Showing papers in "Journal - Association of Official Analytical Chemists in 1977"

Collaborative study of modified AOAC method of analysis for nitrite in meat and meat products

Abstract: A modified version of the AOAC method of analysis for nitrite in meat and meat products was tested collaboratively by 23 laboratories. Results were compared with those obtained by the official AOAC method. Recommended modifications include: (a) substitution of N-(1-naphthyl) ethylenediamine and sulfanilamide for Griess reagent, (b) separate addition and 1:10 dilution of the above reagents, (c) 20 min color development and absorbance read at 540 nm, (d) substitutionstitution of NaNO2 for AgNO2 and NaCL, (e) omission of mercuric chloride, (f) screening of filter paper for nitrite contamination, (g) more precise dilution of sample aliquot, and (h) standard curve linear up to 10 microng N/50 ml. Results were statistically treated by Youden's technique for comparing 2 methods, using a matched pair sample scheme. The random error for the modified method was significantly lower than the random error for the official method. A t-test showed no difference in bias between the 2 methods.

Collaborative study of a method for the detection of Clostridium botulinum and its toxins in foods.

Abstract: The mouse toxicity and protection technique for the detection and identification of Clostridium botulinum and its toxins in foods was collaboratively studied by 11 laboratories. Each laboratory received 4 samples of cream of mushroom soup; 2 contained spores and toxin of C. botulinum type A, 1 contained spores and toxin of C. botulinum type E, and 1 contained spores of C. sporogenes. The media used were cooked meat medium (beef heart or chopped liver broth) and trypticase peptone glucose yeast extract broth with trypsin. The results indicate that this method has a high degree of repeatability and reproducibility. All 11 laboratories correctly identified the toxins and the nontoxic sample in the food and detected and identified the viable spores in the samples by means of the subsequent cultures. This method has been adopted as official first action.

Preparation and characterization of aflatox-n B1-1-(O-carboxymethyl) oxime.

Abstract: A method is described for the preparation and purification of aflatoxin B1-1(O-carboxymethyl) oxime from aflatoxin B1. The overall yield was about 73-83%. The new aflatoxin B1 derivative was characterized by mass, ultraviolet, infrared, and nuclear magnetic resonance spectral analyses, and was nontoxic to 8-day-old chicken embryos when tested at a concentration of 3.48 microgram/egg.

Methodology for recognition of invasive potential of Escherichia coli.

Abstract: Surveillance for dysentery-related invasive potential in bacteria using the Sereny keratoconjunctivitis test is restricted by expense, time factor, and necessity for confirmation. Primary screening of isolates in a standardized mammalian cell culture system is recommended. Bacteria are grown 20 hr in veal infusion, washed, and resuspended in 20% heat-inactivated fetal bovine serum (FBS) supplemented with 0.12% brain heart infusion and 0.1% bile salts. The HeLa culture is grown 20 hr as a monolayer in chamber slides with 90% minimal essential medium (MEM)-10% FBS. The host culture is infected at a ratio of 10 bacteria/mammalian cell for 3 hr at 35 degrees C. The infection medium is replaced with MEM-FBS supplemented with 300 microng lysozyme and 5 microng gentamycin/ml. The infected monolayer is incubated 5 hr at 35 degrees C to permit intracellular multiplication. Specimens are washed, fixed with methanol, and stained successively with May-Grunwald and Giemsa dyes. Bacteria occur within the cytoplasm if invasion has occurred. The criterion for a positive test is that 1% of the host cells possesses at least 5 bacteria in 2 of 3 trials. Invasiveness is correlated with and possibly preconditioned by cytotoxic principle(s). Infectivity rates vary from 0 to 30%. The cytopathic effect is noted in 5-50% of HeLa cells. Positive results must be confirmed by the Sereny test.

Stability of patulin to sulfur dioxide and to yeast fermentation.

Abstract: The affinity of patulin for sulfur dioxide (SO2) is much less than was previously reported and is of little significance at the SO2 concentrations (below 200 ppm) used in the processing of apple juice and cider. However, at concentrations of 2000 ppm SO2 and 15 ppm patulin, combination was 90% complete in 2 days. Removal of SO2 liberated only part of the patulin, which suggests that 2 mechanisms are involved: one reversible (opening the hemiacetal ring) and one irreversible (SO2 addition at the double bond). Test with 2 yeasts used in English commercial cider making confirmed that patulin is effectively removed during yeast fermentation.

Screening method for the detection of aflatoxins, ochratoxin, patulin, sterigmatocystin, and zearalenone in cereals.

Abstract: A screening method has been developed for the detection of aflatoxins, ochratoxin A, patulin, sterigmatocystin, and zearalenone in cereals. After extraction, the sample is cleaned up by gel filtration. The mycotoxins are separated by thin layer chromatography. The limits of detection are about 5 microgram aflatoxins, 10 microgram ochratoxin A, 50 microgram patulin, 10 microgram sterigmatocystin, and 35 microgram zearalenone/kg.

Glucosinolates and derived products in cruciferous vegetables: gas-liquid chromatographic determination of the aglucon derivatives from cabbage.

Abstract: A procedure is described for identifying and quantitatively determining the glucosinolates found in edible cabbage. The intact glucosinolates are extracted and their aglucons are released into solvent after a special enzymatic hydrolysis step. The resulting isothiocyanates and oxazolidinethiones are separated by a gas-liquid chromatographic procedure that allows the individual aglucons to be identified and their amounts to be estimated by comparison with an internal reference.

Butyl ester preparation for gas-liquid chromatographic determination of fatty acids in butter

Abstract: Butter oil is extracted from butter with hexane, using a rolling boil technique. The resulting 10% butter oil in hexane is converted to butyl esters, using butanol in place of methanol as specified in the official final action method, 28.063-28.067. A water wash and centrifuge technique is used to remove butanol from the n-hexane-butyl ester solution. Conversions to butyl esters are quantitative by the boron trifluoride, sulfuric acid, and sodium butoxide procedures. When methyl ester methods are used, there are serious losses of the short chain volatile and water-soluble acids, making the methyl ester procedures questionable for determining the authenticity of milk fat.

Microbiological assay for saponin in alfalfa products.

Abstract: A bioassay is described for determining medicagenin-type saponin in dried alfalfa, leaf protein concentrates, and alfalfa sprouts. Samples are extracted by refluxing 2 1/2 hr with 50% ethanol, ethanol is evaporated, and aliquots of an aqueous solution are added to potato dextrose agar (PDA) and assayed for saponin by using the fungus Trichoderma viride. The growth of the fungus on PDA is compared with a standard saponin, and saponin levels are calculated by means of a slope ratio analysis.

Glucosinolates and derived products in cruciferous vegetables: total glucosinolates by retention on anion exchange resin and enzymatic hydrolysis to measure released glucose.

Abstract: Details are given for determining total glucosinolates in Cruciferae plants by a procedure measuring released glucose. The glucosinolates are separated from about 90% of other material in the plant extract by adsorption on an anion exchange resin. Then, by a selective thioglucosidase hydrolysis of the glucosinolates retained on the exchange resin, the glucose and aglucons are separated from other substances retained by the resin. Glucose is released into an aqueous medium and is equivalent to the total glucosinolates. The aglucons formed by the hydrolysis are extracted into methylene chloride and determined by gas-liquid chromatography. Based on 29 determinations of the glucose from sinigrin, analyzed under different conditions, accuracy of the total glucosinolate determination was 94.8 +/- 7.3%. The coefficient of variation, determined by duplicate analyses on extracts from 58 cabbage samples, was 4.6%.

Reverse phase analytical and preparative high pressure liquid chromatography of aflatoxins.

Abstract: Reverse phase high pressure liquid chroma· k)graphy (HPLC) was investigated and found applicahle for determining 6 aflatoxins. Afla. toxins Mz• Mt• Gz• Gt , and Bt were completely resolved and Bz was satisfactorily separated on aCtS (10 ,urn. 4 mm id X 30 em) column with an eluting solvent of acetonitrile.water (35+ 65) and flow rate of 1.5 ml/min. Compounds were detected by ultraviolet absorbance at 350 nm. Peak height and retention time reproduci. bility of multiple injections was excellent with coefficients of variation of 1.00/0 (Mt ) and 1.9% (Bt ) when laboratory temperatures were relatively constant throughout a day; however, coefficients of variation increased significantly when temperatures varied by 10°F. HPLC determinations of aflatoxin Bt added to uncon· taminated corn extracts at 20 and 50 pph levels were 83::::14 and 92.5::::8%, respectively, of those expected. Comparison of corn extract assays (6-98 pph Bt ) by thin layer chromatog. raphy (TLC) and HPLC revealed that HPLC values averaged 25 % less than TLC values. Numerous peaks and background interferences were present in corn extracts which made interpreting chromatograms difficult. None of the cleanup procedures tried was successful in removing these interferences. Preparative HPLC was used to isolate and purify quantities of aflatoxins l'tlt, B1 , and G1 from silicic acid col. umn mbctures of Mt-Mz• B1\"Bz, and G1\"Gz• Separations were achieved on Cls/Porasil B (35-75 ,urn) columns (%\" od X 8') developed with acetonitrile-water mixtures (M1, 20+80; Bt , 35+65; Gt , 25+75) at 9.0 ml/min. These columns permitted isolation of 40 mg aflatoxin B1 or Gt in less than 3 hr. Aflatoxin Mt required 2 HPLC steps.

Aflatoxins in Egyptian foodstuffs.

Abstract: Six samples each of wheat, corn, lentils, beans, fenugreek, peanuts, and cottonseed cake from various areas of Egypt were analyzed for aflatoxins both at the time of collection and after 12 months' storage. Aflatoxin was found at low levels (3 to 12 ppb total aflatoxins in 14 of 42 samples, as follows: 1 sample each of corn, lentils, and beans; 2 peanut samples; 3 fenugreek samples; and 6 cottonseed cake samples. None of the samples contained aflatoxins above 11.7 ppb.

Direct plating versus dilution plating in qualitatively determining the mold flora of dried beans and soybeans.

Abstract: Two methods presently used for examining whole foods and feeds for viable molds were evaluated for their relative effectiveness in the qualitative determination of the total number of mold species present in soybeans and dried beans: the direct plating method and the serial dilution method. Sixty-nine soybean samples and 40 dried bean samples were examined. Although the quantitative results of this study were inconclusive, the qualitative results show that the direct plating method was substantially more effective in detecting individual mold species. An average of 12.9 and 10.9 species was detected by the direct plating method in whole soybean and dried bean samples, respectively. An average of 4.4 and 2.8 species was detected by the dilution method in ground soybean and dried bean samples, respectively. A total of at least 37 mold species were found in the study, including 10 toxicogenic species. With few exceptions, detection rates of the 37 individual species were substantially greater among the samples examined by direct plating than those examined by serial dilution.

Survey of 1975 wheat and soybeans for aflatoxin, zearalenone, and ochratoxin.

Abstract: Wheat samples (102 lots) were collected from Virginia, North Carolina, southeastern Missouri, southern Illinois, and Kentucky. Soybean samples (180 lots) were collected from Virginia, Illinois, Iowa, Minnesota, Nebraska, Alabama, Arkansas, and Texas. Samples of both commodities were analyzed for zearalenone, aflatoxin, and ochratoxin by the Eppley method. None of the 3 mycotoxins was detected in soybeans. Aflatoxins and ochratoxin A were not detected in wheat, but zearalenone was detected in 19 of 42 samples collected in Virginia. Half of the Virginia samples were collected because they were mold-damaged. Zearalenone levels ranged from 0.36 to 11.05 ppm; the identity of the zearalenone was confirmed by gas-liquid chromatography and mass spectroscopy. Gibberella zea infection (6-60%) was detected in all of the zearalenone-positive samples; 6-60% of the kernels in the samples tested contained G. zea.

Analysis of foods for arsenic and selenium by acid digestion, hydride evolution atomic absorption spectrophotometry.

Abstract: A method based on acid digestion, hydride evolution atomic absorption spectrophotometry for estimating microgram and submicrogram quantities of As and Se in foods was developed and evaluated. Samples up to 3 g dry weight were digested with HNO3-HCIO4-H2SO4. As and Se in aliquots of the digests were reduced with NaBH4 to volatile hydrides, using laboratory-constructed and commercially available generators. As and Se were estimated by transient signal atomic absorbance measurements as the hydrides were decomposed in an Ar-H2-entrained air flame. Recoveries of inorganic As and Se added at levels of 0.1-1.0 microgram/g to a variety of foods ranged from 70 to 125%. Analyses of several standard reference samples indicated the method is capable of recovering native analytes. Detection limits for the determinative step and the method as a whole were as low as 5 and 25 ng, respectively, for both elements.

High performance liquid chromatographic determination of provitamin A in orange juice.

Abstract: A quantitative method has been developed for the determination of alpha- and beta-carotenes and beta-cryptoxanthin, the provitamin A carotenoids in orange juice. The carotenoids were separated by high performance liquid chromatography on a single column in approximately 30 min. The procedure may also be used to measure zeta-carotene and alpha-cryptoxanthin.

Identification of polychlorinated styrene compounds in heron tissues by gas-liquid chromatography-mass spectrometry.

Abstract: Unknown compounds detected in Ardea herodias tissues are identified by gas-liquid chromatography-mass spectrometry as residues of octachlorostyrene. Heptachlorostyrene and hexachlorostyrene were tentatively identified.

Thin layer chromatographic determination of aflatoxin B1 in eggs.

Abstract: A method for determining aflatoxin in dairy products was modified for eggs, initially by additional cleanup steps. The modified method proved practical for use in survey analyses and was sufficiently sensitive to detect aflatoxin B1 at levels less than 1 ng/g in eggs from hens on experimentally contaminated feed and in spiked eggs; interfering compounds in eggs received from many different producing areas were eliminated. Although recovery was greater than 75% when the aflatoxin was extracted immediately after spiking, recovery was usually less than 30% when the aflatoxin was extracted after more than 24 hr. Adding sodium chloride, sodium sulfate, or urea to the extracting solvent remedied this defect, which is thought to be related to the binding of aflatoxin to egg protein.

Determination of Urethane in Wines by Gas-Liquid Chromatography and Its Confirmation by Mass Spectrometry

Abstract: A gas-liquid chromatographic (GLC)-mass spectral (MS) method for the determination and confirmation of urethane in wines has been developed. Analyses of domestic and imported wines indicated urethane to be present at levels ranging from 1 to 20 microng/L. Recoveries of urethane from wines fortified at 10 ppb (microng/L) ranged from 50 to 100% with an average value of 71%. GLC-MS was used to confirm the identity of urethane in wine extracts in which GLC indicated the presence of urethane.

Gas-liquid chromatographic determination of cholesterol and other sterols in foods.

Abstract: A gas-liquid chromatographic (GLC) method, using the butyryl esters of sterols, has been developed for the measurement of cholesterol, stigmasterol, sitosterol, and campesterol in foods. An immobile phase of 1% SE-30 coated on 100-120 mesh Gas-Chrom Q packed in a 6 inch X 4 mm id glass column operated at 255 degrees C was the most satisfactory of 7 column packings evaluated. Extraction with chloroform-methanol gave 98.7% recovery with a coefficient of variation of 1.8% for cholesterol added to a variety of foods. When cholesteryl palmitate was added to vegetable oil and the butyryl derivative was prepared, followed by GLC analysis, the recovery was 99.3% with a coefficient of variation of 0.9%. Amounts as low as 1 mg/100 g food can be detected with a precision of 2.5%. The results of the analysis of a variety of foods for cholesterol, campesterol, sitosterol, and stigmasterol are given.

Sensitive silica gel-packed flowcell for fluorometric detection of aflatoxins by high pressure liquid chromatography.

Abstract: Aflatoxins B1, B2, G1, and G2 were quantitatively detected by high pressure liquid chromatography on a 5 micronm Lichrosorb column, using a Lichrosorb-packed flowcell in the fluorometric detector. The relationship between peak height and the amount injected was linear only up to about 2 ng but showed a linear loglog relationship. Methods for constructing and packing the flowcell are given. A guard column and venting valve were used to minimize deterioration of the analytical column and the adsorbent-packed flowcell. The method was applied to a peanut butter extract, although with the cleanup procedure used, the life expectancy of the flowcell is limited.

Fluorometric Determination of Histamine in Tuna: Development of Method

Abstract: Tuna extracts are treated with an anion exchange resin to remove interfering materials, histamine is derivatized with o-phthaladehyde, and the fluorescence of the resulting compound is measured fluorometrically. Replicate analyses of acceptable and decomposed tuna packed in oil or water agreed within 1 mg at a level of 10 mg/100 g and within 12 mg at a level of 100 mg/100 g. Recoveries of histamine added to fish were greater than 90 and greater than 83% at levels of 10 and 100 mg/100 g, respectively. The new method is more rapid and specific and is simpler than previous methods because no liquid-liquid extractions or chromatographic separations of histamine are required. The sensitivity of the method allows quantitation of less than 10 mg histamine/100 g sample. The accuracy and precision of the fluorometric method are comparable to those of the official AOAC colorimetric method.

Semiautomated method for the fluorometric determination of total vitamin C in food products.

Abstract: A simple method employing simultaneous extraction and oxidation has been developed for the semiautomated determination of ascorbic and dehydroascorbic acids in food products. Recovery studies were conducted on ready-to-eat breakfast cereals and both fresh and canned fruits and vegetables, with average recoveries of 101, 100, and 102%, respectively. Reproducibility data were generated showing a relative standard deviation of 3.5%. The automated method was compared with the manual AOAC fluorometric method and with indophenol titration; correlation coefficients were 0.9960 and 0.9926, respectively. The hydrolysis product of dehydroascorbic acid, 2,3-diketogulonic acid, a reported interference in this method, was prepared and shown not to form an interfering fluorescent derivative.

Reverse phase high pressure liquid chromatography of vitamin A in margarine, infant formula, and fortified milk.

Abstract: Retinal was determined in margarine (50 mg), infant formula (1 ml), and fortified milk (1 ml) by saponification in centrifuge tubes, extraction of the unsaponifiable lipid with hexane, and high pressure liquid chromatography (HPLC) in 90% methanol on a 25 cm x 3.2 mm column containing 10 micrometer LiChrosorb reverse phase. beta-Carotene was determined using the same column and 99% methanol as eluant. The vitamins in the eluate were identified and measured from their absorption at 325 (retinol) and 453 nm (beta-carotene), using a computing integrator. Retinol and carotene were prominent peaks in the chromatograms from properly fortified samples and were satisfactorily separated from other materials. In a survey of 12 different margarines for retinol, the results from liquid chromatography agreed with those of a variety of spectrophotometric and fluorometric procedures but they were obtained with greater ease and they could be interpreted more confidently. The recovery of retinol from oil was better than 99%. The coefficients of variation was 6.8% for 12 replicate analyses of a margarine for retinol and 5.4% for 10 replicate analyses of a margarine for beta-carotene.

Application of reverse phase ion-pair partition chromatography to drugs of forensic interest.

Abstract: A method is described for determining a wide range of abused drugs by using 1 column, a single isocratic system, and a fixed wavelength (254 nm) ultraviolet detector. Paired-ion chromatography is performed on a reverse phase muBondapak C18 column. Acidic, basic, and neutral drugs, including their corresponding salts, can be determined without prior cleanup. A counter ion, 1-heptane sulfonate, is dissolved in the aqueous organic mobile phase to give a final pH of approximately 3.5. This technique is applicable to ergot alkaloids, phenylethylamines, opium alkaloids, local anesthetics, barbiturates, and other drugs of forensic interest. Five major opium alkaloids in gum opium, namely, morphine, codeine, thebaine, narcotine, and papaverine, can be separated in approximately 20 min.

Detection of sprouted wheat by a rapid colorimetric determination of alpha-amylase.

Abstract: A method is described for the rapid, convenient detection or estimation of sprout-damaged wheat by determining its alpha-amylase content colorimetrically. A commercially available substrate in the form of dyed amylose tablets is used. The extent of sprout damage can be determined qualitatively, or quantitatively when actual alpha-amylase concentration is required. Amylase content is determined by visual comparison with prepared colored standards or by spectrophotometric analysis. The method requires only 5 min incubation time and no elaborate equipment, and is sufficiently simple for use at locations having minimal laboratory facilities.

High pressure liquid chromatographic determination of aflatoxins in wines and other liquid products.

Abstract: A previously developed high pressure liquid chromatographic (HPLC) method was evaluated by an extensive recovery study of aflatoxins from wines and other liquid products. The HPLC column and the preliminary cleanup procedures were both modified for this study. Four aflatoxins (B1, B2, and G2) were recovered at 80-116% from 28 samples of various liquid commodities spiked at the 1 microgram/L (1 ppb) level. The detection limit of the proposed method for wines and fruit juices was about 0.02 ppb. A total of 53 samples were analyzed for aflatoxins during this study.