Model Emulsion Systems Research Articles

SYNERGISTIC ACTIVITY OF CAPELIN PROTEIN HYDROLYSATES WITH SYNTHETIC ANTIOXIDANTS IN A MODEL SYSTEM

ABSTRACTCapelin protein hydrolysates (CPHs) were examined in a β‐carotene‐linoleate model system together with synthetic antioxidants, namely butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and tert‐butyl hydroquinone (TBHQ). Addition of CPHs was at 0.25 and 1 mg per 5 mL in the above emulsion. BHA and BHT were added at levels of 2.5 and 5 μg and TBHQ at 5 and 10 μg. Absorbance of model emulsion system at 470 nm was recorded every 30 min for 2 h. CHPs and synthetic antioxidants inhibited oxidation of linoleic acid effectively. In the experiment with BHA, the influence of CPHs was significant (p<0.01) for the samples incubated for 60, 90, and 120 min; and in experiments with BHT and TBHQ during the entire incubation period. The influence of added BHA and BHT on inhibition of bleaching of β‐carotene in the emulsion system was significant (p <0.01) during the incubation period and after 60, 90 and 120 min when TBHQ was used. A synergistic effect was observed only for CPHs and TBHQ when incubation time was 60, 90, and 120 min.

Methylcellulose-induced stability changes in protein-based emulsions

The emulsifying and oil-in-water stabilizing properties of methylcellulose (MeC) were investigated in bovine serum albumin (BSA)-based emulsions. The creaming stability, flocculation, surface concentration of BSA and MeC and droplet size were determined. Results obtained showed modifications of creaming rates that were related to MeC concentrations in the continuous and dispersed phases. Viscosity effects on creaming and changes in average droplet size (d 43) relating to droplet coverage were identified and delineated. Studies performed on macroscopic oil–water and air–water interfaces were used to identify interfacial structuring and composition. A good agreement was found between droplet surface composition and the resistance to coalescence of emulsion droplets. Emulsions that demonstrated a more rigid-like adsorbed interfacial layer were more stable with respect to coalescence. This study involving model emulsion systems provides a new insight into the stability of industrial preparations containing mixtures of proteins and polysaccharides.

MODULATION OF METAL-INDUCED CYTOTOXICITY BY MAILLARD REACTION PRODUCTS ISOLATED FROM COFFEE BREW

Nondialyzable Maillard reaction products (MRPs) were recovered from three different coffee brew extracts (i.e., brewed, boiled, instant) to evaluate the efficacy of MRPs in modulating in vitro metal-induced cytotoxicity in C3H/10T1/2 mouse embryo fibroblast cells, cultured in the presence of Fe2+, Fe3+, or Cu2+ ions. Preliminary experiments were performed in an vitro linoleic acid emulsion model system to characterize the anti- or pro-oxidant activity of coffee MRPs. Cytotoxicity experimental protocols involved both the direct application of metal ions and coffee MRPs to fibroblast cells, and the premixing of metal ions with coffee MRPs at room temperature prior to incubating with fibroblast cells. Fe2+ and Cu2+ significantly lowered the colonization efficiency (CE) of cells at all three concentrations (i.e., 0.1, 10, 50 mu M) used. Similar Fe3+ activity was observed only at 50 mu M concentration. None of the coffee MRPs alone or together with 0.1 and 10 mu M of Fe2+ or Fe3+ produced cytotoxic effects during direct application. The premixing step, however, significantly enhanced the CE of cells compared to the control, denoting cytoprotection, only in the presence of Fe2+. In addition, the application of MRPs with 0.1 or 10 mu M of Cu2+ significantly lowered the CE of cells than the control, but enhanced the CE of cells than the Cu2+ added control. These results corresponded directly with the results of model linoleic acid emulsion test, thereby demonstrating that lipid hydroperoxide generation is the source for fibroblast cell toxicity when MRPs are added to cells together with metal ions. These results further indicate that coffee MRPs can suppress in vitro metal-induced cytotoxicity to a certain extent when Fe2+, Cu2+, or Fe3+ ions are present below a concentration of 50 mu M , possibly by chelating the metal ions. Ionic reducing capacity of coffee MRPs, albeit small, may explain the potential for increased cytotoxicity at higher coffee MRP concentrations.

EFFECT OF SOME POLYSACCHAR1DES ON OXIDATIVE STABILITY OF METHYL LINOLEATE IN EMULSION

ABSTRACT In a model emulsion system consisting of 10% w/w of methyl linoleate and 0.5% w/v of Tween 20 as an emulsifier in a 0.05 M sodium acetate buffer (pH 4.0) with polysaccharide, locust bean gum, xanthan and glucomannan considerably inhibited oxidation, as proved by the change in peroxide value. Carrageenan and chitosan had no or only a small effect on oxidation. There was no evidence of organic radical scavenging activity as shown by ESR, but oxidation inhibiting polysaccharides manifested an iron binding activity.

Experimental investigations on model emulsion systems stabilized with non-ionic surfactant blends

We have performed experimental research into model oil-in-water emulsion systems stabilized with non-ionic surfactant blends: thin aqueous films between oil phases and oil drops coalescing against their homophase. Xylene was chosen as the oil phase, and Tween 20 and Span 20, alone or in mixtures at different molar ratios, were used as stabilizers. The roles of the surfactant mole ratio, the electrolyte concentration and pH were studied. It was shown that there is considerable electrostatic repulsion within the aqueous films. The results obtained on thin film stability and on drop lifetime at constant electrolyte concentration indicate that Tween 20 (when present) is the emulsifier that predominantly determines the stability of the systems. This conclusion can be related to the higher surface activity and higher adsorption of Tween as deducted from interfacial tension data. Some evidence of synergism was observed only at an electrolyte concentration of 10 −3 M (NaCl). We also carried out stability tests on shaken and homogenized batch emulsion systems and the results show good correlation with the data from the model investigations.

Effects of Sulfhydryl Compounds on Lipid Oxidations Catalyzed by Copper and Heme

Effects of cysteine and glutathione on copper- and heme-catalyzed oxidation of methyl linoleate were studied in a model emulsion system. In the copper-catalyzed system, cysteine exerted a strong prooxidative effect, and this prooxi’dative effect increased as the concentration of cysteine increased. Furthermore, oxidized glutathione did not have a prooxidative effect, whereas reduced glutathione showed prooxidative activity. Blocking the sulfhydryl group by treatment of cysteine with iodoacetic acid completely eliminated the prooxidative activity of cysteine. In the heme-catalyzed system, cysteine showed an antioxidative effect that increased as concentration of cysteine increased. This antioxidative effect of cysteine was practically eliminated by treatment with iodoacetic acid. Reduced glutathione showed a greater antioxidative effect than oxidized glutathione. In the presence of sulfhydryl compounds, copper promoted superoxide anion generation whereas heme did not. The addition of cysteine (10 to 1000M) to milk did not inhibit either copper or heme induced lipid oxidation.

ANTIOXIDANT EFFECTS OF SOY PROTEIN HYDROLYSATES ON COPPER‐CATALYZED METHYL LINOLEATE OXIDATION

ABSTRACTOxidation of methyl linoleate in a model emulsion system containing soy protein and copper was studied. The prooxidative effect of soy protein was inhibited following proteolysis. Both the TBA test and diene conjugation measurements showed similar oxidative patterns. The inhibitory effect of the proteolytic treatment was ascribed to the binding of copper by proteolytic products and these copper complexes appeared to be less catalytic than the intact protein‐copper complex. However, the release of bound antioxidant phenolics or copper chelating agents, e.g. phytic acid following proteolysis, may also be involved.

CATALYSIS OF LIPID OXIDATION: A STUDY OF MULLET (Mugil cephalus) DARK FLESH AND EMULSION MODEL SYSTEM

ABSTRACTThe dark flesh of mullet (Mugil cephalus) was compared with beef muscle for total iron, total hemoprotein, and total nonheme iron. Mullet dark flesh contained 57.3 ppm iron, over twice the amount in beef, 26.0 ppm. Total possible nonheme iron content of mullet dark flesh ranged from 56–75%, compared to 11–29% for beef. In a linoleate emulsion model system, mullet dark flesh homogenate was analyzed for heme and nonheme iron activity as lipid oxidation catalysts. Addition of ascorbic acid, EDTA, and cyanide, at different pH levels, indicated the nature of the catalyses. Of the additives, cyanide yielded the strongest inhibition on a molar basis. Based on the criteria of other researchers, these data suggest that heme iron is the major catalyst of lipid oxidation in mullet flesh. The rates of O2 uptake by mullet dark flesh homogenate and by Fe/EDTA increased with increasing acidity, rather than exhibiting a previously reported peak at pH 5.5. The latter appears to be a phenomenon of limited occurrence rather than a general test criteria. In light of this finding, the nature and nomenclature of biological nonheme iron is discussed.

Chemical and organoleptic properties of dried emulsions

AbstractSafflower oil was incorporated into a model emulsion system containing emulsifier, carbohydrates, antioxidants, and protein. Emulsions were spray dried and the dry powders were stored at 60 C. Their oxidation rates were measured by headspace gas analysis (Oxygen absorption and carbon dioxide generation); peroxide and carbonyl values also were run. Although these objective tests all gave good correlation with average flavor scores, results show that oxygen absorption was superior to others as an indicator of flavor deterioration. Stepwise, multiple linear regression analysis showed that oxygen absorption and carbonyl value gave an equation which can predict flavor scores with a high degree of accuracy.

Comparative functionality of soy proteins used in commercial meat food products

AbstractThe use of soy isolates, concentrates, and texturized flours in meat food products is discussed. Functional characteristics of soy products in relation to their market application are reviewed. Soy isolates find more limited usage in meat food systems (2%) than the concentrates and textured soy flours (8–12%). In weak meat systems containing large amounts of fat (30–45%), the concentrate emulsifier and isolate are more important than the texturized soy flour. In chopped meat systems with 18–25% fat, the textural properties of soy flour (extruded) are more important than the use of an isolate. However, combinations of concentrate emulsifier and texturized flour are used. The method of cooking, i.e. fresh, deep fat‐fried, or char‐broiled, will affect the usage of soy combinations. In comminuted cooked cured meat food mixes, soy concentrates, and textured flours currently are being used. Nutritional properties are improved by inclusion of available ingredients high in lysine and methionine. Functional measurements of textural properties have been completed using the Instron with a Lee Kramer cell. Both model emulsion systems and finished product results substantiate the accuracy of textural properties in soy‐meat mixes using the Instron.

The Relation Between Covering Power and Density for Model Emulsion Systems

AbstractThe variation of covering power (CP) with exposure for model emulsions is evaluated to reveal the relation between CP and density and its dependence on grain-size spread. CP is shown to vary almost linearly with density except at small densities where there is a more rapid variation of CPo Negative and reversal processing are considered. Important assumptions in the theoretical treatment are that developable grains are completely reduced, that no interactions occur between neighbouring grains and that there is no loss of halide to the developer solution. Comparison with experimental data shows that the grain-size spread is of little importance in influencing the relation between CP and density compared with the effects of partial development and the solvent effects which occur in most developer solutions.

A phase-rule study of multiple-phase formation in a model emulsion system containing water, n-octanol, n-dodecane and a non-ionic surface-active agent at 10 and 25 degrees.

Abstract A four-component emulsion system containing the non-ionic surfactant C8H17 (O·CH2·CH2)6OH has been investigated, particularly in regions in which liquid crystal or more than two condensed phases are formed. Liquid crystal does not exist in the binary surfactant-water system at 25° but extensive regions form when the organic liquids octanol and dodecane are present, although these are not joined to the main two-liquid regions of the emulsion system. The surfactant is almost completely dissolved in the aqueous phase in water-dodecane mixtures but when substantial amounts of octanol are also present the partition coefficient is reversed in favour of the organic phase. At certain intermediate compositions three liquid phases are present. The significance of these results to the system as an emulsion are briefly discussed.