Abstract
Sugar beet pulp (SBP) fractionated by steam explosion, released sugar beet pectin (SB-pectin) which was selectively hydrolysed using a novel α-l-arabinofuranosidase (AF), yielding monomeric l-arabinose (Ara) and a galacturonic acid rich backbone (GABB). AF was immobilised on an epoxy-functionalised resin with 70% overall immobilisation yield. Pretreatment of SB-pectin, to remove coloured compounds, improved the stability of the immobilised AF, allowing its reutilisation for up to 10 reaction cycles in a stirred tank reactor. Continuous hydrolysis of SB-pectin was subsequently performed using a packed bed reactor (PBR) with immobilised AF. Reactor performance was evaluated using a Design of Experiment approach. Pretreated SB-pectin hydrolysis was run for 7 consecutive days maintaining 73% of PBR performance. Continuous separation of Ara from GABB was achieved by tangential flow ultrafiltration with 92% Ara recovery. These results demonstrate the feasibility of establishing a continuous bioprocess to obtain Ara from the inexpensive SBP biomass.
Highlights
Sugar beet is one the most important crops worldwide mainly used for the production of sugar providing about 20% of the global demand (Finkenstadt, 2014)
SB-pectin contains neutral sugar side chains, such as linear galactans formed of D-galactose (Gal) and highly branched arabinans formed of L-arabinose (Ara); both of these can be feruloylated (Oosterveld et al, 2000)
As the optimum temperature for AF is 80 °C, our results demonstrate that working near the temperature optimum affects long-term enzyme stability
Summary
Sugar beet is one the most important crops worldwide mainly used for the production of sugar (sucrose) providing about 20% of the global demand (Finkenstadt, 2014). Sugar beet pulp (SBP) is the main by-product following sucrose extraction, which is dried in an energy intensive process, pelleted and sold as animal feed. 1 tonne of sugar beet provides approximately 160 kg of wet pulp which is processed into 51 kg of dried pellets (88% dry matter) (Personal communication, British Sugar PLC, 2017). SBP is a copolymer of cellulose (25% w/w) and pectin (50% w/w), and contains low amounts of lignin (< 3% w/w), protein (< 11% w/w) and other compounds (Cardenas-Fernandez et al, 2017; HamleyBennett et al, 2016; Micard et al, 1996). SBP represents an important renewable, carbohydrate-rich biomass feedstock with potential applications for the production of biofuels and value-added chemicals
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