Sung Je Lee

Microencapsulation of avocado oil by spray drying using whey protein and maltodextrin

Cold pressed avocado oil was microencapsulated by spray drying in four different wall systems consisting of whey protein isolate (WPI) alone or in combination with maltodextrin (MD) DE 5 at various ratios (90 : 10, 50 : 50 and 10 : 90). The WPI only or WPI/MD (90 : 10) powders were spherical and smooth, whereas the WPI/MD (50 : 50 and 10 : 90) powders exhibited pronounced surface collapse. Increasing the MD ratio resulted in higher bulk density and wettability, probably due to more compact physical structure and hydrophilic wall matrix. Surface free oil contents and microencapsulation efficiencies of powders were 11–16% and 45–66%, respectively, and no significant differences were observed between the samples. The crude avocado oil used in this study appeared to be stable against oxidation at cold and ambient temperatures, irrespective of microencapsulation. However, at high temperature of 60°C, the oxidative stability decreased significantly in all cases but it was improved to some extent by microencapsulation.

Protein-Stabilized Nanoemulsions and Emulsions: Comparison of Physicochemical Stability, Lipid Oxidation, and Lipase Digestibility

The properties of whey protein isolate (WPI) stabilized oil-in-water (O/W) nanoemulsions (d(43) ≈ 66 nm; 0.5% oil, 0.9% WPI) and emulsions (d(43) ≈ 325 nm; 0.5% oil, 0.045% WPI) were compared. Emulsions were prepared by high-pressure homogenization, while nanoemulsions were prepared by high-pressure homogenization and solvent (ethyl acetate) evaporation. The effects of pH, ionic strength (0-500 mM NaCl), thermal treatment (30-90 °C), and freezing/thawing on the stability and properties of the nanoemulsions and emulsions were compared. In general, nanoemulsions had better stability to droplet aggregation and creaming than emulsions. The nanoemulsions were unstable to droplet flocculation near the isoelectric point of WPI but remained stable at higher or lower pH values. In addition, the nanoemulsions were stable to salt addition, thermal treatment, and freezing/thawing (pH 7). Lipid oxidation was faster in nanoemulsions than emulsions, which was attributed to the increased surface area. Lipase digestibility of lipids was slower in nanoemulsions than emulsions, which was attributed to changes in interfacial structure and protein content. These results have important consequences for the design and utilization of food-grade nanoemulsions.

Chemical changes in bovine milk fat globule membrane caused by heat treatment and homogenization of whole milk

The effects of heat treatment and homogenization of whole milk on chemical changes in the milk fat globule membrane (MFGM) were investigated. Heating at 80 degrees C for 3-18 min caused an incorporation of whey proteins, especially beta-lactoglobulin (beta-Ig), into MFGM, thus increasing the protein content of the membrane and decreasing the lipid. SDS-PAGE showed that membrane glycoproteins, such as PAS-6 and PAS-7, had disappeared or were weakly stained in the gel due to heating of the milk. Heating also decreased free sulphydryl (SH) groups in the MFGM and increased disulphide (SS) groups, suggesting that incorporation of beta-Ig might be due to association with membrane proteins via disulphide bonds. In contrast, homogenization caused an adsorption of caseins to the MFGM but no binding of whey proteins to the MFGM without heating. Binding of caseins and whey proteins and loss of membrane proteins were not significantly different between milk samples that were homogenized before and after heating. Viscosity of whole milk was increased when milk was treated with both homogenization and heating.

Preparation and properties of glutaraldehyde cross-linked whey protein-based microcapsules containing theophylline

Whey protein-based microcapsules containing a model drug, theophylline, were prepared in organic phase, using glutaraldehyde-saturated toluene. In all cases, spherical microcapsules, ranging from <400 to 1000 microm in diameter, were obtained. Results indicated that core crystals were embedded throughout the wall matrix. In all cases, retention efficiency of theophylline was higher than 74% and was not affected by cross-linking conditions. Results of theophylline release in simulated intestinal and gastric fluids at 37 degrees C indicated that the diffusion-governed core release was significantly affected by size of microcapsules, cross-linking conditions, and by type of dissolution medium. In all cases, core release in simulated intestinal fluid was faster than in simulated gastric fluid.

Influence of gastric digestive reaction on subsequent in vitro intestinal digestion of sodium caseinate-stabilized emulsions

In this study, in vitro intestinal lipid digestion and the physicochemical and microstructural changes of sodium caseinate-stabilized emulsions were examined after the emulsions had been digested in a model simulated gastric fluid containing pepsin for different times. The average size, size distribution, microstructure, proteolysis of interfacial proteins and lipolysis of the emulsion droplets were monitored as a function of digestion time. The emulsion droplets underwent extensive droplet flocculation, with some coalescence together with proteolysis of interfacial proteins, in simulated gastric fluid, resulting in changes in the droplet size and the microstructure of the emulsions. In general, digestion in simulated gastric fluid containing pepsin accelerated coalescence of the emulsion droplets during subsequent digestion in simulated intestinal fluid containing pancreatic lipase. However, the changes in the size, the microstructure and the proteolysis of the interfacial proteins of the emulsions under gastric conditions did not influence the rate and the extent of lipid digestion in the subsequent intestinal environment.

Preparation and some properties of water-insoluble, whey protein-based microcapsules.

A method, consisting of double emulsification and chemical cross-linking with glutaraldehyde was used to prepare whey protein-based microcapsules containing anhydrous milk fat as a model core. Effects of emulsion composition and pH on core retention, microstructure, and water-solubility of microcapsules were investigated. In all cases, core retention higher than 88% was accomplished and, in most cases, was not significantly affected by emulsion composition. In all cases, spherical microcapsules, 10-80 microm in diameter, were obtained. Outer topography and the inner structure of microcapsules were significantly affected by the pH of the emulsion. In all cases, microcapsules were practically water-insoluble. Microcapsules similar to the developed prototype may be suitable for controlled core release in application fields where chemical cross-linking is acceptable.A method, consisting of double emulsification and chemical cross-linking with glutaraldehyde was used to prepare whey protein-based microcapsules containing anhydrous milk fat as a model core. Effects of emulsion composition and pH on core retention, microstructure, and water-solubility of microcapsules were investigated. In all cases, core retention higher than 88% was accomplished and, in most cases, was not significantly affected by emulsion composition. In all cases, spherical microcapsules, 10-80 mum in diameter, were obtained. Outer topography and the inner structure of microcapsules were significantly affected by the pH of the emulsion. In all cases, microcapsules were practically waterinsoluble. Microcapsules similar to the developed prototype may be suitable for controlled core release in application fields where chemical cross-linking is acceptable.

Formulation of oil-in-water β-carotene microemulsions: Effect of oil type and fatty acid chain length

The impact of oil type and fatty acid chain length on the development of food-grade microemulsions for the entrapment of β-carotene was investigated. The microemulsion region of a ternary phase diagram containing short chain monoglycerides was larger than for di- and triglycerides when Tween 80 was used as surfactant. The cytotoxicity of microemulsions composed of a 30% monoglyceride oil, 20% Tween 80 and 50% aqueous buffer were evaluated using an in vitro cell culture model (human epithelial colorectal adenocarcinoma, Caco-2). The cytotoxicity test showed that the viability of Caco-2 cells against β-carotene microemulsions at concentrations of 0.03125% (v/v) was higher than 90%. This study suggests that short chain monoglycerides could be used with Tween 80 to prepare transparent β-carotene-encapsulated O/W microemulsions in the particle size range of 12-100 nm.

Antioxidant activity and bioaccessibility of size-different nanoemulsions for lycopene-enriched tomato extract

Lycopene nanoemulsions were prepared to protect the antioxidant activity and improve the bioaccessibility of lycopene-enriched tomato extract (containing 6% of lycopene) by an emulsification-evaporation method. Lycopene nanoemulsions, with droplet sizes between 100 and 200 nm, exhibited higher anti-radical efficiency and antioxidant activity, than did those smaller than 100 nm. Strong protectability of lycopene in droplets smaller than 100 nm was associated with relatively slower rates of DPPH and ABTS reactions. In vitro bioaccessibility values of lycopene-enriched tomato extract, lycopene nanoemulsions with droplets larger than 100 nm (approximately 150 nm on average), and lycopene nanoemulsions with droplets smaller than 100 nm (69 nm on average) were 0.01, 0.53, and 0.77, respectively. Interestingly, nanoemulsions with droplets smaller than 100 nm showed the highest in vitro bioaccessibility, which could be interpreted as evidence of nanoemulsification enhancing the in vitro bioaccessibility of lycopene.

Microencapsulation of theophylline in whey proteins: effects of core-to-wall ratio

Effects of core-to-wall ratio ranging from 1:1.5 to 5:1.5 on formation, properties and core release from whey protein-based microcapsules containing theophylline were investigated. Microcapsules were cross-linked by glutaraldehyde-saturated toluene (GAST) in an organic phase. Size distribution of microcapsules, core content and core retention were affected by core-to-wall ratio. Proportion of small capsules was inversely related to core-to-wall ratio. Core content in microcapsules ranged from 6.7 to 65.7% (w/w) and core retention ranged from 16.8 to 85.4%. Outer topography and inner structure of microcapsules were influenced by core-to-wall ratio. Core release into simulated intestinal- and gastric-fluids was influenced by a combined effect of type of dissolution medium and core-to-wall ratio, through its influence on size, core content and structure of microcapsules. Results indicated that in order to attain a desired core content and release profile, the ratio of core-to-wall components, in suspensions consisting of whey proteins and theophylline, has to be carefully considered and adjusted.

Physicochemical properties of whey protein, lactoferrin and Tween 20 stabilised nanoemulsions: Effect of temperature, pH and salt

Oil-in-water nanoemulsions were prepared by emulsification and solvent evaporation using whey protein isolate (WPI), lactoferrin and Tween 20 as emulsifiers. Protein-stabilised nanoemulsions showed a decrease in particle size with increasing protein concentration from 0.25% to 1% (w/w) level with Z-average diameter between 70 and 90 nm. However, larger droplets were produced by Tween 20 (120-450 nm) especially at concentration above 0.75% (w/w). The stability of nanoemulsions to temperature (30-90°C), pH (2-10) and ionic strength (0-500 mM NaCl or 0-90 mM CaCl2) was also tested. Tween 20 nanoemulsions were unstable to heat treatment at 90°C for 15 min. WPI-stabilised nanoemulsions exhibited droplet aggregation near the isoelectric point at pH 4.5 and 5 and they were also unstable at salt concentration above 30 mM CaCl2. These results indicated that stable nanoemulsions can be prepared by careful selection of emulsifiers.