Dried lactic cultures have storage, handling advantages.

Lactic cultures are well known for their health-promoting effects when they are present in fermented dairy products. Dry lactic cultures are easily handled for use in dairy product manufacturing as starter cultures and as probiotic cultures.

Researchers at Alabama A & M University undertook a study to evaluate the survival of lactic cultures grown in skim milk (SM), in SM and 0.1% gelatinized starch (GS), and in SM and 0.1% guar gum (GG) before and after the product was freeze-dried. These cultures were stored at 4 C and 24 C for four months. The scientists determined that dried lactic cultures offer storage and handling convenience over fresh cultures. This can help companies avoid the expense required for their production and maintenance.

For lactic cultures, the scientists used Lactobacillus delbrueckii ssp. bulgaricus (ATCC 11842) (LB); Lactobacillus gasseri (ATCC 19992) (LG) and Streptococcus thermophilus (14485) (ST). The cultures were grown in sterilized SM, SM/GS and SM/GG until they reached the stationary phase of growth. Then they were freeze-dried.

The investigators divided the dried cultures into two portions. One portion was stored at 4 C, and the second portion was stored at 24 C. Aliquots from each were assayed for viability counts at two weeks, four weeks, two months and four months of storage.

The scientists found that freeze-drying reduced the survival percentage for LB to 65% in SM, to 67% in GS and to 66% in GG. Survival rates for LG and ST grown in SM, GS and GG were 97%, 98% and 98%; and 97%, 99% and 98%, respectively.

Freeze-dried cultures stored at 24 C for four months showed a reduction in viability for LB and LG and total loss of viability for ST. Dried cultures stored at 4 C had greater survival rates for up to four months of storage compared to storage at 24 C. LG and ST grown in supplemented SM had higher survival rates during storage at 4 C.

Further information. Martha Verghese, Department of Food and Animal Sciences, Nutritional Biochemistry, Alabama A & M University, A-124, Carver Complex Thomas Wing, 4900 Meridian Street, Normal, AL 35762; phone: 256-372-4175; email: martha.verghese@email.aamu.edu.