Emulsion stabilization mechanism of combination of esterified maltodextrin and Tween 80 in oil-in-water emulsions.

Esterified maltodextrins (EMs) were prepared using enzyme-catalyzed reaction of maltodextrin (DE of 16 and 9) and palmitic acid. The emulsion stabilization mechanism was investigated of a combination of Tween 80 and EM in oil-in-water emulsion to determine interfacial tension, ζ-potential, non-adsorbed Tween 80 in centrifuged-serum of emulsion, and fluoresced microstructure. The interfacial tension and non-adsorbed Tween 80 content of combination of Tween 80 and EM-stabilized oil-in-water emulsions were closed to those of sole Tween 80-stabilized emulsion. The ζ-potential of sole Tween 80-stabilzed emulsion had a small positive charge but ζ-potential changed to small negative charge as EM was added into Tween 80-stabilzed emulsion. Fluorescence microstructure confirmed that EM was adsorbed on oil droplet surface, stabilized by Tween 80. The mechanism of emulsion stabilization may conclude that Tween 80 was mainly adsorbed at oil surface and EM may interact with Tween 80 to form a double stabilization layer without competitive replacement.

Effect of partial replacement of porcine fat with pre-emulsified soybean oil using fish protein isolate as emulsifier on characteristic of sausage.

Partial replacement of animal fats with n-3 rich oils is a promising way to improve nutritive value of meat products. In the present work, the effects of porcine fat substitution with soybean oil (SBO) on characteristics of sausages were studied at the oil substitution levels of 25, 35, and 45% by weight of porcine fat. SBO was introduced to the sausages alternatively in native or pre-emulsified forms, the latter with fish protein isolate (FPI) or Na-caseinate (Nc) as emulsifier. Characteristics of the sausages, including cooking loss, water holding capacity, texture attributes, microstructure, and color, were then determined. The sausages added with pre-emulsified SBO stabilized by FPI showed better stability than the control (without added SBO), as indicated by lower cooking loss and higher hardness. Microstructure with better homogeneity was also evident in the sausages added with pre-emulsified SBO stabilized by FPI. However, the sausages added with pre-emulsified SBO stabilized by Nc showed poorer stability than the control, and possessed sponge-like microstructure. Generally, increased oil substitution level led to inferior stability of the product, especially in the sausages formulated with pre-emulsified SBO stabilized by Nc. The results suggested that FPI might be used in comminuted meat products with desirable effects, in the pre-emulsification, on replacement level up to 35% of porcine fat.

Antioxidant activities of rice bran protein hydrolysates in bulk oil and oil-in-water emulsion.

BACKGROUND: Recently, utilization of natural antioxidants in food processing has been of growing interest, owing to the concerns of health hazards of synthetic agents. Protein hydrolysates are a potent candidate for this purpose. In this work, rice bran protein hydrolysates (RBPH) with various degrees of hydrolysis (DH) were prepared, and their antioxidant activities in soybean oil and oil-in-water (O/W) emulsion were examined. RESULTS: With increasing DH, RBPH showed increasing antioxidant activities, as evidenced by the increases in DPPH radical scavenging activity, reducing power and ferrous chelating activity (P < 0.05). The improved activity was associated with increasing surface hydrophobicity (SoANS). After hydrolysis for 60 min, the content of hydrophobic amino acids was increased. When RBPH with various DH were incorporated into bulk soybean oil and O/W emulsion stored at 37 °C for up to 15 days, lipid oxidation was successfully retarded, especially when DH increased. The efficiency in prevention of oxidation was dose dependent (0-10 g L(-1)), as indicated by the lower peroxide value and thiobarbituric reactive substances. CONCLUSION: The present work suggests that RBPH might be potently employed as a natural antioxidant in both bulk oil and emulsion models.

Effects of rice bran protein hydrolysates on the physicochemical stability of oil-in-water emulsions.

Isolation of proteins from rice bran was studied, comparing alkaline- and carbohydrase-aided extraction. It was found that protein extractability could be effectively improved using carbohydrases (Viscozyme L and α-amylase), especially when mechanical force was incorporated. Then, rice bran protein hydrolysates (RBPH) were prepared at various degrees of hydrolysis (DH), and employed to stabilize soybean O/W emulsion. Improved colloidal stability of the emulsions could be achieved using RBPH, especially at higher DH level, as indicated by an increase in the emulsifying activity index and better long-term dispersibility. The present work novelty suggested the efficiency of RBPH to improve oxidative stability of the emulsions. The most potent antioxidant activity was exhibited by RBPH with DH of 6.4 and 7.6%. With their efficiency to promote physicochemical stability of the emulsions, RBPH might be potently employed as a natural additive in emulsified food products, which is significant to value addition of rice bran for further industrial application.

The coalescence stability of protein-stabilized emulsions estimated by analytical photo-centrifugation.

Various protein solutions were studied in order to quantify the emulsifying activity of proteins, and to explore oil-water interfacial tension, oil particle size analysis, and oil phase separation behaviors in protein-stabilized oil-in-water (O/W) emulsions. Three proteins, bovine serum albumin (BSA), ß-lactoglobulin (ß-lg), and ß-casein (ß-ca), were employed to disperse hexadecane in various pH and ionic strength solutions in a wide range of oil-water ratios. It was confirmed that the volume mean oil droplet diameter, d(43), changed depending on the oil content, the pH, the ionic strength, and the used protein. In a dilute protein solution (0.01 %) at pH 7, droplet size increased with oil content in so-called surfactant-poor regimes (e.g., above 5%, 10%, and 20% oil content for BSA, ß-lg, and ß-ca emulsion, respectively) but remained constant at ca. 10 mm, 6 mm, and 20 mm, respectively, in lower oil content surfactant-rich regimes. In surfactant-poor regimes, the most important factor determining the oil drop size was the threshold amount of protein adsorption onto the oil-water interface. In surfactant-rich regimes, on the other hand, it is suggested that drop size may be governed mainly by the mechanical strength of protein films covering the oil drops during emulsification, and this was quantified by the critical osmotic pressure, P(CR). In this study, the P(CR) was measured conveniently in the oil phase separation experiments for protein-stabilized emulsions using analytical photo-centrifugal apparatus. The correlation between the P(CR) and oil droplet size prepared by emulsification at different pH and ionic strength media is discussed.

Bovine serum albumin-sugar conjugates through the maillard reaction: effects on interfacial behavior and emulsifying ability.

Bovine serum albumin (BSA) was employed as a model protein emulsifier to conjugate with aldohexose (D-glucose (Glc) or D-allose (All)) and sugar fatty acid ester (6-O-octanoyl-D-glucose (GlcC8)) through the Maillard reaction. It was found during the reaction that rate of decrease of free amino groups in BSA was almost the same for the BSA-sugar mixtures whereas browning and protein aggregation developed in the following order: Glc < All < GlcC8. It was thought that the rate of degradation of the Amadori compound could have been influenced by the OH-group stereochemistry at the C3 position of aldohexose, while denaturation of BSA by GlcC8 enhanced the browning and protein aggregation. To understand the emulsifying ability of the BSA-sugar conjugates, hexadecane-water interfacial tension and the oil droplet size of emulsions prepared by homogenizing hexadecane and aqueous solution of the conjugates were examined. BSA-GlcC8 showed greater improvement in interfacial and emulsifying activity than did BSA-Glc and -All. However, no improvement in emulsion stability was observed for any of the BSA-sugar conjugates, suggesting the weakness of the film formed at the oil droplet interface.