Residual cellulose was measured using the phenol-sulphuric
acid method, adapted for the small quantity of sample available.
Samples were prepared using acetic/nitric acid and
hydrolysed with 67% sulphuric acid as described in Updegraff
[23], except that 2 cm3 of sample was used and all step were
made in 2 cm3 centrifuged tubes. Reducing sugars in the
hydrolysed samples were measured colorimetrically with
phenol-sulphuric acid, as described by Fournier