Temperature and relative humidity profiles during heat treatment of mills and its efficacy against Tribolium castaneum (Herbst) life stages

Heat treatment involves raising the temperature of a food-processing facility to 50-60degreesC and maintaining these elevated temperatures for 24-36 h to kill stored-product insects. The pilot feed and flour mills at Kansas State University, Manhattan, KS, were subjected to heat treatment using gas and steam heaters, respectively, during 4-8 August 2001 to characterize temperature and relative humidity profiles and to determine efficacy against developmental stages of the red flour beetle, Tribolium castaneum (Herbst). Temperature and relative humidity profiles in each mill were electronically monitored in 10 different locations. Susceptibility of eggs, young instars, old instars, pupae, and adults of T castaneum to heat was determined at the same 10 locations within each mill. The number of hours required to reach the target temperature of 50degreesC, number of hours above 50degreesC, and maximum temperatures varied between the mills and among mill locations. Relative humidity decreased predictably with an increase in temperature, and was less than or equal to21% in most locations at 50degreesC or above. Two separate three-parameter non-linear regression models best described temperature and relative humidity profiles observed in each mill. Despite non-uniform heating at the sample locations, mortality of T castaneum life stages was 100% in most locations, except in areas where temperatures were <50degreesC. Old instars and pupae appeared to be relatively heat tolerant when compared with other life stages, especially in the flour mill where lethal temperatures were attained. Possible reasons for the non-uniform heating observed at mill locations and survival of certain T castaneum developmental stages are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.