Production of fermented skim milk supplemented with different grape pomace extracts: Effect on viability and acidification performance of probiotic cultures

The addition of polyphenolic compounds to probiotic dairy products has been proposed as a promising strategy to enhance the beneficial health effects of milk-derived functional foods. In this study, probiotic fermented skim milk was supplemented with pomace extracts obtained from Pinot Noir, Freisa, Croatina and Barbera grape varieties. Regarding acidification kinetics, the addition of Pinot Noir extract increased the maximum acidification rate (V-max) of skim milk by 39.4% compared with control (no pomace extract supplementation). The time required to complete the fermentation (t(pH4.5) = 3.5 h) was shortened when grape pomace extracts were added to the fermented skim milk. It was also observed that after 28 days of storage at 4 degrees C, polyphenolic compound supplementations had a positive effect on cell viability of both Streptococcus thermophilus and Lactobacillus acidophilus. The concentration of polyphenols was also determined in the fermented skim milk samples. These results suggest that Streptococcus thermophilus and Lactobacillus acidophilus can metabolize the supplemented polyphenols, although not all to the same extent. Moreover, this study demonstrates the feasibility of adding phenolic compounds to probiotic products in order to further improve their functional health properties.