Abstract
Skim milk was separated from bulk cow's milk secured from a dairy district in Miyazaki prefecture, and was heated at 85°C for 5min, immediately followed by heating at 135°C in a moment. The effects of Ca and casein micelle on the physical properties (hardness, breaking energy and elastic modulus) of the rennet curd prepared from this high temperature heated milk were investigated by the use of a rheometer. The results obtained were summarized as follows: (1) The physical properties of the high temperature heated milk rennet curd could not be estimated under the experimentel condition employed in this study. (2) An addition of only Ca salt had a little effect on the rennet curd: The physical properties of rennet curd were maximal by the addition of 80mg Ca/100ml, but these were significantly inferior to those of unheated milk because of the heat denaturation of milk proteins. (3) The physical properties of rennet curd of high temperature heated milk could be remarkably improved by the addition of casein micelle (880mg N/100ml). When the unheated casein micelle ratio which was defined as a ratio of added casein micelle against the total casein micelle was 0.3, the rennet curd of high temperature heated milk could attain the physical properties almost the same as those of unheated one due to the increase of native micellar casein in high temperature heated milk. (4) Addition of micellar casein to the Ca-added (80mg/100ml) milk gave a remarkably strong rennet curd. At O.05 or 0.1 of the unheated casein micelle ratio, the physical properties of the prepared rennet curd were comparable to those of unheated milk. (5) From those results it was confirmed that the increases of soluble Ca and native micellar casein were essential for the improvement of rennet curd of high temperature heated milk.
