Maximising high solid loading enzymatic saccharification yield from acid-catalysed hydrothermally-pretreated brewers spent grain

Document Type: Research Paper

Authors

1 Brewing Science Section, Division of Food Sciences, The University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, U.K.

2 SABMiller Plc, SABMiller House, Church Street West, Woking, Surrey, GU21 6HS, U.K.

Abstract

Enzyme saccharification of pretreated brewers spent grains (BSG) was investigated, aiming at maximising glucose production. Factors investigated were; variation of the solids loadings at different cellulolytic enzyme doses, reaction time, higher energy mixing methods, supplementation of the cellulolytic enzymes with additional enzymes (and cofactors) and use of fed-batch methods. Improved slurry agitation through aerated high-torque mixing offered small but significant enhancements in glucose yields (to 53 ± 2.9 g/L and 45% of theoretical yield) compared to only 41 ± 4.0 g/L and 39% of theoretical yield for standard shaking methods (at 15% w/v solids loading). Supplementation of the cellulolytic enzymes with additional enzymes (acetyl xylan esterases, ferulic acid esterases and α-L- arabinofuranosidases) also boosted achieved glucose yields to 58 – 69 ± 0.8 - 6.2 g/L which equated to 52 - 58% of theoretical yield. Fed-batch methods also enhanced glucose yields (to 58 ± 2.2 g/L and 35% of theoretical yield at 25% w/v solids loading) compared to non-fed-batch methods. From these investigations a novel enzymatic saccharification method was developed (using enhanced mixing, a fed-batch approach and additional carbohydrate degrading enzymes) which further increased glucose yields to 78 ± 4.1 g/L and 43% of theoretical yield when operating at high solids loading (25% w/v).

Graphical Abstract

Maximising high solid loading enzymatic saccharification yield from acid-catalysed hydrothermally-pretreated brewers spent grain

Highlights

  • Cellulolytic enzyme saccharification of pre-treated brewers spent grains was investigated at high solids loading.

  • Aerated high-torque mixing offered enhanced glucose yields to 53 g/L.

  • Fed-batch protocols enhanced glucose yields to 59 g/L.

  • Supplementary carbohydrate degrading enzymes boosted achieved glucose yields to 64 g/L.

  • A novel consolidated saccharification protocol further increased glucose yields to 78 g/L at 25% w/v solids loading. 

Keywords


[10] European Brewery Convention, 1998. Free amino nitrogen of malt by spectrophotometry, Method 4.10. Analytica-EBC, 5th ed., Fachverlag Hans Carl: Nuremburg.