Comparative evaluation of enzyme cocktails for conversion of pretreated oat hulls

Abstract

The enzymatic hydrolysis of pretreated lignocellulosic feedstock is a critical step in the production of value-added biosynthesis products. This work presents a comparative evaluation of commercial enzyme preparations and their combinations for converting oat hulls following nitric acid pretreatment. Hydrolysis was carried out at an initial substrate concentration of 30 g/L, pH 4.7, and a temperature of (46±2) °C. The study evaluated three enzyme preparations from different manufacturers, including Agrocell Plus (Agroferment LLC, Russia), Cellolux-A (Sibbiofarm LLC, Russia), and Ultraflo Max (Novozymes A/S, Denmark). The evaluation of the individual preparations revealed that the yield of reducing substances from the substrate mass was 53%, 40%, and 51%, respectively. The addition of supplementary β-glucanase (Ultraflo Max) to the enzyme preparations Agrocell Plus or Cellolux-A, which exhibit high cellulase activity, resulted in a 1.3–1.5-fold increase in reducing substance yield. The maximum yield of reducing substances of 72%, corresponding to 99% hydrolysis of the available substrate portion, was observed during hydrolysis using a combination of all three enzyme preparations. Scanning electron microscopy of the substrate before and after hydrolysis confirmed the effectiveness of the mixed preparations and revealed a difference in the residual fragmented substrate after hydrolysis by the individual preparations versus the multi-enzyme compositions, in favor of the latter. All hydrolysates obtained from the nitric acid-pretreated oat hulls were characterized as glucose-based, with the total concentration of glucose amounting to 85–91%. This composition suggests a high potential for successful use in subsequent biosynthesis processes.