An automated analytical method for determination of polychlorinated biphenyls (PCBs) in fish was developed using supercritical fluid extraction (SFE) in combination with an automated sample preparation instrument (Prep) and GC/MS. By incorporating basic alumina with the sample in the extraction process, and optimizing the amount of carbon dioxide used, fish lipid was selectively reduced. The extract was cleaned up on a Florisil cartridge with Prep. The method was evaluated using naturally contaminated tissues and by comparison of automated analytical method results with those obtained by the conventional method. Mean recovery of PCBs from 3 kinds of fish including hairtail, mackerel and yellowtail were 69.8%, 90.2% and 81.1%, respectively. This method is less laborious and requires far less organic solvent than the conventional method, but produced comparable results.
Natural flavor was accidentally produced from rice cake products in Japan. A non-stick oil had been sprayed on the products during the production process. It was found that a Penicillium corylophilum strain, a contaminant of the oil, produced the flavor from the oil. The ingredients of the flavor were four volatile substances, 2-heptanone, 2-nonanone, 2-heptanol, and 2-nonanol. Challenge tests with the mould strain in a rice cake system were performed under various conditions. The volatile substances were produced in the largest amounts at 25°C, followed by 20 or 30°C then 10°C. 2-Heptanone was produced most remarkably at 25°C, followed by 2-nonanone, 2-heptanol, and 2-nonanol. The growth patterns of the mould were similar between 20-30°C, and the growth at 10°C was delayed. The non-stick oil itself had neither flavor nor volatile substance. The flavor was also produced from coconut oil, which was one of the materials of the non-stick oil. No bacteria or yeasts tested produced any flavor from the non-stick oil, whereas most of the moulds tested produced flavor components.
In the previous investigation, we found that some cans for coffee and black tea drinks released large amounts of bisphenol A (BPA) into their contents. Equivalent cans were obtained and the cause of BPA migration was investigated. Equivalent cans A, B and D contained high levels of BPA in the side seam, in the bottom, and in the bottom and the side seam, respectively, while can C contained some level of BPA in the body, which has a large area, therefore, all of them contained high amounts of BPA in their coatings. In the migration test, there was no BPA migration from the cans into water at 60 and 95°C for 30 min, into 20% ethanol at 60°C for 30 min, or into n-heptane at 25°C for 60 min. However, at 120°C for 30 min, equivalent cans released 35∼124 ng/mL BPA into the water. The total migration was similar to the total residues of BPA in the can coating and was close to the total amount of BPA in the drinks. Thus, BPA migration from the can coating requires heating to more than 105°C, which is the glass transition temperature of the epoxy resin. Improved cans which contained less than 1/10 as much BPA as the equivalent cans showed very low migration levels, i.e., 3∼6 ng/mL.
The daily dietary intake of aluminum was estimated through a total diet study from 1996 to 1998. In ten institutes, total diet study samples were prepared and their aluminum concentration was determined. The average daily intake of aluminum was 3.5 mg and the range was 1.8∼8.4 mg. The validity of the analytical result was supported by analyses of certified reference materials.
Seven lines of genetically modified (GM) maize have been authorized in Japan as foods and feeds imported from the USA. We improved a multiplex PCR method described in the previous report in order to distinguish the five lines of GM maize. Genomic DNA was extracted from GM maize with a silica spin column kit, which could reduce experimental time and improve safety in the laboratory and potentially in the environment. We sequenced recombinant DNA (r-DNA) introduced into GM maize, and re-designed new primer pairs to increase the specificity of PCR to distinguish five lines of GM maize by multiplex PCR. A primer pair for the maize intrinsic zein gene (Ze1) was also designed to confirm the presence of amplifiable maize DNA. The lengths of PCR products using these six primer pairs were different. The Ze1 and the r-DNAs from the five lines of GM maize were qualitatively detected in one tube. The specific PCR bands were distinguishable from each other on the basis of the expected length. The r-DNA could be detected from maize samples containing 0.5% of each of the five lines of GM maize. The sensitivity would be acceptable to secure the verification of non-GMO materials and to monitor the reliability of the labeling system.
We evaluated the TaqMan PCR Salmonella amplification/detection kit (PE Applied Biosystems) for rapid detection of Salmonella from a variety of meat samples. This system uses the 5' nuclease activity of Taq DNA polymerase, which digests an internal fluorogenic probe to monitor the amplification of the target gene. The detection sensitivity of the kit, using 2 kinds of DNA extraction protocols, was compared with that obtained with 4 protocols of official culture methods. A total of 98 meat samples (16 raw beef, 31 pork and 51 chicken) were tested. The results of the TaqMan PCR method and the combined results of the 4 cultural protocols showed excellent agreement. However, no single culture protocol showed optimal recovery of Salmonella comparable to the PCR method. These results suggest that the TaqMan PCR method is a reliable and rapid method useful for detecting Salmonella in meat products.
An HPLC method was developed for the determination of neohesperidin dihydrochalcone (NHDC) in foods. A solid sample was extracted with methanol. The extract was evaporated and the residue was dissolved in methanol-water (2 : 8) mixture. In the case of fluid sample, the sample solution was prepared by dilution with methanol-water (2 : 8) mixture. The sample solution was cleaned up on a C18 cartridge. The cartridge was washed with water and methanol-water (3 : 7) mixture, and NHDC was eluted with methanol-water (7 : 3) mixture. NHDC in the eluate was separated on an ODS column and determined with a UV detector (282 nm). The identity of NHDC in foods was confirmed by means of HPLC with a photodiode-array detector. The recoveries of NHDC added to various kinds of foods were 75.2∼134%. The determination limit of NHDC was 1 μg/g.
A simple and rapid method using HPLC was developed for the determination of isocitric acid in food additive citric acid. One gram of sample was dissolved in 100 mL of water. HPLC separation was performed on an Inertsil ODS-3 column (4.6 mm i.d. × 250 mm) using 0.1% phosphoric acid as the mobile phase at a flow rate of 1 mL/min. Isocitric acid was detected at 210 nm. The calibration graph was rectilinear from 5 to 100 μg/mL. The recoveries of isocitric acid from sample at the levels of 0.1% and 0.4% were 98% and 99%, respectively, and the determination limit was 0.05%.
The presence of plasticizers in PVC toys obtained in October 1998 was investigated. Diisononyl phthalate (DINP), di-2-ethylhexyl phthalate (DEHP), di-n-butyl phthalate (DBP), dinonyl phthalate (DNP), diheptyl phthalate (DHP), and di-2-ethylhexyl adipate (DEHA) were detected. The phthalates were found in all of the 68 samples. The principal phthalate found in toys was DINP, which was present in 48 of 68 samples. The DINP content ranged from 15 mg/g to 580 mg/g, and mean content was 308 mg/g. The highest content was found in a pacifier toy. DEHP was present in 20 of 68 samples and the content ranged from 2.0 mg/g to 380 mg/g. The mean content was 162 mg/g. It was found in 60% of domestic toys.
In an earlier report, we developed a rapid, sensitive and clean method consisting of nonchloroform extraction, clean-up on a commercial multifunctional cartridge column and HPLC with fluorescence detection for the analyses of aflatoxins. In this report, we applied this method to analyze aflatoxins in nuts, giant corn, cereals, spice and black teas. The method was effective for macadamia nuts, walnuts, hazelnuts, brazil nuts, giant corn, rice, wheat and buckwheat, and the recoveries of aflatoxins B1, B2, G1 and G2 spiked in them at the level of 10 ng/g were 85∼106%. However, in the chromatograms of spices and black tea, many background peaks were observed. Therefore, we added a purification step with an affinity column to the clean-up of these samples with the multifunctional cartridge column. After the additional purification, most of the background peaks were gone. The recoveries of aflatoxins B1, B2 and G1 spiked at the level of 10 ng/g were 71∼112% except for the case of B2 in white pepper (48%). The recoveries of G2 were 49∼95%.