Mechanisms of flux decline during ultrafiltration of dairy products and influence of pH on flux rates of whey and buttermilk Original Research Article

The flux pattern during the ultrafiltration (UF) of milk systems (whole milk, skim milk and butter milk) was quite different to sweet or acid whey. With whey, the initial flux was higher, but it fell with time as a result of membrane fouling. Milk systems gave a lower initial flux, but flux remained unaltered during processing despite an increase in the fouling coefficient. The higher concentration of protein in the milk systems seems to promote concentration polarization which controls permeate flux. The flux pattern for sweet whey and buttermilk was strongly influenced by pH. Increasing the pH of buttermilk from 6.6 up to 8.0 tended to reduce initial flux values and reduced deposit formation. Buttermilk flux at high pH range (6.6 and above) was mostly controlled by concentration polarization. Reducing the pH below 6.0 increased the initial flux, but caused more deposit on the membrane. Almost the opposite was noticed in sweet whey. The initial flux increased as pH increased, followed by considerable flux decline during 1-h period of operation, which is linked to greater fouling of the membrane. Reducing the pH significantly reduced initial flux, but deposit formation was at lower levels. These changes are brought about by the effect of pH change on proteins and minerals of milk and whey.