Study On The Physical And Chemical Stabilities Of Citrus Oils Based Emulsions

Citrus oils are natural flavor ingredients with high consumer acceptance wherecitral and limonene are the major flavor components of citrus oils. Citrus oils arecommonly added to foods and beverages in the form of emulsion and microcapsule.Both of the compounds can undergo chemical degradation leading to loss of flavor andthe formation of undesirable off-flavors. Stabilizing citrus oils-based emulsion bydifferent emulsifiers has been one of the hot topics of investigation in the area of foodscience. This study selected different emulsifiers including polysaccharides, proteinsand small molecular surfactants. The physicochemical properties of the emulsifiers werefirst characterized, followed by investigation of the physical and chemical stabilities oflimonene and citral emulsions stabilized with the emulsifiers. The interfacial propertiesof the emulsifiers at the limonene/water and MCT+citral/water were also studied. Thesetogether led to the establishment of the optimal emulsifiers and emulsificationconditions for production of fine citral oils emulsions with acceptable physical andchemical stabilities. The main conclusions are as follows：1、Polysaccharide emulsifiers, such as gum arabic, gum ghatti, and modified starch,produced fine limonene emulsions with smaller particle size and acceptable physicalstability. Though proteins and small molecular surfactants had good emulsifying activityand only very low concentrations were needed to achieve a full surface coverage for10%limonene, they provided unsatisfactory physical stability.2、Gum arabic, modified starch, whey protein isolate, lecithin and quillaja extract,produced fine citral emulsions with the particle size of fresh emulsion less than1μm andacceptable physical stability. The particle size of fresh citral emulsions stabilized withgum ghatti and sugar beet pectin was about1μm and had reasonable stability. Sugarester and pea protein isolate produced coarse emulsions with worse physical stability.3、For limonene emulsions, pea protein isolate provided the best chemical stability,and the emulsions stabilized with modified starch, gum arabic, whey protein isolate,lecithin, lauric arginate and sugar ester also had ideal chemical stabilities. Gum gahtti,sugar beet pectin and quillaja extract, provided worse chemical stabilities. The lowchemical stability of the emulsion stabilized with sugar beet pectin could be due to thehigher content of iron and copper in the sample. For citral emulsions, lecithin providedthe best chemical stability. The protein and small molecular surfactants includingquillaja extract, sugar ester, lauric arginate, whey protein isolate, and pea protein isolate,provided intermediate chemical protection. Sugar beet pectin again provided the worstchemical protection.4、Small molecular surfactants and proteins had faster adsorption rate and lowerequilibrium interfacial tension than polysaccharide emulsifiers when adsorbed on to thelimonene/water and MCT+citral/water interfaces. Nevertheless, the polysaccharideemulsifiers had higher interfacial elastic modulus, compared with the small molecularsurfactants and proteins.