Physical and chemical stability of β-carotene-enriched nanoemulsions: Influence of pH, ionic strength, temperature, and emulsifier type

The enrichment of foods and beverages with carotenoids may reduce the incidences of certain chronic diseases. However, the use of carotenoids in foods is currently limited because of their poor water-solubility, high melting point, low bioavailability, and chemical instability. The potential of utilising oil-in-water (O/W) nanoemulsions stabilised by a globular protein (β-lactoglobulin) for encapsulating and protecting β-carotene was examined. The influence of temperature, pH, ionic strength, and emulsifier type on the physical and chemical stability of β-carotene enriched nanoemulsions was investigated. The rate of colour fading due to β-carotene degradation increased with increasing storage temperature (5-55 °C), was faster at pH 3 than pH 4-8, and was largely independent of ionic strength (0-500 mM of NaCl). β-Lactoglobulin-coated lipid droplets were unstable to aggregation at pH values close to the isoelectric point of the protein (pH 4 and 5), at high ionic strengths (NaCl >200 mM, pH 7), and at elevated storage temperatures (55 °C). β-Carotene degradation was considerably slower in β-lactoglobulin-stabilised nanoemulsions than in Tween 20-stabilised ones. These results provide useful information for facilitating the design of delivery systems to encapsulate and stabilise β-carotene for application within food, beverage, and pharmaceutical products.     

Challenges associated in stability of food grade nanoemulsions

Food grade nanoemulsions are being increasingly used in the food sector for their physico-chemical properties towards efficient encapsulation, entrapment of bioactive compounds, solubilization, targeted delivery, and bioavailability. Nanoemulsions are considered as one of the important vehicles for the sustained release of food bioactive compounds due to their smaller size (nm), increased surface area, and unique morphological characteristics. Nanoemulsification is an ideal technique for fabricating the bioactive compounds in a nano form. Formation and stabilization of nanoemulsion depends on the physi-cochemical characteristics of its constituents including oil phase, aqueous phase, and emulsifiers. This review is mainly focused on the instability mechanisms of nanoemulsion such as flocculation, Ostwald ripening, creaming, phase separation, coalescence, and sedimentation. Further, the major factors associated with these instability mechanisms like ionic strength, temperature, solubilization, particle size distribution, particle charge, pH strength, acid stability, and heat treatment are also discussed. Finally, safety issues of food grade nanoemulsions are highlighted.     

A novel nanoemulsification method of stirring at the Θ-point with the tocopherol-based block co-polymer nonionic emulsifier PPG-20 Tocophereth-50

Nanoemulsions have recently become increasingly important as potential vehicles for the controlled delivery of cosmetics and for the optimized dispersion of active ingredients in particular skin layers. The preparation of conventional nanoemulsions requires mainly high‐pressure homogenization, which is unproductive and requires high energy due to its lower efficiency, limiting their practical applications. In order to solve these problems novel nanoemulsions were studied using a model system of pseudo‐ternary water/emulsifier/paraffin oil. Nanoemulsions were prepared by stirring a mixture of the tocopherol‐containing block co‐polymer emulsifier PPG‐20 Tocophereth‐50, paraffin oil, and distilled water at the Θ‐point using weight fractions of the dispersed phase (φ) of 0.31 to 0.82 and an emulsifier content of 1.0 to 9 wt.%. The emulsifying property of PPG‐20 Tocophereth‐50 in nanoemulsions was compared with that of the conventional emulsifiers Tocophereth‐43, a mixture of polysorbate 60 and sesquioleate (3/1), and phospholipids. Also the emulsifying property of PPG‐20 Tocophereth‐50 in the more hydrophilic oils caprylic/capric triglyceride and octyldodecanol was compared with that in paraffin oil. The stability and morphology of the resulting nanoemulsions were studied by visual inspection, optical microscopy, particle size analysis, and cryo‐scanning electron microscopy. In the nanoemulsion systems containing caprylic/capric triglyceride and octyldodecanol, respectively, as an oil phase PPG‐20 Tocophereth‐50 showed emulsification properties similar to those in paraffin oil. The conventional emulsifiers Tocophereth‐43, a mixture of polysorbate 60 and sesquioleate (3/1), and phospholipids did not give nanoemulsions with high‐speed stirring. The block co‐polymer nonionic emulsifier PPG‐20 Tocophereth‐50 was found to produce stable nanoemulsions of mean droplet diameters ranging from 204 to 499 nm. The emulsification method of high‐speed stirring at the Θ‐point using PPG‐20 Tocophereth‐50 was found to be very effective for the preparation of stable nanoemulsions useful for applications in skincare cosmetics, cosmeceuticals, and drugs.     

Effect of processing parameters on physicochemical characteristics of microfluidized lemongrass essential oil-alginate nanoemulsions

The purpose of this work was to study the effect of processing parameters (pressure and cycles) on the formation of microfluidized lemongrass oil-alginate nanoemulsions considering their average droplet size and size distribution, ζ-potential, viscosity and whiteness index. To confirm that nanoemulsions were in the nano-range, samples were also observed through transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques. Average droplet size, viscosity and whiteness index of nanoemulsions decreased by increasing the processing pressure and the cycles through the interaction chamber of the microfluidizer device. Nanoemulsions obtained at 150 MPa for 10 cycles exhibited a minimum average droplet size of 6 nm. Moreover, the droplet electrical charge of nanoemulsions ranged between −36.66 and −51.95 mV while it was −17.61 mV in the coarse emulsion. Furthermore, nanoemulsions obtained at 150 MPa for 3 times or more through the microfluidization system were almost transparent. Results obtained in the present study reveal that microfluidization is a potential technology to be used to produce nanoemulsions of essential oils. However, more information is needed about the influence of microfluidization conditions on the antimicrobial properties of essential oils dispersed in nano-sized emulsions.     

Inhibition of β-carotene degradation in oil-in-water nanoemulsions: Influence of oil-soluble and water-soluble antioxidants

The utilisation of carotenoids as functional ingredients (pigments and nutraceuticals) in many food and beverage products is currently limited because of their poor water-solubility, high melting point, chemical instability, and low bioavailability. This study examined the impact of antioxidants on the chemical degradation of β-carotene encapsulated within nanoemulsions suitable for oral ingestion. β-Carotene was incorporated into oil-in-water nanoemulsions stabilized by either a globular protein (β-lactoglobulin) or a non-ionic surfactant (Tween 20). Nanoemulsions were then stored at neutral pH and their physical and chemical stability were monitored under accelerated stress storage conditions (55 °C). β-Carotene degradation was monitored non-destructively using colour reflectance measurements. The rate of β-carotene degradation decreased upon addition of water-soluble (EDTA and ascorbic acid) or oil-soluble (vitamin E acetate or Coenzyme Q10) antioxidants. EDTA was more effective than ascorbic acid, and Coenzyme Q10 was more effective than vitamin E acetate. The utilisation of water-soluble and oil-soluble antioxidants in combination (EDTA and vitamin E acetate) was less effective than using them individually. Emulsions stabilized by β-lactoglobulin were more stable to colour fading than those stabilized by Tween 20. These results provide useful information for designing effective nanoemulsion-based delivery systems that retard the chemical degradation of encapsulated carotenoids during long term storage.