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Isolation and Partial Characterization of an Astringent Fraction from Milk and Nonfat Dry Milk

Food Research Institute, Research Branch, Canada Department of Agriculture, Ottawa, Canada

ABSTRACT

Samples of milk and reconstituted skimmilk powder that were chalky were acidified to pH 4.5 or lower and separated into curd and whey. The untreated milk, acidified milk, and the curd, curd washings, and whey portions were freeze dried and extracted with chloroform-methanol (2:1 v/v). Astringent components were extracted from the acidified milk and its curd but not from the untreated milk or the acid whey. Astringent components were bound to curd by weak ionic forces disrupted by water dilution. The extracted astringent substance was in the methanolic phase.

The astringent fraction showed ultraviolet absorption spectra typical of proteins. Absorptivity was 2 to 5 at 280 nm compared with 12 to 15 for the cheese astringent fraction. Polyacrylamide gel electrophoresis of astringent fractions yielded main bands in the region of whole--caseim. Calcium was only .08% in contrast to 1.4% in the heat-induced astringent fraction.