STUDIES ON DISTINGUISHING FEATURES FOR EV ALUATING HEAT-TREATMENT OF MILK

The project was concerned with studies on the distinguishing features which allow heat treatment of milk to be evaluated. The aim of the pro ject was to establish chemical, physical, processing and sensory param eters, which enable the reliable differentiation between heating range s as normally applied in dairies such as thermisation, pasteurization, (short-time- and long-time heating, high temperature pasteurization), UHT treatment and sterilization and which provide, thus, the scientif ic grounds for establishing defined limits for each milk type. They al low, further, measures to be taken with which the thermal effect on mi lk can be reduced to a necessary minimum which is possible as regards the production process and is required from the hygienic viewpoint. Th ey are, thus, a useful tool in improving the quality of fluid milk in the interest of the consumer. Raw milk from the experimental farm Scha edtbek of the Federal Dairy Research Centre was thermally treated usin g different temperature-time combinations in the range between 62-140 degrees C and holding times extended up to some minutes and the heat-i nduced changes of milk and their components analytically controlled. F or thermal treatment of the milk samples a very broad temperature-time spectrum was, thus, selected. This was possible by use of a discontin uously operating autoclave and a continuous pilot heating plant with e xchangeable holders at the Institute for Process Engineering of the Ce ntre. In the range studied all legally admitted heating processes coul d be incorporated. As a basis for calculating the equivalent holding t ime the sterilization value F-0 was used. As chemical parameters furos ine, N6-methyladenosine, lactulose, native (acid-soluble) alpha-lactal bumin and beta-lactoglobulin (genetic variants A+B) and immunoglobulin s were analytically determined. Further, the contents of free amino ac ids, caseinophosphorus and free amino groups (OPA reaction) were deter mined and the thermally induced changes in the triglyceride/fatty acid pattern of milk examplarily investigated. Thermally induced protein c hanges were followed up analytically by measuring the degree with whic h enzymic proteolysis of milk protein was possible. As physical parame ters the freezing point depression of milk, pH-and SH-values, as well as gelling- and browning behaviour were considered in evaluating the t hermal effect on milk. As processing parameters for assessing the heat treatment process of milk all sterilization values (F0 values), on wh ich the adjusted temperature-time combinations were based, were taken into consideration. As to sensory parameters a sensory profile analysi s of the heat treated milk was performed, if possible, and included in the evaluation. The results from this study show that, without doubt, there exist, from the technological point of view, a number of suited chemical parameters which can also be analytically controlled. As hea t indicators for establishing upper limits for the heating ranges of h igh temperature pasteurization, UHT treatment and sterilization they a re, hence, suited to be used for limiting the heat load in these milk types to the minimum required for product safety in order to come, thu s, up to the particular image of milk in terms of ''Naturbelassenheit' ' and health promotion.