Determination of Diacetyl production by a local isolate of Lactobacillus casei collected from raw milk

An isolate was isolated from raw milk of cow. It was identified as Lactobacillus casei. The test for Gram staining, Biochemical test and Sugar fermentation tests were performed. The cells of isolate were rod shaped. Colony was small circular and creamy white. Isolate was gram positive. Catalase, Oxidase, Indole and VP negative, MR and NR positive. The sugar fermentation test revealed that the isolate was Glucose, Lactose, Mannitol and Raffinose positive while Fructose, Sucrose and Arabinose negative. It was tested for Diacetyl production. Diacetyl is a natural flavour producing compound. Several bacteria including Lactic acid bacteria are capable of producing diacetyl as by-product. Due to diacetyl production some lactic acid bacteria gives buttery flavour to milk products. Diacetyl is a volatile compound extensively used in Dairy Industries and Pharmaceutical industries. Diacetyl formation was maximum on 2nd week of incubation when the pH falls to pH-6.1 (6.73ppm).