THE ROLE Of PROPIONIC ACID BACTERIA METABOLITES IN SOME DAIRY PRODUCTS

Abstract

Wagih Ibrahim El-Kholy. The role·oipropionic a id ltacteria metabolites in some dairy dairy products. Unpublished Ph. D. Thesis, Food Science Department, Faculty of Agriculture, Ain Shams University , 2000. Comparing metabolites of I6 different propionibacteria strains for inhibitory activity against some Gram negative and Gram-positive food spoilage and pathogenic microorganism. The highest inhibitory activity was achieved by metabolities of P.thoenii strain P.127, as produced at pH 7.0 and incubation for 96h at 32°C in sodium lactate broth supplemented with 1.5% lactate, I% Tryptone I.5% yeast extract and O.OI5% from each ofMnSo4 , KH2 P04 and Cobalt nitrate, or produced in reconstituted non fat dried milk containing I% glucose, 0.5% yeast extract and O.OI5% cobalt nitrate. Noticeable supression for growth of the examined mould and yeast strains was recorded with presence of 5% of P. thaenii (P I27) milk culture supernatant. Less supress10n was achieved with lactate cultuare supernatant. The same supernants stimulated some lactic cultures. Gas chromatography analyses reveal the presence of ethanol, propanol, n-amyl alchol acetaldehyde in addition to acetic, citric, lactic and propionic acids. Addition of P. thoenii culture supernatant in different fonns by l% to yoghurt and soft cheese obviously prolonged the expiry dates of the yoghurt to more than 3 weeks and the soft cheese (Tallagah) to more than 4 weeks.