comparative study on the quality of plain and probiotic yoghurt

ABSTRACT

A total of 40 random samples of plain and probiotic yoghurt [20 of each] were collected from different markets in Kaliobia governorate to evaluate their quality. The sensory characteristic score of probiotic yoghurt [91.69 +/- 7.86] was significantly better than plain one [77.91 +/- 8.16]. The chemical examination indicated that the average values of pH and titratable acidity were 3.63 +/- 0.07 and 0.91 +/- 0.07 for plain yoghurt and 4.29 +/- 0.05 and 0.72 +/- 0.06 for probiotic yoghurt. On the other hand, the bacterial counts in the examined plain and probiotic yoghurt samples were 1.35 x 10[4] +/- 0.22 x 10[4] and 2.12 x 10[3] +/- 0.39 x 10[3]/g for aerobic spore formers count, 4.78 x 10[2] +/- 0.61 x 10[2] and 1.31 x 10[2] +/- 0.17 x 10[2] /g for B.cereus count, 2.01 x 10[3] +/- 0.34 x 10[3] and 4.73 x 10[2] +/- 0.52 x 10[2] /g for staphylococci count and 7.24 x 10[2] +/- 1.83 x 10[2] and 2.58 x 10[2] +/- 0.41 x 10[2] /g for coliform, respectively. Furthermore, B.cereus, B.circulans, B.coagulans, B.licheniformis, B.macerans, B.stearothermophilus and B.subtilis, S.aureus and S.epidermidis as well as micrococci were isolated from both plain and probiotic yoghurt with varying percentages. However, Enteropathogenic Escherichia coli [EEC] were isolated from 5% of plain yoghurt samples and serologically identified as O26 K60 [B6] and O128 K67 [B12]. In contrast, all examined samples of probiotic yoghurt were free from E.E. coli. According to sensory, chemical and bacteriological results, probiotic yoghurt appeared to be better and more safe for human consumption as compared with plain one