Studies on Preservation of Lactic Acid Bacteria by Freezing
IV. Effects of Various Substances on Survival of Lactobacilli below Freezing Point
1964 Volume 35 Issue 1 Pages 55-59
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1964 Volume 35 Issue 1 Pages 55-59
Experiments were continually performed to discover substances stimulating the growth of lactobacilli once frozen and thawed.
Lactobacillus bulgaricus and L. acidophilus were used as test strains. Each strain was suspended in 10 per cent reconstituted skim milk (basic medium) and each of four kinds of modified reconstituted skim milk to which had been added glucose, corn steep liquor (C. S. L.), yeast extract, or L-glutamic acid at a concentration of 1 per cent. The freezing-thawing test was carried out by the two methods, the direct and the indirect incubation methods, mentioned in the previous paper.
L-glutamic acid had no effect of preventing the organisms from death from freezing and a little effect of promoting their acid production after thawing. It also acted effectively in the indirect incubation method. Yeast extract, C. S. L., and glucose were less effective than L-glutamic acid. Long cells were observed in L. bulgaricus suspension in 10 per cent reconstituted skim milk with or without glucose added, which had been held in a frozen state for a month, then thawed and incubated at 37°C for 24 hours. The other cells in the suspension were of normal shape after the same period of incubation.
