Factors affecting the interfacial rheology of films of food proteins and surfactants at air-water and oil-water interfaces are reviewed. A distinction is made between interfacial shear rheology and interfacial dilatational rheology, and between soluble and insoluble films. A comparison is made between properties of adsorbed layers of small-molecule surfactants, proteins, and mixed systems of protein+surfactant. The relationship between interfacial rheology and the stability of emulsions and foams is critically discussed.
The thermal properties of polyol-aqueous solutions (xylitol, sorbitol, maltitol and lactitol) in concentrations from 5% to 30% (0.15-2.86 molal) were analyzed by differential scanning calorimetry at temperatures from 0°C to -52°C and compared with those of their corresponding reducing sugars (xylose, glucose, maltose and lactose). The freezing point depression (ΔT) values in samples of both groups increased linearly with their concentrations (molal) and were similar to their corresponding sugars. On the other hand, the ice fraction (%) in their samples decreased somewhat depending on the concentration. It was generally observed that the ice fraction in the polyol-aqueous solution was slightly higher than in the corresponding sugar, as estimated by plotting the ice fraction as a function of molality multiplied by the number of -OH groups.
For the basic study on removal of methyl mercaptan from coffee volatiles, adsorption characteristics on zeolite 5A were evaluated for 6 model components in a coffee aroma-containing gas. They were methyl mercaptan, acetaldehyde and 2,3-butanedione as aroma components, and nitrogen, carbon dioxide and water as coexisting gas components. Adsorption isotherms for the above components were measured, and heats of adsorption were calculated from the measured isotherms. From the breakthrough curves for binary mixture, the order of adsorption selectivity was determined as water>acetaldehyde>methyl mercaptan>carbon dioxide>2,3-butanedione>nitrogen. The order roughly corresponded to the relative order of heats of adsorption. The results suggest that it is necessary to remove water vapor in the aroma-containing gas before the adsorption process for improving the adsorption efficiency of methyl mercaptan. Partial condensation was calculated for a model component system, and it was found that the condensation operation would be useful for the removal of water vapor from an aroma-containing gas.
For simulating the process of cooking rice grains or rice starch-related foods, the knowledge of the water diffusion coefficient as a function of temperature and moisture content is essential. Unfortunately, however, little reliable published data are available. In this paper, the water diffusion coefficient (WDC) in rice starch/water mixture with a selected moisture content was measured by PFG-NMR over a range of temperature. The WDC in a heated sample (0.42-0.89 g H2O/g sample), which was prepared by heating at 90°C for 60 min and cooling in advance, was measured over the temperature range 20-78°C, and that in a non-heated sample (0.465-0.55 g H2O/g sample) was measured at 16-53°C. The correlations between WDC and temperature as well as between WDC and moisture content were examined, and some empirical equations were developed with which the estimation of the WDC at an arbitrary combination of temperature and moisture content was enabled.
Near-infrared (NIR) transflectance spectroscopy scanning from 1100 nm to 2500 nm was applied for the determination of palmitic acid (C16:0), oleic acid (C18:1) and linoleic acid (C18:2), the major fatty acids in edible oils. Edible oil samples were divided into two sets: 95 and 46 samples as a calibration and a prediction set, respectively. The multiple regression equations (MREs) established for the calibration set between the reference data analyzed by gas chromatography (GC) and the NIR raw spectral data gave the multiple correlation coefficients of 0.996, 0.989 and 0.993 for C16:0, C18:1 and C18:2, respectively. The best MREs were established with the NIR raw spectral data recorded at 1724, 1756, 2140 and 2180 nm. The Fourier transform mid-infrared spectra of the standard C16:0, C18:1 and C18:2 supported the belief that the absorptions at these wavelengths were attributed to the CH2 of the straight carbon chain and the C=C of the unsaturated fatty acid. Standard errors of predictions between the data calculated from the best MREs and the reference data analyzed by GC for the prediction samples were 0.925%, 2.186% and 2.011%, and the correlation coefficients between those were larger than 0.99 for C16:0, C18:1 and C18:2, respectively. The obtained results indicate that the NIR procedure can potentially be used as a nondestructive analysis method for the purpose of rapid and simple determination of C16:0, C18:1 and C18:2 in edible oils.
The culture supernatant of Lactococcus lactis IO-1, which was isolated in our laboratory, inhibited the cell growth of various Gram-positive bacteria but did not inhibit the nisin A-producing strain, L. lactis NCDO 497. A nisin-like peptide antibiotic produced by L. lactis IO-1 was efficiently purified sequentially by acid treatment (at pH 3), ammonium sulfate precipitation, cation-exchange chromatography and reversed-phase high performance liquid chromatography. Dissociation of the peptide aggregates with high molar concentrations of urea resulted in successful purification. The molecular mass of this peptide antibiotic was 3335.67 by fast atom bombardment-mass spectrometry, confirming that the peptide antibiotic from L. lactis IO-1 is nisin Z, a natural nisin variant. The purification method used is rapid, simple and effective, permitting the specific activity to increase 122-fold, and the recovery was 24%.
Volatile compounds were isolated from cooked squid (Todarodes pacificus STEENSTRUP) using a porous polymer resin with Tenax TA column chromatography. Aroma extract dilution analysis determined the following six compounds as the main potent odorants of cooked squid: 4,5-dimethylthiazole (green), 2-acetyl-2-thiazoline (nutty), 2,5-dimethylpyrazine (popcorn-like), methional (potato, soy sauce), furaneol (caramel-like) and an unidentified compound (floral). Among them, based on the high concentration and odor characteristics, it is concluded that furaneol was the most important compound contributing to the sweet aroma of cooked squid.
Gene B and gene Del involved in the biosynthesis of carotenoids, particularly xanthophylls such as tunaxanthin, lutein and zeaxanthin, which are contained in the fruits of various tomato strains and their hybrids were studied. It is known that gene B blocks the biosynthesis of lycopene and transforms lycopene to β-carotene via β-zeacarotene and γ-carotene. This study revealed that gene B is also involved in the biosynthesis of zeaxanthin, a xanthophyll of the β-ionone end group, and increases the production of lutein. Gene Del is also known to block the biosynthesis of lycopene and produce δ-carotene, α-carotene and ε-carotene. It was revealed by the present study that gene Del also markedly increases the biosynthesis of lutein, a xanthophyll of the ε-ionone end group. Further, tunaxanthin which was previously undetected in tomatoes was observed for the first time. This study has thus confirmed that gene Del induces its production.
Twenty cultivars of citrus fruit were harvested at two stages of development: young fruit (weight about 2.5 g per fruit) and fully ripe fruit of which the ascorbate oxidase (AAO) activities were determined. Among the different cultivars, the specific activity of AAO in the young fruits ranged from 47 to 2120 units per mg protein, while fully ripe fruits had AAO specific activity ranging from 18 to 97 units per mg protein. Significant differences were also observed between tissue types in the AAO specific activity with the highest activity in the albedo (64-70%), followed by the flavedo (26-34%) and the pulp (2-3%). Further examination of the seasonal changes in AAO specific activity in the peel (flavedo and albedo) of Satsuma mandarin fruit indicated the highest AAO activity when a fruit weight was between 2-4 g. The AAO activity then decreased as the fruit became more mature. Similar changes in the pattern of AAO specific activity were also observed for the different harvest years 1994 and 1995.