Creation of reduced fat foods: Influence of calcium-induced droplet aggregation on microstructure and rheology of mixed food dispersions

The impact of calcium-induced fat droplet aggregation on the microstructure and physicochemical properties of model mixed colloidal dispersions was investigated. These systems consisted of 2 wt% whey protein-coated fat droplets and 4 wt% modified starch granules heated to induce starch swelling (pH 7). Optical and confocal microscopy showed that the fat droplets were dispersed within the interstitial region between the swollen starch granules. The structural organisation of the fat droplets within these interstitial regions could be modulated by controlling the calcium concentration: (i) at a low calcium concentration the droplets were evenly distributed; (ii) at an intermediate calcium concentration they formed a layer around the starch granules; (iii) at a high calcium concentration they formed a network of aggregated droplets. Paste-like materials were produced when the fat droplets formed a three-dimensional network in the interstitial region. The properties of fat droplet–starch granule suspensions can be modulated by altering the electrostatic interactions to alter microstructure.     

Stability of citral in protein- and gum arabic-stabilized oil-in-water emulsions

Citral is a major flavor component of citrus oils that can undergo chemical degradation leading to loss of aroma and formation of off-flavors. Engineering the interface of emulsion droplets with emulsifiers that inhibit chemical reactions could provide a novel technique to stabilize citral. The objective of this study was to determine if citral was more stable in emulsions stabilized with whey protein isolate (WPI) than gum arabic (GA). Degradation of citral was equal to or less in GA- than WPI-stabilized emulsion at pH 3.0 and 7.0. However, formation of the citral oxidation product, p-cymene was greater in the GA- than WPI-stabilized emulsion at pH 3.0 and 7.0. Emulsions stabilized by WPI had a better creaming stability than those stabilized by GA because the protein emulsifier was able to produce smaller lipid droplets during homogenization. These data suggest that WPI was able to inhibit the oxidative deterioration of citral in oil-in-water emulsions. The ability of WPI to decrease oxidative reactions could be due to the formation of a cationic emulsion droplet interface at pH 3.0 which can repel prooxidative metals and/or the ability of amino acids in WPI to scavenge free radical and chelate prooxidative metals.     

Lemon oil solubilization in mixed surfactant solutions: Rationalizing microemulsion & nanoemulsion formation

Lipophilic functional ingredients are usually incorporated into aqueous-based foods and beverages in the form of colloidal dispersions. In this study, we investigated the rate and extent of solubilization of emulsified lemon oil in mixed non-ionic surfactant solutions (buffer: propylene glycol = 2:1): sucrose monopalmitate (SMP) and/or Tween 80 (T80). The influence of surfactant concentration, type, and mixing ratio on lemon oil solubilization was investigated, with the aim of identifying suitable conditions for preparing stable microemulsions and nanoemulsions. Solubilization was monitored by measuring changes in light scattering by lemon oil droplets after they were dispersed in surfactant solutions (pH 7). The solubilization process was rapid (<few minutes), with the rate increasing with increasing surfactant concentration. For a particular surfactant type and concentration, lemon oil was transferred from nanoemulsion droplets into microemulsion droplets until a critical lemon oil concentration (C_sat) was reached, after which it remained as nanoemulsion droplets. The value of C_sat increased with increasing surfactant concentration and was higher for SMP than Tween 80. The impact of storage at pH 3.5 on the physical stability of microemulsions and nanoemulsions was examined. Acid stable colloidal dispersions could not be formed using SMP alone. However, relatively stable nanoemulsions and microemulsions could be formed when ≥75 or 50 wt% Tween 80 was incorporated into the surfactant phase, respectively. This study provides important information for the rational design of food-grade colloidal delivery systems for encapsulating and delivering functional lipids for food and beverage applications.     

Minor components in food oils: a critical review of their roles on lipid oxidation chemistry in bulk oils and emulsions

Food oils are primarily composed of triacylglycerols (TAG), but they may also contain a variety of other minor constituents that influence their physical and chemical properties, including diacylglycerols (DAG), monoacylglycerols (MAG), free fatty acids (FFA), phospholipids (PLs), water, and minerals. This article reviews recent research on the impact of these minor components on lipid oxidation in bulk oils and oil-in-water emulsions. In particular, it highlights the origin of these minor components, the influence of oil refining on the type and concentration of minor components present, and potential physicochemical mechanisms by which these minor components impact lipid oxidation in bulk oils and emulsions. This knowledge is crucial for designing food, pharmaceutical, personal care, and other products with improved stability to lipid oxidation.     

Utilisation of spontaneous emulsification to fabricate lutein‐loaded nanoemulsion‐based delivery systems: factors influencing particle size and colour

Factors influencing the formation and properties of lutein‐loaded nanoemulsions fabricated using spontaneous emulsification (SE) were investigated. Nanoemulsion formation depended on oil type: small droplets (diameter ≈ 200 nm) with a narrow monomodal particle size distribution (polydispersity index ≈ 0.23) could be formed using medium‐chain triglycerides (MCT), but not long‐chain triglycerides. Nanoemulsion formation also depended on surfactant type and concentration, with Tween 80 being the most effective surfactant. Optimisation of lutein‐loaded nanoemulsions formed by SE led to systems with a final composition of 10 wt% oil phase (0.12 wt% lutein + 9.88 wt% MCT), 10 wt% Tween 80, and 80 wt% aqueous phase. The nanoemulsions were stable to droplet aggregation when stored at ambient temperature for up to 1 month; however, some colour fading occurred due to lutein degradation. This study indicated the potential of nanoemulsion‐based delivery system fabricated using a low‐energy method for encapsulation and protection of lutein.     

Impact of dietary fiber coatings on behavior of protein-stabilized lipid droplets under simulated gastrointestinal conditions

Multilayer emulsions containing lipid droplets coated by lactoferrin (LF) - anionic polysaccharide layers have improved resistance to environmental stresses (such as pH, salt, and temperature), but their behavior within the gastrointestinal tract (GIT) is currently unknown. The objective of this research was therefore to monitor changes in the physicochemical properties and digestibility of these systems under simulated GIT conditions. Primary emulsions (5% corn oil, 0.5% LF) were prepared using a high-pressure homogenizer. Secondary emulsions (5% corn oil, 0.5% LF, 0.5% polysaccharide) were prepared by incorporating alginate, low methoxyl pectin (LMP) or high methoxyl pectin (HMP) into primary emulsions. Emulsions were then subjected to simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) conditions in sequence. LF, LF-LMP and LF-HMP emulsions were stable to droplet aggregation in the stomach but aggregated in the small intestine, whereas LF-alginate emulsions aggregated in both the stomach and small intestine. The presence of a dietary fiber coating around the initial lipid droplets had little influence on the total extent of lipid digestion in SIF, but LF-alginate emulsions had a slower initial digestion rate than the other emulsions. These results suggest that the dietary fiber coatings may become detached in the small intestine, or that they were permeable to digestive enzymes. Pepsin was found to have little influence on the physical stability or digestibility of the emulsions. The knowledge obtained from this study is important for the design of delivery systems for encapsulation and release of lipophilic bioactive ingredients.     

Nanoemulsion-based delivery systems for poorly water-soluble bioactive compounds: Influence of formulation parameters on Polymethoxyflavone crystallization

Polymethoxyflavones (PMFs) extracted from citrus peel exhibit potent anti-cancer activity, but are highly hydrophobic molecules with poor solubility in both water and oil at ambient and body temperature, which limits their bioavailability. The possibility of encapsulating PMFs within nanoemulsion-based delivery systems to facilitate their application in nutraceutical and pharmaceutical products was investigated. The influence of oil type (corn oil, MCT, orange oil), emulsifier type (β-lactoglobulin, lyso-lecithin, Tween, and DTAB), and neutral cosolvents (glycerol and ethanol) on the formation and stability of PMF-loaded nanoemulsions was examined. Nanoemulsions (r < 100 nm) could be formed using high pressure homogenization for all emulsifier types, except DTAB. Lipid droplet charge could be altered from highly cationic (DTAB), to near neutral (Tween), to highly anionic (β-lactoglobulin, lyso-lecithin) by varying emulsifier type. PMF crystals formed in all nanoemulsions after preparation, which had a tendency to sediment during storage. The size, morphology, and aggregation of PMF crystals depended on preparation method, emulsifier type, oil type, and cosolvent addition. These results have important implications for the development of delivery systems for bioactive components that have poor oil and water solubility at application temperatures.     

Flocculation of Whey Protein Stabilized Emulsions as Influenced by Dextran Sulfate and Electrolyte

The creaming stability and viscosity of oil-in-water emulsions stabilized by whey protein isolate were monitored as functions of dextran sulfate (DS) and electrolyte (NaCl) concentration. At a specific DS concentration (the critical flocculation concentration, CFC), the droplets became flocculated, which promoted creaming. Addition of electrolyte caused an increase in CFC. At NaCl concentrations <0.5 wt%, addition of electrolyte decreased emulsion viscosity, but at concentrations >0.5 wt% it caused an increase in viscosity due to increased flocculation. The results were due to the influence of electrostatic screening on the effective volume of DS molecules and colloidal interactions between droplets.     

Formulation and properties of model beverage emulsions stabilized by sucrose monopalmitate: Influence of pH and lyso-lecithin addition

There is a growing trend toward utilizing more label friendly ingredients in foods and beverages. In this study, we focused on the utilization of sucrose monopalmitate (SMP) as a non-ionic surfactant for stabilizing acidic beverages. Orange oil-in-water emulsions (5% (w/w) oil) stabilized by SMP were prepared using high pressure homogenization (pH 7). The minimum droplet diameter was around 130 nm, while the minimum mass ratio of SMP-to-oil required to produce small droplets was 0.1-to-1. Extensive droplet aggregation occurred when the pH of the emulsions was reduced from pH 7 to 3, with the mean particle diameter increasing from around 0.13 to 7.25 μm. This effect was attributed to an appreciable reduction in droplet charge when the pH was reduced (ζ ≈− 35 mV at pH 3 and − 2 mV at pH 3) thereby decreasing the electrostatic repulsion between droplets. It was proposed that the negative charge on the SMP-coated droplets was due to the presence of anionic substances within the droplets, such as palmitic acid (pK_a ≈ 4.9). Palmitic acid may have been an impurity in the original ingredient or it may have been generated due to degradation of SMP during storage. The addition of anionic lyso-lecithin markedly improved the stability of the emulsions to droplet aggregation and phase separation at low pH, which was attributed to an increased electrostatic repulsion between the droplets. This study has important consequences for the formulation of acidic beverage emulsions with improved stability and physicochemical performance.     

Influence of maltodextrin addition on the freeze-dry stability of β-lactoglobulin-based emulsions with controlled electrostatic and/or steric interactions

Three types of emulsions (β-Lg-, β-Lg-pectin-, and β-Lg-ι-carrageenan-coated emulsions) with controlled electrostatic and/or steric interactions were prepared, and then examined for their freeze-dry stability in the absence or presence of 6% maltodextrin (MD). In the absence of MD, all emulsions were highly unstable to freeze-drying, nevertheless, the β-Lg-pectin-coated emulsions (d ₃₂ =5.37, d ₄₃ =35.11 μm) that were stabilized mostly by steric repulsion showed better stability than the other 2 emulsions (no dried power was obtained). The freeze-dry instability of all emulsions was improved with MD addition, particularly in the β-Lg- (d ₄₃ =1.10 μm) and β-Lg-ι-carrageenan-coated emulsions (d ₄₃ =0.58 μm) that were stabilized by electrostatic repulsive force. In the presence of MD, the β-Lg-ι-carrageenan-coated emulsions showed the highest stability to freeze-drying, which was attributed to the cooperative impact of steric and electrostatic repulsion. This study implicates that the major mechanism for stabilizing emulsions against freeze-drying could be different depending on the absence or presence of MD.