Diffusion through fat crystal networks: fluorescence analysis and correlations with physico chemical properties

Oil migration in lipid-based multiphase food products is a concern in the food industry. It leads to defects in appearance, texture, and mouthfeel, which also shortens the shelf life of the food products. Thus, it is imperative to accurately characterize oil diffusion in multiphase systems to optimize product formulation and minimize adverse effects during production and storage. In order to study oil diffusion in fat crystal networks, oil diffusivity was measured using a Franz Cell diffusion test coupled with fluorescence spectroscopy using a fluorescent probe, Nile Red. Diffusivity was then correlated with the solid fat content (SFC), fractal dimensions of the fat crystal network, and micro-viscosity of the oil confined in the crystal networks. A set of binary triacylglycerol systems were prepared by mixing tricaprylin with 30 to 90 wt% tristearin (at 10% intervals), resulting in SFC ranging from 46 to 90% in the system. The diffusion tests were conducted by placing the binary mixture disks in thermostated Franz Cell chambers kept at 25℃. The diffusion of tricaprylin-Nile Red mixtures through the solid disks of the binary mixtures was monitored using a Jaz Spectrophotometer (Ocean Optics, Dunedin, FL) equipped with a fiber optic attachment and a high intensity LED light source (ex=505 nm). Measurements were taken at set intervals during a period of 120 hours. The fractal dimension of the fat crystal networks was determined using a box-counting method. Micro-viscosity of the liquid oil in the system was assessed based on the fluorescence intensity of a molecular rotor, Citrus red (CR) 2, embedded in the fat mixtures, which was monitored using fluorescent spectroscopy. The study provided an effective approach to measure the oil diffusion in fat-based networks. The developed technique is non-disruptive, highly-sensitive, inexpensive and allows real-time changes to be monitored. The results showed that the correlations between oil diffusivity and SFC, fractal dimension and micro-viscosity could all be divided into two regimes, characterized by linear models. The transition between the two linear regimes occurred at values corresponding to ~68% SFC, which indicated that microstructure parameters might have a greater impeding effect on oil diffusion at higher SFCs. These correlations showed that the three parameters were interrelated, while reflecting different characteristics of a fat crystal network, including diffusion rate, space-filling pattern of the network by crystals, and micro-environment confinement. Moreover, the relationships obtained from this study can provide theoretical evidence that it was possible to tailor oil migration in lipid systems by tweaking SFC, microstructural characteristics or micro-viscosity.M.S.Includes bibliographical referencesby Nanxi L