Food-grade microemulsions and nanoemulsions: Role of oil phase composition on formation and stability

Lemon oil is widely used as a flavoring component in beverages, foods, cosmetics, and household products. Lemon oil comes in a variety of chemical compositions depending on its biological origin, extraction methods, and purification procedures. At present, there is a relatively poor understanding of the influence of lemon oil composition on its functional properties. In this study, we examined the influence of lemon oil fold (1×, 3×, 5× and 10×) on the formation and properties of oil-in-water microemulsions and nanoemulsions. The concentration of both polar (high water solubility and low log P) and non-polar (low-water solubility and high log P) components increased with increasing oil fold. The nature of the colloid dispersions formed was established using an emulsion titration method that involved titrating lemon oil droplets into a surfactant micelle solution (1% Tween 80). Oil fold affected the rate and extent of solubilization, as well as the stability of lemon oil droplets to growth. The maximum amount of lemon oil that could be solubilized within the micelles increased with increasing oil fold, as did the stability of lemon oil droplets to growth. The results were interpreted in terms of the ability of different lemon oil molecules to be incorporated within water or surfactant micelles, and the influence of lemon oil polarity on Ostwald ripening. This study provides valuable information about the relationship between lemon oil composition and its performance in colloidal delivery systems suitable for use in the food and beverage industries.     

Impact of lemon oil composition on formation and stability of model food and beverage emulsions

Lemon oil is a complex organic compound isolated from citrus peel, which is commonly used as a flavouring agent in beverages, foods, cosmetics, and household products. We have studied the influence of lemon oil fold (1×, 3×, 5× and 10×) on the formation and properties of oil-in-water emulsions. Initially, the composition, molecular characteristics, and physicochemical properties of the four lemon oils were established. The main constituents in single-fold lemon oil were monoterpenes (>90%), whereas the major constituents in 10-fold lemon oil were monoterpenes (≈35%), sesquiterpenes (≈14%) and oxygenates (≈33%). The density, interfacial tension, viscosity, and refractive index of the lemon oils increased as the oil fold increased (i.e., 1× < 3× < 5× < 10×). The stability of oil-in-water emulsions produced by high pressure homogenisation was strongly influenced by lemon oil fold. The lower fold oils were highly unstable to droplet growth during storage (1×, 3×, and 5×) with the growth rate increasing with increasing storage temperature and decreasing oil fold. Droplet growth was attributed to Ostwald ripening, i.e., diffusion of lemon oil molecules from small to large droplets. The highest fold oil (10×) was stable to droplet growth, which was attributed to the presence of an appreciable fraction of constituents with very low water-solubility that inhibited droplet growth through a compositional ripening effect. This study provides important information about the relationship between lemon oil composition and its performance in emulsions suitable for use in food and beverage products.     

Encapsulation of functional lipophilic components in surfactant-based colloidal delivery systems: Vitamin E,vitamin D,and lemon oil

The fabrication and stability of surfactant-based colloidal delivery systems (microemulsions and emulsions) suitable for encapsulation of lipophilic active agents (vitamins and flavours) was investigated. An emulsion titration method was used to study the influence of surfactant type (Tween 20, 60 and 80) and oil type (Vitamin E, vitamin D₃ and lemon oil) on the incorporation of lipophilic components into surfactant micelles. Oil-in-water emulsions were formed and then different amounts were titrated into surfactant micelle solutions. The influence of surfactant-to-oil ratio (SOR) and oil type on the formation of colloidal dispersions was examined using dynamic light scattering and turbidity measurements. SOR, oil type, and surfactant type had a pronounced influence on the nature of the colloidal dispersions formed. Microemulsions could not be formed using vitamin D or E in 1% Tween solutions, due to the relatively large size of the lipophilic molecules relative to the hydrophobic interior of the surfactant micelles. On the other hand, microemulsions could be formed from lemon oil at relatively high SORs. There was not a major impact of non-ionic surfactant type (Tween 20, 60 or 80) on the formation and properties of the colloidal dispersions. However, Tween 20 micelles did appear to be able to solubilise less lemon oil than Tween 60 or 80 micelles, presumably due to their smaller dimensions. This study provides useful information for the rational design of food grade colloidal delivery systems for encapsulating flavour oils, oil-soluble vitamins, and other functional lipids for application in foods and beverages.     

Optimization of lipid nanoparticle formation for beverage applications: Influence of oil type,cosolvents, and cosurfactants on nanoemulsion properties

The influence of flavor oil composition, cosolvents (glycerol and propylene glycol), and cosurfactant (lysolecithin) on the formation and stability of lemon oil nanoemulsions stabilized by sucrose monoesters was examined. At ambient temperature, nanoemulsions containing 1-, 3-, and 5-fold lemon oils were stable to droplet growth, whereas those containing 10-fold lemon oil were unstable. For 10-fold lemon oil nanoemulsions, the droplet growth rate increased with increasing temperature, cosolvent addition, and decreasing lysolecithin concentration, which was attributed to the influence of these factors on the phase inversion temperature. Clear nanoemulsions could be formulated that maintained small mean particle diameters (d ≈ 81 nm) during storage at ambient temperature for 1 month. The information generated in this study is useful for designing stable flavor nanoemulsions for applications in functional foods and beverages.     

Food-grade microemulsions,nanoemulsions and emulsions: Fabrication from sucrose monopalmitate & lemon oil

Sucrose monopalmitate (SMP) is a non-toxic, biodegradable, non-ionic surfactant suitable for use in foods and beverages. This study aimed to establish conditions where stable microemulsions, nanoemulsions or emulsions could be fabricated using SMP as a surfactant and lemon oil as an oil phase. Emulsions (r > 100 nm) or nanoemulsions (r < 100 nm) were formed at low surfactant-to-oil ratios (SOR < 1) depending on homogenization conditions, whereas microemulsions (r < 10 nm) were formed at higher ratios (SOR > 1). The impact of simple mixing, thermal treatment, and homogenization on the formation of the different colloidal systems was investigated. Blending/heating was needed to produce microemulsions or emulsions, whereas blending/heating/homogenization was needed to produce nanoemulsions. The impact of environmental stresses (pH, ionic strength, temperature) on the functional performance of nanoemulsions and microemulsions was examined. Relatively stable nanoemulsions could be formed at pH 6 and 7 and stable microemulsions at pH 5 and 6, but extensive particle growth/aggregation occurred at lower and higher pH values. Microemulsions were relatively stable to salt addition (0–200 mM NaCl), but nanoemulsions exhibited droplet aggregation/growth at ≥50 mM NaCl after 1 month storage at pH 7. Microemulsions formed gels at low temperatures (5 °C), were stable at ambient temperatures (23 °C), and exhibited particle growth at elevated temperatures (40 °C). Nanoemulsions were stable at refrigerator (5 °C) and ambient (23 °C) temperatures, but exhibited coalescence at elevated temperatures (40 °C). This study provides important information for optimizing the application of sucrose monoesters to form colloidal dispersions in food and beverage products.