Basic knowledge of dynamic properties, i.e., viscosity and elasticity, and their application to food engineering were reviewed. Viscosity relates shear stress τ to shear rate for substances; and elasticity, shear stress τ to shear strain γ. Steady flow viscosity μ of liquid can be measured by a cone-and-plate viscometer, as a function of . Viscoelasticity values are obtained by static or dynamic methods. In particular, from dynamic viscoelastic measurements, several viscoelastic parameters, which reflect inner structure and state of material, can be obtained: the storage modulus G’, the loss modulus G”, the complex modulus G^＊(＝G’＋iG”; i, imaginary unit), the dynamic viscosity η’, and the complex viscosity η^＊(＝η’−iη”). Food hydrocolloids are rheologically classified into 4 groups according to the angular frequency (ω) dependence of G’ and G”: true gel, weak gel, true polymer solution, and dilute polymer solution. According to Cox-Merzs’ empirical law, η^＊＝μ at ω＝. The velocity of thickener solutions through the human pharynx was measured by the ultrasonic pulse Doppler method to give an index for thickener solutions as foods for dysphagic patients. The value of V_max of the solutions approached that of yogurt, which is rarely aspirated by dysphagic patients, as the concentrations (μ) increased. The parameter V_max of the thickener solutions correlated well with μ.

View full abstract

Endothelin-1 (ET-1), a powerful vasoconstrictor and mitogen for melanocytes, might be responsible for pigmentation that occurs after ultraviolet (UVB) -irradiation. We have previously reported that Sechium edule (S. edule) extract reduces ET-1 secretion in cultured human keratinocytes following UVB irradiation. In this study, we investigated the effect of S. edule extract on melanin synthesis and analyzed the polyphenols contained in the extract. A three-dimensional human skin model comprising normal epidermal keratinocytes and melanocytes was subjected to macroscopical pigmentation and quantitative analysis. The S. edule extract showed an inhibitory effect on macroscopic and microscopic darkening and melanin content; however it did not show an inhibitory effect on tyrosinase enzyme activity. High-performance liquid chromatography with coulometric array detection was employed to determine the polyphenols contained in the extract. The luteolin, ferulic acid, p-coumaric acid, vanillic acid, protocatechuic acid and p-hydroxybenzoic acid were found to be 6.6μg/g, 5.6μg/g, 3.3μg/g, 6.1μg/g, 1.5μg/g and 0.8μg/g (dry weight), respectively. This polyphenolic complex might result in the inhibitory effect of melanin synthesis.

View full abstract

Static headspace gas chromatography is one of the most frequently used techniques for the analysis of flavor components in foods and beverages. Although the technique has many advantages over other methods, one of its major drawbacks is low sensitivity for substances of intermediate and high boiling point. The purpose of this study is to analyze the effect of salting-out on the sensitivity of static headspace gas chromatography (SHS-GC) and static headspace solid phase micro extraction gas chromatography (SPME-GC) for flavor components in foods and beverages. In the present study, we analyzed flavor components in La France pear juice and in an aqueous solution containing alcohols and esters by SHS-GC and SPME-GC after salting-out with saturated sodium chloride. We then analyzed the differences in detection sensitivity obtained with and without using a salting-out procedure during sample preparation. The detection sensitivity for almost all flavor components in both samples was improved by the addition of sodium chloride. The improvement in detection sensitivity by the addition of sodium chloride tended to increase as the molecular weight of the alcohols increased and as that of the esters decreased. In conclusion, addition of sodium chloride was extremely effective for improving the sensitivity of detection of flavor components by SHS-GC and SPME-GC.

View full abstract

A heating system using superheated steam (SHS) in combination with a spray of hot water micro droplets (WMD) has been developed to prevent drying of food material during SHS heating. In the SHS＋WMD system, a mixture of SHS (115℃) and WMD is generated by throttling boiling water and steam (120 to 140℃) with a nozzle. If the moisture content of food material can be controlled through regulation of the SHS/WMD ratio, the combination system is expected to provide flexible application of SHS for food processing. In this study, methods for measuring and regulating the ratio of SHS and WMD in the nozzle jet were investigated. It was found that the SHS/WMD ratio could be easily determined from the difference between the water uptake rate of the system and the theoretical steam flow rate through the nozzle (derived from the internal pressure of the nozzle). The WMD ratio increased as the nozzle internal pressure increased; by decreasing the nozzle throat diameter or by increasing the water uptake rate. SHS＋WMD was generated when the nozzle internal pressure was greater than 0.188 MPa and the steam velocity at the nozzle throat was sonic, regardless of the nozzle throat diameter.

View full abstract

The respective oxidation processes of linoleoyl residue esterifies with a variety of hydrophobic substances were measured at 80℃. The relationship between the molecular weight of the hydrophobic substance and the rate of oxidation of linoleoyl residue was investigated. The autocatalytic rate expression was proposed to describe the entire oxidation process of each sample, and rate constants involved in the expression were evaluated. Phenol, 2-naphthol, 1-undecanol, stearyl alcohol and cholestanol were respectively used as the hydrophobic substance, and they synthesized linoleoyl compound with linoleic acid. Linoleic acid, methyl linoleate, ethyl linoleate, isopropyl linoleate and cholesterol linoleate, which available in the market, were also used as the experimental samples in this study. It can be concluded that as the molecular weight of the hydrophobic substance becomes lager, the rate constant tends to become smaller. However, for the molecular weights exceeding 150, the values of the rate constants were found to be similar.

View full abstract