Rapid dilute sulfuric acid hydrolysis of soy flour to amino acids for microbial processes and biorefining

Authors: Slininger, Patricia - Pat; Shea Andersh, Maureen; Dien, Bruce

Submitted to: Fermentation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2023
Publication Date: 12/16/2023
Citation: Slininger, P.J., Shea Andersh, M.A., Dien, B.S. 2023. Rapid dilute sulfuric acid hydrolysis of soy flour to amino acids for microbial processes and biorefining. Fermentation. https://doi.org/10.3390/fermentation9121028.
DOI: https://doi.org/10.3390/fermentation9121028

Interpretive Summary: Biorefineries are of interest to produce a portfolio of products, such as biofuels, from renewable resources using innovative biological and chemical techniques. Microbes will be used in a biorefinery to accomplish the conversion of sugars made available by dilute sulfuric acid hydrolysis of cellulosic biomass like switchgrass. In order to grow and make products, microbes need to consume both sugars and amino acids. Some kinds of biomass, like switchgrass, have a very low protein content at harvest such that when they are broken down, amino acids will be in short supply. Soy flour is a low-cost source of protein requiring hydrolysis to free soluble amino acids. In this research project we showed that dilute sulfuric acid hydrolysis could serve this purpose in a biorefinery. Dilute sulfuric acid hydrolysis has already been proven as a preferred low-cost method for pretreating cellulosic biomass to start the process of sugar release from biomass. Now the new data support an added utility of dilute sulfuric acid to break proteins, such as those from soy flour, into individual amino acids for microbial conversions to biofuels and other useful products. The data additionally indicate that the extended application of sulfuric acid hydrolysis technology to proteins could support manufacturing of amino acids and their derivatives as higher valued portfolio products for the growing amino acids market. These findings are important to bringing profitable biorefineries online that will utilize renewable biomass and help to reduce the use of fossil fuels, slow climate change, conserve the environment, and stimulate the rural economy.

Technical Abstract: Amino acids have relevance in biorefining as fermentation nutrients but also as valued coproducts obtainable from plant biomass. Soy flour was studied as a representative low-cost protein source requiring hydrolysis to free primary amino acids for utilization. Within the context of biorefining, process schemes, reactant concentrations, times, and temperatures were varied to explore the efficiency of dilute sulfuric acid hydrolysis of soy flour to release amino acids. Two process strategies were optimized. Either soy flour was co-processed with switchgrass biomass using a dilute-acid pretreatment, or it was hydrolyzed alone with dilute acid. Significant improvement to hydrolysate fermentability was accomplished by adding 2.5–10 g/L soy flour to switchgrass pretreatment with dilute sulfuric acid (0.936% v/v) for 15 min at 160 'C. This practice optimized accumulation of neutral sugars and resulted in a 25% reduction in furfural while boosting xylose 7% and up to doubling primary amino nitrogen (PAN), as compared to no soy flour addition to switchgrass pretreatment. When soy flour was hydrolyzed alone, PAN titers were optimized to 1588 mg N/L (9.9 g amino acids/L) and yield to 0.0529 g PAN/g flour (61% of theoretical) using a 10% (v/v) (1.8 M) sulfuric acid hydrolysis 30 min at 160 'C.