USE OF SMALL RUMINANTS MILK SUPPLEMENTED WITH AVAILABLE NITROGEN AS GROWTH MEDIA FOR BIFIDOBACTERIUM-LACTIS AND LACTOBACILLUS-ACIDOPHILUS

Growth of, and acid production by Bifidobacterium lactis and Lactobaci llus acidophilus using ovine and caprine milk as media were evaluated for their potential use in cheese-making. A protein hydrolysate (MHP, obtained from incubation of bovine milk with protease) or a mixture of free amino acids (FAA, similar to the amino acid fraction of MHP) was added as a nitrogen enrichment source. Bifidobacterium lactis and Lac t. acidophilus were inoculated at 50 ml l(-1) and incubated at 37 degr ees C with growth supplements added at ratios in the range 25-50 ml l( -1). The maximum viable counts of Bif. lactis were lower in plain ovin e and caprine milk than in nitrogen-enriched milk, and MHP was a bette r growth promoter than FAA. A similar trend was observed with the acid ity values de developed, and attempts to correlate growth with acidity were successfully performed. The highest uptake rates of amino acids in ovine milk were observed for lysine, isoleucine, leucine and prolin e, but only isoleucine was taken up at a similar rate in caprine milk. Final bacterial viable counts of Lact. acidophilus in the plain and e nriched forms of ovine milli did not differ greatly from each other, a lthough FAA was statistically a better growth promoter than MHP. Unlik e results in ovine milk, cultures of Lact. acidophilus in caprine milk exhibited drops of 1-1.5 log cycles in viable cell counts by 24 h of fermentation, irrespective of the nature of the nitrogen source. Paral lel studies indicated that the excess of fatty acid residues in caprin e milk could be responsible for the poor growth of Lact. acidophilus.