Efficacy of eight liquid smoke fractions on Tyrophagus putrescentiae infestation in semi-moist pet food

The storage mite Tyrophagus putrescentiae contaminates a wide range of foods including pet food. Liquid smoke is a naturally derived flavor and preservative with known antimicrobial properties. The objective of this study was to investigate the efficacy of eight liquid smoke fractions, S1-S8, with varying phenol and carbonyl concentrations and pH, on T. putrescentiae orientation behavior and survivability in semi-moist pet food. Untreated pet food cubes were dipped in smoke fractions at 100%, 50%, 25%, 10%, 5%, 1% or 0.3% concentration, and used in two-choice behavioral assays. The attraction or repulsion of mites towards treatments was determined by releasing 20 mites in an arena (90×20 mm petri-dish) with test samples and enumerating them at 2h, 8h and 24h, and repellency index was calculated. Among treatments, S3 (carbonyl), S4 (buffered organic acid+carbonyl) and S8 (carbonyl+phenol+organic acid) repelled (-10% to +60% RI) mites (P< 0.05). Survivability and reproduction of T. putrescentiae on treated (0.3% S1-medium carbonyl+low phenol) and untreated (0% smoke) pet food samples were determined by enumerating their population at 7, 14, and 28 days after inoculation with 20 mites. At 14 days, the mean mite population among smoke treatments were 207-244 when compared with untreated (212 mites), positive control (propylene glycol; 0 mites) and negative control (mite rearing diet; 454 mites). There was no difference among treatments (P>0.05) for survivability. Liquid smoke did not kill or inhibit mite population growth; however, some liquid smoke fractions may provide repellency to retard mite infestation in stored semi-moist pet foods.