Mechanistic Insights and Process Optimization of Acid-Treated Soybean Hulls as Aquatic Feed Binders

Abstract

This work utilizes soybean hull (SBH) as a low-cost feedstock for the development of an acid-treated aquatic feed binder based on whole biomass utilization. Currently, SBH is generated in large amounts (34.17 - 42.72 million metric tons annually) with most of its utilization being limited to animal feed applications, landfilling, and incineration. A single-stage acid treatment was applied to untreated SBH at both 10% and 50% solids, pH = 1.8, and different treatment times (i.e. 0.5-hour, 1-hour, 1.5-hour, and 2-hour) to evaluate changes in physical and chemical properties. This acid treatment results in a reduction of neutral sugars and pectin content due to the respective degradation and extraction into ethanol (EtOH) extractives during the chemical composition analysis. It also leads to a 40-60% increase in carboxylic acid content, a 70-90% increase in water solubility, and up to a 23.63% reduction in geometric mean particle diameter. These properties improved with increasing treatment time, with the 1.5-hour and 2-hour treatment at 50% solids exhibiting the best properties. However, prolonged treatment also promoted agglomeration, requiring additional size reduction during drying to avoid compromising binder performance during incorporation into fish feed production processes. Given the high cost associated with transporting wet binder, the effect of productions solids content and drying methods, including oven drying at different temperatures and freeze drying, were evaluated to identify optimal processing conditions. Finally, a technoeconomic analysis (TEA) was conducted for the 1.5-hour 50% solids binder production process to assess the economic feasibility and profitability of a batch plant producing 6-ton dry binder per day. The minimum sales price of the SBH binder was determined and compared against common commercial aquatic feed binders such as carboxymethyl cellulose (CMC), wheat gluten, and corn starch.