INCORPORATION AND SURVIVAL OF BIFIDOBACTERIUM SP STRAIN BO AND LACTOBACILLUS-ACIDOPHILUS STRAIN KI IN A CHEESE PRODUCT

There is increasing interest in dairy products containing specific bac terial species with potential health-improving properties, e.g. the fe rmentation of milk with such intestinal species as Lactobacillus acido philus and Bifidobacterium sp. The use of these species as an additive to cheese is not a new idea; however, literature on the possibility o f using a starter entirely composed of Bifidobacterium sp. strain Bo a nd Lactobacillus acidophilus strain Ki for the manufacture of Gouda ch eese is virtually non-existent, and so that topic was selected as the focus of our research effort. The technology of Gouda cheese manufactu re was adapted for the purpose of producing a probiotic counterpart. R elatively large inocula of both strains were required to achieve the p roper acidification rates. An inoculum size of 3.5% was found to meet all the criteria regarding the technological requirements of Gouda che ese production. Lactobacillus acidophilus strain Ki was able to grow a nd produce acid in the cheese. The numbers of L. acidophilus strain Ki observed in the cheese were 2-4 x 10(8) cfu/g (an increase of one log cycle or more), provided that the scalding temperature was 38 degrees C. On the other hand, Bifidobacterium sp. strain Bo showed no growth under any of the conditions chosen, even when the milk was supplemente d with milk hydrolysate. The numbers of Bifidobacterium sp. strain Bo present in the cheese were 2-4 x 10(9) cfu/g. The acetic acid values f ound demonstrate that Bifidobacterium sp. strain Bo actively contribut es to the acidification of the cheese, a factor which probably also ac counts for the significant difference in the organoleptic quality of t he cheese. Survival of the bacteria was monitored during ripening stor age for a period of 9 weeks. After 1 week, Bifidobacterium sp. strain Bo reached average levels of 3-4 x 10(9) cfu/g and 2 x 10(9) cfu/g for initial inocula of 7 and 3.5% (w/v), respectively. During the whole s torage period studied, the average numbers of L. acidophilus strain Ki decreased by two log cycles to 0.2-5 x 10(7) cfu/g, whereas those of Bifidobacterium sp. strain Bo decreased by less than one log cycle to 6-18 x 10(8) cfu/g. The presence of a bifidogenic factor (milk hydroly sate) had no detrimental effect on the bacterial counts; however, such hydrolysate proved unsuitable for cheese manufacture because it contr ibutes to the development of undesirable flavours even at low levels. The relation between the salt concentration and the survival of the st rains was studied by assaying longitudinal samples of the cheese. In a cheese with 4% (w/w) salt, the survival of Bifidobacterium sp. strain Bo during the 9 weeks of ripening ranged from ca. 55% in the centre r egion of the cheese to ca. 35% in the outer rind region, whereas the s urvival of L. acidophilus strain Ki was 1.5% in the rind and 27% in th e centre of the cheese. From the relatively good survival of both spec ies in cheese, it can be concluded that the incorporation of Bifidobac terium spp. and L. acidophilus as starters in a Gouda-type cheese is f easible and can offer an alternative and interesting route of administ ering them to human beings.