This is not supported by the results, which show similar proportional rates of activity loss for both enzyme dosages. apparent, the dependence of hydrolysis maxima on the enzyme dosage was best explained by partial irreversible product inhibition. Cellulose surface area correlated with the total cellulose content, which is thus an appropriate approximation of the substrate concentration for kinetic modelling. Kinetic models of cellulose hydrolysis should be simplified enough to include reversible and irreversible product inhibition and reduction of hydrolysability, as well as their possible nonlinear relations to hydrolysis degree, without overparameterization of particular factors. Electronic supplementary material The online version of this article (doi:10.1186/s13068-016-0431-3) contains supplementary material, which is available to authorised users. represent the standard deviation of duplicate hydrolysis reactions For the sake of comparability, it should be noted that a portion of 2?FPU?g?1 was incubated for an extra 72?h, so a small increase in hydrolysis could have been expected. However, extending the reaction time generally has Rabbit polyclonal to ADRA1C a small effect on cellulose hydrolysis [2, 4, 5], and further so, if it only concerns the portion of 2?FPU?g?1. Changes in cellulose and lignin surfaces and dissolution of phenols The surface areas of cellulose and lignin (accessible phenolic hydroxyls) were determined in the course of hydrolysis by determining the adsorption maxima of the dyes Congo Red and Azure B on the material, respectively Tenidap [25, 39]. The cellulose area per DM of AH-straw was decreased from 90 Tenidap to 68?m2?g?1 and the cellulose area of NaOH-straw (Fig.?2a) first rapidly decreased from 112 to 90?m2?g?1, possibly representing removal of amorphous cellulose or collapse of the material structure, and then eventually increased close to the initial value. While the surface area per DM describes the changes in the material, it is more relevant for hydrolysis kinetics to describe the total area available in the reaction suspension (m2 per mL). The total cellulose area per mL was most affected by mass reduction of the substrate by hydrolysis, decreasing from 4.6C5.6 to 1 1.7C2.0?m2?per?mL with both substrates (Fig.?2b). For enzyme kinetics, the cellulose area has been considered to represent the substrate concentration better than the total Tenidap carbohydrate content in the material [24, 32, 36]. However, since the cellulose area per mL shows a roughly linear correlation with hydrolysis degree, the carbohydrate content seems to be an appropriate approximation of the substrate concentration after all. The specific cellulose area (m2 per g cellulose) indicates changes in the cellulose shape and association with other lignocellulose components. The specific cellulose area was increased by hydrolysis, particularly with AH-straw (Fig.?2c), where an increase from 165 to 302?m2?per?g cellulose was observed. This may reflect in increasing cellulose surface roughness and thinning of cellulose crystals by hydrolysis occurring on a particular side , which may be emphasised in crystals partially embedded in lignin. It has been suggested that only 2?% of total cellulose is located at accessible fibril surfaces . Hydrolysing a cellulose molecule on the crystal surface reveals fresh surface underneath and the total area thus depends on the shape and roughness of the crystals and the proportion of sterically hindered cellulose. Tenidap In accordance with these results, surface roughness of cellulose has been reported to increase during hydrolysis [33, 40]. Open in a separate window Fig.?2 Surface areas of cellulose and lignin and dissolution of phenols as a function of hydrolysis. a Cellulose area per DM, b the total cellulose area per mL in the reaction, c specific cellulose surface area, d lignin area per DM, e total lignin area per mL reaction, f dissolved phenols (gallic acid equivalent, GAE). represent the.