Enzymic release of cellobiose from sugar beet pulp, and its use to favour vanillin production in Pycnoporus cinnabarinus from vanillic acid

Abstract

This study was undertaken in order to optimise the release of cellobiose from sugar beet pulp by enzymic treatment, and to evaluate the effect of this cellobiose in activating the vanillin production by filamentous fungi. Cellulose-rich residues were obtained from sugar beet pulp by a pectinase treatment, and they were then hydrolysed by a commercial cellulase. Various pretreatments (drying, grinding) and storage were applied, in order to modify the physical state of the cellulose-rich residues, such as degree of crystallinity of cellulose. After cellulase treatment, 51–64% of the initial cellulose was degraded into cellobiose and glucose, depending on the pretreatment. Whatever the pretreatment applied, cellobiose was maximally produced after 2–4 h of hydrolysis. Thereafter, cellobiose was degraded by the β-glucosidase present in the commercial cellulase, but this activity could be inhibited by the addition of d-glucono-δ-lactone. Only in some cases, could the extent of degradation of cellulose be related to the physical state of cellulose-rich residues. The best conditions were used to produce large quantities of cellobiose in order to test its influence in the bioconversion of vanillic acid into vanillin by the filamentous fungus, Pycnoporus cinnabarinus. Addition of cellobiose to a 3-day-old culture yielded a 3.3-fold increase in vanillin production when compared to a control culture devoid of cellobiose.