Interpreting customer complaints: Heat treatment inhibits melanin formation in larvae of the Indian meal moth, Plodia interpunctella (Hübner)

Abstract: The manufacturers of food products try to interpret some customer complaints on final products that are contaminated by insect pests. Question thus arises – if this insect larva found in food has passed the processing, and was it treated by heat? To answer this question one should observe the post mortal processes that occur in insect body. Melanisation of insect body after death results from loss of control over chemical reactions leading to melanin formation. Insects employ phenoloxidase and dopachrome (decarboxylating) isomerase for melanin biosynthesis. It is suggested that heat treatment inhibits activity of these enzymes responsible for melanin formation, and thus reduces or eliminates melanisation of insect body after death. Therefore, fully-grown larvae of the Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera, Pyralidae), were killed by heat (60 °C and 80 °C for 30 sec.), and observed for whole body melanisation. Control larvae rapidly melanised after freezing and thawing, whereas heat-killed larvae failed to show typical melanisation. Thus, lack of melanization could be an indicator of heat treatment of those insects that were found in the final food product. Sometimes people want to know where and when the contamination of final product occurred: at consumer house, in a shop, in distribution centre, or in the factory that produces this product. From time to time, an entomologist is asked “Can you determine if this insect was cooked?”. If it was heat treated, then contamination occurred at the factory during a processing of raw materials.