Influence of chitosan on stability and lipase digestibility of lecithin-stabilized tuna oil-in-water emulsions

The influence of chitosan concentration (0–0.3 wt%) and molecular weight (120, 250 and 342.5 kDa) on the physical stability and lipase digestibility of lecithin-stabilized tuna oil-in-water emulsions was studied. The ζ-potential, droplet size, creaming stability, free fatty acids and glucosamine released was measured for the emulsions when they were subjected to an in vitro digestion model. The ζ-potential of the oil droplets in lecithin-chitosan stabilized emulsions changed from positive (≈+53 mV) to negative and the emulsions were unstable to droplet aggregation for all chitosan concentrations and molecular weights used after being subjected to the digestion model. The amount of free fatty acid and glucosamine released per unit amount of emulsion was higher when pancreatic lipase was included in the digestion model. These results suggest that lecithin-chitosan coated droplets can be degraded by lipase under simulated gastrointestinal conditions. Consequently, chitosan coated lipid droplets may serve as useful carriers for the delivery of bioactive lipophilic nutraceuticals.     

Influence of chitosan and NaCl on physicochemical properties of low-acid tuna oil-in-water emulsions stabilized by non-ionic surfactant

An influence of low molecular weight (LMW) chitosan on physicochemical properties and stability of low-acid (pH 6) tuna oil-in-water emulsion stabilized by non-ionic surfactant (Tween 80) was studied. The mean droplet diameter, droplet charge (ζ-potential), creaming stability and microstructure of emulsions (5 wt% oil) were evaluated. The added chitosan was adsorbed on the surface of oil droplets stabilized by Tween 80 through electrostatic interactions. Such addition of chitosan at different concentrations (0–10 wt%) to emulsions showed slight effect on the mean droplet diameter. However, the degree of flocculation was a function of chitosan concentration assessed by emulsions' microstructure and creaming index. The impact of chitosan on the strength of the colloidal interaction between the emulsion droplets increased with increasing chitosan concentration. The mean diameter of droplet in emulsions increased with increasing NaCl because of the electrostatic screening effect. The addition of LMW chitosan could be performed to create tuna oil emulsions with low-acid to neutral character, as well as various physicochemical and stability properties suitable for health food products.     

In Situ Observation and Physical–Chemical Characteristics of Rambutan (Nephelium lappaceum L.) Kernel Olein Crystals Obtained from Acetone Fractionation

Hard fat stocks containing highly saturated fats are a necessary ingredient for fabrication of trans-free plastic fats. Crystal fractions obtained from the fractionation of fats naturally containing saturated fatty acids (SFA) may be a promising approach to produce the desired hard fat stocks. Influences of cooling rate (0.4, 2.0 and 10.0 °C·min⁻¹) and fractionation temperature (15 and 20 °C) on the formation of solid fat crystals of rambutan (Nephelium lappaceum L.) kernel olein (RKOle) during acetone fractionation were examined using in situ observation with polarized light microscopy (PLM). The resulting stable crystals were then separated and characterized by their iodine values, fatty acid compositions, crystal polymorphism, solid fat index, and melting behavior. PLM results showed that cooling rate affected crystal formation. Entrained oil on the surface and number of small crystals increased at higher cooling rates of RKOle. Stable crystals were obtained at a cooling rate of 2.0 °C·min⁻¹ and 6 hours, which had lower iodine value and contained more SFA with a higher amount of solid fat than incipient RKOle. Crystals fractionated at 20 °C were larger in size, fewer in number, and had less entrained oil compared to those fractionated at 15 °C. Their main polymorph was the β' form with a melting range comparable to common fully hydrogenated oils. Results suggested that RKOle crystals have potential for use as hard fat stocks for various purposes.     

Encapsulation of emulsified tuna oil in two-layered interfacial membranes prepared using electrostatic layer-by-layer deposition

Tuna oil-in-water emulsions (5 wt% tuna oil, 100 mM acetate buffer, pH 3.0) containing droplets stabilized either by lecithin membranes (primary emulsions) or by lecithin–chitosan membranes (secondary emulsions) were produced. The secondary emulsions were prepared using a layer-by-layer electrostatic deposition method that involved adsorbing cationic chitosan onto the surface of anionic lecithin-stabilized droplets. Primary and secondary emulsions were prepared in the absence and presence of corn syrup solids (a carbohydrate widely used in the micro-encapsulation of oils) and then their stability to environmental stresses was monitored. The secondary emulsions had better stability to droplet aggregation than primary emulsions exposed to thermal processing (30–90 °C for 30 min), freeze-thaw cycling (−18 °C for 22 h/30 °C for 2 h), high sodium chloride contents (200 mM NaCl) and freeze-drying. The addition of corn syrup solids decreased the stability of primary emulsions, but increased the stability of secondary emulsions. The interfacial engineering technology used in this study could lead to the creation of food emulsions with novel properties or improved stability to environmental stresses.     

Ability of crystal promoters to delay fat bloom development in heat‐resistant compound chocolate with or without the presence of crystal inhibitor

Three additives that acted as crystal promoters (CP1, CP2 and CP3), at varying concentrations, were studied to determine their effect on fat bloom inhibition in heat‐resistant compound chocolates. CP1 was composed of mono‐ and diglycerides and polyglycerol esters from high‐oleic sunflower oil. CP2 consisted of mono‐ and diglycerides, lecithin and citric acid esters from blended canola oil and palm stearin. CP3 was composed of triglycerides from fully hydrogenated canola oil. Based on instrumental and sensory evaluations, all crystal promoters significantly (P ≤ 0.05) delayed fat bloom formation. Although compound chocolate with 0.25% CP1 showed more rapid bloom development than those with CP2 and CP3, addition of the crystal inhibitor sorbitan tristearate (STS) to the sample at 0.5% concentration further delayed (P ≤ 0.05) fat bloom development. The considerable delay in fat bloom formation suggests that the addition of carefully selected crystal modifier additives can improve the quality of heat‐resistant compound chocolates.