Optimisation of enzymatic hydrolysis of apple pomace for production of biofuel and biorefinery chemicals using commercial enzymes

Abstract

Apple pomace, a waste product from the apple juice industry is a potential feedstock for biofuel and biorefinery chemical production. Optimisation of hydrolysis conditions for apple pomace hydrolysis using Viscozyme L and Celluclast 1.5L was investigated using 1 L reaction volumes. The effects of temperature, pH, β-glucosidase supplementation and substrate feeding regimes were determined. Hydrolysis at room temperature using an unbuffered system gave optimal performance. Reactors in batch mode resulted in a better performance (4.2 g/L glucose and 16.8 g/L reducing sugar, 75 % yield for both) than fed-batch (3.2 g/L glucose and 14.6 g/L reducing sugar, 65.5 and 73.1 % yield respectively) in 72 h. The addition of Novozyme 188 to the core mixture of Viscozyme L and Celluclast 1.5L resulted in the doubling of glucose released. The main products (yield %) released from apple pomace hydrolysis were galacturonic acid (78 %), glucose (75 %), arabinose (90 %) and galactose (87 %). These products are potential raw materials for biofuel and biorefinery chemical production.

Using an artificial neural network to predict the optimal conditions for enzymatic hydrolysis of apple pomace

“…Sodium azide (NaN 3 ) at a final concentration of 0.03% (w/v) was added as a microbial preservative to buffers and apple pomace. The composition of apple pomace was as follows: glucose 22.3%, arabinose 12.5%, galactose 5.1%, xylose 1.1%, galacturonic acid *38% and lignin 19.8%, as previously reported (Gama et al 2015).…”

“…Viscozyme L and Celluclast 1.5L were used on a ratio of 50:50 and Novozyme 188 as 10% of the total protein (Gama et al 2015).…”

“…Lignocellulosic biomass is heterogeneous and insoluble and requires multiple enzymes working in synergy for its degradation (Dashtban et al 2009;Teeri 1997). Apple pomace, a waste product from the apple juice industry, is a potential lignocellulosic feedstock for the production of biofuels and biorefinery chemicals (Gama et al 2015). Apple pomace is composed mainly of cellulose, pectin and hemicellulose, which can be converted to sugar monomers and other value-added products using multiple enzymes working in synergy (Bhushan et al 2008;Gama et al 2015;Joshi and Attri 2006;Parmar and Rupasinghe 2013).…”

“…Apple pomace, a waste product from the apple juice industry, is a potential lignocellulosic feedstock for the production of biofuels and biorefinery chemicals (Gama et al 2015). Apple pomace is composed mainly of cellulose, pectin and hemicellulose, which can be converted to sugar monomers and other value-added products using multiple enzymes working in synergy (Bhushan et al 2008;Gama et al 2015;Joshi and Attri 2006;Parmar and Rupasinghe 2013). Enzymes required for the degradation of the cellulose component include cellobiohydrolases, endo-glucanases and b-glucosidases (Teeri 1997).…”

“…Enzymes required for the degradation of the cellulose component include cellobiohydrolases, endo-glucanases and b-glucosidases (Teeri 1997). Pectin degradation requires enzymes such as methyl esterase, acetyl esterase, pectate lyase, pectin lyase, endo-polygalacturonase, exopolygalacturonase, arabinase and galactanase (Gama et al 2015;Voragen et al 2009), while degradation of hemicellulose requires enzymes like endo-xylanases, bxylosidases, xyloglucanases, as well as possible debranching enzymes. Commercial enzyme cocktails are available which act on lignocellulosics, with different cocktails optimised for different substrates (Gama et al 2015;Parmar and Rupasinghe 2013).…”