Effect of Drying Methods on the Moisture Content and Microbiological Properties of Three Varieties of Dried Onion Slices (Allium cepa)

Abstract

Post-Harvest losses of onions occurring due to poor handlings and spoilage by microorganisms is worthy of concern. Value addition through drying during peak seasons can reduce losses remarkably. This study sought to evaluate the effects of different drying methods on the microbial load of dried onion slices. Three varieties of onion (red, white and cream) were purchased National Institute for Horticultural Research (NIHORT) Kano sub-station and processed into dried slices using three dryers namely; Solar Cabinet Dryer (SCD), Electric Powered Dryer (EPD) and Kerosene Powered Dryer (KPD) at three different temperatures (50, 60 and 70oC). The dried onion slices were then evaluated for their microbial load; Aerobic Plate Counts (APC), Coliform Counts (CC) and Fungal Counts (FC) using three different media and according to standard methods. The results revealed that MC of onions were reduced from 88.29% to as low as 5.19% during drying. The APC, CC and FC of red onion ranged from 3.67–5.39×102 cfu/g, 1.35–5.39×102 cfu/g and 3.44–4.83×102 cfu/g respectively. The load for white onion ranged from 3.11–5.19×102 cfu/g, 1.31–5.29×102 cfu/g and 3.43–4.53×102 cfu/g respectively while that of cream onion ranged from 3.30–5.33×102 cfu/g, 1.33–5.39×102 cfu/g and 3.42–4.57×102 cfu/g respectively. All the readings fell below the international recommended safe limit for food consumption. The EPD samples at 60oC and 70oC had the significant lowest (p≤0.05) fungal counts in all the onion varieties. Therefore, electric oven dryer at 70oC was the best drying methods and temperature for onion for long time storage.