Effect of milk fat replacement by polyunsaturated fatty acids on the microbiological, rheological and sensorial properties of fermented milks

A modified milk (W3DD) where fat had been replaced by oils enriched in (omega)-3 polyunsaturated fatty acids was used for the manufacture of a set -type fermented product. In order to improve the organoleptic properties of the product, 30 g l^-1 whey protein concentrate (WPC) was added during the manufacturing process. Samples were fermented employing a commercial probiotic starter culture (ABT-2), which contained Streptococcus thermophilus ST-20Y, Lactobacillus acidophilus LA-5 and Bifidobacterium lactis BB-12. The acidification process was dependent on the WPC addition, which favoured the increase of viable counts, but fermentation was not influenced by the milk fat composition. The highest counts of the probiotic strains, L acidophilus LA-5 (3.3 × 10^5 cfu g^-1) and B lactis BB-12 (5.5 × 10^7 cfu g^-1), after 21 days of storage at 4 °C, were found in fermented products derived from W3DD supplemented with WPC. Addition of WPC also increased the firmness of the products and reduced syneresis. No apparent colour changes due to fat composition or WPC supplementation were observed in the products. Milk fat replacement by oils rich in (omega)-3 polyunsaturated fatty acids had a negative influence on the product texture but did not affect the typical yoghurt flavour. These defects were overcome by the addition of 30 g l^-1 WPC, which improved the appearance, texture and general acceptability scores in the product.