Prediction of the shelf‐life of pasteurized milk at different storage temperatures

Abstract

Initial psychrotroph counts determined by a Most Probable Number technique were correlated with shelf‐lives of pasteurized milk determined at a number of storage temperatures. The initial psychrotroph count was also correlated with a bacterial count carried out on milk agar containing crystal violet penicillin and nisin after previous incubation of the milk at 15°C for 25 h. Pre‐incubation counts carried out at a variety of temperatures and on a variety of media were examined for their relation to shelf‐life. Shelf‐lives at four pre‐set temperatures (2, 6, 10 and 14°C) could best be predicted by pre‐incubation of pasteurized milk at 15°C before inoculation on milk agar. An equation which allows prediction of shelf‐life of pasteurized milk at any storage temperature is described.

Modelling the relation between bacterial growth and storage temperature in pasteurized milks of varying hygienic quality

“…As with previous studies, a variety of growth parameters, such as length of lag phase, specific growth rate or the time to reach a specific point in the growth cycle, gave the same To value when substituted in the 'square root' equation (Chandler & McMeekin, 1985b;. The To value was correlated with shelf-life (Griffiths & Phillips, 1988) and this probably reflected the different bacterial flora reponsible for spoilage of good and bad quality milks. In milks of poor quality, spoilage at temperatures below 10°C was due primarily to Pseudomonas species, whereas in good quality milks a greater variation was noted in the bacterial population.…”

“…Above this temperature both growth parameters remained relatively constant; 15°C was also the temperature at which mesophilic bacterial growth was observed to exceed psychrotrophic growth (Bester, Groeneveld & Lombard, 1986). This temperature may, therefore, be a useful preincubation temperature for predicting the shelf-life of pasteurized milk samples (Kirihara, 1983;Griffiths & Phillips, 1988). A temperature of 15°C was also found to be that at which the 'square root' plot for growth of bacteria in both raw and pasteurized milks deviated from linearity (Chandler & McMeekin, 1985a,b).…”

Best-before date – food storage temperatures recorded by Swedish students

“…The combination of temperature and time are important factors. For instance, if milk or meat is stored a few degrees colder, the shelf-life increases (Griffiths and Phillips, 1988;Zhang et al, 2011). Appropriate cold storage of perishable food items is important from a health perspective.…”

Mathematical Modeling of Microbial Growth: A Review

“…The equation was satisfactory in fitting growth curves of pure cultures and binary mixtures of the psychrotrophic microorganisms. Phillips and Griffiths (1987) and Griffiths and Phillips (1988) used the sigmoidal Stannard equation to fit microbial growth data obtained from the spoilage of various dairy products. They incorporated the equation into a temperature integrator to predict spoilage at some reference temperature.…”

“…MPN is the most probable number obtained from a 6-tube MPN experiment and s is the number of challenge spores present in each test portion. MPN can be calculated as In (n/q) (Halvorson and Ziegler 1933), where n is the number of sausages analyzed and q represents the number of nontoxigenic test portions. Hauschild (1982) also used the expression log (UP) to represent the number of spore log units required for one microorganism to germinate and produce toxin in vacuumpackaged bacon.…”