Chemical Papers 67 (7) 737–742 (2013) DOI: 10.2478/s11696-013-0365-1 ORIGINAL PAPER Evaluation of temperature effect on growth rate of GG in milk using secondary models Ľubomír Valík*, Alžbeta Medveďová, Michal Čižniar, Denisa Liptáková Department of Nutrition and Food Quality Assessment, Faculty of Chemical and Food Technology, Slovak University of Technology in Bratislava, Radlinského 9, 812 37 Bratislava, Slovakia Received 18 October 2012; Revised 17 January 2013; Accepted 21 January 2013 The application of secondary temperature models on growth rates of Lactobacillus rhamnosus GG, the much studied probiotic bacterium, is investigated. Growth parameters resulting from a primary fitting were modelled against temperature using the following models: Hinshelwood model (H), Ratkowsky extended model (RTK2), Zwietering model (ZWT), and cardinal temperature model with inflection (CTMI). As experienced by other authors, the RTK2, ZWT, and CTMI models provided the best statistical indices related to fitting the experimental data. Moreover, with the biological background, the following cardinal temperatures of L. rhamnosus GG resulted from the study by the model application: tmin = 2.7 ◦ C, topt = 44.4 ◦ C, tmax = 52.0 ◦ C. The growth rate of the strain under study at optimal temperature was 0.88 log10 (CFU mL -1 h -1 ). c  2013 Institute of Chemistry, Slovak Academy of Sciences Keywords: temperature, growth modelling, L. rhamnosus GG Introduction Quantitative food microbiology and predictive modelling are usually closely focused on issues lim- iting food safety and quality. Within the risk assess- ment tools, quantification is generally concerned with the presence and growth of pathogens in foods and the proper determination of food shelf-life (Gibson & Roberts, 1989; McMeekin et al., 1993; McKellar & Lu 2004; Brul et al., 2007). Several primary and sec- ondary models are used in quantitative or predictive microbiology to characterise the growth of microor- ganisms in relation to time and food environmental factors, respectively. On the other hand, they also serve as a basis for tertiary model systems used for the prediction of microbial behaviour in foods (Ross & McMeekin, 1994). However, the areas of food safety and food quality still provide relevant challenges for predictive microbiology, one of which is the growth description of lactic acid bacteria during food fermen- tations or probiotic microorganisms in food matrices. This would enable the use of modelling methodology not only in dairy product quality but also in product functionality. These ideas were endorsed by the review by Roupas (2008). Lactobacillus rhamnosus is a Gram-positive, non- spore forming, facultative anaerobic or microaerophi- lic, non-motile, and catalase-negative microorganism. It is a mesophile but, depending on the strain, may grow at temperatures below 15 ◦ C or above 40 ◦ C. The optimal pH value for its growth is in the range from 6.4 to 6.9 (Liew et al., 2005) and the minimal pH can be found within the range from 4.4 to 3.4, depend- ing on the buffering capacity of the medium (Hel- land et al., 2004). Its growth requirements include folic acid, riboflavin, niacin, pantothenic acid, and calcium (Curry & Crow, 2004). The metabolism of L. rhamnosus is facultative heterofermentative (lacto- bacilli Group 2). It converts hexoses into L(+) lactic acid, in accordance with the Embden–Meyerhof path- way; due to aldolase and phosphoketolase, pentoses are also fermented. Up to 1.5 % of lactic acid is usu- ally produced in a glucose medium. In the absence of glucose, it produces lactic acid, acetic acid, formic *Corresponding author, e-mail: lubomir.valik@stuba.sk Author copy