Survival and growth of Aeromonas hydrophila on modified atmosphere packaged normal and high pH lamb

The growth of A. hydrophila on normal pH (5.5-5.8) and high pH (> 6.0) lamb stored under modified atmospheres was examined, Lamb pieces and mince, inoculated with A. hydrophila were packaged in air, vacuum pack, 80% 0(2)/20% CO2, 50% CO2/50% N-2 or 100% CO2 and stored at 5 or O degrees C for up to 42 days. Samples were examined for the survival and/or growth of A. hydrophila by enrichment in alkaline peptone water and/or direct plating on starch ampicillin agar. The pH of each sample was estimated. On lamb pieces and mince of normal pH, A. hydrophila numbers decreased during storage at 5 and O degrees C under all the packaging conditions. The organism was not detected after 21 days storage. In contrast, A. hydrophila numbers were maintained or increased on high pH lamb under most storage regimes. Storage at 5 degrees C allowed significant increases in A. hydrophila numbers on high pH lamb under all the atmospheres, except 100% CO2. In lamb held at 5 degrees C under 100% CO2, for up to 42 days, A. hydrophila was recovered from most samples, although cell numbers decreased during storage. After storage at O degrees C, A. hydrophila was recovered from high pH packs stored under all atmospheres. Significant increases in cell numbers were only observed in minced lamb of high pH stored under air or vacuum. The pH values of lamb pieces and mince held at 5 or O degrees C under any of the packaging atmospheres did not change in a uniform manner during storage.