Abstract:
Fermented milk products are important due to their nutritional and functional
properties. However, shelf-life assessment of these products is often performed using
single parameters, which may reduce the reliability of prediction results. Therefore,
this study aimed to assess the shelf life of different flavoured drinking yoghurts using
physicochemical and microbial quality parameters. Samples of vanilla, strawberry,
mango, and aloe vera flavoured drinking yoghurts were obtained from a commercial
dairy processing unit in Sri Lanka and stored under similar refrigerated conditions
(4℃) throughout the experimental period. Key physicochemical parameters, including
pH, titratable acidity, water-holding capacity, and syneresis, as well as microbial
parameters such as yeast and mold count, and coliform count, were evaluated weekly
over a four-week storage period. The results revealed a significant (P < 0.05) decrease
in pH (4.30-3.97) and an increase in titratable acidity (0.75-1.40%). Syneresis and
water-holding capacity remained within acceptable limits, while yeast and mold
counts were TFTC and coliforms were absent in all samples. Graphical trend analysis
and regression modelling demonstrated progressive product deterioration during
storage. The statistically significant regression model (Y=a+b(pH)+c(TA))
demonstrated a relationship between storage time, pH, and titratable acidity. Shelf life
was estimated based on physicochemical limits (pH 4.0 and titratable acidity 1.2%)
and trend extrapolation. The developed prediction models indicated shelf lives of 29,
26, 25, and 24 days for vanilla, mango, strawberry and aloe vera flavoured drinking
yoghurts, respectively. These findings indicate that physicochemical and
microbiological parameters combined with trend analysis provide a reliable approach
for shelf-life estimation.
