Effects of crystalline microstructure on oil migration in a semisolid fat matrix

Oil migration from a 60:40 (w/w) mixture of peanut oil and chemically interesterified and hydrogenated palm oil (IHPO) was a strong function of the cooling rate experienced by the fat mixture during crystallization, namely, 0.4, 1.2, and 6.0 degreesC/min. The relative oil loss determined gravimetrically was inversely proportional to the cooling rate. Oil loss was also inversely related to the storage modulus (G') and the yield force of the fat. After 1 day storage at 20 degreesC, the start of the oil loss studies, the composition and polymorphism of the fat crystals crystallized at different rates were similar, as judged by differential scanning calorimetry and powder X-ray diffraction. Crystals were in the same beta' modification and had similar peak melting temperatures. Microstructure, on the other hand, was profoundly affected by the cooling rate: average crystal size decreased from 8.2 mum (at 0.4 degreesC/min) to 3.9 mum (at 6.0 degreesC/min). Using Darcy's Law, it was possible to calculate permeability coefficients using the structural parameters obtained in this work. Decreases in permeability coefficient as a function of increasing cooling rate were mainly related to decreases in crystal size.