Evaluation of aroma production and survival of Streptococcus thermophilus, Lactobacillus delbrueckii subsp bulgaricus and Lactobacillus acidophilus in fermented milks

The fat, the non-fat milk solid and the inoculum size of Lactobacillus acidophilus IPVR 224 were modulated according to a Central Composite Design. The aim was to evaluate the effects of these variables and their interactions on the decrease in pH during fermentation, the qualitative and quantitative composition of the aroma profile, as well as the loss in viability of Streptococcus thermophilus IPVR 161, Lactobacillus delbrueckii subsp. bulgaricus IPVR 132 and L. acidophilus IPVR 224 strains during five weeks of storage. In addition, the overall acceptability of the fermented milks was assessed by means of a sensory panel. The polynomial quadratic equations obtained allowed to individuate the variables that significantly affected the aroma profile, organoleptic properties and microbiological counts of the various fermented milks. The survival of the L. acidophilus strain during storage was higher at low concentration of non-fat milk solids and its presence did not affect the acetaldehyde content of fermented milks. From the response surfaces analysis it was possible to select optimum conditions for enhanced positive organoleptic traits and for improved survival of the probiotic culture. (C) 1999 Elsevier Science Ltd. All rights reserved.