Abstract:
Drinking yoghurt (DY) is one of the most popular fermented dairy products in the market
which can be used as a carrier of probiotics and prebiotics. According to new
findings, Streptococcus thermophilus (ST) can be considered as a probiotic
microorganism. Fruits contain prebiotic carbohydrates such as oligosaccharides,
antioxidants, and polyphenols. In this study, the changes of microbiological, chemical,
and sensory properties of fruit pulps incorporated DY which produced using single strain
ST culture was evaluated. DY was prepared using two levels of (5% and 10%) strawberry
pulp or mixed berry pulp and with control. The control sample was prepared without
adding fruit pulps. The viability of ST was evaluated for 28 days of refrigerated storage (4
℃ ) with 7 days interval using M17 agar with 𝛽 -glycerophosphate. The sensory
evaluation was conducted by using 30 untrained panelists according to the 9 points
hedonic scale. The sensory evaluations showed that the DY, containing 5% strawberry
and 10% mixed berry had better overall acceptability than other treatments. Fruit pulp
incorporated DY showed a lower (p<0.05) pH value and higher titratable acidity than that
of the control during storage at 4. Strawberry 5% incorporated DY and mixed berry 5%
incorporated DY showed higher (p<0.05) ST counts throughout the storage period,
compared to the 10% strawberry or mixed berry incorporated DY and that of the control.
This may be due to the low initial pH and higher titratable acidity due to the addition of
fruit pulps. The DY samples incorporated with 5% strawberry pulp showed higher
(p<0.05) ST counts (8.53 0.03) log cfu g-1
at 28 days of refrigerated storage compared to
the 5% mixed berry incorporated DY (8.44 0.01) log cfu g-1
and that of the control (8.21
0.02) log cfu g-1
. These results revealed that the addition of fruit pulps increased the
viability of ST during refrigerated storage.
Keywords: Drinking yoghurt, Microbiology, Probiotic, Streptococcus thermophilus
