Abstract #M137

# M137
Evaluation of relationship between water activity, pH and Escherichia coli survival of powdered whole caprine milk during 4 months of storage.
B. I. Davis*1, A. Siddique1, Y. W. Park1, 1Fort Valley State University, Fort Valley, GA.

Water activity (aw) is important indicator for food quality, safety and storage stability, where aw is directly related to bacterial growth, especially when aw is above 0.90. Water activity in relation to bacterial counts of dehydrated bovine milk may have been studied extensively, while no report has been available for the correlation between aw, pH and Escherichia coli survival in powdered caprine milk (PCM). The objectives of this study were to determine aw, pH and Escherichia coli counts of PCM, and evaluate correlations among these parameters at 4°C and 22°C for 0, 2, and 4 mo storage. Three different lots of commercial whole PCM were purchased at a local retail outlet and divided the total amount of each lot into 2 equal portions to assign them to 2 treatment groups: control and E. coli inoculated groups. Ten grams of the experimental PGM samples were inoculated with 50 μL of E. coli K12, and control samples without inoculation of the pathogens were subjected to the temperature and storage treatments. Water activity was measured by AquaLab aw meter (cx-2; Decagon Devices, Pullman, WA). All experimental PGM samples were also analyzed for E. coli counts according to the manufacturer’s procedure (3M Center, St. Paul, MN). Results showed that aw values were significantly (P < 0.05) reduced, where mean aw for 0, 2 and 4 mo storage were 0.266, 0.251, 0.243; 0.291, 0.266, 0.219, respectively. No differences in pHs were found between 2 temperature groups, while pHs were slightly higher at 2 mo storage. Mean E. coli counts of 4 and 22°C at 0, 2 and 4 mo storages were: 5.01, 4.16; 3.43, 1.85; and 3.77, 1.48 cfu/g, respectively, indicating that E. coli counts significantly (P < 0.01) decreased during 4 mo storage. E. coli counts were significantly correlated with aw, having r = −0.857 at 4°C and −0.771 at 22°C, respectively. Correlations between levels of pH and aw at both temperature treatments were also negatively correlated. It was concluded that E. coli counts of the powder goat milk were negatively correlated with levels of water activity as the storage time advanced.

Key Words: water activity, Escherichia coli, powder goat milk