The effect of dry grinding upon gels.

Abstract

The writers have shown that dry grinding in a pebble mill renders starch largely soluble in cold water 1 . They are now able to report that similar treatment renders gelatin temporarily soluble in cold water. Solutions thus prepared set to a gel after a time. The water insoluble colloids, gliadin and glutenin which together form wheat gluten, are not rendered materially soluble by sixteen hours grinding of the flour from which they are prepared, though their physical properties are changed. If gluten be washed from such flour in the usual way, and if its swelling in acid be studied by the method of Upson and Calvin 2 , it is found that the gluten, prepared from the excessively ground flour, swells less than the control gluten prepared from the same flour before it was subjected to overgrinding. The difference is so definite that it is possible by mere inspection to distinguish the two kinds of swollen gluten. The control gluten, as it swells in weak acid, becomes translucent, slimy and runny; while gluten from the same flour after grinding, remains more opaque, swells less and is much firmer to the touch.

It is thus apparent that rather mild miechanical treatment is capable of affecting profoundly the physical properties of the biologically important gel-forming colloids so far studied. It is difficult to harmonize the results herein recorded with the hypothesis defended Katz 3 that swelling is1 merely a special case of solution. They rather speak for the view that swelling is dependent-at least in some degree-upon structure and that grinding possibly modifies this structure. The character of the structure thus modified may be relativelly coarse, such as a reticulum represenited by the continuous phase.