Acid hydrolysis of soybean hulls for lipid production by Rhodotorula mucilaginosa CCT 7688

Abstract To make lipid synthesis through microorganisms economically viable, developing low-cost culture media is essential. This study investigates the dilute acid hydrolysis of soybean hulls (SBH), an agro-industrial byproduct, under varying conditions of pressure, temperature, acid concentration, and particle size. The goal was to release fermentable sugars suitable for lipid synthesis by the yeast Rhodotorula mucilaginosa CCT 7688. Optimal results were achieved at 1.1 atm pressure, 122 °C temperature, a particle size of ≤ 1 mm, and 1.8 mmol of H 2 SO 4 per gram of SBH. The resulting fermentable sugar yields included 11.59 g·L -1 of xylose, 4.37 g·L -1 of arabinose, 1.24 g·L -1 of glucose, and 0.60 g·L -1 of cellobiose, totaling 17.80 g·L- 1 . Acetic acid (1.08 g·L -1 ) and hydroxymethylfurfural (0.06 g·L -1 ), recognized as growth inhibitors, were also detected. This hydrolysate was concentrated and used as a culture medium without detoxification. Individual tests of arabinose, cellobiose, glucose, and xylose as carbon sources showed that glucose (32.26%) and the sugar mix (11.52%) were the most effective for lipid accumulation. Oleic, palmitic, and linoleic acids were the primary fatty acids synthesized from all carbon sources tested. Although R. mucilaginosa CCT 7688 showed low lipid content in the hydrolysate, it grew well in this complex medium, suggesting that future optimization could enhance lipid accumulation.