Optimisation of Ultrasonic-assisted Protein Extraction from Brewer's Spent Grain

Response surface methodology was employed to optimise the ultrasonic-assisted extraction of protein from brewer's spent grain. Three variables, namely the extraction time (min), ultrasonic power (W/100 ml of extractant), and solid-liquid ratio (g/100 ml) were investigated. Optimal conditions were determined and tri-dimensional response surfaces were plotted using mathematical models. The ANOVA analysis indicated that all the quantities determined, i.e. the extraction time, ultrasonic power, and solid-liquid ratio, had significant positive linear and negative quadratic effects on the protein yield. Optimum conditions for the extraction of protein were found to be: the extraction time of 81.4 min, ultrasonic power of 88.2 W/100 ml of extractant, and solid-liquid ratio of 2.0 g/100 ml. The optimal predicted protein yield obtained was 104.2 mg/g BSG while the experimental yield of protein was in agreement with the predicted value.