Yasuyuki Sagara

Gas chromatography/olfactometry and electronic nose analyses of retronasal aroma of espresso and correlation with sensory evaluation by an artificial neural network.

To develop a method for evaluating and designing the retronasal aroma of espresso, sensory evaluation data was correlated with data obtained from gas chromatography/olfactometry (GC/O, CharmAnalysis™) and from an electronic nose system αFOX4000 (E-nose). The volatile compounds of various kinds of espresso (arabica coffee beans from 6 production countries: Brazil, Ethiopia, Guatemala, Colombia, Indonesia, and Tanzania; 3 roasting degrees for each country: L values, 18, 23, and 26) were collected with a retronasal aroma simulator (RAS) and examined by GC/O and E-nose. In addition, sensory descriptive analysis using a 7-point scale for RAS effluent gas was performed by 5 trained flavorists using sensory descriptors selected based on the frequency in use and coefficient of correlation. The charm values of 10 odor descriptions obtained from GC/O analysis exhibited the significant (P < 0.05) differences among both roasting degrees and origins. Also, linear discriminant analysis (LDA) on the E-nose-sensor resistances and factor analysis on the sensory evaluation scores showed that the differences of aroma characteristics among the roasting degrees were larger than those among the origins. Based on an artificial neural network (ANN) model applied to the data from GC/O analyses and sensory evaluations, the perceptual factor of the RAS aroma was predicted to be mainly affected by sweet-caramel, smoke-roast, and acidic odors. Also, 3 metal oxide semiconductor sensors (LY2/Gh, P30/1, and T40/1) of E-nose were selected for analyses of RAS aroma and correlated with the sensory descriptive scores by the ANN to support sensory evaluation.

MEASUREMENT OF TRANSPORT PROPERTIES FOR THE DRIED LAYER OF COFFEE SOLUTION UNDERGOING FREEZE DRYING

ABSTRACT A mathematical model has developed to determine the thermal conductivity and permeability for the dried layer of liquid sample undergoing sublimation dehydration. A microcomputer-based automatic measurement system has developed for the data acquisition as well as determination of these transport properties applying the drying data to the model. Aqueous solutions of 29-45 % soluble coffee solid were freeze dried under drying conditions used in commercial operations. Thermal conductivity decreased in proportion to the porosity of the dried layer, and its temperature and pressure dependances were not appeared. The permeability increased with increasing the porosity, pressure and temperature of the dried layer. The results indicated that in commercial operations the solute concentration is one of the critical processing factors since this factor decisively governs the structure of a solute matrix formed during freezing of coffee solutions and the transport properties mainly depend upon the nature of ...

Three-Dimensional Visualization of Internal Structural Changes in Soybean Seeds During Germination by Excitation-Emission Matrix Imaging

A novel method of three-dimensionally visualizing the internal structure of a soybean seed, which was based on excitation-emission matrix (EEM) measurement and EEM pattern analysis, was developed. Cross-sectional images of three soybean samples at different germination stages were taken at 561 different excitation and emission wavelength conditions so that the EEM at each pixel was calculated. By applying principal component analysis (PCA) to these EEM data, two wavelength condition sets were selected for a simplified EEM measurement. Serial cross-sectional images at various depths of soybean seeds at pre-, early, and late germination stages were taken under the two wavelength condition sets. The difference in the simplified EEM pattern was converted into the difference in color by PCA and the color assignment of each pixel. Then, cross-sectional images were accumulated by a volume rendering method to develop three-dimensionally reconstructed models. Finally, six different three-dimensional reconstructed models of samples at each germination stage under the two wavelength condition sets were developed. Observations of these images suggested that vascular bundles or constituents forming them already existed in soybean seeds at the pre-germination stage. It was also considered that a soybean seed, similar to a cereal seed, has a specific part that emits autofluorescence between the seed coat and the endosperm. In addition, it was supposed that, at the early germination stage of a soybean seed, chlorophyll or related constituents were expressed in the cotyledon on the hypocotyl side, not throughout the seed, and spread along the vascular-bundle-like structure as germination progressed.

Characteristic coloring curve for white bread during baking.

The effect of heating conditions on the crust color formation was investigated during the baking of white bread. The surface temperatures were monitored with thermocouples attached to the inside surface of the loaf pan cover. The trace of the surface color in the L * a * b * color coordinate system is defined as the characteristic coloring curve. The overall baking process was classified into the following four stages based on the characteristic coloring curve: i) pre-heating (surface temperature < 110 °C), ii) Maillard reaction (110–150 °C), iii) caramelization (150–200 °C), and iv) over-baking (surface temperature>200 °C). A linear relationship was observed between the L * decrease and the increase in weight loss of a sample at each oven air temperature. The L * value appeared to be suitable as an indicator to control the surface color by baking conditions.

Human brain activation in response to olfactory stimulation by intravenous administration of odorants

To identify the BOLD effects related to olfaction in humans, we recorded functional magnetic resonance imaging (fMRI) scans in response intravenously instilled thiamine propyl disulfide (TPD) and thiamine tetrahydrofurfuryl disulfide monohydrochloride (TTFD). TPD and TTFD evoked a strong and weak odor sensation, respectively. Since we did not spray the odor stimuli directly, this method is expected to reduce the effect caused by direct stimulation of the trigeminal nerve. For the analysis of fMRI data, statistical parametric mapping (SPM2) was employed and the areas significantly activated during olfactory processing were located. Both strong and weak odorants induced brain activities mainly in the orbitofrontal gyrus (Brodmanns area: BA 11) in the left hemisphere. TPD (a strong odorant) induced activity in the subthalamic nucleus in the left hemisphere and the precentral gyrus (BA 6) and insula in the right hemisphere. TTFD (a weak odorant) induced activity in the superior frontal gyrus (BA 11) in the right hemisphere. In both circumstances, there was an increase in blood flow at the secondary olfactory cortex (SOC) but not the primary olfactory cortex (POC), probably due to a habituation effect in the POC. From the present results, we found brain activity in not only odor-specific regions but also regions whose levels of activity were changed by an intensity difference of odor stimuli.

STRUCTURAL MODELS RELATED TO TRANSPORT PROPERTIES FOR THE DRIED LAYER OF FOOD MATERIALS UNDERGOING FREEZE-DRYING

The values of thermal conductivity and permeability have been presented for the dried layer of raw beef, coffee solutions and sliced as well as mashed apples. A structural model for beef, coffee solution and mashed apple was developed for predicting the permeability of water-vapor flowing through the dried layer. In modeling the porous dried layer was assumed to be a bundle of capillary tubes with the pore space having an equivalent pore radius, porosity, and tortuosity factor. These results indicated that the structure for the solution systems was controllable by both solute concentration and freezing manners. Another cellular structural model has been presented for predicting the permeability of a sliced apple. The resistance of a cell membrane to the molecular transfer of water vapor was determined from the value of permeability and the size as well as number of the cells existed in the dried layer. Since the drying rate of cellular materials was limited by the mass flux across the dried layer, the model was considered to play an important role in predicting the optimum heating program for the surface temperature of cellular food materials such as fresh fruits and vegetables.

Transport Properties Of Cellular Food Materials Undergoing Freeze-Drying

The samples of sliced and mashed apples were freeze-dried by controlling their surface temperatures over the usual pressure range of commercial operations. The surface of sliced samples could not be maintained at above 10°C in order to prevent the frozen layer from melting, while that of mashed samples was allowed to heat up to 70°C. Thermal conductivities and permeabilities were determined by applying the uniformly-retreating-ice front model to the dried layer of the samples undergoing freeze-drying. The values of permeability for the mashed samples were found to depend on the ice-crystallization time during freezing. The results indicated that the drying rate of sliced samples was limited by the transfer rate of water vapor flowing through the dried layer. A cellular structural model is proposed for predicting the permeability of the dried layer, based on the resistance of the cell membrane to molecular transfer of water vapor.

Odorant Transfer Characteristics of White Bread during Baking

The potent odorants in the crust and crumb of white bread were identified and quantified by gas chromatography-mass spectrometry and gas chromatography/olfactometry. The weight loss ratio of the samples baked at 220 °C was controlled in the range of 0–28%. The odorants were classified into 5 types by the transfer characteristics: i) All amounts of odorant transferred from the crust to external space (type-I). ii) All transferred from the crust to the crumb and external space (type-II). iii) Certain amount remaining in the crust and the rest transferred to the crumb and external space (type-III). iv) All transferred from the crumb to external space (type-IV). v) Certain amount remaining in the crumb and the rest transferred to the crust and external space (type-V). The odorants of type-IV were not apparent after the crust had formed. The results indicate that the crust could be a barrier to prevent the odorants from being transferred to external space.

Measurement of Evaporation Coefficient of Water During Vacuum Cooling of Lettuce

Experimental investigations had been carried out to measure the evaporation coefficient of water from lettuce undergoing vacuum cooling, applying an evaporation boundary-layer model developed for the free surface of pure liquids. The value of evaporation coefficient for lettuce was found to be dependent on mass flux from the leaf surface, and about 4 times lower than that for the free surface of water. The effects of operating pressure to the coefficient were not appeared definitely under the experimental conditions.

Characteristic Evaluation for Volatile Components of Soluble Coffee Depending on Freeze-Drying Conditions

Abstract Volatile aroma compounds of freeze-dried soluble coffee were investigated to evaluate the effects of freeze-drying temperature conditions on their intensities and aroma characteristics by employing both GC/MS and charm-analysis, which is a GC/Olfactometry (GC/O) method. The coffee solutions with 40% solid content were freeze-dried changing freezing and drying temperatures. According to the results, it was demonstrated that the compounds identified based on human olfactory sense were different from those detected by GC/MS, and that the GC/O analysis method enabled evaluation of the characteristics and intensity of each compound as well as aroma profiles under various freezing and drying temperatures. Subsequently, GC/O method was found to be effective to detect and identify the volatile compounds giving the aroma peculiar to freeze-dried coffee, and useful to obtain the fundamental information for designing the optimal aroma characteristics of final product to conform the consumer preference based on the characteristic changes in aroma affected by freeze-drying conditions.