Protein-Fatty Acid Interaction in Spread Monolayers

The pressure-area isotherms at air-water interface of pure protein (bovine serum albumin, β-lactoglobulin, α-lactalbumin) and pure fatty acid (stearic acid and arachidic acid) and their mixtures of different weight fractions have been studied at pH 3.0, 7.0 and 12.0 respectively using Langmuir balance method. The surface pressures π of protein monolayer at different surface areas A of the pure proteins at different pH-values of the subphase are fitted in a virial equation expressed in linear form so that virial coefficients of different proteins have been evaluated at fixed pH. From the plot of second virial co-efficient Bs against several pH values, the isoelectric pH of BSA adsorbed at air-water interface is observed to be 7.0. From the analysis of π-A curves for the fatty acid and pure protein of several binary surface compositions, π-A curves for their mixtures have been obtained. These experimental values have been compared with their ideal values using additivity rule. Such analysis indicates that fatty acid and protein undergo binding interaction in monolayer phase at a given value of in many cases.