Seiichi Oshita

Rapid detection of Escherichia coli contamination in packaged fresh spinach using hyperspectral imaging.

A rapid method based on hyperspectral imaging for detection of Escherichia coli contamination in fresh vegetable was developed. E. coli K12 was inoculated into spinach with different initial concentrations. Samples were analyzed using a colony count and a hyperspectroscopic technique. A hyperspectral camera of 400-1000 nm, with a spectral resolution of 5 nm was employed to acquire hyperspectral images of packaged spinach. Reflectance spectra were obtained from various positions on the sample surface and pretreated using Sawitzky-Golay. Chemometrics including principal component analysis (PCA) and artificial neural network (ANN) were then used to analyze the pre-processed data. The PCA was implemented to remove redundant information of the hyperspectral data. The ANN was trained using Bayesian regularization and was capable of correlating hyperspectral data with number of E. coli. Once trained, the ANN was also used to construct a prediction map of all pixel spectra of an image to display the number of E. coli in the sample. The prediction map allowed a rapid and easy interpretation of the hyperspectral data. The results suggested that incorporation of hyperspectral imaging with chemometrics provided a rapid and innovative approach for the detection of E. coli contamination in packaged fresh spinach.

Discrimination of odors emanating from ‘La France’ pear by semi-conducting polymer sensors

Abstract Odors emanating from ‘La France’ pears were examined by the electronic odor detection system based on the adsorption on to and subsequent desorption of volatile compounds from an array of semi-conducting polymers, a so-called electronic nose. ‘La France’ pears were grouped in three storage treatments after being harvested. The first group was the pears stored for 115 days at 277 K, the second and third groups were the pears ripened in a chamber at 303 K for 1 and 5 days, respectively, after the storage of 115 days at 277 K. The physiological states of pears in the three treatments were thought to be different. Pears of the first group were judged to be immature, those of the second group were mature, and those of the third group were over mature. Gas chromatography separation of volatile compounds emanating from ‘La France’ pear resulted in seven peaks representing acetaldehyde, ethanol, methyl acetate, ethyl acetate, butanol, butyl acetate and hexyl acetate. Odors from pears were detected by the sensor array with 32 different polymers. The odors were classified into three classes dependent on their physiological states through distinctive odor pattern formed by 32 outputs. It was observed that there was the strong relationship between the results obtained by headspace GC and the electronic nose.

Non-invasive analytical technology for the detection of contamination, adulteration, and authenticity of meat, poultry, and fish: A review

The requirement of real-time monitoring of food products has encouraged the development of non-destructive measurement systems. Hyperspectral imaging is a rapid, reagentless, non-destructive analytical technique that integrates traditional spectroscopic and imaging techniques into one system to attain both spectral and spatial information from an object that cannot be achieved with either digital imaging or conventional spectroscopic techniques. Recently, this technique has emerged as one of the most powerful and inspiring techniques for assessing different meat species and building chemical images to show the distribution maps of constituents in a direct and easy manner. After presenting a brief description of the fundamentals of hyperspectral imaging, this paper reviews the potential applications of hyperspectral imaging for detecting the adulteration, contamination, and authenticity of meat, poultry, and fish. These applications envisage that hyperspectral imaging can be considered as a promising non-invasive analytical technique for predicting the contamination, adulteration, and authenticity of meat, poultry, and fish in a real-time mode.

Transmission electron microscopic observations of nanobubbles and their capture of impurities in wastewater

AbstractUnique properties of micro- and nanobubbles (MNBs), such as a high adsorption of impurities on their surface, are difficult to verify because MNBs are too small to observe directly. We thus used a transmission electron microscope (TEM) with the freeze-fractured replica method to observe oxygen (O2) MNBs in solutions. MNBs in pure water and in 1% NaCl solutions were spherical or oval. Their size distribution estimated from TEM images close to that of the original solution is measured by light-scattered methods. When we applied this technique to the observation of O2 MNBs formed in the wastewater of a sewage plant, we found the characteristic features of spherical MNBs that adsorbed surrounding impurity particles on their surface. PACS: 68.03.-g, 81.07.-b, 92.40.qc

Non-destructive evaluation of ATP content and plate count on pork meat surface by fluorescence spectroscopy.

The potential of fluorescence spectroscopy was investigated for the non-destructive evaluation of ATP content and plate count on pork meat surface stored aerobically at 15 °C during three days. Excitation (Ex) Emission (Em) Matrix of fluorescence intensity was obtained and fluorescence from tryptophan (Ex=295 nm and Em=335 nm) and NADPH (Ex=335 nm and Em=450 nm) was detected. Because tryptophan and NADPH fluorescence changed along with the growth of microorganisms, microbial spoilage on meat could be detected from fluorescence. By applying PLSR (Partial Least Squares Regression) analysis, ATP content and plate count were predicted with good determination coefficient (0.94-0.97 in calibration and 0.84-0.88 in validation).

Parsimonious model development for real-time monitoring of moisture in red meat using hyperspectral imaging.

A hyperspectral imaging system in the spectral range of 400-1000 nm was investigated to develop a multispectral real-time imaging system allowing the meat industry to determine moisture content in red meat including beef, lamb, and pork. Multivariate calibration models were developed using partial least-squares regression (PLSR) and least-squares support vector machines (LS-SVM) in the full spectral range. Instead of selection of different sets of feature wavelengths for beef, lamb, and pork, a set of 10 feature wavelengths was selected for convenient industrial application for the determination of moisture content in red meat. A quantitative linear function was then established using MLR based on these key feature wavelengths for predicting moisture content of red meat in an online system and creating moisture distribution maps. The results reveal that the combination of hyperspectral imaging and multivariate has great potential in the meat industry for real-time determination of moisture content.

Concentration of liquid foods by the use of gas hydrate

Abstract The formation of gas hydrate in both distilled water and coffee solutions was studied to provide the basic data for the development of liquid foods concentration by the use of gas hydrate. Experiments were carried out with xenon gas. Coffee solution samples were prepared to the concentration of 1.5, 5.1, 9.9 and 14.7 wt.%. Temperature was set from 2°C to 10°C and the range of xenon pressure was from 0.20 to 1.00 MPa. It was found that xenon hydrate could form in coffee solutions. The time required for xenon hydrate formation in coffee solutions, that is induction time, depended on the concentration of solution. Longer induction time was required for higher concentration of solution. The growth of xenon hydrate was examined through the change in size distribution of xenon hydrate with time. The effect of temperature on the size of xenon hydrate was clearly observed at the temperature–pressure condition that showed low xenon solubility. Finally, lower xenon pressure and higher temperature created the larger size of xenon hydrate crystals but it required longer time.

Accumulation Mechanism of γ-Aminobutyric Acid in Tomatoes (Solanum lycopersicum L.) under Low O2 with and without CO2

The storage of ripe tomatoes in low-O(2) conditions with and without CO(2) promotes γ-aminobutyric acid (GABA) accumulation. The activities of glutamate decarboxylase (GAD) and α-ketoglutarate-dependent GABA transaminase (GABA-TK) were higher and lower, respectively, following storage under hypoxic (2.4 or 3.5% O(2)) or adjusted aerobic (11% O(2)) conditions compared to the activities in air for 7 days at 25 °C. GAD activity was consistent with the expression level of mRNA for GAD. The GABA concentration in tomatoes stored under hypoxic conditions and adjusted aerobic conditions was 60-90% higher than that when they are stored in air on the same day. These results demonstrate that upregulation of GAD activity and downregulation of GABA-TK activity cause GABA accumulation in tomatoes stored under low-O(2) conditions. Meanwhile, the effect of CO(2) on GABA accumulation is probably minimal.

Stimulation of γ-Aminobutyric Acid Production in Vine-Ripe Tomato (Lycopersicon esculentum Mill.) Fruits under Modified Atmospheres

Stimulation of gamma-aminobutyric acid (GABA) production under low O2 and high CO2 conditions (adjusted aerobic atmosphere) under which ethanol fermentation could be avoided was studied. Vine-ripe tomato fruits were stored under hypoxia conditions and adjusted aerobic atmospheres as well as in the air at 15 degrees C for 13 days and at 30 degrees C for 6 days. At 30 degrees C tomato fruit GABA concentration under the adjusted aerobic atmosphere (O2 11%, CO2 9%) was significantly higher by 48% than that in air after 6 days from the start of storage. Increased accumulation of alanine under the adjusted aerobic atmosphere supports the observation that this atmosphere stimulates GABA production. The results demonstrate that the concentration of GABA as a beneficial substance for antihypertensive effects and so on can be increased by storing tomato fruits under adjusted aerobic atmospheres for the first time.

Effect of NaCl on the Lifetime of Micro- and Nanobubbles

Micro- and nanobubbles (MNBs) are potentially useful for industrial applications such as the purification of wastewater and the promotion of physiological activities of living organisms. To develop such applications, we should understand their properties and behavior, such as their lifetime and their number density in solution. In the present study, we observed oxygen MNBs distributed in an electrolyte (NaCl) solution using a transmission electron microscope to analyze samples made with the freeze-fracture replica method. We found that MNBs in a 100 mM NaCl solution remain for at least 1 week, but at higher concentrations decay more quickly. To better understand their lifetimes, we compared measurements of the solutions dissolved oxygen concentration and the ζ-potential of the MNBs. Our detailed observations of transmission electron microscopy (TEM) images allows us to conclude that low concentrations of NaCl stabilize MNBs due to the ion shielding effect. However, higher concentrations accelerate their disappearance by reducing the repulsive force between MNBs.