Hydrolysis of whey protein isolate in a tangential flow filter membrane reactor: II. Characterisation for the fate of the enzyme by multivariate data analysis

Abstract

The fate of Protease N (IUB 3.4.24.28, Bacillus subtilis) enzyme was monitored while being used to hydrolyse an initial concentration of 5% (w/v) whey protein isolate (86.98% Kjeldahl nitrogen × 6.38) continuously for 5 h at pH 7.0 and 55 °C in an enzymatic membrane reactor (EMR) fitted with a 10 kDa tangential flow filter (TFF). The retentate temperature (A: 25–55 °C), initial water permeate flux, J i (B: 1.6–18.4 mL/min) and enzyme concentration (C: 0.5–5.5 g) were varied and optimised using response surface methodology (RSM) central composite rotatable design (CCRD). The residual enzyme activity ( A residual), enzyme leakage ( A leakage), enzyme loss ( A loss), average permeate flux ( J average) and nitrogen recovered in permeate (apparent sieving, S apparent) were determined. A leakage was independent of enzyme concentration but increased concomitant with increasing A and B, while both A residual and A loss decreased with increasing J i . Protease N was inhibited by WPI and hydrolysates. At 50 °C Protease N enzyme solubilised the concentration polarisation layer (GPL), stabilised J average and led to higher A leakage. Principal components analysis isolated the EMR hydrodynamics due to the retentate temperature, S apparent, A leakage and J average as factors providing prominent influence in the EMR (principal components 1 and 3 which caused ca. 60% of the EMR variance) while principal component 2 (‘measure’ of Protease N enzyme property within the reactor) contributed 27.78%. The fate of the enzyme was accounted for as a balance between A residual, A leakage and A loss.