Effect of Nisin on Technological and Microbiological Characteristics of Stirred Yoghurt

Purpose of this paper: Growing worldwide inclination towards healthful foods has compelled food processors to search for natural preservatives to enhance the shelf-life and extend the market reach. Limited shelf-life of cultured milk products arising from post-acidification could be enhanced with the application of bacteriocins such as nisin. Application of nisin in stirred yoghurt may retain its desirable properties during extended shelf-life. Design/Methodology/Approach: Stirred yoghurt containing nisin was obtained by culturing cow milk, heated at 95 °C / 5 min with 3% Yoghurt-YH-3 incubated at 42 ± 1 °C for 5 h and then stirred for incorporating 25 RU/ml nisin, followed by further 1 h incubation. Effect of incorporation of nisin on technological (titratable acidity, diacetyl and acetoin content, volatile acidity and extent of proteolysis and microbiological (total viable microbial contents, coliform count, yeast and mould, lipolytic organism and proteolytic organisms) and antibacterial characteristics of stirred yoghurt were assessed during 40 days of storage at 10 ? 15 °C. Findings: Incorporation of nisin in yoghurt induced lower acid and volatile acid development, but a significantly higher proteolytic activity as well as diacetyl + acetoin production. Nisin exhibitedantagonism against viable population but ineffective to yeast,mould and proteolytic organisms in yoghurt Nisin containing yoghurt exhibited lower degree of antagonism against various pathogenic test organisms, which progressive increased during storage.