Soluble protein fractions from pH and heat treated sodium caseinate: physicochemical and functional properties

The physicochemical (solubility and hydrophobicity), and functional (emulsifying activity index and emulsifying capacity) properties of soluble sodium caseinate fractions were studied as a function of pH (3-8) and temperature (50-100 degrees C). Solubility was determined by measuring protein with the Bradford and 280 nm absorbency methods. Hydrophobicity was determined fluorometrically wi th 1-anilino-8-naphtalenesulfonate (ANS), and cis-parinaric acid (CPA). Sodium caseinate solubility was minimal at pH 3.75-4 but the ANS and CPA-hydrophobicities and the functional properties of the soluble proteins increased in this pH range. Circular dichroic and 280 nm absorptivity measurements detected conformational changes. SDS-PAGE and reversed phase HPLC revealed substantial losses of alpha s(1) and beta caseins following pH and heat treatment (pH 3.75 and 92.5 degrees C) and the concomitant appearance of modified compounds. Under these same conditions, the o-phtaldialdehyde values increased suggesting partial hydrolysis of sodium caseinate. The soluble protein fractions from sodium caseinate heat treated near the pi of the caseins were shown to have enhanced emulsifying activity and capacity. (C) 2000 Elsevier Science Ltd. All rights reserved.