International Dairy Journal 15 (2005) 989–997 Effect of temperature on growth and metabolism of probiotic bacteria in milk Hilde M. Østlie à , Janneke Treimo, Judith A. Narvhus Department of Chemistry, Biotechnology and Food Science, Agricultural University of Norway, P. Box 5003, N-1432 A ˚ s, Norway Received 24 February 2003; accepted 25 August 2004 Abstract The growth and metabolism of six probiotic strains with documented health effects were studied in ultra-high temperature (UHT) treated milk supplemented with 0.5% (w/v) tryptone or 0.75% (w/v) fructose at different temperatures. The probiotic strains were Lactobacillus acidophilus La5, Lb. acidophilus 1748, Lb. johnsonii LA1, Lb. rhamnosus GG, Lb. reuteri SD 2112 and Bifidobacterium animalis BB12. Fermentation was followed for 48 h at 20, 30, 37 and 45 1C and the samples were analysed for pH, log cfumL À1 , volatile compounds, organic acids and carbon dioxide. All six probiotic strains showed very different profiles of metabolites during fermentation, however, the two Lb. acidophilus strains were the most alike. All strains, except Lb. reuteri SD 2112, showed viable cell numbers above 6.5 log cfu mL À1 after 48h fermentation at 30, 37 and 45 1C. The probiotic strains produced different amounts of metabolic products according to temperature and fermentation time illustrating the importance of controlling these parameters. r 2004 Elsevier Ltd. All rights reserved. Keywords: Fermented milk; Probiotic bacteria; Organic acids; Volatile compounds; CO 2 1. Introduction During the past twenty years there has been a tremendous increase in the worldwide sales of cultured products containing probiotic bacteria. Today, most probiotic strains are used in yoghurts, fermented milks, ice creams and pharmaceutical products for their anecdotal health effect (Mattila–Sandholm, 1999). Increasing knowledge underlines the important role of the intestinal flora for maintaining health and in the prevention of disease. Probiotics offer dietary means to support the balance of intestinal flora (Holzapfel, Haberer, Snel, Schillinger, & Huis in’t Veld, 1998). The microorganisms primarily associated with this balance are lactobacilli and bifidobacteria. Several aspects have to be taken into consideration in the selection process of probiotic organisms. Safety aspects reviewed lately by Salminen et al. (1998) and Saarela, Mogensen, Fonde´n, Ma¨tto¨, and Mattila–Sand- holm (2000) include specifications as to human origin, non-pathogenicity and antibiotic resistance character- istics. Factors related to the technological and sensory aspects of the probiotic food products are of utmost importance since only by satisfying the demands of consumers can the food industry succeed in promoting the consumption of functional products in the future (Mattila–Sandholm, Mylla¨ rinen, Crittenden, Mogensen, Fonde´n, & Saarela, 2002). To maintain confidence in probiotic products it is important to demonstrate good survival of the bacteria in food products during their specified shelf life. In order for any beneficial effect in humans to develop, the viable cell count should be above 6logcfug À1 in order to supply a sufficient ‘‘daily dose’’ of 10 6 –10 9 viable bacteria (Samona & Robinson, 1991; Lee & Salminen, 1995; Vinderola, Bailo, & Reinheimer, 2000). In addition, a pleasant taste and an attractive texture are essential for all food products, regardless of the ‘‘health message’’ of the product (Saxelin, Grenov, Svensson, Fonde´n, Reniero, & ARTICLE IN PRESS www.elsevier.com/locate/idairyj 0958-6946/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.idairyj.2004.08.015 à Corresponding author. Tel.: +4764948578; fax: +4764943789. E-mail address: hilde.ostlie@ikbm.nlh.no (H.M. Østlie).