Chemical and viability changes during fermentation and cold storage of fermented milk manufactured using yogurt and probiotic bacteria

Abstract

The objective of the present work was to study probiotic fermented milks during fermentation process and cold storage. Two strains of probiotic bacteria were used: Lactobacillus acidophilus (LA) and Bifidobacterium animalis subsp. lactis (BL). The yogurt culture Lactobacillus bulgaricus (LB) was used as control. All strains were employed in coculture with the starter Streptococcus thermophilus (ST). Commercial skimmed milk powder was diluted in distilled water (12.4g 100g) and heat treated. All inoculated milks were incubated for fermentation at 42°C in a water bath until pH 4.50 was reached. Chemical changes during fermentation were followed by measuring: Vm (maximum acidification rate that measures the decrease of pH units per minute and the values are expressed as mUpH/min), tVmax (time to achieve the maximum acidification rate, in h), tpH5,0 (time to achieve pH5.0, in h) and tpH4.5 (time necessary to reach pH 4.5, in h). Rheological behavior was determined at d1 and firmness, pH and viability were followed until 28 days of storage at 4oC. Fermentation time for probiotic cultures was longer than for yogurt culture. pH decreased and firmness increased during storage. The main change occurred in the first week. Probiotic bacteria grow during fermentation. ST dominated over the other strains and remained stable during all storage period. B. lactis and L. bulgaricus attain the final storage period stable. L. acidophilus, however, decreased before 14 days of storage and at d 28 doesn’t fit the minimum requirements to achieve beneficial properties to health. Key-words: probiotic, kinetics, viability and texture * Corresponding author: tel: +55 11 3091 3690 E-mail address: monolive@usp.br INTRODUCTION Major developments in functional foods area include the selection and use of beneficial probiotic microorganisms. They are defined as “microbial cells preparations or components of microbial cells that have a beneficial effect on health and well being of the host” (Gardiner et al., 2002). Although the probiotic market development includes many dairy foods, fermented foods remain the main vehicle of administration of probiotic and yogurt is far the most important in this group (Tamime et al., 1995; Lourens-Hatting and Viljoen, 2001). Health related benefits associated with the consumption of probiotic micro-organisms could be summarized as: enhancement of immune modulation and prevention of certain diseases and/or ailments in humans (Goldin, 1998; Holzapfel et al., 1998; Salminen et al., 1998; Mattila-Sandholm et al., 1999; Ouwehand et al., 2003). IUFoST 2006 DOI: 10.1051/IUFoST:20060635