Optimization of pretreatment and enzymatic hydrolysis of spent coffee ground for the production of fermentable sugar

Abstract

Spent coffee ground (SCG) is solid residue produced after the coffee being brewed. Since SCG contains carbohydrate that is useful for the production of fermentable sugar, the optimization of the pretreatment method and enzymatic hydrolysis of SCG to produce fermentable sugar was carried out for the purpose of producing higher yield of fermentable sugar. Screening of methods between acid and alkaline pretreatment methods were initially conducted to determine which method produced higher yield of fermentable sugar. Concentration of sodium hydroxide (0.5-5 %(v/v)), temperature (50-100°C) and weight of SCG (5-20% (w/v)) were investigated by using Response Surface Methodology (RSM) and Central Composite Design (CCD) to optimize retreatment condition. 20 runs of experiments were produced from RSM method with the conditions of the combination of the parameters. Software Design-Expert was used to get the optimum condition of producing high yield of fermentable sugar. Sugar analysis was done by using dinitrosalicylic acid method at absorbance of 540nm. The optimized condition of alkaline pretreatment was 0.5% (v/v) of alkali, temperature of 100°C and 5% (w/v) of SCG for a maximum response of 57.02 mg/ml of sugar concentration. SCG was then prepared based on the optimized condition of alkaline pretreatment for the enzymatic hydrolysis process. Three parameters such as temperature (35-55°C), pH (4-8) and enzyme dosage (0.01-0.03 ml) were optimized by using the RSM method. The optimized condition for enzymatic hydrolysis was at pH 4.8, 0.01 ml of enzyme and temperature of 55°C for a maximum response of 1.824 mg/ml of sugar concentration. In conclusion, the alkaline pretreatment was better than acid pretreatment. The model of pretreatment and enzymatic hydrolysis were validated at the optimized condition.