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