Static headspace analysis of volatile compounds released from β-lactoglobulin-stabilized emulsions determined by the phase ratio variation method

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The release of volatile organic compounds (VOCs) from oil-in-water emulsions stabilized by β-lactoglobulin (βLG) was studied under equilibrium conditions. The effects of lipid type and mass fraction were investigated using soy oil (SO) and anhydrous milk fat (AMF). The release was compared using systems of a buffered aqueous solution, pure oil and emulsions. Gas–matrix partition coefficients (K) for five volatile compounds: 1-propanol, ethyl butyrate, heptanal, octanol and 2-decanone, were determined by static headspace gas chromatography (GC). The compounds were chosen based on their polarity, vapour pressure and functional groups. Two indirect methods to measure K were used: phase ratio variation (PRV) and phase ratio calibration (PRC). These two methods were found to be simple and accurate alternative to measure K without using external calibration. The VOC release depended mainly on the physiochemical properties and affinity of the compounds to the matrix. Higher retention in oil and emulsion systems than in aqueous solution was observed for all VOCs except the more hydrophilic 1-propanol. Ethyl butyrate showed the highest K value for emulsions whereas 2-decanone had the lowest. There was a significant decrease in K values for emulsions with higher lipid content. When comparing lipid type, emulsions made with the more saturated AMF, compared to SO, resulted in lower K values for the more hydrophobic compounds. The role of βLG on VOC release was compared with Tween 20, both as emulsifiers. A significant decrease in the headspace concentration was seen above the aqueous solution for heptanal, octanol and 2 decanone. This may be attributed to the hydrophobic cavity site of the protein and covalent bonds with the aldehyde. In emulsion systems, the presence of the emulsifier conformation at the interface had an effect on the affinity with intermediate hydrophobic VOCs. This study provides an important understanding of how VOC release can be controlled using βLG stabilized emulsions in food systems.