Effect of Temperature on Drying Characteristics and Quality of Three Nigerian Onion Varieties Using a Fabricated Electrically Powered Dryer
Asian Food Science Journal,
The research work is done to evaluate the effect of temperature on drying characteristics and quality of red, cream and white varieties Nigerian onion using a locally fabricated electrically powered dryer. Clean onion samples of 1.5 kg from each of the three varieties were sliced into 3 mm thickness. Fresh samples of the three onion varieties were analyzed to determine the initial values of protein, fat, ash, crude fibre, and moisture content on a dried basis (m.c.d.b.) using recommended AOAC methods.. Vitamin C and microbial loads content were determined before loading into a locally fabricated electrically-powered dryer. The onion samples were dried at varying pre-determined temperatures of 50, 60, and 70 oC. After drying, the proximate compositions, vitamin C and microbial loads were also determined. The protein, fat, ash and crude fibre of the fresh onion samples were 1.5, 0.5, 0.6 and 0.5%, respectively, while m.c.d.b, vitamin C content and microbial loads ranged from 85.1-88.2%, 8.1-8.3 mg/100 gm and 4.45-5.39 mg. Red onion samples were dried for 13:15h, 12:10h and 10:30h; white onion samples for 13:00h, 12:25h and 10:40h; while cream onion samples for 13:10h, 12:35h and 10:15h at 50, 60, and 70 oC, respectively. The protein, fat, ash, crude fibre, m.c.d.b, vitamin C content and microbial loads of the dried onion samples at all the drying temperatures ranged from 10.110.4, 1.1-1.5, 3.3-3.5, 5.5-5.8, 5.5-6.9%, 3.1-4.9 mg/100 gm, 1.314.17 mg, respectively. The drying temperature had a significant effect (p-value < 0.05) on the quality of all the onion samples. At 70 oC, protein, fibre, ash, fat and pungency retention were significantly (p< 0.05) high and within acceptable limits while microbial loads were low with the reduction in Vitamin C contents in all the onion varieties. Therefore, onion can best be dried at 70 oC to achieve the optimum quality and flavour required for its use as a spice.
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