Simultaneous recovery of ferulic acid and sugars from wheat bran enzymatic hydrolysate by diananofiltration

A new strategy for joint separation of ferulic acid (FA) and sugars from enzymatic hydrolysate of wheat bran was evaluated. Nanofiltration membranes with molecular weight cut-off (MWCO) in the range 150–800 g mol−1 were studied. Among them, NTR7450 and NTR7470 (Hydranautics) with MWCO between 600 and 800 g mol−1 allowed ferulic acid to be retained and sugars to permeate provided operating pH was maintained at pH > 7 and ideally pH 9. In this condition, the negative charge of the membranes and the full ionization of FA conjugate to allow FA retention by electrostatic effects whereas pore size is large enough to allow sugars to permeate. Retentions obtained on model hydrolysate at 10 bar were 85% for FA and 20% for xylose. When processing real hydrolysate, however, sugar retention was more than 40%. During diafiltration, pH decrease in the retentate was observed. Manual addition of concentrated NaOH did not allow to counterbalance completely this decrease and to ensure the optimal pH of 9 in the retentate. This led to a significative increase in sugar retention, and consequently, sugar removal in the retentate reached only 56% for a diafiltration factor Vd of 4.5. These observations were supported by a diafiltration model with variable retention.