Growth Kinetics of Kefir Biomass: Influence of the Incubation Temperature in Milk

Abstract

Kefir is a fermented milk that can be produced from kefir grains or industrial starter cultures. It differs from other fermented milks by the performance of various types of microorganisms on the milk components. The kefir grains are gelatinous and irregular, formed by a set of microorganisms, such as yeasts and lactic acid bacteria, which are incorporated in a matrix of polysaccharides called kefiran. Lactobacilli make up most of the microbial population, but the total composition of the grains is not fully elucidated. There are few studies that evaluated the kinetics of kefir biomass growth at different temperatures, but the exact behavior was not explained in a consistent form, such as using mathematical models. In this context, this work aimed to improve the procedure of kefir production by studying the kinetics of the growth of kefir biomass in milk at different temperatures (298, 303 and 308 K) and characterize it by Scanning Electron Microscopy (SEM). Furthermore, the application of mathematical models to determine the growth function of the kefir biomass in relation to the time and temperature of the fermentation process was evaluated. An amount of 2% kefir grains was added to the milk and the fermentation process was carried out at 298, 303 and 308 K for 5 days. The biomass growth (increase in mass) was evaluated daily and four different mathematical models (Richards, Logistic, Gompertz and Quadratic) were applied to the data. The samples were visualized in a double-beam scanning electron microscope. The Gompertz model showed the highest values ??of the coefficient of correlation (R², 0.97-0.99) and the smallest standard deviations for the increase in the kefir grain biomass, being considered the most appropriate mathematical model. The temperature of 298 K was the most suitable for the incubation of the grains in milk, resulting in a higher increase in the biomass and a larger quantity of lactobacilli, coccus-like bacteria and yeast observed in the SEM. It can be concluded that 298 K may be used as the temperature for fermentation of kefir grains in milk, resulting in higher kefir biomass, which could be useful in the production of kefir fermented milks, because of the reduction in the processing time.