Transglutaminase Enzymes And Metabolites Of Propionibacterium Yogurt Quality

The effects of transglutaminase (TGase) and propionibacteria metabolites(PM) on yoghurt quality were studied. Main results are as follows:TGase has significant effects on physicochemical properties of yoghurt. With the addition of TGase, the texture of yoghurt was improved, yoghurt treated with TGase had a higher hardness, breaking force, and chewiness than untreated ones, TG treatment of milk prior to fermentation led to prolonged fermentation ,while the concomitant use of TG and culture had no influence on fermentation. Post acidification of yoghurt during storage was lower for products from enzyme-treated milk. This applies both for products cross-linked prior to fermentation with enzyme inactivation, and for simultaneous use of culture and TG without inactivation of the enzyme. Sensory studies revealed that odour and consistency properties of products from TG-treated milk were assessed as less "yoghurt specific". On the other hand, products from TG-treated milk were described as being more creamy, indicating that a TG treatment may simulate fat in fermented milk products.In addition to the investigations for characterzing the chemo-technological properties of yoghurts with and without enzymatic crosslinking of the milk proteins by TG. The influence on microbiological properties and on shelf life of stirred yoghurt products after addition of TG has been analyzed. The result shows that addition of a non-inactivated TG product has a stabilizing effect on the living cell counts of the lactobacilli in the (cooled) yoghurt product during storage.Because of the formation of casein macropolymer, the extractability of acetic acid-soluble gluten proteins decreased substantially after TGase treatment. The macropolymer molecules were so large that they were unable to penetrate the stacking or the separation gels in SDS-PAGE. Using scanning electron microscopy (SEM) method, it was found that the casein modified appeared more tight and uniform than untreated . The TGase treatment resulted in a substantial increase in storage modulus values of casein.Propionibacteria metabolites(PM) is produced by growing propionibacteria cells in a liquid growth medium to produce a mixture containing the metabolite material. When PM was incorporated into agar media. Gram-positive bacteria were insensitive to PM; Bifidobacteria was stimulated. PM was an inhibitor for Gram-negative bacteria. Yeast and mold were partially suppressed. Optimum activity of PM was at low pH; the concentration that gave complete inhibition depended upon the number of bacteria present as well as the genus tested. Some components of media reversed the antagonistic activity of PM.When PM was incorporated into yoghurt. PM was an inhibitor for Gram-negative bacteria Yeast and mold .Sensory studies revealed that PM does not affect yoghurt odour and consistencyThus, PM can be applied in yoghurt to prolong its shelf life.