LAUSR

Abstract This study aimed to quantify the contribution of Streptococcus thermophilus cell deposition to the flux decline observed during ultrafiltration of cheese whey constituents using an unstirred batch cell system. Bacterial cells were suspended in model solutions of sodium chloride, of sodium chloride supplemented with either whey protein isolate, β-lactoglobulin or α-lactalbumin, or of whey permeate. Permeate fluxes were compared with those of sterile solutions. Normalised flux dropped by 20 to 27 percent points when bacterial cells were filtered with whey proteins and only by 5.0 to 6.7 percent points in the absence of whey proteins. Whey proteins filled void spaces between bacteria by behaving like an extracellular matrix, reducing the fouling layer’s permeability. It was hypothesised that electrostatic interactions between bacteria and protein led to a more cohesive cake. This study provides insight on possible interactions between bacterial cells and whey proteins that might exacerbate fouling during industrial whey ultrafiltration.