Transfer of available and recognized mathematical models to technological and probiotic strains to assess growth: a preliminary study

Introduction Lactobacillus plantarum and Lactobacillus paracasei are species generally used as starters in food fermentation and/or as probiotics. The growth cardinal values of these strains, characteristic parameters independent from the food matrix, can be exploited in predictive microbiology to set the appropriate food processing/manufacturing conditions. The aim of this study was to transfer available and validated mathematical models used to ensure food safety to technological microflora in order to assess the impact of environmental conditions on bacterial growth for further industrial applications. Material and methods A total of 4 strains of L. plantarum isolated from sourdough and table olives as well as 4 strains of L. paracasei strains isolated from table olives and probiotic human isolates were investigated to determine growth cardinal values. For that purpose strains were grown in liquid medium and incubated at nine temperature levels from 5.5 to 40°C. The growth was automatically monitored by a Bioscreen C using the turbidimetry method or determined manually after static incubation. Maximum growth rates (?max) for each temperature were obtained fitting data by the Rosso model. To estimate the cardinal growth values, the ?max values relevant to each temperature were fitted to the growth cardinal model using Sym'Previus decision making tool (www.symprevius.eu). Results Cardinal values were determined for Lactobacillus plantarum strains with the following average values for Tmin 2.05±0.54°C, Topt 33.74±0.63 °C and Tmax 39.79±0.50°C. In the case of L. paracasei strains, a wider diversity was obtained with average values for Topt 34.90±1.70 °C and Tmax 38.99±1.72°C. The Tmin values were lower than 0°C for three out of four strains. The ?opt values ranged from 0.778 and 0.90 h-1 for L. plantarum strains and from 0.553 and 0.654 h-1 for L. paracasei strains. Discussion The determination of growth cardinal values is useful to assess variability in bacterial growth abilities. This preliminary study also demonstrates the transfer of already available mathematical models to technological and probiotic strains. Indeed several user friendly tools are available to facilitate the practical use recognized mathematical models for growth prediction. The generic approach used in Sym'Previus is applicable to pathogenic, spoilage and technological microflora to further predict the impact of environmental conditions on bacterial growth. Besides the importance of using real life strains, this study further underlines the importance of characterized collection for the selection of the bacterial strain to be used in challenge test to optimize process/shelf-life and ensure food safety and quality.