Interactions responsible for fouling layer formation during apple juice microfiltration

Microfiltration of model solutions was conducted to identify the principal interacting species in foulant produced during membrane clarification of apple juice. Tannin and gelatin solutions did not foul microfiltration membranes, whereas both low-methoxy (LMP) and high-methoxy pectin (HMP) produced a fouling layer with only modest resistance. However, solutions containing high concentrations of both tannin and gelatin had very low fluxes, indicating that the interaction of these two species is key to fouling layer formation. With unclarified apple juice, tannin addition did not increase flux resistance because these compounds were in excess. On the other hand, LMP or HMP addition significantly enhanced flux resistance, probably by stabilizing colloidal particles. At low concentrations, gelatin-induced flocculation produced large aggregated particles with lower fouling layer resistances, hut at elevated concentrations, gelatin addition stabilized colloidal particles, increasing flux resistance. A direct correlation between particle flocculation behavior and fouling laver resistance was observed.