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Photoacoustic spectroscopy in the 350-700 nm range proved a useful tool for discriminating between a variety of opaque, light-scattering samples. Spectral features originating from powdered food specimens of different colour and grain size were observed. These results suggest the feasibility of photoacoustics for quality control in the food-processing industry.
The isolation of Listeria monocytogenes from food is carried out using a double enrichment. It is believed that the double enrichment can allow the overgrowth of Listeria innocua in samples where both species are present. In this study, we have evaluated the impact of overgrowth between Listeria species and strains during each step of the enrichment process. The effect of factors minimizing interactions between strains or phage inhibitory effects has also been estimated. In an artificially contaminated food undergoing enrichment, overgrowth could result from competitive interactions between Listeria spp. resulting from the production of bacteriocins and bacteriophage at high initial contamination levels (>10(4) cfu/g), but not at lower levels (50-100 cfu/g) as generally found in contaminated foods. At high levels of inoculation, the competitive effect could be reduced by solidification of the selective broths, to limit the diffusion of the inhibitors. Overgrowth resulting from differences in growth rate occurred independent of the initial contamination level. However, in naturally contaminated foods undergoing enrichment, there were no absolute correlations between growth rates or inhibitory profiles in terms of strain evolution during enrichment. In fact, Listeria strains which were predominant in the original sample in most cases remained the dominant strains at the end of the enrichment, although the relative proportion of any given strain could change significantly over the enrichment process. Additional factors which have yet to be identified impact on the evolution of Listeria in the two-step enrichment process. Analysis of strain evolution in eight naturally contaminated foods has indicated that the second enrichment step in Fraser broth can be reduced from 48 to 24 h without impacting on the recovery of L. monocytogenes. Our limited survey of naturally contaminated foods also demonstrated that maximum recovery of L. monocytogenes and other Listeria strains was found following 24 h incubation in 1/2 Fraser Broth. This finding suggests that it may be possible to shorten the current two-step isolation method further without reducing method sensitivity.
Procyanidins are phenolic oligomers, mainly composed of (+)-catechin and (-)-epicatechin units that exhibit certain sensorial and physiological properties of interest (e.g., astringency and bitterness of food, antioxidant activity, etc.). This paper shows the development of a micellar electrokinetic chromatography (MEKC) method for the separation of three procyanidin dimers (B1, B2, and B3), their monomers ((+)-catechin and (-)-epicatechin), and the cis- and trans-forms of p-coumaric acid. Separation conditions are optimized in terms of buffer pH, SDS concentration, and washing routine between injections. The best results in terms of peak resolution and reproducibility between separations were obtained with a MEKC running buffer at pH 5 with 100 mM SDS and a washing routine that includes a rinse step with 0.1 M sodium hydroxide. Using this new MEKC method it is possible to separate in less than 5 min the seven substances. More interestingly, it is demonstrated that the low pH used in this MEKC method allows one to obtain clean electropherograms when samples are injected. The method is shown to be reproducible between different days with relative standard deviation (RSD) values lower than 1% for migration times and lower than 7% for peak areas (3 days, 24 injections). The usefulness of this procedure to determine these compounds in effluents from food processing (i.e., soaking water from lentils, white beans and black beans) and in food by-products (i.e., almond peels) considered as potential procyanidin sources is demonstrated. To our knowledge, this is the first report of separation and determination of procyanidins in food samples done by capillary electrophoresis.
The Ministry of Health, Labor and Welfare (former MHW) of Japan issued a Directive in 1997 advising restaurants and caterers to freeze portions of both raw food and cooked dishes for at least 2 weeks. This system has been useful for determining vehicle foods at outbreaks. Enumeration of bacteria in samples of stored food provide data about pathogen concentrations in the implicated food. Data on Salmonella concentrations in vehicle foods associated with salmonellosis outbreaks were collected in Japan between 1989 and 1998. The 39 outbreaks that occurred during this period were categorized by the settings where the outbreaks took place, and epidemiological data from each outbreak were summarized. Characteristics of outbreak groups were analyzed and compared. The effect of new food-storage system on determination of bacterial concentration was evaluated. Freezing and nonfreezing conditions prior to microbial examination were compared in the dose-response relationship. Data from outbreaks in which implicated foods had been kept frozen suggested apparent correlation between the Salmonella dose ingested and the disease rate. Combined with results of epidemiological investigation, quantitative data from the ingested pathogen could provide complete dose-response data sets.
A comprehensive survey of the use of capillary zone electrophoresis for the determination of organic acids in food and beverage samples is presented. The analytes discussed in this paper include low-molecular-mass organic acids, amino acids, vitamin related compounds and free fatty acids.
The contamination of foods with ochratoxin A can be determined very sensitively by high-performance liquid chromatography (HPLC) with fluorescence detection. A novel procedure is described to confirm OA-positive results quantitatively down to the HPLC detection limit of 0.1 ppb. For this, ochratoxin A in the sample extract is converted into its O-methylochratoxin A methyl ester derivative, which is identified subsequently by gas chromatography-mass spectrometry negative-ion chemical ionization and multiple ion detection modes using the hexadeuterated O-methyl-d3-ochratoxin A methyl-d3 ester derivative as internal standard for quantification. In the analysis of more than 60 contaminated samples, the procedure was found to be very accurate.
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Epithermal instrumental neutron activation analysis (EINAA) has been used to determine the iodine content of many individual food materials that constitute the typical Libyan diet. The selected samples include different varieties of local and imported foods such as wheat and barley products, rice, bread, legumes such as chick peas and lentil, table salt, and commonly used spices, including thyme and fenugreek. Both conventional and anticoincidence gamma-ray spectrometry techniques have been employed. Epithermal INAA in conjunction with anticoincidence counting has been found to provide the most reliable results. For quality control purposes, a number of NIST biological reference materials were analyzed. The range of daily dietary intake has been calculated as 100-180 microg of iodine per day, which is within the recommended range. Bread was identified as a significant source of iodine in the Libyan diet, as it contributed 99 microg/d.
A rapid method is proposed for the determination of 16 polycyclic aromatic hydrocarbons (PAH) in non-fatty food (mashed potato, potato and toasted bread samples) based on their extraction with ethyl ether-methylene chloride (1:1) by sonication, and subsequent separation by high-performance liquid chromatography (HPLC) with fluorimetric detection. A Hypersil Green PAH column was used with a gradient of acetonitrile-water as the mobile phase, together with a programme of ten excitation and emission wavelength pairs. At levels 1.60-2320 microg kg(-1), mean recoveries of PAH were in the range 70-86% for mashed potato, potato and toasted bread samples. The relative standard deviations were in the range 4.2-11% (n = 6). Total PAH found in mashed potato were in the range 9.35-17.1 microg kg(-1), in potato samples 8.47-17.2 microg kg(-1) and in toasted bread samples 7.38-18.0 microg kg(-1), with relative standard deviations in the range 0.8-12%. Only chrysene, determined in Ortiz toasted bread (7.38 microg kg(-1)), has carcinogenic properties.
High-throughput capillary gas chromatography (CGC) methods, developed during the Belgian 1999 "dioxin" food crisis, for the determination of the contaminating polychlorinated biphenyls (PCBs) and the fatty acid composition of the lipids are described. For PCB analysis, the fat obtained by ultrasonic extraction is fractionated by matrix solid-phase dispersion, and the PCBs are analyzed by CGC-electron capture detection on a 10-mL x 100-microm-i.d. HP-5MS column. Analytical conditions for the high-speed column are deduced from analyses on conventional CGC columns using the method translation software. The concept of retention time locking is implemented to facilitate the elucidation of the PCB markers. The fatty acid methyl esters (FAMEs) are prepared by the sodium methylate procedure on part of the ultrasonic extract followed by analysis on 10-mL x 100-microm-i.d. HP-WAX or BPX-70 capillary columns. By optimizing both the sample preparation and CGC analysis, the throughput is more than fifty PCB and FAME samples per day with the same robustness as conventional methods.
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The purpose of this study was to analyse the fluoride content of Japanese infant foods and foods in Brazil and to estimate daily fluoride intake calculated for a 6-month-old infant which reflects supplemental fluoride increased from infant foods and decreasing breast-feeding and commercial milk-feeding. Fluoride concentrations of 26 samples were assessed by a modified microdiffusion method and fluoride ion selective electrode. The fluoride content varied from 0.53 to 1.33 microgram/g for milk-base formulas, from 0.46 to 2.94 micrograms/g for infant foods in Japan, and from 0.06 to 0.25 microgram/g for foods in Brazil. The daily fluoride intake was calculated according to feeding pattern. The minimum and maximum fluoride values were 0.080 mg/day and 0.248 mg/day, respectively. These fluoride intakes, expressed in milligrams per kg of fluoride intake, ranged from 0.010 to 0.033 mg F/kg body weight. No significant differences in fluoride intake values were found between Japanese infant foods and foods in Brazil. The results of this study indicate that daily fluoride intakes of Japanese infant foods and foods in Brazil could be considered within the optimal recommended level.
It is difficult to obtain precise and accurate estimates of the true mycotoxin concentration of a bulk lot when using a mycotoxin-sampling plan that measures the concentration in only a small portion of the bulk lot. A mycotoxin-sampling plan is defined by a mycotoxin test procedure and a defined accept/reject limit. A mycotoxin test procedure is a complicated process and generally consists of several steps: (1) a sample of a given size is taken from the lot, (2) the sample is ground (comminuted) in a mill to reduce its particle size, (3) a subsample is removed from the comminuted sample, and (4) the mycotoxin is extracted from the comminuted subsample and quantified. Even when using accepted test procedures, there is uncertainty associated with each step of the mycotoxin test procedure. Because of this variability, the true mycotoxin concentration in the lot cannot be determined with 100% certainty by measuring the mycotoxin concentration in a sample taken from the lot. The variability for each step of the mycotoxin test procedure, as measured by the variance statistic, is shown to increase with mycotoxin concentration. Sampling is usually the largest source of variability associated with the mycotoxin test procedure. Sampling variability is large because a small percentage of kernels are contaminated and the level of contamination on a single seed can be very large. Methods to reduce sampling, sample preparation and analytical variability are discussed.
Rapid identification of filamentous fungi is becoming increasingly important in food mycology both for monitoring the production process and for the identification of food spoilers. This paper describes the development and trial of two specific PCR primer sets. A 336 bp fragment from species belonging to Penicillium subgenus Penicillium was amplified by the primers ITS 212d and ITS 549. The other primer set, ITS 183 and ITS 401 specifically identified two species, Penicillium roqueforti and P. carneum, both known as spoilers in the bread industry, by amplification of a 300 bp fragment. The future perspectives of PCR based identification of filamentous fungi in food are discussed.
A spectrophotometric method using a flow-injection system is proposed for the determination of nitrosamines in foods (cured-meats). The method is based on the photochemical cleavage of the N-NO bond of the nitrosamine to yield the corresponding amine and nitrite. The nitrite is then detected spectrophotometrically, at 542 nm, by use of its reaction with a modified Griess reagent. Different linear ranges between 0.8 and 2000 ng mL(-1) are obtained for the method, depending on the time of exposure of the sample to the UV radiation. The relative standard deviation varies between 2.0 and 3.9% and the sample throughput is between three and seven samples per hour, depending on the experimental conditions. The proposed method was successfully applied to the analysis of N-nitrosodimethylamine in cured ham and loin, bacon, and sausages.