Buttermilk is a suitable substrate for fermentation with proteolytic strains of Lactobacillus in order to release peptide fractions able to enhance the gut mucosal immune system. We aimed to determine the influence of the degree of proteolysis of buttermilk proteins on their functionality. Animals received for seven consecutive days the cell-free fraction of 10 or 20% (w/v) buttermilk fermented with Lactobacillus delbrueckii subsp. lactis 210 at pH 6. The pH was controlled either with NaOH or Ca(OH)2. No significant differences in the number of IgA-producing cells in the small intestine of mice were found. The functional capacity of the product under study was not affected by the technological variables considered.