Physicochemical Insights Into Structuring Olive Oil With Dry-Fractionated Anhydrous Milk Fat

Anhydrous milk fat (AMF) and its dry-fractionated derivatives were evaluated as structurants for olive oil oleogels designed to reduce the overall saturated fat content compared to conventional solid fats. AMF was subjected to sequential dry fractionation at temperatures ranging from 5°C to 30°C to produce liquid and solid fractions differing in fatty acid composition and thermal behavior. The fractions were characterized using GC-FID, Raman and ATR-FTIR spectroscopy, polarized and confocal microscopy, rheological measurements, and thermal analysis. Based on their distinct physicochemical properties, the 30°C fractions (S30 and O30) were further investigated as oleogelators in olive oil. The S30 fraction was enriched in saturated fatty acids, exhibited higher melting temperatures and formed dense microstructures composed of numerous fine crystals. Rheological measurements revealed that the S30 generated robust oleogels at significantly lower concentrations than unfractionated AMF, demonstrating high structuring efficiency through the formation of a strong crystalline network. However, these oleogels also exhibited greater brittleness, consistent with their denser crystal packing. Overall, dry-fractionated AMF effectively structured olive oil into stable oleogels. Despite its higher saturated fatty acid content, the S30 fraction formed self-supporting oleogels at a structurant concentration of only 25% (w/w). Consequently, oleogels containing 25% S30 and 75% olive oil may provide structured lipid systems with a lower overall saturated fatty acid content than formulations based entirely on AMF or conventional solid fats while maintaining desirable mechanical and functional properties. These findings highlight the potential of dry-fractionated AMF as a natural, food-grade oleogelator for developing alternative structured lipid systems.