Indication of proliferation of lactic acid bacteria in mixed cultures

Summary

The supply and consumption of probiotic foods, and particularly probiotic dairy products, has grown steadily in recent years. In the production of dairy products of this type other microbes must also be used in addition to the microbes which provide the probiotic effect and which generally have a proliferation optimum at 37°C. The probiotic microbes have a neutral taste in dairy products consequently the taste of fermented dairy products is supplied by other microbes. These microbes are likewise lactic acid bacteria, and their proliferation optima are either below (mesophilic) or above (thermophilic) that of the probiotic microbes. It is imperative to have an indication of whether the probiotic bacteria have multiplied at the fermentation temperature used during the technology, since they provide the beneficial physiological effect of the product. Isothermic calorimetry appeared a suitable method for the indication of this process, because the amount of heat released during lactic acid bacterial proliferation differs from the probiotic one. In order to analyze the heat flow curves a deconvolutional program was developed which decomposed them into Gaussian curves, because the proliferation of individual microbes follows a lognormal distribution. The Gaussian curve characteristic for the culture was determined, and from the area under the curve the heat liberated during the creation of one microbe was calculated.