Kohei Nakano

Investigation of color-deepening phenomenon in catechin-(4 → 8)-dimer as a proanthocyanidin model and structural determination of its derivatives by oxidation

To elucidate the mechanism of the color-deepening phenomenon in aged red rice samples, a partial structure of proanthocyanidin, (+)-catechin-(4→8)-dimer (1), was synthesized as a model compound and subjected to chemical oxidation. HPLC analysis of oxidized 1 revealed new peaks which were isolated; among these, four compounds (2-5) having formed intramolecular bonds between the D and B rings were determined. These compounds and their derivatives in red rice extracts were identified by multiple reaction monitoring mass spectrometry. The UV-Vis spectra of 1-5 were recorded to clarify the correlation between the color-deepening effect and their chemical structures. Hence, the spectral absorption maxima between 300 and 500nm, corresponding to the oxidation products, increase. Therefore, the color-deepening phenomenon of red rice is thought to proceed via the formation of intramolecular bonds in proanthocyanidin by oxidation.

CO2 processing and hydration of fruit and vegetable tissues by clathrate hydrate formation

CO2 hydrate can be used to preserve fresh fruits and vegetables, and its application could contribute to the processing of carbonated frozen food. We investigated water transformation in the frozen tissue of fresh grape samples upon CO2 treatment at 2-3 MPa and 3°C for up to 46 h. Frozen fresh bean, radish, eggplant and cucumber samples were also investigated for comparison. X-ray diffraction indicated that after undergoing CO2 treatment for several hours, structure I CO2 hydrate formed within the grape tissue. Phase-contrast X-ray imaging using the diffraction-enhanced imaging technique revealed the presence of CO2 hydrate within the intercellular spaces of these tissues. The carbonated produce became effervescent because of the dissociation of CO2 hydrate through the intercellular space, especially above the melting point of ice. In addition, suppressed metabolic activity resulting from CO2 hydrate formation, which inhibits water and nutrient transport through intercellular space, can be expected.

A consideration on afterripening management of kiwifruits based on relation between fruit density and sugar content

A high precision non-destructive measurement technique for early kiwifruit sugar content estimation was proposed. Sugar contents of matured kiwifruits were estimated at harvest when the fruits were still immature. By estimating density of the immature fruit, starch content can be determined that was found closely related to sugar content of the fruit when it is fully matured. The fruit density was calculated from weight and volume information of the fruit. Considering the fact that the range of densities of kiwifruit is very narrow (about 1.02~1.06g/cm3), the measurement of volume requires high accuracy. In this study, the volume of about 2000 kiwifruits at harvest was measured with a Helmholtz acoustic resonance method that offered good correlation with a reference method with R2=0.9254, SEP=0.0019g/cm3. The fruit weight was measured with an electronic scale. The relationship between the fruit density at harvest and sugar content following ethylene treatment was also verified. The proposed system can be used for precision grading of kiwifruit quality based on prediction of sugar contents.

Identification of a freshness marker metabolite in stored soybean sprouts by comprehensive mass-spectrometric analysis of carbonyl compounds

The objective of this study was to identify metabolites that quantitatively indicate degrees of freshness of soybean sprouts. Self-cultivated soybean sprouts were stored at 5 °C, 10 °C or 20 °C, and respiratory CO2 production rates were monitored using gas chromatography during storage. Carbonyl compounds (CCs) were analyzed comprehensively using mass-spectroscopic metabolomics analyses. CCs were derivatized using dansyl hydrazine (DH) and were then analyzed using high performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-MS/MS) with multiplexed multiple reaction monitoring (MRM). In the MRM chromatogram, 171 to 358 peaks were observed from stored soybean sprouts. Principle component analysis and discriminant analysis (PCA-DA) selected the CC-DH derivative ion with a m/z 512 at a retention time of 9.34 min as the most significant metabolite. Searching online metabolomics databases and matching fragment patterns of product ion mass spectra of an authentic standard revealed abscisic acid is a freshness marker of soybean sprouts.

Nondestructive Freshness Evaluation of Spinach Leaves under Low Oxygen Storage Using Visible and Near Infrared Spectroscopy

Abstract The objective of this study was to develop a nondestructive technology for evaluating freshness in fruits and vegetables through nondestructive measurement of malondialdehyde (MDA) equivalent using visible and near infrared (VIS-NIR) spectroscopy. In this study, the behaviour of MDA equivalent of spinach leaves under low oxygen storage was investigated, and a multivariate calibration model of MDA equivalent was constructed using VIS-NIR diffuse reflectance spectra with a methodology of chemometrics. Low oxygen storage reduced significantly the peroxidation of lipid in spinach leaves after harvest. VIS-NIR spectroscopy with partial least square regression (PLSR) allowed constructing a prediction model for MDA equivalent in the leaves with sufficient accuracy.