Effect of storage methods on some selected mineral and ascorbic acid content of red and white onion (Allium cepa)

The study investigated the influence of three different storage conditions in minimising the postharvest losses of onions. The fresh onion walla-walla variety (red and white) were obtained from Modibbo Isah Farms, Bichi, Kano State, Nigeria. The onions were stored for eight weeks under three different storage conditions which include: Ambient temperature (30 ± 2 ºC), refrigeration storage (5-7 ºC) and control cupboard temperature storage (45-50 ºC) during which the samples were analysed weekly. During the storage period of onion bulbs, the temperature ranged between (29-32 ºC) while the relative humidity was between (70 – 95 % RH).The mineral (calcium, sodium and potassium) content was determined by Atomic Absorption Spectrophotometry while Ascorbic acid was determined by the 2, 6- dichlorophenol indophenol (DCPIP) titration. The result showed that some components of the stored onions decreased with an increase in the storage period and these include: ascorbic acid (9.62-3.87mg/100g) and sodium content (12.13-11.77mg/kg). While some parameters also showed an increase with an increase in the storage period and these include: potassium content (30.00-72.12mg/kg) and calcium content (55-105mg/kg).