Studies on Some Fermented Dairy Products Produced by Using L. acidophilus and B. bifidum

Authors: Emel SEZGİN, Zeliha YILDIRIM, Yonca KARAGÜL

Abstract: In this study, three different fermented-milk products were produced using L. acidophilus. B. bifidum, L. bulgaricus and S. thermophilus cultures, and some important properties of these products were investigated. The protein content of the milk was standardized at 3.81% using skimmed-milk powder, then the milk was divided into three equal portions of 30 liters. Each portion was homogenized at 60¼C under 200 kg/cm2 of pressure and heat treated at 80¼C for 30 minutes. Afterwards, the first and second portions were cooled to 37¼C and the third portion was cooled to 40¼C. To the first portion (AB milk), L. acidophilus (1.5 g) and B. bifidum (1.5 g) were added: to the second portion (AB yoghurt), L. acidophilus (7.5 g), B. bifidum (3.0 g) and yoghurt culture containing L. bulgaricus and S. thermophilus (1.5 g); and to the third portion (ABT milk) a mixture of L. acidophilus, B. bifidum and S. thermophilus (6.0 g) was added and the products were incubated at the temperatures mentioned above until the pH value reached 4.4 in the AB milk and 4.5 in the AB yoghurt and ABT milk. The total solids, fat, protein, titratable acidity, pH, lactic acid, total volatile fatty acids, acetaldehyde, tyrosine, consistency, viscosity and whey separation were measured and the organoleptic properties were evaluated in the fermented milk products after 1, 7 and 21 days of storage. The total solids, fat and protein contents were analyzed only on the first day. A questionnaire was prepared in order to determine if these products were acceptable to consumers. The titratable acidity, total volatile fatty acids and tyrosine levels were found to be the highest and the pH value the lowest in the AB milk, whereas these properties were similar in the AB yoghurt and ABT milk. Lactic-acid levels were found to be almost the same in the AB yoghurt and AB milk, but the level was slightly lower in the ABD milk. The amount of acetaldehyde was higher in the AB yoghurt than in the AB milk and ABT milk. However, the difference inthe acetaldehyde contents of the AB milk and ABT milk was not sifnificant. The curd stability, consistency and viscosity were all better and the whey separation was lower in the AB milk and ABT milk compared to the AB yoghurt. From the results of the organoleptic evaluation and questionnaire, it was clear that the ABT milk was the product most preferred by the respondents. This was followed by the AB yoghurt and then the AB milk.

Keywords: Fermented milk products, L. acidophilus, B. bifidum, Quality Cirteria