Recycling Rhizopus oryzae resting cells as biocatalyst to prepare near eutectic palmitic-stearic acid mixtures from non-edible fat

Here we studied non-edible fat waste as a starting material to prepare eutectic mixtures of biomaterials. Initially, the fat was hydrolyzed using water and R. oryzae resting cells. The hydrolysis was performed in organic solvent-free media and the degree of hydrolysis at 1 h was 42% while hydrolytic values of 86% and 98% were achieved at 12 and 48 h, respectively. To recover the resting cells, they were extracted in consecutive cycles with solvents or supercritical CO₂. Compared with solvents, supercritical CO₂ allowed the highest reuse. Hence, R. oryzae was used for 336 h (7 reaction cycles), yielding 56.5 g of free fatty acid/g biocatalyst. Crude glycerol was recovered, showing a purity of 66.0% and an ash and water content of 2.3% and 1.8%, respectively. The hydrolyzed fat was crystallized with several solvents to yield palmitic and stearic acid mixtures with melting point characteristics of eutectic mixtures. We recovered 76% to 90% of the palmitic and stearic acids present in the initial hydrolyzed animal fat, depending on the solvent. The palmitic:stearic acid ratios determined by GC-FID were similar to those reported for eutectic mixtures whit phase change materials properties, as were the melting points, which ranged from 51.5 °C to 54.8 °C.