However, the production of 3-HP from biomass faces several challenges. One of the key challenges is the recalcitrant nature of biomass, which makes it difficult to access enzymes for fermentation. To overcome this challenge, pretreatment is essential to loosen the lignocellulosic complex and expose structural carbohydrates to hydrolytic enzymes. Several biomass pretreatment methods have been explored, including acid, alkali, deep eutectic solvents, ionic liquids, organosolv, etc. While these methods have shown promising results, they often result in the separation of carbohydrate-rich solid residues from the slurry. Additionally, extensive post-washing is required to remove unwanted components like lignin and chemical residues, which can lead to chemical and water overconsumption.
This study introduces a novel approach that integrates metal oxides for pretreatment and mineral acids (MAMO) for pH adjustments. We tested two mineral acids, H2SO4 and H3PO4, to modify the pH of slurries made from biomass pretreated with metal oxides, specifically CaO or MgO. Surprisingly, the pH-adjusted slurry could be used directly for enzymatic hydrolysis and subsequent fermentation for 3-HP production without the need for additional washing or liquid-solid separation. Our findings show that this MAMO pretreatment method produces comparable 3-HP concentration (8 g/L) with engineered Saccharomyces cerevisiae and Issatchenkia orientalis while significantly reducing the formation of inhibitory compounds like furfural and hydroxymethylfurfural, as well as soluble salts. Additionally, the acid-induced pH decrease facilitates the partial precipitation of salts (calcium- or magnesium-based) and dissolved lignin, improving enzyme accessibility. This research provides valuable insights into cost-effective pretreatment techniques that produce hydrolysates suitable for fermentation to generate high-value platform chemicals.