RELEASE OF FERULIC ACID FROM SUGAR-BEET PULP BY USING ARABINANASE, ARABINOFURANOSIDASE AND AN ESTERASE FROM ASPERGILLUS-NIGER

Aspergillus niger cinnamoyl esterase (CinnAE) is shown to be active to wards a wide range of feruloylated oligosaccharides derived from sugar -beet pulp (SEP), The esterase hydrolysed ferulic acid ester-linked to either C-2 of arabinose or C-6 of galactose and demonstrated the high est activity the feruloylated arabinose trisaccharide. However, CinnAE was able to release only 0.88% of total alkali-extractable ferulic ac id from SEP in 24 h when acting alone, To determine whether cell-wall- degrading enzymes could increase the release of ferulic acid by CinnAE , SEP was incubated with various carbohydrases [cellulase, polygalactu ronase, endo-arabinanase, alpha-L-arabinofuranosidase, endo-(1,4)-beta -D-galactanase, beta-D-galactosidase]. These were added alone and in p airs, both in the presence and absence of CinnAE, We showed that all t he carbohydrases tested were free of esterase activity, When individua l carbohydrases were incubated with SEP, whether in the presence or ab sence of CinnAE, less than 1% of the feruloyl groups were released, Wh en incubated with a mixture of endo-arabinanase and alpha-L-arabinofur anosidase, the esterase was able to release 14 times more of the alkal i-extractable ferulic acid present in the whole pulp as free acid than CinnAE alone, Ferulic acid is linked either to L-arabinose or D-galac tose in SEP, but no corresponding increase in ferulic acid release was detected when SEP was incubated with CinnAE plus endo-(1,4)-beta-D-ga lactanase and beta-D-galactosidase (both from A, niger), Hence feruloy lated arabinans in SEP are readily available for hydrolysis by arabina n-degrading enzymes, whereas feruloylated galactans are not available for hydrolysis by galactan-degrading enzymes.