High-Temperature-Short-Time (HTST) disinfestation of wheat grain infested by Sitophilus spp. pre-emergent stages with a laboratory scale fluidized-bed


Abstract: A laboratory test-bench was built up to simulate high-temperature-short-time (HTST) exposure of infested grain samples by hidden stages of Sitophilus granarius or Sitophilus oryzae in a fluidized bed in order to model temperature exposure time relationship. The reduction of emergence of the two weevil species (S. granarius in bread making wheat and S. oryzae in durum wheat) was determined after different exposure times in the fluidized bed exposure chamber crossed by 2 m/s airflow at inlet air temperatures of 60, 90, 120 and 150 °C. The influence of a grain moisture content from 14 to 19% w.b. on lethal time 50% (LT50) and lethal time 99% (probit 8 or LT100) was also observed. The main microbiological and technological characteristics checked on grain samples after heat treatment were measured. Higher the moisture content longer the exposure time required for the same mortality rate to be achieved. The “temperature-exposure time products” assessed at LT50 and LT100 were modeled as asymptotic negative regression curves. LT100 was observed in less than 10 s exposure time for temperature at air inlet of 120 and 150 °C, whatever the moisture content level. The reduction of fungal colonies was more important with long exposure time at moderately high temperature (90 °C) than with short exposure time at very high temperature (150 °C) (giving similar levels of insect mortality rate). For bread-making wheat, it was not observed significant changes in alveogramme rheological test parameters processed with white flour extracted from heat-treated wheat samples, provided that air temperature and initial grain moisture content are at moderately high level (less than 150 °C and 15% m.c.). The HTST treatment of cereal grain is an efficient and rapid method of control of weevil internal feeder stages and may be developed at practical scale for organic cereals or high-added-value use for special healthy cereal food disinfestations.

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