Enumeration of fungi in grain flours and meals as influenced by settling time in diluent and by the recovery medium

Abstract

A study was undertaken to determine if the time elapsed, i.e., settling time, after homogenizing grain flours and meals in a primary diluent and withdrawing samples for serially diluting and plating has an effect on populations of yeasts and molds detected. Sixty samples of flour and meal were analyzed. Samples were withdrawn from the top, middle, and bottom areas of graduated cylinders containing homogenates after settling times of 0, 2, 6, and 10 min and plated on dichloran 18% glycerol agar and dichloran rose bengal chloramphenicol agar. As the settling time between homogenizing plain and self-rising wheat flours and rye flour increased, the population of fungi detected in the top area of primary homogenates decreased significantly (P ≤ 0.05), whereas the population detected in the bottom area increased significantly. Dichloran 18% glycerol agar was clearly superior to dichloran rose bengal chloramphenicol agar for recovering fungi from wheat and rye flours, regardless of settling time. Populations detected in buckwheat flour and in plain and self-rising corn meal were largely unaffected by settling time, sampling location, and recovery medium.