Survival of Lactobacillus reuteri RC-14 and Lactobacillus rhamnosus GR-1 in milk

Dairy products are suitable vehicles for delivering beneficial microorganisms to consumers. Both Lactobacillus reuteri RC-14 and Lactobacillus rhamnosus GR-1 are considered as probiotic agents with therapeutic properties. The objective of this study was to monitor growth and survival of these bacteria in milk during storage period. Four formulations of milk (1% fat) with 0.33% yeast extract (Y), 0.4% inulin (I), 0.33% yeast extract and 0.4% inulin (YI) and one with no additives (N) were prepared. The mixtures were autoclaved for 15 min, cooled to 37 degrees C and inoculated with 1% of starter culture. They were then incubated anaerobically at 37 degrees C overnight. Viable numbers of L. reuteri RC-14 and L. rhamnosus GR-1 were determined after 1, 7, 14, 21 and 28 days of storage at 4 degrees C. Both bacteria were able to grow and survive in all samples; however, they showed a higher survival rate (P < 0.05) in YI treatment. After 1 day of storage, the total colony counts of treatment YI for L. reuteri RC-14 and L. rhamnosus GR-1 were 2 x 10(8) and 1 x 10(9) CFU mL(-1), respectively. The total colony counts for treatment YI decreased by 1 log cycle for both bacteria after 28 days of storage. The results of this study indicate that these bacteria can remain viable over the storage period, and there is potential for incorporating them into fermented dairy products.