The syneresis of the probiotic yoghurts with different levels of roselle syrup ranged between 51.70 – 84.11%. During the first 3d storage, the syneresis of probiotic yoghurt which contained no syrup significantly increased. This might be due to its initial pH which was a bit higher compared to the other two yoghurts and the growth could be better. The addition of roselle syrup into the probiotic yoghurt also affected the viscosity of the yoghurt as shown in Figure 2. The increase of viscosity of the syrup mixed yoghurts was due to the additional soluble solids especially sucrose and it tended to decrease with increasing time as the cultures have grown and started to produce proteolytic enzymes (Shihata & Shah, 2002). The antioxidant activity of
probiotic yoghurt with syrups was shown in Figure 3. The antioxidant activity of the yoghurts increased as the syrup content increased and then contained more anthocyanin, the antioxidant agent. However, the activity gradually disappeared after 6d storage due to the loss of anthocyanin stability as supported by the data from Panichajakul et al. (1988). They reported the decrease of anthocyanin content of Hisbicus sabdariffa L. up to 42.8% after keeping the extract at 20oC for 13 weeks. The growth of L. bulgaricus, S. thermophilus and probiotic L. casei in the yoghurts mixed with roselle syrups during storage at 4oC are shown in Figure 4, 5 and 6, respectively.
Figure