Succinic acid production via simultaneous saccharification and fermentation of oil palm empty fruit bunch

Abstract

Oil palm empty fruit bunch (EFB), a plentiful agricultural waste in Malaysia has never been utilized for the production of succinic acid via simultaneous saccharification and fermentation (SSF). The presence of lignin and hemicellulose makes the biomass difficult to be hydrolysed by enzymes and microbes. Hence, effective pretreatment method is required to release cellulose from the crystalline complex structure of lignocellulose. The novelty of this study is the production of succinic acid via SSF from EFB by a rumen bacteria Actinobaccilus succinogenes ATCC 55618. The effect of three different methods; autoclave/alkali (AA), dilute acid (DA) and sequential dilute acid microwave/alkali (DA-MwA) pretreatment on the physical and chemical properties of EFB were analysed and their influence on enzymatic hydrolysis and SSF process were also assessed. Results revealed that maximum amount of cellulose (86.8 g/100g) was achieved for DA-MwA as compared with AA (53.3 g/100g) and DA (46.7 g/100g). The highest glucose concentration among all pretreated EFB was DA-MwA (20.3 gL-1) method using cellulase enzyme. The effect of different cellulase: cellobiase ratios on enzymatic hydrolysis of DA-MwA pretreated EFB showed that ratio of 7:1 produced 34.45 % higher glucose as compared when only cellulase was used. Succinic acid concentration via SSF from DA-MwA (33.4 gL-1) was the highest followed by AA (20.9 gL-1) and DA (14.4 gL-1). The SSF media for the succinic acid production was optimized using Full Factorial Design (FFD) by varying the EFB loading (10-70 gL-1 ), yeast extract (0-20 gL-1) and corn steep liquor (0-20 gL-1) followed by Face Central Composite Design. The best concentration of succinic acid (39.14 gL-1) was obtained when the values of EFB, yeast extract and corn steep liquor were set at 70 gL-1, 30 gL-1 and 10 gL-1, respectively. The influence of three independent SSF process variables: enzyme loading (10-70 FPU/g), temperature (36-40 oC) and pH (5-8) were investigated for succinic acid production using FFD. When the enzyme loading was set at 40 FPU/g, temperature 36 oC and pH 5; the experimental values were in good agreement with the predicted Response Surface Methodology model where the best succinic acid production of 42.5 gL-1 was achieved. The present study revealed that using DA-MwA pretreated EFB, cellulose was utilized by cellulase and cellobiase enzymes via optimized SSF conditions resulting in optimum production of succinic acid.