Investigation of caking by fat bridging in aged infant formula

•Surface free-fat and caking strength increased significantly at 60 °C.•High-melting point fatty acids were present on surface of P1 powder particles.•Melting characteristics by DSC were consistent with fatty acid composition analysis.•CLSM analysis showed large fat globules after 6 weeks' storage.

Three commercial infant formulas (denoted as P1, P2 and P3) were stored at 25, 45 and 60 °C for up to 6 weeks to study the caking phenomenon caused by fat bridging. At 60 °C, both the surface free-fat content and the caking strength increased significantly. Analysis of the fatty acid composition of P1 showed that high-melting-point fatty acids were present on powder surface whereas low-melting-point fatty acids remained within powder particles. There was no preferential migration or retention of specific fatty acids in P2. The stearic acid content in the surface free-fat of P3 increased, largely due to a concentration gradient which contributed to the increased caking strength. The melting characteristics of surface free-fat analyzed by DSC were consistent with their fatty acid compositions analyzed by GC-MS/FID. Confocal laser scanning microscopy (CLSM) showed higher occurrence of large fat globules after 6 weeks' storage.