Pakistan Journal of Nutrition 7 (5): 689-694, 2008 ISSN 1680-5194 © Asian Network for Scientific Information, 2008 689 Characterization of Lactococcus Phages from Dahi Whey Kashif Hussain , Tariq Masud , S. Maqsud and Talat Mahmood 1 1 2 1 University of Arid Agriculture, Rawalpindi, Pakistan 1 Quaid-I-Azam University, Islamabad, Pakistan 2 Abstract: For the production of yogurt and related products, the local and the commercial yogurt manufacturers of Pakistan are still, by and large using an undefined, unclassified mixture of lactic acid bacteria together with a large number of contaminated strains. Phages isolated in our part of world show different characteristics in terms of phage morphology, lytic patterns and burst size etc, compared to phages isolated elsewhere in the world cause serious problems to fermentation process and ultimate economic losses to dairy industry. In order to develop indigenous resistant starter cultures phages were isolated from samples of Dahi whey isolated phages were characterized on the basis of host range, latent period and burst size. Five virulent phages KT-1, KT-2, KT-3, KT-4 and KT-5 were isolated from twelve samples of whey using Lactococcus lactis strains as host. These phages caused lysis and ultimately retarded acid production of host strains. Three phages i.e. KT-1, KT-2 and KT-3 have shown multiple host specificity. Phages KT-1 and KT-2 have same latent period of 15 minutes but exhibited a slightly different rise period that is 20 minutes and 25 minutes respectively, the burst size of 90 and 65 phages per cell were detected for KT-1 and KT-2 respectively. KT-4 showed burst size of 80 phages per infected cell, whereas KT-5 showed burst size of 90 phages per cell. The results reveal that bacteriophages from this region are different from phages isolated in other parts of world. Key words: Lactococcus, bacteriophages, Whey, yogurt Introduction Lactococcus bacteria have found their use in the manufacture of several fermented dairy products in which they are responsible for the acidity and characteristic flavor. Sufficient lactic acid formation by lactic acid bacteria during the manufacture of fermented Materials and Methods dairy products is of utmost importance. Factors Bacterial strains and media: Bacterial strains used in contributing to a slow starter are composition of milk, this study were isolated and characterized in the contaminating microorganisms, changes in Department of Food Technology, University of Arid fermentation behavior and most commonly encountered Agriculture Rawalpindi, Pakistan. The M-17 media was bacteriophages attack (Klaenhammer, 1984). The first to used in this study for the growth and maintenance of attribute the cause of starter failure to bacterial cell bacterial strains and M-17 broth was also used for the dissolving activities of bacteriophages. Since then failure phage propagation. Phage suspensions that were used due to phages have been observed throughout the world regularly in this research were kept refrigerated at 4°C in (Whithead and Cox, 1985). M-17 broth. Elaborate studies on various aspects of phage including morphological and structural characterization, host Whey samples: Twelve samples of whey were collected phage interaction, effect on lactic fermentation and from different localities of Rawalpindi city. Samples were product quality and genetic studies have been carried collected randomly in sterilized bottles. Samples were out in order to combat phage attacks in dairy industry cooled on ice immediately after collection for (Klaenhammer, 1984). However, such a detailed study transportation and brought to the laboratory for further on the phages isolated from our indigenous dairy analysis. products such as Dahi, Lassi and Whey, has not been attempted despite its tremendous significance. The Isolation of bacteriophages: Isolation of bacteriophages present work is concerned with the isolation and was performed according to methods described by characterization of Lactococcus phages specifically from Jarvis (1989). First whey was centrifuged at 3000g for 20 Dahi whey as it provides an excellent medium for the minutes and supernatant was collected and filtered propagation of bacteriophages. The prime objective of through 0.45 μm sterilized filter and filtrate was kept at this work was to isolate and characterize Lactococcus 4°C for further isolation of bacteriophages. Aliquots (0.1 bacteriophages. The with respect to their of host range, latent period and burst size and to study the effect of these bacteriophages on lysis and ultimate reduction in acid formation.