Postharvest storage systems affect phytochemical content and quality of traditional Portuguese onion cultivars

• Published in: Acta horticulturae no. 9342; pp. 1327 - 1334
• Main Authors: Rodrigues, A.S, Almeida, D.P.F, García-Falcón, M.S, Simal-Gándara, J, Pérez-Gregorio, M.R
• Format: Journal Article
• Language: English
• Published: International Society for Horticultural Science 2012
• Subjects: Allium cepa; ambient temperature; cold storage; cultivars; firmness; flavonols; landraces; metabolism; onions; soluble solids; sprouting; storage quality
• ISSN: 0567-7572

Onion (Allium cepa L.) cultivars differ widely in their keeping quality. In the traditional onion growing region of Póvoa de Varzim, northwestern Portugal, landrace cultivars are harvested in July and stored in traditional non-refrigerated clamps in the field for up to 5 (white onion) or 7 months (red onion). The aim of this work was to assess the effect of two storage systems, refrigerated storage at 2°C and traditional field clamps, on phytochemicals and physicochemical quality of two Portuguese landrace cultivars of onion ('Branca da Póvoa' and 'Vermelha da Póvoa'). Flavonoid composition, dry matter (DM), pH, soluble solids content (SSC) and pungency were measured at harvest and following 3 and 6 months in storage. The red cultivar was more pungent, had higher DM, SSC, and about twice the flavonol level than the white cultivar. Results from two consecutive years in 2004 and 2005 showed that pH and pungency increased during storage, at a higher rate in the refrigerated system. Flavonols also increased significantly during storage of both cultivars, but SSC and firmness tended to decrease. Red onion stored in field clamps reached higher levels of flavonols (64% maximum, at 6-months of storage in 2004) than refrigerated onions (40% maximum). In white onions, the increase in flavonol increase was also higher in field storage (60% increases, at 5-months of storage in 2005). Sprouting and weight losses were lower in refrigerated storage than in traditional storage. These results suggest that storage at fluctuating ambient temperatures can positively affect flavonol metabolism while maintaining the flavonol profile, but control of sprouting is only feasible during the first 3 or 6 months, for white and red onion, respectively.