Abstract #T58

Section: Dairy Foods
Session: Dairy Foods IV
Format: Poster
Day/Time: Tuesday 7:30 AM–9:30 AM
Location: Exhibit Hall B
# T58
Population dynamics of a common dairy sporeformer, Bacillus licheniformis, in spiked raw milk samples stored at low temperatures.
N. Awasti*1,2, R. Suliman3, S. Anand1,2, G. Djira3, 1Midwest Dairy Food Research Center, Brookings, SD, 2Department of Dairy and Food Science, South Dakota State University, Brookings, SD, 3Department of Mathematics and Statistics, South Dakota State University, Brookings, SD.

Bacillus licheniformis is a widely reported sporeformer in raw milk, and milk powders. The organism, being thermotolerant, is considered a challenge during milk processing. It would be of interest to understand its growth dynamics during raw milk storage at low temperature in plant silos. The current study was conducted to observe the changes in population of vegetative cells and spores of B. licheniformis, spiked in raw milk samples at about 4.0 log cfu/mL. The spiked milk samples were stored at 4°, 6° and 8°C, for durations of 0, 36 and 72 h. Standard protocols were followed for microbial analysis. Spore enumeration was done by heating the spiked milk samples at 80°C for 12 min before plating on Brain Heart Infusion agar. Three trials, in replicates of 3 were conducted, and the data were analyzed using 2 sample t-test, ANOVA, and first order regression model. While log vegetative counts increased to 4.09 after 72h at 4°C, the counts were 4.42 logs at 8°C. A significant difference (P < 0.02) was thus observed in the mean counts after 72 h of holding for 4 and 8°C. On the other hand, the spore counts mainly remained unchanged during 72 h at different storage temperatures. The results thus suggest that B. licheniformis may multiply to a greater extent, when milk is held at the higher temperature of 8°C. Moving forward, to accurately approximate the true response surface for vegetative cells, the fitted first order model suggests using the second degree model including additional design points. Whereas, no lack of fit (P = 0.294) was observed for spore values, and the entire regression surface was not significant. A higher degree model with additional design points will thus give us the optimum temperature and time combinations where no significant change or a minimum shift in vegetative cell numbers is observed, which may reduce the chance of sporeformer build up during low temperature storage of raw milk.

Key Words: spore, sporeformer, dairy silos