ADENOSINE-DEAMINASE (EC-3.5.4.4) - A POTENTIAL INDICATOR OF HEAT-TREATMENT FOR THE DISTINCTION OF SHORT-TIME AND HIGH-TEMPERATURE PASTEURIZED MILK FROM THE MARKET

In accordance with the German Milk Regulation the heat treatment of sh ort-time and high temperature heated milk is defined with respect to t he activities of the milk enzymes alkaline phosphatase and lactoperoxi dase. In a previous work it could be shown, that the contents of indiv idual ribonucleosides - which belong to the group of minor milk consti tuents - in milk which has been subjected to thermization, in particul ar holder and short-time pasteurization are enzyme-controlled. The mil k enzyme adenosine deaminase oxidatively deaminates the milk ribonucle oside adenosine to inosine. By milk heating experiments it was demonst rated for the first time, that the adenosine deaminase activity increa ses up to a heating-temperature of about 75 degrees C, whereas at 85 d egrees C the enzyme is inactive. In further investigations kinetic dat a (e. g. half-life time, decimal reduction value) of this enzyme were estimated. Compared to alkaline phosphatase adenosine deaminase shows a higher thermal stability. In dairy model experiments it could be sho wn, that the degree of the deaminase activity is not influenced by hom ogenization. The results from the aforementioned heating experiments w ere confirmed by investigations of random milk samples (different type s of heat treated milk) from the market. In short-time heated milk sam ples adenosine deaminase activity was found to be positive, whereas in high- and ultra-high-heated milk samples the deaminase activity was n egative. According to our present knowledge the activity of adenosine deaminase seems to be suited as a potential indicator for the distinct ion of short-time and high-temperature pasteurized milk.