Powdered rooibos tea extract (RTE), which is rich in polyphenols, is made from rooibos tea by freeze-drying. “Rooibos” is Afrikaans for “red bush,” and the scientific name is “Aspalathus linearis.” It is a broom-like member of the legume family of plants and is used to make an herbal tea which has been popular in South Africa for generations and is now consumed in many countries. In the present work, the anti-oxidative effect of RTE on oils and fats in autoxidation or thermal oxidation was studied, and it was confirmed that RTE has a very strong anti-oxidative effect on emulsifying oils owing to the water-soluble polyphenols such as rutin and quercetin contained in RTE. RTE was found to have a strong ability to quench radicals generated in the water phase, and to confer higher thermal stability against deep fat frying than tocopherol. But RTE showed little anti-oxidative effect on frying oil because of its lower oil-solubility.
An expression for the surface tension of an aqueous mixed solution of surfactants and electrolyte ions in the presence of the common ions was derived from the Helmholtz free energy of an air/water surface. By applying the equation to experimental data for the surface tension, the adsorption constant of surfactant ions onto the air/water interface, the binding constant of counterions on the surfactants, and the surface potential and surface charge density of the interface were estimated. The adsorption constant and binding constant were dependent on the species of surfactant ion and counterion, respectively. Taking account of the dependence of surface potential and surface charge density on the concentration of electrolyte, it was suggested that the addition of electrolyte to the aqueous surfactant solution brings about the decrease in the surface potential, the increase in the surface density of surfactant ions, and consequently, the decrease in the surface tension. Furthermore, it was found that the configurational entropy plays a predominant role for the surface tension, compared to the electrical work.
Although conjugated oils are paid much attentions to their interesting physiological properties such as anticancer, anti-arteriosclerosis, anti-hypertension activities, loss in body fat etc, there is few information on their oxidation behavior. In the present work, their oxidation behavior and oxidation prevention method were evaluated to utilize as functional foods or drugs. As results, an oxidation behavior of conjugated oils was different from that of corresponding non-conjugated oils, and conjugated oils were supposed to form not only hydroperoxides but also kinds of cyclic peroxides as primary oxidation products in the autoxidation. In a thermal oxidation, polymerization reaction might be prior to decomposition reaction owing to form a large quantity of more polymerized products in conjugated oils. Solidification of conjugated oils by thermal oxidation was prevented for long time by addition of tocopherol, and optimal addition amounts of tocopherol into conjugated oils were 1,000 ppm either in autoxidation or thermal oxidation. Equi-molar of phosphatidyl ethanolamine showed synergistic effect slightly on 1,000 ppm tocopherol for preventing thermal oxidation of conjugated oil.
We investigated the melting point of the hydrated solid and rheological property of wormlike micellar solutions in the water/sucrose monopalmitate (C16SE)/tri (oxyethylene) dodecyl ether (C12EO3) system when a part of C16SE was substituted with the surfactants which have lower Krafft point than C16SE. The melting point of the hydrated solid of the water/C16SE/C12EO3 system is around 34°C. When C16SE is substituted with sodium dodecyl sulfate (SDS), the melting point of the hydrated solid decreases below 5°C at α (weight fraction of SDS in C16SE+SDS mixture) being greater than 0.3 and the zero shear viscosity (η0) increases from the original nonionic system. When C16SE is substituted with octa (oxyethylene) dodecyl ether (C12EO8), the melting point of the hydrated solid decreases down to 24°C and the maximum zero shear viscosity (η0max) decreases with the increase in α (weight fraction of C12EO8 in C16SE+C12EO8 mixture). η0max is dramatically increased by the substitution of C16SE with SDS. With further increase of α, η0max decreases gradually. The dynamic rheology data of highly viscous wormlike micellar solutions fit well to the Maxwell’s mechanical model of viscoelastic material, indicating the formation of rigid network of entangled wormlike micelles. Shear (plateau) modulus G0 is almost unchanged, whereas relaxation time τR shows similar behavior to η0max. Hence, the behavior of η0max can be explained from the behavior of τR by considering the equation relating these quantities, η0=G0τR. Since τR is proportional to the length of wormlike micelles, the behavior of η0max can be explained in terms of the change in the length of wormlike micelles caused by the addition of SDS.
The present study investigated whether or not muscle triacylglycerol (MTG) contributed as a main energy source and MTG level and utilized fatty acid (FA) composition decreased during a 4-hour swimming exercise in rats fed a normal diet or a high-fat diet (HFD). Sixty male Wistar rats aged 5 weeks were fed a normal diet (CE-2, n = 25, experiment A) or HFD (n = 35, experiment B) for 22 days. On the final day, rats in both experiments were killed either without exercise or 1, 2, 3, or 4 hours after beginning the swimming exercise. MTG accumulation was higher in rats fed the HFD than those fed the CE-2 in both slow- and fast-typed muscles. Serum concentrations of free fatty acids (FFA) and glucose were increased and muscle glycogen contents were decreased with the continuance of swimming exercise, especially in rats fed the CE-2. The prolonged swimming did not influence MTG contents and FA compositions of MTG in either the experiment. These results might indicate that specific FA of MTG was not oxidized and MTG did not contribute as a main energy source during the prolonged swimming exercise in rats; instead, serum FFA, glucose, and muscle glycogen were mainly used.
Oxidation of cyclohexanediol derivatives with 12-tungstophospholic acid-hydrogen peroxide system was investigated focusing on a reaction mechanism in the preparation of dicarboxylic acids from olefin because oxidative cleavage of vicinal diols would be a rate-determining step in oxidative cleavage of carbon-carbon double bonds. trans-1,2-Cyclohexanediol (DHC) was converted to adipic acid almost quantatively, while 1-hydroxy-2-methoxycyclohexane (HMC) gave a mixture of adipic acid, glutaric acid and monomethyl adipate. In the case of 1,4-cyclohexanediol, 4-hydroxy-cyclohexanone and many hyperoxidated products were obtained. Based on results for HMC, it is concluded that following route would be also reasonable in oxidative cleavage of vicinal diol with 12-tungstophospholic acid-hydrogen peroxide system: (1) first oxidation of vicinal diol to α-hydroxyketone, (2) nucleophilic attack of hydrogen peroxide attacks to carbonyl carbon, (3) Baiyer-Villiger rearrangement of dihydroxy-hydroperoxide to a cyclic ester, (4) hydrolysis and final oxidation to dicarboxylic acid.
The effect of droplet size on the oxidative stability of triacylglycerol (TAG)-in water emulsion was examined. Microchannel (MC) emulsification was used to make monodispersed emulsion of soybean oil TAG and fish oil TAG with different droplet size. The main polyunsaturated fatty acids (PUFA) of soybean oil TAG and fish oil TAG were linoleic acid (LA; 53%) and docosahexaenoic acid (DHA; 37.3%), respectively. Oxidation was induced by the addition of 2,2’-azobis(2-amidinopropane)-dihydrochloride (AAPH) or ferrous ion. The oxidative stability was followed by the decrease in the oxygen consumption in the solution, peroxide formation, and decrease in the unoxidized PUFA during oxidation, indicating that the oxidative stability of fish oil TAG increased with decreasing the droplet size, while the reverse effect of the droplet size was observed on the oxidation of soybean oil TAG. The decrease in the droplet size induces the increase in the droplet interface, from which the oxidation proceeds to the oil droplet interior. DHA in fish oil TAG would take highly protective interface against oxidative attack of free radicals and metal ions, whereas LA in soybean oil TAG would be more easily oxidized at the interface because of its less protective conformation. The reverse effect of the droplet size on fish oil TAG and soybean oil TAG could be explained by the different interface conformation of both TAG.