Microwave-Assisted Valorization of Waste Animal Adipose Biomass Through Fat Recovery: Compositional, Thermal, and Rheological Characterization

Waste animal fats represent an underutilized biomass resource for biofuel production. This study evaluated microwave-assisted extraction as a rapid alternative to Soxhlet extraction for recovering fats from beef tallow, chicken fat, and pork lard derived from waste adipose tissues. Extraction yield, fatty acid composition, acid value, saponification value, density, rheological behavior, and cold-flow properties were compared. Microwave-assisted extraction reduced processing time from 7 h to approximately 5 min and provided fat recoveries comparable to those of Soxhlet extraction for beef (47.0 vs. 48.2 g/100 g fresh tissue) and pork (59.5 vs. 58.8 g/100 g), and higher for chicken (43.7 vs. 35.3 g/100 g; p < 0.05). Fatty acid profiles remained essentially unchanged between extraction methods, indicating that microwave processing preserved the chemical integrity of the recovered lipids. In contrast, acid value, saponification value, density, and viscosity differed moderately, suggesting changes in lipid microstructure and co-extraction of minor constituents. Thermal characterization showed that cloud and freezing points were governed primarily by feedstock composition, with only minor differences between Soxhlet- and microwave-extracted fats. Overall, microwave-assisted extraction provides a rapid, energy-efficient, and scalable approach for recovering animal fats while maintaining the key physicochemical properties required for biofuel applications. These results support its potential for the valorization of waste animal biomass within circular-economy and energy-transition strategies.