ACIDIC COAGULATION OF CASEIN MICELLES - MECHANISMS INFERRED FROM SPECTROPHOTOMETRIC STUDIES

The acidic coagulation of casein micelles was monitored turbidimetrically at 400 nm using a Cary 219 spectrophotometer. Following acidification with HCl, the rate of coagulation during the initial stage of coagulation was proportional to the rate during the immediate subsequent stages, indicating that progressive stages of coagulation were controlled by similar factors and the slope at any portion of the reaction profile could be used to characterize the kinetics of the coagulation reaction. The rate of coagulation following acidification by glucono-б-lactone was proportional to the reciprocal of the rate of acidification. The effects of environmental factors on the rate of the acidic coagulation of casein micelles over a range of pH values were evaluated from the smooth, hyperbolic profiles of pH v. coagulation rate. Determination of the pH required to initiate coagulation of casein micelles in skim milk ultrafiltrate at 5–25 °C, together with the maximum rates of coagulation at 5–25 °C, suggested that repulsive forces are reduced by acidification and consequently facilitate hydrophobic interactions resulting in the coagulation of casein micelles. © 1990, Proprietors of Journal of Dairy Research. All rights reserved.