Simultaneous determination of N-methylcarbamate pesticides and their metabolites in agricultural products

We investigated the determination of N-methylcarbamate pesticides and their metabolites in agricultural products by HPLC with post-column fluorescence detection after clean-up with an SPE cartridge. The homogenate of agricultural products was extracted with acetone. The crude extract was partitioned between 5% sodium chloride solution and dichloromethane, and the dichloromethane layer was concentrated to dryness. The residue was dissolved with a mixture of acetone and n-hexane, and purified by using Supelclean ENVI-Carb SPE, Bond Elut Extraction Cartridge PSA and SAX in series with a mixture of acetone and n-hexane. N-Methylcarbamate pesticide was analyzed by HPLC with post-column reaction and fluoresce detection. N-Methylcarbamate pesticide in citrus fruits and various kinds of agricultural products could be analyzed accurately by the presented method. Recoveries of N-methylcarbamate pesticides added to several agricultural products at the level of 0.10 ppm were mostly in the range of 60-110%. The limit of detection was 0.005 ppm.     

Identification of chemical detected in kiwi fruit during analysis for residual pesticide

An unknown peak was detected in a GC chromatogram of many kiwi fruit extracts during analysis for pesticide residues. It was identified by GC/MS as diphenyl 2-ethylhexyl phosphate (DPEHP), used as a plasticizer and flame retardant. The concentration of DPEHP was investigated in 15 samples of kiwi fruit, and it was detected at between 0.02 and 0.14 microgram/g in 10 of the samples. It might be due to migration of DPEHP into the fruit from the printed portion of the polyethylene terephthalate (PET) package.     

In vitro inhibition of α-glucosidases and glycogen phosphorylase by catechin gallates in green tea

We investigated in vitro inhibition of mammalian carbohydrate-degrading enzymes by green tea extract and the component catechins, and further evaluated their inhibitory activities in cell cultures. The extract showed good inhibition toward rat intestinal maltase and rabbit glycogen phosphorylase (GP) b, with IC₅₀ values of 45 and 7.4 μg/ml, respectively. The polyphenol components, catechin 3-gallate (CG), gallocatechin 3-gallate (GCG), epicatechin 3-gallate (ECG), and epigallocatechin 3-gallate (EGCG), were good inhibitors of maltase, with IC₅₀ values of 62, 67, 40, and 16 μM, respectively, and EGCG also showed good inhibition toward maltase expressed on Caco-2 cells, with an IC₅₀ value of 27 μM. The ungallated catechins, such as catechin, gallocatechin (GC), epicatechin (EC), and epigallocatechin (EGC), showed no significant inhibition toward GP b, whereas the gallated catechins CG, GCG, ECG, and EGCG inhibited the enzyme, with IC₅₀ values of 35, 6.3, 27, and 34 μM. From multiple inhibition studies by Dixon plots, GCG appears to bind a new allostelic site, the indole inhibitor site. These gallated catechins also inhibited glucagon-stimulated glucose production dose-dependently, with IC₅₀ values ranging from 33 to 55 μM. Dietary supplementation with these gallated catechins or the green tea extract containing them, which inhibits both α-glucosidases and GP in vitro and in cell culture, would contribute to the protection or improvement of type 2 diabetes.     

Survey of pesticide residues in rice (April, 1995-March, 2005)

Pesictide residues in 343 samples of domestic rice and 32 samples of imported rice purchased on the Tokyo market from April 1995 to March 2005 were investigated. Residues of eleven kinds of pesticides (including organophosphorus, organochlorine, carbamate, pyrethroid and organonitrogen pesticides and bromide) were detected at levels between trace and 1 ppm in 47 domestic rice samples. DDVP and bromide residues were detected at levels between 0.01 ppm and 5 ppm in 18 imported rice samples. For rice samples that were found to containing pesticides, the amounts of pesticide intake were calculated according to the daily intake of rice, and they were compared with the ADI values. Since residual pesticide levels were 17/10,000-2/5 of ADI, all the rice samples were considered to be safe for human consumption.     

Application of liquid chromatography-nuclear magnetic resonance spectroscopy for the identification of ethyldimethylpyrazine, a food flavouring agent

The application of liquid chromatography-nuclear magnetic resonance spectroscopy (LC-NMR) for the direct identification of ethyldimethylpyrazine, a food flavouring agent, has been studied. The commercial product is a mixture of two regio-isomers, 2-ethyl-3,5-dimethylpyrazine (1) and 2-ethyl-3,6-dimethylpyrazine (2); however, the exact composition of the mixture is unknown. Structural characterization by LC-MS and GC-MS was not possible because both regio-isomers yield the same molecular related ion and ion fragmentation. To rapidly identify the two regio-isomers, the product was analyzed by LC-NMR with on-flow and fraction loop modes. From the results, the structure elucidations of the two regio-isomers could be carried out without the need to isolate the isomers by the usual procedures.     

EFFECT OF HEATING RATE OF BIOMASS FEEDSTOCK ON CARBON GASIFICATION EFFICIENCY IN SUPERCRITICAL WATER GASIFICATION

The effect of feedstock heating rate on the efficiency of gasification of a biomass in supercritical water was investigated using a continuous bench-scale reactor. A glucose solution (biomass model compound) and a cabbage slurry were gasified in supercritical water at various heating rates in a preheater. The results show that in the range of 10-30 K/s, carbon gasification efficiency improved as the heating rate increased.     

In situ XAFS analysis of Pd–Pt catalysts during hydrotreatment of model oil

Supported Pd–Pt catalysts are efficient for hydrodesulfurization (HDS) and hydrodearomatization (HDA) reactions of diesel fuel and their activity varied with the kinds of supports. Concerning HDA, alumina supported catalysts showed four times higher TOF (turn over frequency) than silica supported one. In order to elucidate the difference in activity, the structural analysis of the active phase was performed. After reduction pretreatment, relatively uniform and large metallic alloy Pd–Pt particles were formed on SiO₂, whereas, Pd and Pt atoms formed rather segregated particles on Al₂O₃. Subsequent X-ray absorption of fine structure (XAFS) analysis under HDS conditions showed no contribution of sulfur for SiO₂ supported catalyst, whereas, formation of sulfided metal species was observed in XAFS spectra for the Al₂O₃ supported catalyst. It is suggested that on Pd–Pt/SiO₂, thin sulfide layer on the metal cluster surface blocked the active sites and lowered the HDA activity. Presence of partially sulfided phase originated from rather segregated structure like Pd–Pt/Al₂O₃ is thought to be requisite for high HDA activity.     

Biosynthesis of sterols and ecdysteroids in Ajuga hairy roots

Hairy roots of Ajuga reptans var. atropurpurea produce clerosterol, 22-dehydroclerosterol, and cholesterol as sterol constituents, and 20-hydroxyecdysone, cyasterone, isocyasterone, and 29-norcyasterone as ecdysteroid constituents. To better understand the biosynthesis of these steroidal compounds, we carried out feeding studies of variously ²H- and ¹³C-labeled sterol substrates with Ajuga hairy roots. In this article, we review our studies in this field. Feeding of labeled desmosterols, 24-methylenecholesterol, and ¹³C₂-acetate established the mechanism of the biosynthesis of the two C₂₉-sterols and a newly accumulated codisterol, including the metabolic correlation of C-26 and C-27 methyl groups. In Ajuga hairy roots, 3α-, 4α-, and 4β-hydrogens of cholesterol were all retained at their original positions after conversion into 20-hydroxyecdysone, in contrast to the observations in a fern and an insect. Furthermore, the origin of 5β-H of 20-hydroxyecdysone was found to be C-6 hydrogen of cholesterol exclusively, which is inconsistent with the results in the fern and the insect. These data strongly support the intermediacy of 7-dehydrocholesterol 5α,6α-epoxide. Moreover, 7-dehydrocholesterol, 3β-hydroxy-5β-cholest-7-en-6-one (5β-ketol), and 3β,14α-dihydroxy-5β-cholest-7-en-6-one (5β-ketodiol) were converted into 20-hydroxyecdysone. Thus, the pathway cholesterol→7-dehydrocholesterol→7-dehydrocholesterol 5α,6α-epoxide→5β-ketol→5β-ketodiol is proposed for the early stages of 20-hydroxyecdysone biosynthesis. 3β-Hydroxy-5β-cholestan-6-one was also incorporated into 20-hydroxyecdysone, suggesting that the introduction of a 7-ene function is not necessarily next to cholesterol. C-25 Hydroxylation during 20-hydroxyecdysone biosynthesis was found to proceed with ca. 70% retention and 30% inversion. Finally, clerosterol was shown to be a precursor of cyasterone and isocyasterone.     

Production of 8,11,14,17-cis-eicosatetraenoic acid (20:4ω-3) by a Δ5 and Δ12 desaturase-defective mutant of an arachidonic acid-producing fungus Mortierella alpina 1S-4

A Δ5 and Δ12 desaturase-defective mutant of an arachidonic acid-producing fungus, Mortierella alpina 1S-4, produced 8,11,14,17-cis-eicosatetraenoic acid (20:4ω3) intracellularly when grown with linseed oil. Dihomo-γ-linolenic acid was the only C₂₀ polyunsaturated fatty acid (4.9 wt% of total mycelial fatty acids) other than 20:4ω3. AA and 5,8,11,14,17-cis-eicosapentaenoic acid were not detected. The mycelial lipids consisted of 82.2% (by mol) triacylglycerol (TG), 7.1% diacylglycerol, 8.9% phospholipids (PL), and 1.9% free fatty acids. The percentage of 20:4ω3 was higher in PL (30.1%) than in TG (11.6%), and highest in phosphatidylcholine (38.9%). Under the optimal conditions with a 5-L jar fermenter, 20:4ω3 production amounted to 97.4 mg/g dry mycelia with a mycelial yield of 23 g/L on the twelfth day (corresponding to 2.24 g/L medium and 37.1% of total mycelial fatty acids).