B. Ranganathan

Lipase activity of Lactobacillus brevis

SummaryThe intracellular lipase from a strain of Lactobacillus brevis was partially purified and properties of the enzyme studied. Of the simple triglycerides, tripropionin was hydrolysed most easily by the enzyme as compared to others such as tributyrin, tricaproin and tricaprylin. Of the natural triglycerides such as butter oil and coconut oil, the former was degraded more readily than the latter. Among unsaturated triglycerides, the enzyme preferentially hydrolysed triolein as compared to olive oil. Highest enzymatic activity was observed at 30° C after 3.5 h incubation at pH 6.5. Salts of manganese, magnesium, sodium and calcium stimulated lipase activity while silver, mercury and Zinc were inhibitory. The enzyme was completely inactivated at 62.8° C after 30 min and at 71.7° C after 16 sec.

Prevalence of enterococci in frozen dairy products and their pathogenicity

Enterococci were present in all the samples of frozen dairy products examined in the present study. The total bacterial counts as well as enterococcal counts were generally very high in Kulfi (a frozen product similar to ice cream) and Kulfi mix. Among 161 enterococcal isolates recouered, the predominant type was Streptococcus faecalis var. faecalis, the majority of isolates coming from Kulfi and Ku& mix samples. Although 58 cultures produced deoxyribonuclease, only two of them exhibited thermonuclease (TNase) production. Hyaluronidase activity was shown by three strains. However, 31 strains were alpha haemolytic, while five showed beta haemolysis on rabbit blood agar. Out of these haemolytic strains tested, 21 produced lethal toxicity in mice and 20 strains showed culture virulence, postmortem studies revealed congestion of heart, liver, kidney and spleen. The two TNase positive strains of Streptococcus faecium produced fluid accumulation in ligated ileal loops of rabbits and distension in the gastrointestinal tracts of infant mice.

Acid Production and Proteolytic Activity in Milk by Gamma-Irradiation Induced Mutants of Lactobacilli

Biochemical changes in selected gamma-irradiation induced mutants of Lactobacillus bulgaricus and Lactobacillus casei were examined. Cultures were tested after 24 h of incubation at 37 C for titratable and volatile acidities and proteolytic activity. The gamma-irradiation induced mutants exhibited 50-95% greater proteolytic activity than the unirradiated parent culutres. Some of the mutants produced greater titratable and volatile acidities in milk as compared to parent cultures. Two mutant cultures, Lb/G-1 from L. bulgaricus 59 and Lc/G-1 from L. casei RTS released significantly greater amounts of soluble nitrogen and amino nitrogen in whole casein and selected fractions than did parent cultures. Combining the mutant cultures with Streptococcus lactis C10 or Streptococcus cremoris C1 resulted in greater acid producing ability than that of the parent cultures mixed with the streptococci.

Activity of Streptococcus diacetilactis and its UV- Induced Mutant in Dahi Prepared from Different Types of Milk1

Streptococcus diacetilactis and one of its UV-induced mutants were individually used to prepare dahi from cows and buffaloes milk and reconstituted full-cream dried cows milk. Dahi samples were analysed for titratable and volatile acidities, diacetyl and proteolytic activity. Each sample was evaluated organoleptically and acceptability of the product was measured by the 9-point hedonic scale. The dahi prepared with the mutant scored better in all the types of milk used, as compared to the parent culture.