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 bacterial species with potential health-improving properties, e.g. the fermentation of milk with such intestinal species as Lactobacillus acidophilus and Bifidobacterium sp. The use of these species as an additive to cheese is not a new idea; however, literature on the possibility of using a starter entirely composed of Bifidobacterium sp. strain Bo and Lactobacillus acidophilus strain Ki for the manufacture of Gouda cheese is virtually non-existent, and so that topic was selected as the focus of our research effort. The technology of Gouda cheese manufacture was adapted for the purpose of producing a probiotic counterpart. Relatively large inocula of both strains were required to achieve the proper acidification rates. An inoculum size of 3.5% was found to meet all the criteria regarding the technological requirements of Gouda cheese production. Lactobacillus acidophilus strain Ki was able to grow and 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 °C. On the other hand, Bifidobacterium sp. strain Bo showed no growth under any of the conditions chosen, even when the milk was supplemented 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 found demonstrate that Bifidobacterium sp. strain Bo actively contributes to the acidification of the cheese, a factor which probably also accounts for the significant difference in the organoleptic quality of the cheese. Survival of the bacteria was monitored during ripening storage 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 storage period studied, the average numbers of L. acidophilus strain Ki decreased by two log cycles to 0.2 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 hydrolysate) had no detrimental effect on the bacterial counts; however, such hydrolysate proved unsuitable for cheese manufacture because it contributes to the development of undesirable flavours even at low levels. The relation between the salt concentration and the survival of the strains 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 region of the cheese to ca. 35 % in the outer rind region, whereas the survival of L. acidophilus strain Ki was 1.5% in the rind and 27% in the centre of the cheese. From the relatively good survival of both species in cheese, it can be concluded that the incorporation of Bifidobacterium spp. and L. acidophilus as starters in a Gouda-type cheese is feasible and can offer an alternative and interesting route of administering them to human beings.