Almeida D.P.F.,University of Porto
Food Control

Onions are major sources of flavonoids in the human diet. However, little information is available regarding the effects of long-storage or exposure to specific stress conditions on flavonoids content of onions. The aim of this work was to assess the effect of different post-harvest treatments on the flavonoid composition of two Portuguese landrace varieties of onions ('Branca da Póvoa' and 'Vermelha da Póvoa'). The evolution of the content of some major flavonols and anthocyanins was measured in red and white onion bulbs (from 2005 and 2006 harvests) during 7 months of storage, under refrigerated and under traditional bulk storage in the field. Total flavonols increased up to 64% after 6 or 7 months of storage. This increase was especially important during the first 3 months of storage (58% increase). In red onions, with the largest concentrations in flavonols, bulbs stored in the field reached higher levels of flavonoids (64% maximum) than refrigerated onions (40% maximum). For red onions, the increase after 6-months storage usually has place when the flavonol post-harvest levels are low (40-64% increase), whereas for white onions the increase after 6-months storage is important for onions with higher levels after harvest (44-60% increase). These results suggest that storage at fluctuating ambient temperatures can positively affect flavonol metabolism, while keeping the flavonols profile. There were no significant modifications of the total levels of anthocyanin pigments after 6 months of storage of red bulbs, but after 7 months total anthocyanin content was reduced between 40% and 60%. Post-harvest UV (40 kJ/m2, 1 week storage) and ethylene (100 μL/L for 24 h, 2 months storage) treatments did only affect the flavonol content of the edible portion of onions with a profitable increase. © 2009 Elsevier Ltd. All rights reserved. Source

Rodrigues A.S.,Escola Superior Agraria de Ponte de Lima | Perez-Gregorio M.R.,University of Vigo | Garcia-Falcon M.S.,University of Vigo | Simal-Gandara J.,University of Vigo | Almeida D.P.F.,University of Porto
Food Chemistry

Although onion (Allium cepa L.) bulbs are good sources of phenolic compounds, the levels of these secondary metabolites are highly variable, depending on the cultivar, production, metereological conditions and post-harvest practices. The aim of this study was to characterize the interannual variation of flavonoid content in two Portuguese landrace varieties of onion ('Branca da Póvoa', white, and 'Vermelha da Póvoa', red), grown in the Spring-Summer of 2004, 2005, 2006, 2007 and 2008. HPLC-DAD was used to determine flavonoid concentration.Quercetin 3,4'-diglucoside and quercetin 4'-monoglucoside were the main flavonols in both varieties. Additionally, six cyanidin derivatives were identified in the red variety. Total and individual flavonoids levels varied significantly among seasons, with higher levels in 2005, a very dry and hot season. The red onion variety did not accumulate detectable amounts of anthocyanins in 2007, the year with the lowest air and soil temperature and highest soil water content. © 2010 Elsevier Ltd. Source

Perez-Gregorio R.M.,University of Vigo | Garcia-Falcon M.S.,University of Vigo | Simal-Gandara J.,University of Vigo | Rodrigues A.S.,Escola Superior Agraria de Ponte de Lima | Almeida D.P.F.,University of Porto
Journal of Food Composition and Analysis

Onions are rich in different types of phenolics, mainly flavonols, and in red varieties anthocyanins are also present. This is significant because these classes of phenolics are antioxidants and hence may impart important functional properties to onions. The aim of the present work was to simultaneously determine flavonol and anthocyanin concentrations in different onion varieties, two white (Branca da Póvoa and the hybrid SK409) and three red (landrace Vermelha da Póvoa, a selected line of Vermelha da Póvoa and Red Creole). Flavonols (quercetin 7,4-diglucoside, quercetin 3,4-diglucoside, isorhamnetin 3,4-diglucoside, quercetin 3-glucoside, quercetin 4-glucoside and isorhamnetin 4-glucoside) were the predominant polyphenolic compounds. White cultivars had the lowest total flavonol content, with values of 89.3 ± 38.5 and 101.0 ± 18.9. mg. quercetin/kg. fresh. weight for Branca da Póvoa and the hybrid SK409, respectively. The red onions had the highest levels of flavonols, especially the selected population of Vermelha da Póvoa and Red Creole, with values of 280.2 ± 41.5 and 304.3 ± 81.2. mg. quercetin/kg. fresh weight, respectively. Red onions are not only richer in flavonols, but also contain anthocyanins. Four anthocyanins (cyanidin 3-glucoside, cyanidin 3-laminaribioside, cyanidin 3-(6″-malonylglucoside), and cyanidin 3-malonylaminaribioside) were quantified in all red onions, with Red Creole presenting the highest concentration (28.6 ± 8. mg. cyanidin/kg. fresh. weight). Red onions may be recommended for their major potential functional properties. A distinct gradient in total flavonoid content was found between the outer, central and inner edible scales and along the longitudinal axis of the bulb. Differences in flavonol levels between small- and large-sized onions were also found. All of these factors are of paramount importance for sampling and characterizing onions with regard to flavonoids. © 2009 Elsevier Inc. Source

Brito L.M.,Escola Superior Agraria de Ponte de Lima | Mourao I.,Escola Superior Agraria de Ponte de Lima | Coutinho J.,University of Tras os Montes e Alto Douro | Smith S.R.,Imperial College London
Compost Science and Utilization

Cattle slurry solid fraction (SF) was composted with increasing rates (0,25,33 and 50% v/v) of either Italian ryegrass (Lolium multiflorum L.) straw or gorse (Ulex europaes) to determine the effects of these bulking agents on the physicochemical properties during the composting process and to identify approaches to improve final compost quality. Composting temperatures increased to a maximum of 65°C after 42 days for unamended SF. In contrast, temperatures increased more rapidly in piles mixed with straw (68°C at day 7) or with gorse (74°C at day 3). Gorse or straw addition to SF, therefore, also increased the initial rates of organic matter mineralization. However, potential organic matter (OM) mineralization and compost N concentration decreased with the addition of the bulking agents. C/N ratios declined from 32-38 to a value of 13-17 towards the end of composting and followed a similar trend for all compost treatments. Low compost temperature, low C/N ratio and the small content of NH4 + combined with increased concentrations of NO - indicated SF composts were stabilized and suitable for use in agriculture. High concentrations of OM (780-840 g kg -1 dry matter (DM)) and total N (28-35 g kg-1 DM), and low electrical conductivity (0.7-1.2 dS m-1) suggested that SF composts would be effective soil amendments with agronomic and environmental advantages. The addition of straw or gorse also enhanced compost sanitation. Source

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