Determination of low levels of mite and insect contaminants in food and feedstuffs by a modified flotation method.

Extraneous material was separated from feed and food products by a modified technique in which kerosene is used in a specially designed flotation flask. This technique, although effective for analyzing feed and foods, presented limitations in the analysis of finely powdered materials. Some procedural modifications and an increased in the capacity of the flotation flask from 500 to 750 mL allowed a larger sample weight (20 g) to be analyzed for mites, insect fragments, and rodent hairs, with considerably reduced residue interference. In trials with a variety of products seeded with known numbers of mites, average recovery was 83%. Recoveries of 89% were obtained from flour samples seeded with insect fragments and rodent hairs. A new process of suspending extracted mites in a mixture of industrial methylated spirit (46%) and glycerol (54%) by volume was used to allow rapid and more precise estimates of mite populations in heavily infested samples.