High-Temperature Continuous-Flow Curing of Sweet Onions

A study was undertaken to investigate the feasibility of heat-treating sweet onions under controlled commercialconditions. Three test runs were conducted whereby approximately 4 m3 of onions for each test were passed through acontinuous-flow drier. Set-point temperatures of 43.C, 43.C, and 46.C and durations of heat treatment of 17, 24, and 24h were used, respectively, during the three tests. Samples of heat-treated onions were taken from the dryer at regular intervalsand, after prescribed storage intervals, were inspected for the presence of Botrytis allii with the aid of a dye. The increasein disease was calculated. There was a significantly (P < 0.01) less increase in disease during storage for those onions havingreceived heat treatment compared with onions conventionally cured. In comparing the least square means, 24 h of heattreatment resulted in a lower incidence of disease than 17 h. Similarly, a set-point temperature of 46.C resulted in a lowerincidence of disease than 43.C . Based upon the results of the study, a combination of heat treatment and conventional curingwas recommended.