Effective recovery of casein from its aqueous solution by ultrasonic treatment assisted foam fractionation: Inhibiting molecular aggregation

Abstract

In this work, a novel technology of ultrasonic treatment assisted foam fractionation was developed for the effective recovery of casein from its aqueous solution. Experimental results indicated that ultrasound wave could be used to significantly inhibit the aggregation of casein molecules through decreasing particle size and strengthening interfacial adsorption. At an ultrasonic power of 600 W, the excess surface of casein in foam fractionation with ultrasonic treatment was increased by 46% compared to that without ultrasonic treatment. Under the suitable operation conditions of temperature 25 °C, pH 6.0, casein concentration 0.20 g/L, pore diameter of gas distributor 180 μm, liquid height 300 mm, feed feeding rate 2 mL/min, volumetric air flow rate 150 mL/min, ultrasonic power 600 W and ultrasonic treatment time 2 min, the enrichment ratio and recovery percentage of casein were 7.3 ± 0.36 and 90.2 ± 4.51%, respectively. SEM and AFM analysis showed that ultrasonic treatment could not only inhibit the self-aggregation of casein molecules in the solution, but also weaken the aggregation induced by the interfacial adsorption during foam fractionation. Subunits composition analysis revealed that ultrasonic treatment in foam fractionation had no effect on the structural integrity of casein molecules, but it could change the loose degree of the molecular structure.