Impact of Surface Active Compounds on Iron Catalyzed Oxidation of Methyl Linolenate in AOT–Water–Hexadecane Systems

Edible oils contain minor surface active components that form micro-heterogeneous environments, such as reverse micelles, which can alter the rate and direction of chemical reactions. However, little is known about the role of these micro-heterogeneous environments on lipid oxidation of bulk oil. Our objective was to evaluate the ability of water, cumene hydroperoxide, oleic acid, and phosphatidylcholine to influence the structure of reverse micelles in a model oil system: sodium bis(2-ethylhexyl) sulfosuccinate (aerosol-OT; AOT) in n-hexadecane. The influence of reverse micelle structure on iron catalyzed lipid oxidation was determined using methyl linolenate as an oxidizable substrate. The size and shape of the reverse micelle were investigated by small-angle x-ray scattering, and water contents was determined by Karl Fischer titrations. Lipid hydroperoxides and thiobarbituric acid reactive substances were used to follow lipid oxidation. Our results showed that AOT formed spherical reverse micelles in hexadecane. The size of the reverse micelles increased with increased water or phosphatidylcholine concentration, but decreased upon addition of cumene hydroperoxide or oleic acid. Iron catalyzed oxidation of methyl linolenate in the reverse micelle system decreased with increasing water concentration. Addition of phosphatidylcholine into the reverse micelle systems decreased methyl linolenate oxidation compared to control and reverse micelles with added oleic acid. These results indicate that water, cumene hydroperoxide, oleic acid, and phosphatidylcholine can alter reverse micelle size and lipid oxidation rates. Understanding how these compounds influence reverse micelle structure and lipid oxidation rates could provide information on how to modify bulk oil systems to increase oxidative stability.     

Comparison of Emulsifying Properties of Plant and Animal Proteins in Oil-in-Water Emulsions: Whey,Soy, and RuBisCo Proteins

There is increasing interest within the food industry in replacing animal-derived ingredients with plant-derived alternatives. In this study, we compared the emulsifying properties of an emerging plant protein (RuBisCo protein) with those of a well-established plant (soy protein) and animal (whey protein) protein. The RuBisCo protein (ribulose 1,5-bisphosphate carboxylase) was isolated from duckweed (lemna minor), which is an abundant plant material with a higher protein yield and biomass per unit area than most other plant protein sources. The ability of the three proteins to form and stabilize 10 wt% soybean oil-in-water emulsions was examined. The minimum amount of protein required to produce small droplets (d <?350 nm) decreased in the following order: RuBisCo > soy > whey protein. This effect was mainly attributed to the fact that the molar mass of the proteins decreased in the same order. Even so, the RuBisCo proteins were able to form stable emulsions when used at sufficiently high concentrations (≥ 1%). All three types of protein-coated oil droplets aggregated at pH values near their isoelectric points and at high ionic strengths but there were differences between them. In the absence of added salt, extensive droplet aggregation occurred from pH 4 to 5 for whey protein, from pH 2 to 5 for soy protein, and from pH 2 to 6 for RuBisCo protein. The isoelectric points of all three protein-coated droplets were around pH 5, but the magnitude of the surface potential at low and high pH values was higher for whey protein than for the two plant proteins. At pH 7, extensive droplet aggregation occurred at ≥100 mM NaCl for RuBisCo- and soy protein-coated droplets, but only at ≥400 mM NaCl for whey protein-coated ones. The RuBisCo-coated oil droplets were more prone to flocculation when heated, especially in the presence of salt (100 mM NaCl). Overall, these results show that RuBisCo protein can be used to form and stabilize oil-in-water emulsions, but the pH, salt, and temperature conditions must be carefully controlled to avoid droplet aggregation. We should note that droplet aggregation is advantageous in some applications because it leads to an increase in emulsion viscosity or gelation.

     

Two-dimensional rotating-frame Overhauser spectroscopy (ROESY) and (13)C NMR study of the interactions between maltodextrin and an anionic surfactant

Rotational frame nuclear Overhauser effect spectroscopy (ROESY) and (13)C NMR measurements were carried out to study the molecular interaction between maltodextrin, a digestive byproduct of starch, and an anionic surfactant. Significant differences in chemical shifts were observed when sodium dodecyl sulfate (SDS) was introduced into the maltodextrin (DE 10) solutions. (13)C NMR measurement indicated that there were downfield shifts and broadening of peaks, especially in the region of 75-81 and 100-103 ppm, which were assigned to carbons 1 and 4 of the d-glucopyranose residues of maltodextrin, respectively. ROESY spectra indicated cross-peaks between the SDS and maltodextrin protons. These peaks can arise only in the case of the designated SDS protons and maltodextrin protons being less than 0.5 nm apart for a substantial period of time. The most intense cross-peaks are those between the central CH(2) protons of SDS near 1.2 ppm and the maltodextrin protons ranging from 3.5 to 3.9 ppm. The SDS-H3 CH(2) protons were resolved from the bulk of the SDS protons, with peaks and shoulders at 1.25 ppm, which indicated an especially strong interaction of the SDS hydrophobic tail with MD6 and some less intense interactions with MD2, 4, and 5.     

Influence of Interfacial Composition on in Vitro Digestibility of Emulsified Lipids: Potential Mechanism for Chitosan's Ability to Inhibit Fat Digestion

The objective of this study was to investigate the influence of interfacial composition and electrical charge on the in vitro digestion of emulsified fats by pancreatic lipase. An electrostatic layer-by-layer deposition technique was used to prepare corn oil-in-water emulsions (3 wt% oil) that contained droplets coated by (1) lecithin, (2) lecithin–chitosan, or (3) lecithin–chitosan–pectin. Pancreatic lipase (1.6 mg mL⁻¹) and/or bile extract (5.0 mg mL⁻¹) were added to each emulsion, and the particle charge, droplet aggregation, and free fatty acids released were measured. In the presence of bile extract, the amount of fatty acids released per unit amount of emulsion was much lower in the emulsions containing droplets coated by lecithin–chitosan (38 ± 16 μmol mL⁻¹) than those containing droplets coated by lecithin (250 ± 70 μmol mL⁻¹) or lecithin–chitosan–pectin (274 ± 80 μmol mL⁻¹). In addition, there was much more extensive droplet aggregation in the lecithin–chitosan emulsion than in the other two emulsions. We postulated that lipase activity was reduced in the lecithin–chitosan emulsion as a result of the formation of a relatively thick cationic layer around each droplet, as well as the formation of large flocs, which restricted the access of the pancreatic lipase to the lipids within the droplets. Our results also suggest that droplets initially coated by a lecithin–chitosan–pectin layer did not inhibit lipase activity, which may have been because the chitosan–pectin desorbed from the droplet surfaces thereby allowing the enzyme to reach the lipids; however, further work is needed to establish this. This information could be used to create food emulsions with low caloric level, or to optimize diets for individuals with lipid digestion problems.     

Non-covalent interactions between proteins and polysaccharides

Foods with novel or improved properties can be created by utilizing non-covalent interactions between proteins and polysaccharides. In solution, either attractive or repulsive interactions between proteins and polysaccharides can be used to create microstructures that give foods novel textural and sensory properties. At interfaces, attractive electrostatic interactions can be used to create food emulsions with improved stability to environmental stresses or with novel encapsulation-release characteristics.     

Impact of Electrostatic Interactions on Lecithin-Stabilized Model O/W Emulsions

Natural emulsifiers, particularly those extracted from plants, are highly wanted by food industry to meet consumers demand for clean label food and beverage products. The potential utilization of soy lecithin as an emulsifier in model coffee creamer was investigated in this study. The model oil-in-water (O/W) emulsions consisted of 10 wt% medium chain triglyceride were stabilized using either 1% or 5% soy lecithin (pH 7.0). The O/W emulsions were of whitish milky color (L*?=?88–92) and were able to whiten black coffee solutions (L* from 5.5 for black coffee to 44–56 for white coffees). Model O/W emulsions with smaller mean droplet diameters (0.11 to 1.09 μm), higher surface potentials (ζ?=??62 to ?72 mV), and better stabilities in hot coffee were fabricated using higher lecithin levels because there was more emulsifier to coat the oil droplet surfaces. Alteration of the electrostatic interactions in the model O/W emulsions (5% lecithin) by pH adjustment or calcium addition led to droplet aggregation under certain conditions, which was attributed to charge reduction by protonation of lecithin head groups and electrostatic screening by counter-ion accumulation and ion-binding. In particular, phase separation of the model creamer occurred at pH value around 4.5 when the system was acidified at a slow rate. Overall, this study suggests that lecithin-stabilized O/W emulsions may become unstable in coffee solutions with high acidity or calcium levels. The information obtained from this study provides insights on the use of plant-based emulsifiers in commercial food and beverage systems.     

Chemical and Physical Stability of Astaxanthin-Enriched Emulsion-Based Delivery Systems

Astaxanthin (AST) is carotenoid that is considered to have many potential benefits for human health. However, its poor water-solubility and chemical instability hamper its use as a functional food ingredient. The present study evaluated the effects of storage temperature, pH, ionic strength, and light exposure on the physical and chemical stability of AST-enriched emulsions prepared using caseinate as emulsifier. The chemical degradation of AST increased with increasing temperature, but the emulsions remained physically stable (droplet diameter = 230 nm; ζ-potential = ?40 mV) at all incubation temperatures (5–70 °C). Solution pH, ionic strength and light exposure had little impact on the chemical stability of AST, except at pH 4 and 5. Conversely, the emulsions were highly unstable to droplet aggregation at pH values near the isoelectric point of the caseinate. This work highlights the benefits and drawbacks of using caseinate-stabilized emulsions as delivery systems for AST in functional foods and beverages.     

Characterization of the herpes simplex virus origin binding protein interaction with OriS.

The origin binding protein (OBP) of herpes simplex virus (HSV), which is essential for viral DNA replication, binds specifically to sequences within the viral replication origin(s) (for a review, see Challberg, M.D., and Kelly, T. J. (1989) Annu. Rev. Biochem. 58, 671-717). Using either a COOH-terminal OBP protein A fusion or the full-length protein, each expressed in Escherichia coli, we investigated the interaction of OBP with one HSV origin, OriS. Binding of OBP to a set of binding site variant sequences demonstrates that the 10-base pair sequence, 5' CGTTCGCACT 3', comprises the OBP-binding site. This sequence must be presented in the context of at least 15 total base pairs for high affinity binding, Ka = approximately 0.3 nM. Single base pair mutations in the central CGC sequence lower the affinity by several orders of magnitude, whereas a substitution at any of the other seven positions reduces the affinity by 10-fold or less. OBP binds with high affinity to duplex DNA containing mismatched base pairs. This property is exploited to analyze OBP binding to DNA heteroduplexes containing singly substituted mutant and wild-type DNA strands. For positions 2, 3, 5, 6, 7, 8, and 9, substitutions are tolerated on one or the other DNA strand, indicating that base-mediated interactions are limited to one base of each pair. For both Boxes I and II, these interactions are localized to one face of the DNA helix, forming a recognition surface in the major groove. In OriS, the 31 base pairs which separate Boxes I and II orient the two interaction surfaces to the same side of the DNA.     

Influence of Disperse Phase Transfer on Properties of Nanoemulsions Containing Oil Droplets with Different Compositions and Physical States

Food Biophysics - The impact of the initial oil droplet composition and physical state on molecular exchange processes in mixed oil-in-water nanoemulsions was investigated. Nanoemulsions consisting...