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In this paper, we discuss and utilize the multiple-reflection attenuated total reflectance (ATR) method of near-infrared spectroscopy (NIRS) for the determination of glycogen content in Japanese wagyu beef. We have also conducted experiments on diffuse reflection to compare the experimental results. Glycogen, as a reservoir of glucose units, has a positive effect on the palatability of wagyu beef. The obtained nontreated spectra were preprocessed by several different methods, then a calibration and prediction model between spectral data and glycogen content was developed by partial least squares regression (PLSR). We found that when the multiple-reflection ATR method and the diffuse reflection method are used for NIR spectroscopy methods, there is a significant difference in their ability to predict the glycogen content in wagyu beef. The determination coefficient of the best prediction model for the spectra obtained by the multiple-reflection ATR method was 0.72 for the measurement of glycogen content in wagyu beef, whereas that obtained by the diffuse reflection method was only 0.29. Through experiments and data analysis, we found that the multiple-reflection ATR method is promising for predicting glycogen content in wagyu beef. The results of these experiments have important implications for the development of future small portable beef glycogen sensors. [ABSTRACT FROM AUTHOR]

The first taste sensor was developed 30 years ago, and its use has become widespread in the food and pharmaceutical industries. Numerous efforts have been made to improve taste sensor technology since that time. Now, over 600 taste sensors are used around the world to quantify and visualize the taste of food. In this article, we first explain the mechanisms underlying the operation of taste sensors and how they respond to the five basic sensations of taste. A taste map of beers that presents their taste in a visual manner will be introduced as a typical application of the taste sensors used in the food industry. We then discuss the ability of the taste sensor to detect taste interactions, such as bitterness-suppressing effects as well as attempts to produce tasty low-calorie foods. Recent attempts to visualize personal preferences and the dynamic changes in the taste of food during chewing using the taste sensor are also explained. The environment surrounding taste sensors and the taste sensors themselves have progressed considerably, with new food services appearing constantly. We are entering an era where we can increase our enjoyment of eating. [ABSTRACT FROM AUTHOR]

Recently, food production technologies using a 3D food printer have been developed. A taste sensor is expected to be used for food design in such food production. In this study, as the first step toward food design, we attempted to visualize the changes in the taste of food during the chewing process using a model food of a monaka (a traditional Japanese sweet with a wafer coating) with a three-layer structure composed of three ingredients: a salty gel, mashed potato, and the wafer. The temporal changes in the six taste qualities of the model food, namely, saltiness, sweetness, umami, bitterness, sourness, and astringency, were analyzed. Sensory tests using the temporal dominance of sensation (TDS) method were performed at the same time. The difference in the release of chemicals associated with the tastes of the three ingredients with the number of times that they were mashed as a simulation of chewing was analyzed. We found that texture and bitterness were dominant in the wafer, saltiness was dominant in the salty gel, and umami was dominant in the mashed potato. The results of the sensory tests using the TDS method and those of the measurement using the taste sensor were in good agreement: the saltiness of the salty gel and mashed potato was perceived in the initial and middle stages of the chewing process, whereas the umami of the mashed potato was perceived from the middle stage onwards. Moreover, the texture of the wafer was perceived in the initial stage, whereas its bitterness and texture were perceived in the final stage. These findings indicate the possibility of visualizing the release of chemicals associated with taste along with the breakdown of food in the mouth using a taste sensor. [ABSTRACT FROM AUTHOR]

The deterioration or oxidation of the mineral oil in transformers poses the risk of short circuits. Convenient and effective methods are expected to be developed. Carbon-based sensor arrays were used in this study to identify the quality variations of mineral oil for oil-filled transformers by odors. The sensitive layers of the odor-sensing system consisted of different types of GC stationary phase materials and carbon black (CB) mixtures. We made a targeted selection of GC materials by utilizing the polarities to make a sensor array based on the distinct components of mineral oil such as alkanes and xylenes by gas chromatography mass spectrometry (GC/MS) analysis. The response characteristics of the sensitive layers were used to recognize the mineral oil odors by machine learning. With laboratory air as the carrier gas, the system could distinguish mineral oil that has been in use for over 20 years from new mineral oil with an accuracy of about 93.8%. The identification accuracy achieved was about 60% for three different concentrations of unused mineral oil and the oxidized mineral oil created by the transformer's leakage. When detecting the oxidized mineral oil with a concentration of more than 50%, the accuracy rate reached more than 80%. The odor-sensing system in this study will help inspect mineral oils in the transformer and make leakage judgments in a short time. [ABSTRACT FROM AUTHOR]

We have developed a method to quantify the sweetness of negatively charged high-potency sweeteners coexisting with other taste substances. This kind of sweetness sensor uses lipid polymer membranes as the taste-sensing part. Two types of outputs have been defined in the measurement of the taste sensor: one is the relative value and the other is the CPA (the change in membrane potential caused by adsorption) value. The CPA value shows a good selectivity for high-potency sweeteners. On the other hand, the relative value is several times higher than the CPA value, but the relative value is influenced by salty substances. In order to obtain both high sensitivity and selectivity, we established a model for predicting the concentration of sweeteners with a nonlinear regression analysis method using the relative values of both the sweetness sensor and the saltiness sensor. The analysis results showed good correlations with the estimated concentration of acesulfame potassium coexisting with salty substances, as represented by R² = 0.99. This model can correspond well to the prediction of acesulfame K in a concentration of 0.2–0.7 mM, which is commonly used in food and beverages. The results obtained in this paper suggest that this method is useful for the evaluation of acesulfame K using the taste sensors. [ABSTRACT FROM AUTHOR]

A 2,4,6-trinitrotoluene (TNT) molecule recognition peptide-modified potentiometric device was developed in a multiparallel way using microelectrodes. The change in potential caused by the explosive target and recognition peptide was monitored in real-time sensorgrams through our laboratory-built analysis system. The peptide-modified microelectrode-based potentiometric device demonstrated the highly selective and sensitive sensing of the TNT molecule over other aromatic analogues. [ABSTRACT FROM AUTHOR]

Glycogen and moisture contents are associated with palatability, especially the flavor of Japanese wagyu beef samples. In this study, near-infrared (NIR) absorbance spectroscopy (12500-4000 cm-1) was carried out to predict the glycogen and moisture contents in Japanese wagyu beef. Calibration and prediction models were established by partial least-squares regression (PLSR) between the measured reference glycogen and moisture contents and the spectral data. Different spectral preprocessing methods were used, and the loading coefficient obtained from PLSR models was employed to select feature spectra. As a result, the prediction model of glycogen with the selected spectral region of 9000-4300 cm-1 after smoothing-standard normalized variate (SNV) yielded optimum results with a determination coefficient (Rp²) of 0.415, a root-mean-squared error of prediction (RMSEP) set of 0.386 mg/g, and a ratio of prediction to deviation (RPD) of 1.218. In addition, the prediction model of moisture content in the full spectral region of 12500-4000 cm-1 after smoothing-multiplicative scatter correction (MSC) yielded optimum results with Rp² of 0.795, RMSEP of 2.669%, and RPD of 2.008. The results of this study demonstrated that NIR spectroscopy offers great potential for the prediction of glycogen and moisture contents in Japanese wagyu beef samples. [ABSTRACT FROM AUTHOR]

Representation of the "taste" of sake in an easy-to-understand manner is an important issue in the alcohol beverage industry. To visualize the taste of sake and wine in an objective manner, we have developed an application program named "SAKELAVO" to search for brewed beverages on the basis of the results of instrumental analysis using taste sensors as well as sensory evaluation. In this study, with the purpose of developing additional functions of SAKELAVO to meet consumer needs and thus promote the widespread practical use of SAKELAVO, we developed (1) a function to search for products by consumer preference and (2) a function to search for products of similar taste for sake and wine, as well as (3) a function to search for the compatibility of brewed beverages, namely, sake and wine with different foods. As a result, SAKELAVO is now an application that not only visualizes the taste of brewed beverages but also has search functions based on consumer preferences, allowing it to better reflect consumer needs. [ABSTRACT FROM AUTHOR]

Sake brewing is a complicated process. Different kinds of sake with various tastes are produced depending on the raw materials [e.g., rice, water, rice malt (koji), and sake yeast (kobo)], brewing process, and storage period. To represent the complicated taste of sake in an easy-tounderstand manner, two-dimensional charts based on the analysis results of taste and aroma components have been developed. However, various issues related to the difference between the evaluations by panelists in actual sake tasting and those in charts as well as the lack of objectivity still remain. The purpose of this study is to visualize the taste of sake using a scale that is different from the conventional one by combining taste sensors and sensory evaluation. In this study, measurement using taste sensors, general analysis, and sensory evaluation of 135 kinds of sake were carried out. Using the results obtained, a scatter diagram of sake samples with small differences in the evaluations by panelists in actual sake tasting and those in charts was developed using saltiness determined with taste sensors and a sake meter value (specific gravity of sake). We called the scatter diagram the sake flavor chart. From the obtained results, we succeeded in visualizing the flavor of sake using a new objective scale that faithfully simulates the human sense of taste. [ABSTRACT FROM AUTHOR]

This paper reports the improvement of a bitterness sensor based on a lipid polymer membrane consisting of phosphoric acid di-n-decyl ester (PADE) as a lipid and bis(1-butylpentyl) adipate (BBPA) and tributyl o-acetylcitrate (TBAC) as plasticizers. Although the commercialized bitterness sensor (BT0) has high sensitivity and selectivity to the bitterness of medicines, the sensor response gradually decreases to almost zero after two years at room temperature and humidity in a laboratory. To reveal the reason for the deterioration of the response, we investigated sensor membranes by measuring the membrane potential, contact angle, and adsorption amount, as well as by performing gas chromatography-mass spectrometry (GC-MS), liquid chromatography-tandem mass spectrometry (LC-MS/MS).We found that the change in the surface charge density caused by the hydrolysis of TBAC led to the deterioration of the response. The acidic environment generated by PADE promoted TBAC hydrolysis. Finally, we succeeded in fabricating a new membrane for sensing the bitterness of medicines with higher durability and sensitivity by adjusting the proportions of the lipid and plasticizers. [ABSTRACT FROM AUTHOR]

In this study, a rationally-designed 2,4,6-trinitrotoluene (TNT) binding peptide derived from an amino acid sequence of the complementarity-determining region (CDR) of an anti-TNT monoclonal antibody was used for TNT detection based on a maleimide-functionalized surface plasmon resonance (SPR) sensor. By antigen-docking simulation and screening, the TNT binding candidate peptides were obtained as TNTHCDR1 derived from the heavy chain of CDR1, TNTHCDR2 derived from CDR2, and TNTHCDR3 from CDR3 of an anti-TNT antibody. The binding events between candidate peptides and TNT were evaluated using the SPR sensor by direct determination based on the 3-aminopropyltriethoxysilane (APTES) surface. The TNT binding peptide was directly immobilized on the maleimide-functionalized sensor chip surface from N--maleimidobutyryl-oxysuccinimide ester (GMBS). The results demonstrated that peptide TNTHCDR3 was identified and selected as a TNT binding peptide among the other two candidate peptides. Five kinds of TNT analogues were also investigated to testify the selectivity of TNT binding peptide TNTHCDR3. Furthermore, the results indicated that the APTES-GMBS-based SPR sensor chip procedure featured a great potential application for the direct detection of TNT. [ABSTRACT FROM AUTHOR]

Mimicking the biological olfaction, large odor-sensor arrays can be used to acquire a broad range of chemical information, with a potentially high degree of redundancy, to allow for enhanced control over the sensitivity and selectivity of artificial olfaction systems. The arrays should consist of the largest possible number of individual sensing elements while being miniaturized. Chemosensitive resistors are one of the sensing platforms that have a potential to satisfy these two conditions. In this work we test viability of fabricating a 16-element chemosensitive resistor array for detection and recognition of volatile organic compounds (VOCs). The sensors were fabricated using blends of carbon black and gas chromatography (GC) stationary-phase materials preselected based on their sorption properties. Blends of the selected GC materials with carbon black particles were subsequently coated over chemosensitive resistor devices and the resulting sensors/arrays evaluated in exposure experiments against vapors of pyrrole, benzenal, nonanal, and 2-phenethylamine at 150, 300, 450, and 900 ppb. Responses of the fabricated 16-element array were stable and differed for each individual odorant sample, proving the blends of GC materials with carbon black particles can be effectively used for fabrication of large odor-sensing arrays based on chemosensitive resistors. The obtained results suggest that the proposed sensing devices could be effective in discriminating odor/vapor samples at the sub-ppm level. [ABSTRACT FROM AUTHOR]

The detection and recognition of metabolically derived aldehydes, which have been identified as important products of oxidative stress and biomarkers of cancers; are considered as an effective approach for early cancer detection as well as health status monitoring. Quartz crystal microbalance (QCM) sensor arrays based on molecularly imprinted sol-gel (MISG) materials were developed in this work for highly sensitive detection and highly selective recognition of typical aldehyde vapors including hexanal (HAL); nonanal (NAL) and bezaldehyde (BAL). The MISGs were prepared by a sol-gel procedure using two matrix precursors: tetraethyl orthosilicate (TEOS) and tetrabutoxytitanium(TBOT). Aminopropyltriethoxysilane (APT); diethylaminopropyltrimethoxysilane (EAP) and trimethoxy-phenylsilane (TMP) were added as functional monomers to adjust the imprinting effect of the matrix. Hexanoic acid (HA); nonanoic acid (NA) and benzoic acid (BA) were used as psuedotemplates in view of their analogous structure to the target molecules as well as the strong hydrogen-bonding interaction with the matrix. Totally 13 types of MISGs with different components were prepared and coated on QCM electrodes by spin coating. Their sensing characters towards the three aldehyde vapors with different concentrations were investigated qualitatively. The results demonstrated that the response of individual sensors to each target strongly depended on the matrix precursors; functional monomers and template molecules. An optimization of the 13 MISG materials was carried out based on statistical analysis such as principle component analysis (PCA); multivariate analysis of covariance (MANCOVA) and hierarchical cluster analysis (HCA). The optimized sensor array consisting of five channels showed a high discrimination ability on the aldehyde vapors; which was confirmed by quantitative comparison with a randomly selected array. It was suggested that both the molecularly imprinting (MIP) effect and the matrix effect contributed to the sensitivity and selectivity of the optimized sensor array. The developed MISGs were expected to be promising materials for the detection and recognition of volatile aldehydes contained in exhaled breath or human body odor. [ABSTRACT FROM AUTHOR]

A first person narrative is presented that expores the author's experience of the development of taste and odor sensing technologies.

A taste sensor that uses lipid/polymer membranes can evaluate aftertastes felt by humans using Change in membrane Potential caused by Adsorption (CPA) measurements. The sensor membrane for evaluating bitterness, which is caused by acidic bitter substances such as iso-alpha acid contained in beer, needs an immersion process in monosodium glutamate (MSG) solution, called "MSG preconditioning". However, what happens to the lipid/polymer membrane during MSG preconditioning is not clear. Therefore, we carried out three experiments to investigate the changes in the lipid/polymer membrane caused by the MSG preconditioning, i.e., measurements of the taste sensor, measurements of the amount of the bitterness substance adsorbed onto the membrane and measurements of the contact angle of the membrane surface. The CPA values increased as the preconditioning process progressed, and became stable after 3 d of preconditioning. The response potentials to the reference solution showed the same tendency of the CPA value change during the preconditioning period. The contact angle of the lipid/polymer membrane surface decreased after 7 d of MSG preconditioning; in short, the surface of the lipid/polymer membrane became hydrophilic during MSG preconditioning. The amount of adsorbed iso-alpha acid was increased until 5 d preconditioning, and then it decreased. In this study, we revealed that the CPA values increased with the progress of MSG preconditioning in spite of the decrease of the amount of iso-alpha acid adsorbed onto the lipid/polymer membrane, and it was indicated that the CPA values increase because the sensor sensitivity was improved by the MSG preconditioning. [ABSTRACT FROM AUTHOR]

It is possible to evaluate the taste of foods or medicines using a taste sensor. The taste sensor converts information on taste into an electrical signal using several lipid/polymer membranes. A lipid/polymer membrane for bitterness sensing can evaluate aftertaste after immersion in monosodium glutamate (MSG), which is called "preconditioning". However, we have not yet analyzed the change in the surface structure of the membrane as a result of preconditioning. Thus, we analyzed the change in the surface by performing contact angle and surface zeta potential measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photon spectroscopy (XPS) and gas cluster ion beam time-of-flight secondary ion mass spectrometry (GCIB-TOF-SIMS). After preconditioning, the concentrations of MSG and tetradodecylammonium bromide (TDAB), contained in the lipid membrane were found to be higher in the surface region than in the bulk region. The effect of preconditioning was revealed by the above analysis methods. [ABSTRACT FROM AUTHOR]

A taste sensor using lipid-polymer membranes has been developed to evaluate the taste of foods, beverages and medicines. The response of the taste sensor, measured as a change in the membrane potential caused by adsorption (CPA), corresponds to the aftertaste felt by humans. The relationships between the CPA value and the amount of adsorbed taste substances, quinine and iso-α acid (bitterness), and tannic acid (astringency), have been studied so far. However, that of epigallocatechin gallate (EGCg) has not been clarified, although EGCg is abundantly present in green tea as one of its astringent substances. This study aimed at clarifying the response of the taste sensor to EGCg and its relationship with the amount of EGCg adsorbed onto lipid-polymer membranes. The lipid concentration dependence of the CPA value was similar to that of the amount of adsorbed EGCg, indicating a high correlation between the CPA value and the amount of adsorbed EGCg. The CPA value increased with increasing amount of adsorbed EGCg; however, the CPA value showed a tendency of leveling off when the amount of adsorbed EGCg further increased. [ABSTRACT FROM AUTHOR]

This review describes an "electronic dog nose" based on a surface plasmon resonance (SPR) sensor and an antigen-antibody interaction for security and safety. We have concentrated on developing appropriate sensor surfaces for the SPR sensor for practical use. The review covers different surface fabrications, which all include variations of a self-assembled monolayer containing oligo(ethylene glycol), dendrimer, and hydrophilic polymer. We have carried out detection of explosives using the sensor surfaces. For the SPR sensor to detect explosives, the vapor or particles of the target substances have to be dissolved in a liquid. Therefore, we also review the development of sampling processes for explosives, and a protocol for the measurement of explosives on the SPR sensor in the field. Additionally, sensing elements, which have the potential to be applied for the electronic dog nose, are described. [ABSTRACT FROM AUTHOR]

The bitterness of bitter substances can be measured by the change in the membrane electric potential caused by adsorption (CPA) using a taste sensor (electronic tongue). In this study, we examined the relationship between the CPA value due to an acidic bitter substance and the amount of the bitter substance adsorbed onto lipid/polymer membranes, which contain different lipid contents, used in the taste sensor. We used iso-α-acid which is an acidic bitter substance found in several foods and beverages. The amount of adsorbed iso-α-acid, which was determined by spectroscopy, showed a maximum at the lipid concentration 0.1 wt% of the membrane, and the same phenomenon was observed for the CPA value. At the higher lipid concentration, however, the amount adsorbed decreased and then remained constant, while the CPA value decreased monotonically to zero. This constant adsorption amount was observed when the membrane potential in the reference solution did not change with increasing lipid concentration. The decrease in CPA value in spite of the constant adsorption amount is caused by a decrease in the sensitivity of the membrane as the surface charge density increases. The reason why the peaks appeared in both the CPA value and adsorption amount is based on the contradictory adsorption properties of iso-α-acid. The increasing charged lipid concentration of the membrane causes an increasing electrostatic attractive interaction between iso-α-acid and the membrane, but simultaneously causes a decreasing hydrophobic interaction that results in decreasing adsorption of iso-α-acid, which also has hydrophobic properties, onto the membrane. Estimates of the amount of adsorption suggest that iso-α-acid molecules are adsorbed onto both the surface and interior of the membrane. [ABSTRACT FROM AUTHOR]

Taste evaluation technology has been developed by several methods, such as sensory tests, electronic tongues and a taste sensor based on lipid/polymer membranes. In particular, the taste sensor can individually quantify five basic tastes without multivariate analysis. However, it has proven difficult to develop a sweetness sensor, because sweeteners are classified into three types according to the electric charges in an aqueous solution; that is, no charge, negative charge and positive charge. Using membrane potential measurements, the taste-sensing system needs three types of sensor membrane for each electric charge type of sweetener. Since the commercially available sweetness sensor was only intended for uncharged sweeteners, a sweetness sensor for positively charged high-potency sweeteners such as aspartame was developed in this study. Using a lipid and plasticizers, we fabricated various lipid/polymer membranes for the sweetness sensor to identify the suitable components of the sensor membranes. As a result, one of the developed sensors showed responses of more than 20 mV to 10 mM aspartame and less than 5 mV to any other taste. The responses of the sensor depended on the concentration of aspartame. These results suggested that the developed sweetness sensor had high sensitivity to and high selectivity for aspartame. [ABSTRACT FROM AUTHOR]

Recently, highly functional biosensors have been developed in preparation for possible large-scale terrorist attacks using chemical warfare agents. Practically applicable sensors are required to have various abilities, such as high portability and operability, the capability of performing rapid and continuous measurement, as well as high sensitivity and selectivity. We developed the detection method of capsaicinoids, the main component of some lachrymators, using a surface plasmon resonance (SPR) immunosensor as an on-site detection sensor. Homovanillic acid, which has a vanillyl group similar to capsaicinoids such as capsaicin and dihydrocapsaicin, was bound to Concholepas concholepas hemocyanin (CCH) for use as an immunogen to generate polyclonal antibodies. An indirect competitive assay was carried out to detect capsaicinoids using SPR sensor chips on which different capsaicin analogues were immobilized. For the sensor chip on which 4-hydroxy-3-methoxybenzylamine hydrochloride was immobilized, a detection limit of 150 ppb was achieved. We found that the incubation time was not required and the detection can be completed in five minutes. [ABSTRACT FROM AUTHOR]

Highly sensitive and selective detection of 2,4-DNT, a representative explosive, was achieved by the synergic effect of molecular imprinting and host (cyclodextrin)–guest interaction in ultrathin layers of TiO2 and SiO2 gel; the detection limit using cSPI measurements reached nM concentration. [ABSTRACT FROM AUTHOR]