Indian J Dairy Sci 69(3), 2016 336 RESEARCH ARTICLE Shelf-life study of pouch packed UHT milk- a qualitative approach Nihir Shah, Ami Patel, Aparna Sudhakaran, Ankur Ojha, PR Patel and JM Dave Received : 24 April 2015 / Accepted: 22 November 2015 Nihir Shah 1 (), Ami Patel 1 , Aparna Sudhakaran 1 , Ankur Ojha 2 , PR Patel 3 and J M Dave 4 1 Department of Dairy & Food Microbiology, Mansinhbhai Institute of Dairy and Food Technology, Dudhsagar Dairy Campus, Mehsana, Gujarat 2 Department of Dairy & Food Technology, Mansinhbhai Institute of Dairy and Food Technology, Dudhsagar Dairy Campus, Mehsana, Gujarat 3 Mansinhbhai Institute of Dairy and Food Technology, Dudhsagar Dairy Campus, Mehsana, Gujarat 4 Mansinhbhai Institute of Dairy and Food Technology, Dudhsagar Dairy Campus, Mehsana, Gujarat Nihir P. Shah, Department of Dairy and Food Microbiology, Mansinhbhai Institute of Dairy and Food Technology-MIDFT, Dudhsagar Dairy campus, Mehsana- 384 002, Gujarat State, India Phone: +91 9925605480, E-mail: Nihir@midft.com Abstract: The analysis of raw milk subjected to UHT process revealed no seasonal variations in any of the physico-chemical parameter except significant increase in microbial spore count. During storage of UHT pouch milk, significant changes were observed after 45 days for overall acceptability score, pH, protein content, lactose content at 37±1 ºC whereas no microbial spores were found during entire shelf-life study. Based on results, it seems that the Maillard browning could be responsible for bringing pronounced changes in physico-chemical parameters as well as decreasing the degree of overall acceptability of UHT milk. The initially cooked/burnt flavour noticed by panellist was overruled by other off-flavours like chalky, stale, etc. after 45 days. However, the UHT milk was acceptable till the end of storage period. Key words: UHT milk, mesophilic spore count, lactose content, shelf life, seasonal variation Introduction India continues to be the largest producer of milk in the world since the last 15 years and estimated milk production is 132.4 million tons in 2014-15. The country accounts for around 17 percent of world’s total milk production with a per capita availability 322 grams per day in the year 2014-15 (Source: Ministry of Agriculture, Government of India). India is not only the leading milk producer but is also the largest consumer of milk in the world. Milk is considered as complete food and is an integral part of Indian diet. Moreover; its high nutritive value makes it an ideal food not only for humans but for a wide variety of microorganisms. Milk is highly perishable as microbes can grow rapidly in milk under unhygienic production and also during storage at ambient temperatures. India being in the tropical climate zone, milk can be kept only for fewer hours at ambient temperature after milking. More over affordable cold chain management is in its infancy. So, it is necessary to develop appropriate technologies or methods for milk preservation prior to distribution and sale. One such advancement where the country’s dairy sector witnesses tremendous growth is the Ultra High Temperature (UHT) processing of milk. The popularity for UHT milk is growing for many Indian consumers who do not want to compromise on quality and nutrition. Increasing urbanization and working women culture will increase the demand for safe, convenient and ready – to - drink milk like UHT. Milk is subjected to a high heat treatment during UHT for various aspects such as destruction of microbes, enzyme inactivation, to increase shelf-life and to minimise physico- chemical changes occurring in milk during/after heat treatment. In UHT processing the sterile product is filled into sterile packages within the sterile zone of an aseptic packaging system. UHT processing uses continuous flow and subjects milk to 135 to 150°C for 3 to 5 seconds followed by aseptic packaging with an anticipated shelf life of 6 months stored/distributed under ambient temperature. UHT processing ensures commercial sterility as well as acceptable sensory attributes throughout shelf life. It eliminates all the spoilage microorganisms and harmful bacteria for human consumption without affecting the nutritional value of the product. According to the WHO/FAO, commercial sterility of low-acid food is defined as follows: “Commercial sterility means the absence of microorganisms capable of growing in the food at normal non-refrigerated conditions at which the food is likely to be held during manufacture, distribution and storage.” (Codex Alimentarius Commission (WHO/ FAO) CAC/RCP 40-1993). The first system consisting of indirect heating with continuous flow (125ºC for 6 minutes) was manufactured in 1893. Patented in 1912, the continuous flow direct heating method mixed steam with milk to achieve temperatures of 130 to 140ºC. In 1953, UHT milk was filled aseptically into cans after heat treatment with an