Shear effects on the diffusive movement of oil in triacylglycerol networks

Abstract

Oil migration is the foremost contributor to the quality loss of many high fat food products; thus, developing an understanding on how this phenomenon takes place in food systems is crucial for the food industry. Diffusion of triacylglycerols (TAG) through the fat network has often been modeled using simplified solutions to Fick's second law. However, a drawback of the use of diffusion models is the lack of sensitivity toward some microstructural characteristics of the matrix. This work reports the study of molecular and macroscopic oil diffusion coefficients of fat crystal networks using nuclear magnetic resonance measurements and from gravimetric determinations of oil loss, respectively. Blends of fully hydrogenated soybean oil (FHSO) in soybean oil (SO) were crystallized statically, under laminar shear rates of 30 and 240 s⁻¹ at different wall temperatures (−10, 0, 20 °C). Another batch of similar blends prepared with and without emulsifier was crystallized in a scraped surface heat exchanger. The results showed a good correlation between diffusion coefficients obtained using both methodologies only when samples exhibited low oil loss, particularly in blends crystallized statically or under mild-shearing conditions. This work suggests that although the Ziegleder model has great advantages and provides valuable insight into the oil migration in fat matrices, there remains a large need for further evaluating its suitability, principally in cases where crystalline structure is severely affected by processing conditions and where oil migration mechanisms other than diffusion may be involved.