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The Viability of Lactobacillus Acidophilus as Affected by Freezing in a Sherbet Mixture^*

Washington Agricultural Experiment Station, Pullman, Washington

ABSTRACT

Twenty-eight sherbets were prepared from acidophilus milk and a study was made of the numbers of viable organisms remaining after 1, 2, 3, 5 and 7 days of storage at temperatures below –17°C. Four strains of L. acidophilus were used in the preparation of these sherbets.

A variation was found in the viability of these strains when exposed to the conditions prevailing in such a frozen product. The numbers of viable organisms in sherbets carrying strain A organisms were reduced to only a few million per cc. after five days storage, while under similar conditions several hundred millions of viable organisms were usually present in the sherbets carrying the other strains of L. acidophilus.

A variation in viability was found to occur in cultures of the same strain. Whether or not this variation was due to the age of the cells or some combination of factors was not determined.

A number of these sherbets were prepared so that they differed in reaction only. A more rapid reduction of organisms was found to occur in the sherbets of the higher titratable acidity.

The sugar concentration, as it was varied in the sherbet mixtures, caused no significant variation in the viability of the organisms.

It was possible to prepare sherbets in which large numbers of organisms remained viable after five to seven days of storage at temperatures below –17°C. when the more resistant strains of L. acidophilus with a high initial count were used and the titratable acidity was not permitted to become excessive, preferably not in excess of 1.0 per cent.

^* Published as Scientific Paper No. 235, College of Agriculture and Experiment Station, State College of Washington.