Assisted-enzymatic hydrolysis vs chemical hydrolysis for fractional valorization of microalgae biomass

Abstract

Despite the interest in the utilization of photobioreactors as an alternative wastewater treatment, the research about posterior recovery and valorization of nutrients accumulated in the biomass is still limited. This work compared several hydrolysis methods for the recovery of proteins and carbohydrates from the biomass grown in a photobioreactor treating swine wastewater. Ultrasound-assisted and microwave-assisted enzymatic hydrolysis at mild conditions and chemical methods at different temperatures (40, 60, 120ºC) were applied to the microalgae and bacteria biomass. Alkaline hydrolysis provided the greatest peptide recoveries, increasing with temperature up to a maximum of 81%, but with very small peptide sizes in all temperature range. Acid hydrolysis provided the highest carbohydrate recoveries (60.7% at 120ºC) but degraded proteins, even at mild temperatures. Protein degradation did not vary with temperature in each chemical hydrolysis, obtaining similar peptide sizes in all temperatures, while carbohydrate losses were higher at lower temperatures. Ultrasound-assisted enzymatic extraction recovered 43.6% of the initial proteins as large peptides (up to 135 kDa) with the highest peptide purity (46.7%). Microwave-assistance increased the carbohydrate solubilization of enzymatic hydrolysis, achieving yields of 73% of xylose, but with significant losses.