ROLE OF CRYSTALLINE MONOGLYCERIDE IN THE OIL PHASE ON VOLATILE RELEASE FROM O/W EMULSIONS THROUGH GC HEADSPACE ANALYSIS

Like Mao ^1,2 Luisa Barba ³ Yrjö Roos ² Song Miao ¹

¹Department of Food Chemistry and Technology, Teagasc Food Research Centre, Cork
²School of Food and Nutritional Sciences, University College Cork, Cork
³Institute of Crystallography, National Council of Research, Trieste

Monoglycerides (MG) can form self-assembled structures (liquid crystals) in oil, changing the properties of O/W emulsions, which can be used to modify (structure) the emulsion for functional delivery. In this study, MG was incorporated in Tween 20-stabilized O/W emulsions, and the properties of MG structured emulsions and release profiles of four different flavor compounds were investigated. Differential scanning calorimetry (DSC) analysis of MG indicated that b form crystalline structure was developed at 25 °C within 4 days, while a and sub-a forms occurred at 4 °C. Polymorphic transitions occurred during storage at different temperatures. Synchrotron X-ray diffraction (XRD) study revealed that MG liquid crystals (25 °C) were stacking in a well ordered lamellar style, where MG molecules were spreaded in sheets without systematic arrangement. Rheological measurements showed that emulsions with MG bform crystalline structure had gel-like properties (storage modulus > loss modulus), and variation in oil content or MG content affected viscosities, storage modulus and fluid types (shear thinning or Newtonian) of the emulsions. Meanwhile, emulsions with higher MG content had smaller droplet size and better creaming stability. GC static headspace analysis results revealed that air-emulsion partition coefficients of flavor compounds from MG structured emulsions were significantly lower than those from unstructured emulsions (P<0.05). Of the different flavor compounds studied, limonene showed the lowest air-emulsion partition coefficient, and diacetyl showed the highest. Results of GC dynamic headspace analysis showed that the initial (30s) headspace concentrations of all flavor compounds above structured emulsions were significantly lower than those above unstructured emulsions. However, the release rate of these compounds tended to increase with increasing MG content. When oil content of emulsions was reduced from 20% to 10%, initial headspace concentrations of limonene and hexanal increased, while decreased propanol and diacetyl headspace concentration were observed.

Principal investigator: Dr. Song Miao, song.miao@teagasc.ie