Effect of incorporation of cottage cheese whey solids and Bifidobacterium bifidum in freshly made yogurt

Fresh rennet-coagulated cottage cheese whey was vacuum concentrated to 400 g total solids kg(-1), and part of this evaporated whey was acidified to pH 4.6 to prepare whey protein concentrate. Both products were used separately to replace non-fat dried milk in yogurt. Diacetyl concentration increased on fortification with whey protein concentrate, and acetaldehyde increased with evaporated whey. However, the use of Bifidobacterium bifidum as a supplementary starter culture in addition to Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus reduced the concentration of diacetyl and acetaldehyde. Incorporation of whey solids stimulated the growth of Str. thermophilus and Bifid. bifidum in yogurt but the count of Lb. bulgaricus was reduced when Bifid. bifidum was incorporated. Examination of the organoleptic properties of the yogurts showed that both forms of whey solids were satisfactory replacements for non-fat dried milk. Fortification by whey protein concentrate improved the textural properties. Supplementation by Bifid. bifidum had only a marginal effect on the flavour of the product.