Shelf life prediction: status and future possibilities

Although there is rapid progress in the field of chemical detection technology, little of this technology appears to have found application in estimation of the remaining shelf life of foods and early detection of spoilage. Predictive microbiology aims to summarise the probable behaviour of specific spoilage organisms and the progression of spoilage processes in foods. The quantitative knowledge generated in the field of predictive microbiology provides a sound basis for the rational development of devices with which to monitor loss of product shelf life during storage, distribution and retail sale. To predict remaining shelf life accurately it is necessary, however, to consider the microbial ecology of the food system. Aspects of microbial ecology and physiology relevant to the spoilage of foods are briefly reviewed and the potential benefits of the use of predictive microbiology in shelf life estimation are described. These points are exemplified by reference to a modelling program undertaken to develop, validate and ‘package’ in an easily useable form, models of the effect of temperature, water activity and pH on the growth rate of psychrotrophic spoilage pseudomonads. Necessary properties of devices to monitor loss of shelf life are discussed. ‘Bioindicators’ are identified as potential monitors of spoilage and suggestions made for their development based on the concept of ‘upper limiting bacterial growth’ rates, for which preliminary evidence is presented.