RRJFDT | Volume 1 | Issue 1 | July – September, 2013 8 Research and Reviews: Journal of Food and Dairy Technology Effect of Heat Treatment of Milk on the Sensory and Rheological Quality of Dahi Prepared from Cow Milk Sudeep Shekhar, Joe J, Rahul Kumar, Jyothis J, Ketan Kumar RM, Priya YA, Jayaraj Rao K* and Pagote CN. DT Section, NDRI, Adugodi, Bangalore 560 030, Karnataka, India Research Article Received: 31/10/2012 Revised: 10/11/2012 Accepted: 18/11/2012 *For Correspondence Dr. K. Jayaraj Rao, Senior Scientist, DT Section, NDRI, Adugodi, Bangalore 560 030, Karnataka, India E-mail: jaysharm@yahoo.com Key words: Dahi, Heat treatment, Milk, Rheological, Firmness, Consistency ABSTRACT Dahi is a popular fermented Indian dairy product prepared by fermenting the milk by lactic acid bacteria. The texture of dahi depends mainly on the heat treatment given to milk. Cow milk (3.5% fat and 8.5% SNF) was subjected to two separate treatments: (1) heating at 63 o C for 30 min and (2) boiling treatment without holding period. The milk was cooled to about 40 o C and inoculated with Lactococcus lactis culture and incubated at 30 o C for about 12 hours. The dahi formed was chilled to 5 o C and evaluated for quality. Firmness, consistency and index of viscosity as measured by Texture Analyser increased with increased heat treatment and the highest values were observed in dahi prepared from boiled milk. Boiling treatment of milk resulted in least syneresis of whey in the curd. Based on the results, it was recommended that milk be subjected to boiling treatment to produce best quality dahi. INTRODUCTION Dahi is the most popular fermented dairy product in the Indian sub-continent and consumed by most people almost every day with each meal. It is similar to leben in Iran, Jugurt in Turkey, Roba in Iraq,Mazun in Armenia,Villi in Finland, Shosim in Nepal [1] . Its chemical composition is similar to that of laban in Saudi Arabia [2] . Dahi is so popular that a meal is considered incomplete without consuming it towards the end of the meal. In southern parts of India, dahi is eaten with rice (popularly known as curd rice) and is used to prepare several culinary dishes. The beneficial aspects of milk, dahi and other dairy products are well documented [3, 4, 5, 6, 7] . Bhattacharay and Das [8] isolated from dahi a few lactobacilli which produced bacteriocins effective against human pathogens. Thus, the therapeutic properties of dahi are well known, hence dahi is used in several of Ayurvedic formulations (traditional Indian medicinal system) [9, 10] . Dahi prepared from buffalo milk is white in colour and possesses firm body and slightly granular texture, whereas dahi prepared from cow milk is les firm and smooth in texture [11] . These differences are attributed to inherent variations in the protein make up of both the milks [12] . The huge market of dahi in the sub-continent is being tapped by most of the organized sector dairies. It is estimated that 6.9% of total milk produced in India is utilized for dahi production in India [1] . Still a large portion of market remains to be tapped. Dahi is also used as a vehicle to incorporate probiotics into the health conscious consumers because of the fact that it is consumed by people daily [13] . Varieties of dahi were also developed for the benefit of consumers, like fruit dahi [13] . Dahi is mostly sold in polythene pouches, but also in set form in HDPE containers. Dahi sold in pouches does not have the three dimensional network structures which is typical of set dahi. Whereas that sold in the rigid plastic containers possesses a firm body and smooth texture which appeals to consumers. However, flavour is the foremost quality of dahi that determines its acceptance. The pleasant flavour of dahi is attributed to its diacetyl content which is produced by lactic acid bacteria [1, 4] . Next to flavour, the acceptability is determined by the texture of the curd, which is governed by many factors including type of milk, composition of milk etc. [14] Heat treatment of milk also plays an important role in determining the textural quality of dahi by way of denaturation of milk proteins. Hence, a study was conducted to examine the effect of heat treatment on the quality of dahi.