Zeta-Potential as a Way to Determine Optimal Conditions During Fruit Juice Clarification

Cloudy fruit juice is caused by colloidal suspension where the continuous medium is a solution of pectin, sugars and organic acids, and the dispersed matter is mainly formed by cellular tissue comminuted during fruit processing. To obtain a clear juice, these suspended particles have to be removed. This process is known as clarification or fining, one of the most important unit operations in apple juice processing. The procedure helps also to remove active haze precursors, and thus decreases the potential for haze formation during storage, while providing a more limpid juice (Hsu et al., 1987; 1989; 1990). Therefore, the fining step is an important procedure that must be carefully controlled during the processing of clarified apple juice.

Genovese et al. (1997) determined that cloudy apple juice particles measure 450 nm diameter on average. If particles in a cloudy juice adhere together and form aggregates of increasing size (flocculation), they may settle due to gravity. If flocks change to a much denser form, it is said to undergo coagulation, which is an irreversible process. It may seem simple merely to filter them out, but unfortunately some soluble pectin remains in the juice, making it too viscous to filter quickly. A dose of commercial enzyme is the accepted way of removing unwanted pectin. Enzyme depectinization has two effects: It degrades the viscous soluble pectin, and it also causes the aggregation of cloud particles.