Abstract
The kinetic growth parameters [maximal specific growth rate μm (h-1), and generation time g (h)] and viability after stress treatments (dehydration with glycerol solution of increasing concentration, freezing or heating stress) of four lactic acid bacteria [Lactobacillus plantarum (LP), L. fermentum (LF), Leuconostoc spp. (M1) and Lactococcus spp. (M2)] were determined. The maximal specific growth rate (μm) and generation time g ranged between 0.51 h-1 to 0.14 h-1 and 0.61 h to 1.33 h, respectively. We observed that the strains were sensitive to a change in water activity (aw 0.32 final), storage and incubation temperatures. The Strain LF obtained a higher cell concentration and viability, as well as a lower g compared to those obtained by the other strains. The kinetic growth parameters (μm, g) together with viability after stress treatments could be used for the screening of dried lactic acid starter cultures.
Highlights
Traditional fermented cereal based foods consumed in Africa are processed by natural fermentation of maize, sorghum and/or millet and are important as weaning foods for infants and dietary staples for adults [1, 2]
The selection needs to take into account many parameters, this work proposes a first approach based upon kinetics growth parameters and the ability to overcome stressful conditions
The generation time (g) is the time needed for doubling the initial bacterial population during the exponential growth
Summary
Traditional fermented cereal based foods consumed in Africa are processed by natural fermentation of maize, sorghum and/or millet and are important as weaning foods for infants and dietary staples for adults [1, 2]. The use of dried lactic acid bacteria (LAB) starter cultures during fermented cereal based foods processing could result in a high degree of control over the fermentation process and standardization of the end product. Commercial starter cultures are supplied in concentrated form by freeze-drying, vacuumdrying, spray-drying, drum-drying, fluidized bed drying or air-drying. These techniques impose environmental stress on the bacterial cells, such as freezing, drying, long-term exposure to low water activities and re-hydration. During cereal fermentation processes, LAB are exposed to various environmental stress conditions, such as temperature fluctuations, acid, pH, high osmotic pressure and absence of available nutrients
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