Acid Coagulation of Skimmilk Powder by Extrusion Processing

Effect of coagulation and washing conditions on fines, water holding capacity and microstructure of acid casein curd

Acid casein was prepared under various conditions of pH, concentration and wash regimens (temperature, time, agitation and wash water ratio) according to a response surface experimental design. The resulting product was analysed for water-holding capacity and loss of fines, and the structure of the curd assessed by scanning electron microscopy. Concentration, pH and temperature were the major factors in terms of influencing fines, water-holding capacity and the microstructure of the curd. Fines could be minimized by selecting appropriate pH, concentration and agitation conditions. The final moisture content of the curd was mainly controlled by pH, concentration and temperature and may aid in the selection of parameters to obtain good dewatcring and drying efficiencies. Microstructural analysis visualized the effects of pH, concentration, temperature and their interactions on the casein structural network and the effects of the process parameters are discussed in relation to those changes. Response surface methodology was shown to be an effective tool for examining which variables used in the process were significant and provided guidance as to the type of physicochemical mechanisms affecting the system.