Varietal Effect on Drying Behaviour and Quality Characteristics of Onion

Experiments were carried out to study the drying behaviour and its effect on the quality characteristics of onions for three commonly grown varieties of onion. The quality characteristics studied were pyruvic acid concentration, colour and moisture content for each of the three varieties i.e. PBW-1, Punjab Naroya and PRO-6. The onions were dried for 495 min in the form of rings at constant drying temperature of 60°C in a through flow Satake dryer. The variety PBW-1 was found more suitable for commercial dehydration on account of lower drying ratio of 6.49 as compared to 7.26 for Pb Naroya and 7.90 for PRO-6, respectively. Constant drying rate period was not observed across all the experiments conducted for the three varieties. The whole process of drying of onions occurred in two to three falling rate drying period. The pyruvic acid, an important quality determining factor in onion, showed maximum loss of 71.20% for variety PRO-6 as compared to the loss of 63.61% in PBW-1 on dry weight basis during drying of onion rings at 60°C. It was observed that the total colour difference (ΔE) of 7.47 for the samples dried at 60°C was more in variety PRO6 as compared to variety PBW-1(ΔE = 6.13) and Pb Naroya (ΔE = 5.22).