Kinetics of Thiamine and Color Degradation in Onion Drying Under Various Temperatures

The onion drying aims to reduce moisture content in outer layer of onion. So, the inside part of onion can be protected from microbial activity. However, in conventional convective drying, the thiamine content in onion as well as the color can degrade with introduction of heat. This research studied kinetic of thiamine and color degradation in onion drying under various temperatures. The study is useful to predict recommended drying temperature and time for high thiamine retention. In this case, onion was dried at various temperatures for 120 minutes. As the responses, thiamine content and color were observed every 30 minute. Results showed that thiamine degradation was categorized as first order reaction. The constant rate of thiamine degradation depends on temperature change referring to Arrhenius correlation. In example, thiamine degradation was about 85.62% under temperature drying of 50 degrees C for 5 hours. Meanwhile, Onion color changed close to brown with the increase of temperature. The lower temperature or shorter drying time, resulted higher thiamine and color retention.