Determination of the End of Shelf-life for Milk using Weibull Hazard Method

The shelf life of pasteurized milk is traditionally estimated by the counts of both total and psychrotrophic microbial load. This study examins the relationship between the total and psychrotophic microbial growth in milk and its sensory shelf life as measured using the Weibull hazard method. Milk was stored at five constant temperatures (2, 5, 7, 12 and 15 °C) and both total and psychrotrophic microbial counts were used to obtain the lag time and the growth rate values. The lag time of the total and psychrotrophic growth responded to temperature following the Arrhenius equation. The loss of sensory quality of the milk followed a log shelf life vs. temperature dependency. It was found that there was no correlation between the microbial count at the end of shelf life and the sensory quality of the milk. It is therefore suggested that microbial counts should not be used to determine the sensory shelf life of milk. The Weibull method gave end of shelf life values fairly similar to that of prior work using the American Dairy Science Association scoring method.