Enhancement of onion bulb drying with air dehumidification assisted dryer

Drying is an important process in onion bulb processing to preserve product quality and storage time. This paper discusses how to find an onion bulb with acceptable moisture content and high ingredient retention rate with minimized heat usage. As indicators, moisture content, riboflavin (Vitamin B2) content, and heat efficiency are evaluated at different drying temperatures and air relative humidity. In doing so, the response surface method is employed to find the most favorable drying condition. Polynomial regression was found to be a good fit in predicting moisture content, while heat efficiency response is significantly fit after dehumidification is applied. Moreover, onion drying with air dehumidification has more advantages than that of without dehumidification. With low air relative and medium drying temperature, the heat efficiency of the onion bulb drying can be positively improved with an acceptable riboflavin retention. Analysis of variance revealed that air dehumidification and drying temperature have a significant impact on the drying time and heat efficiency. However, at high air temperatures, the effect of air dehumidification is limited.