Characterization of oligo- and polypeptides isolated from yoghurt

Skimmed milk was inoculated with a mixed culture of Streptococcus salivariu s ssp. thermophilus and Lactobacillus delbrueckii ssp. bulgaricus and ferme nted at 44 degrees C. Peptides were isolated by treatment with a Dowex 50 W X 2 cation exchanger and then fractionated by ultrafiltration using membran es with cut-off sizes of 10, 5 and 1 kDa. Final separation of the oligopept ides was carried out by reversed-phase HPLC using gradient elution with an aqueous trifluoroacetic acid/acetonitrile mixture. Structure determination was performed by automated Edman degradation. Several peptides were additio nally characterized by electrospray ionization-mass spectrometry. Peptides were evaluated for their hydrophobicity according to Ney's rule. Among the 30 peptides characterized, several pre cursors of bioactive peptides were d etected.