Residual Casein Fractions in Ripened Cheese Determined by Polyacrylamide-Gel Electrophoresis

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Abstract
Polyaerylamide-gel electrophoresis (PAE) of ripened-cheese caseins provides an ideal means of studying cheese-ripening by detecting small changes in the specific casein fractions. Properties, such as molecu- lar sieving, and the facility to use simulta- neously casein standards, apparently are important advantages of PAE. Rennet enzymes appear specifically to alter a~-casein after curd formation in Cheddar cheese manufacture, fl-Casein ev- idently is unaltered by the rennet enzymes. The caseins were hydrolyzed to different extents in the cheese varieties examined. The a~-fraction is degraded in every cheese ; however, /g-casein appears largely intact in some varieties, whereas its content is ap- preciably diminished in others. This re- flects important differences in the proteoly- tic abilities of microorganisms peculiar to a given variety of cheese. An elucidation of these microbial enzymes should lead to a better understanding of the ripening process. Chemical and microbial changes occurring during cheese-ripening have been studied widely (1, 2, 6). However, nearly all of these studies have been concerned with either the measure- ment of compounds formed or the identification of microorganisms occurring during the pro- tracted ripening process. Present electrophoretic techniques provide an ideal means for a novel approach to the study of cheese-ripening by detecting inlportant changes in the intact caseins of cheese. In the past, Lindquist and Storgards (4) used moving- boundal T electrophoresis in their studies. Others (13, 14) have also used moving-boundary eleetro- phoresis in working with caseins. Paper electro- phoresis, as well, has been used (15). Wake and Baldwin (12) point out that in moving-boundary electrophoresis at neutral pH and near 0 C, casein is not dispersed molecularly but contains large aggregates. Complexing of some fl-easein