Thermodynamic analysis of the effect of palm stearin on fully hydrogenated soybean oil coatings in granular micronutrient premixes

This study examined the phase behaviour and temperature-dependent viscosity of palm stearin and fully hydrogenated soybean oil (FHSBO) mixtures to understand the stability of FHSBO coatings on micronutrient premixes. The Hildebrand equation showed that palm stearin/FHSBO mixtures form liquid solutions, while DSC data indicated partial immiscibility in the solid phase. The melting temperatures and enthalpies of fusion are composition dependent, ranging from 67 °C and 138 J/g for 100 % FHSBO to 13 °C and 71 J/g for 100 % palm stearin. The Arrhenius model provided an excellent fit for the viscosities of the binary mixtures above their melting points, with activation energies of 26-27 kJ/mol and pre-exponential factors of 131-207 MPa.s. At the processing conditions of bouillon cubes, a binary fat coating can form on premix granules and contain approximately 70 % palm stearin at equilibrium. At processing temperatures of 30-60 °C, the premix fat coating contains 68-84 % liquid.