Comparison of the resistance of mono- and multilayer packaging films to stored-product insects in a laboratory test

Stored-product insects frequently infest packaged food, causing significant monetary losses to both the food industry and consumers worldwide. This work compared the resistance of 9 new monolayer and multilayer food-packaging films to infestation by 4 key insect food pests (Sitophilus granarius, Rhyzopertha dominica, Oryzaephilus surinamensis and Plodia interpunctella). A series of laboratory tests were conducted over 3 months to determine the package penetration by the stored-product insects. The tested pest species differed in their chewing capacity and in the size of their entrance hole (P. interpunctella larvae, 15 ± 17 mm2 penetrated area/hole; S. granarius, 6 ± 5 mm2; R. dominica, 6 ± 2 mm2; and O. surinamensis, unable to penetrate). The insects also caused mechanical weakening of the film surface by creating multiple small superficial holes covering a 10–20× larger area of the film surface than the penetrated area. For insect invaders (S. granarius, R. dominica, and P. interpunctella), porous paper and an unprinted polyethylene monolayer (40 μm thick) provided the least mechanical resistance, while the highest level of mechanical resistance was recorded for 50-μm-thick polypropylene/metalized-polypropylene. The most innovative findings of this study were that the unprinted parts of the polypropylene monofilm were less protective against R. dominica penetration than the printed parts and that duplex and triplex films were more resistant to insect feeding and penetration than single-layer films, irrespective of their thickness. Some multilayer films showed (in our experimental settings and for the packaging machines used) low resistance to O. surinamensis invasion through crevices caused by sealing imperfections. The results of this study are discussed in the context of film application to protect packaged foods against insect contamination.