Spectrofluorometric determination of histamine in fish and meat products

A method has been developed for spectrofluorometric determination of histamine in fish and meat products. After a perchloric extract is obtained from samples, histamine is extracted with n-butanol and transferred to hydrochloric acid. Finally, histamine is subjected to a condensation reaction with o-phthalaldehyde (OPT). The method was tested for lack of interference from other amines. Precision of the method in fish products was 6.60% CV; recovery was 96.50%. In meat products, precision was 5.42% CV; recovery was 96.20%. By analysis of variance (P = 0.05), no significant statistical differences were found for recovery values vs histamine content in both foods.     

Purification of ethoxyquin and its two oxidation products

2,6-Dihydro-2,2,4-trimethyl-6-quinolone (QI) and 1,8'-bis(1, 2-dihydro-6-ethoxy-2,2,4-trimethylquinoline) (DM) are two oxidation products of 1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline (ethoxyquin, EQ). This paper describes several methods for the purification of technical grade EQ and for the production of pure QI and DM as standards with the purity required (>99%) for calibration of quantitative determination methods. EQ of high purity was obtained through vacuum distillation followed by a quick column chromatographic purification on silica gel. Preparative scale purity DM could be obtained through recrystallization from methanol, but QI could be purified only by a high-pressure liquid chromatographic method.     

两种测定土壤微生物量氮方法的比较初探

用氯仿熏蒸-0.5mol/L的K2SO4直接浸提,280nm紫外比色法和熏蒸-淹水培养法测定了20种有机质、全氮和速效氮差异较大的土样的土壤微生物量N。研究结果表明,两种方法测得20种土样的土壤微生物量N数值呈极显著正相关;280nm紫外比色法操作步骤简单、产生误差的环节少、测定所需时间短、且测定数据比熏蒸-淹水培养法有更好的重现性。初步认为,280nm紫外比色法来反映土壤微生物量的大小。结果还表明,两种方法的测定结果都与土壤的全氮含量呈极显著正相关关系,与有机碳含量有一定的正相关关系,与速效氮无明显的相关关系;但在不同的土壤类型上,与全氮、有机碳和速效氮的相关性有所不同。用280nm紫外比色法测定两种土壤的新鲜和风干样的微生物生物量的结果说明,可用风干土经预培养后测定土壤微生物生物量。风干土样的预培养时间初步确定为10天。     

Lipid oxidation in milk, yoghurt, and salad dressing enriched with neat fish oil or pre-emulsified fish oil

This study compared the oxidative stabilities of fish-oil-enriched milk, yoghurt, and salad dressing and investigated the effects on oxidation of adding either neat fish oil or a fish-oil-in-water emulsion to these products. Milk emulsions had higher levels of a fishy off-flavor and oxidized faster, as determined by the peroxide value and volatile oxidation products, than fish-oil-enriched yoghurt and dressing, despite the fact that dressings had a higher fish oil content and were stored at room temperature. Additionally, fish-oil-enriched yoghurt generally had higher oxidative stability than fish-oil-enriched dressings, irrespective of the mode of fish oil addition. Yoghurt thus seemed to be a good delivery system of lipids containing n-3 polyunsaturated fatty acids. Different effects of adding fish oil either as neat fish oil or as a fish-oil-in-water emulsion were observed for milk, yoghurt, and dressing. Yoghurt and dressing enriched with neat fish oil were more stable than those enriched with a fish-oil-in-water emulsion, whereas milk enriched with neat fish oil was less stable than milk enriched with the fish-oil-in-water emulsion. Overall, it seemed that application of neat fish oil was a good option for preserving the final quality in yoghurt and dressings, but a pre-emulsion may still be considered for the fish oil enrichment of certain food products, for example, milk.     

HPLC separation and determination of 12 cholesterol oxidation products in fish: comparative study of RI, UV, and APCI-MS detectors

A simple, fast, and sensitive method for the extraction through direct saponification, separation, quantification, and identification of 12 cholesterol oxidation products (COPs) and cholesterol in a single isocratic, normal-phase, high-performance liquid chromatography (HPLC) was developed. Three detectors were compared for determination of COPs and cholesterol in fish samples: refractive index (RI), ultraviolet (UV), and atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The results did not show significant differences (p > 0.05) between the concentration of the cholesterol oxides and cholesterol obtained with these detectors. The present study demonstrated the presence of 19-hydroxycholesterol, 22"R"-hydroxycholesterol, 22"S"-hydroxycholesterol, 24"S"-hydroxycholesterol, and 25"R"-hydroxycholesterol for the first time in fish samples.     

A comparison of wet oxidation methods for determination of total phosphorus in soils

For 15 soils with widely different extractability of phosphorus (P) two newly introduced digestion techniques for determining total P (P_t) were compared with the standard perchloric acid digestion procedure. The two digestion techniques were: (1) concentrated H₂SO₄ plus 30 % H₂O₂ at 360 °C, (2) concentrated HCl plus concentrated HNO₃ in the ratio 3:1 (aqua regia) at 140 °C. Almost equal amounts of P_t were extracted by the two methods (mean = 188.7 mg kg^—1 for H₂SO₄/H₂O₂ and 188.4 mg kg^—1 for aqua regia) which were slightly higher than the standard method (mean = 183.8 mg kg^—1). However, there is no statistical difference among the three digestion methods, suggesting that the tested methods should be useful for estimating P_t in soils with high content of organic C, eliminating the danger of explosion when hot concentrated HClO₄ is used.     

The relationship between the physicochemical properties of antioxidants and their ability to inhibit lipid oxidation in bulk oil and oil-in-water emulsions

Chain-breaking antioxidants differ in their effectiveness at inhibiting lipid oxidation because of their chemical properties and physical location within a food. Our objective was how the physicochemical properties of four structurally related lipid-soluble antioxidants were related to their antioxidant activity. Antioxidants differed in the number of methyl (alpha-tocopherol and delta-tocopherol) or hydroxyl (butylated hydroxytoluene (BHT) and 4-hydroxymethyl-2,6-ditertiarybutylphenol) groups. Surface activity of the antioxidants was in the order of delta-tocopherol > alpha-tocopherol approximately 4-hydroxymethyl-2,6-ditertiarybutylphenol > BHT. Free-radical scavenging activity was similar between alpha-tocopherol and delta-tocopherol as well as BHT and 4-hydroxymethyl-2,6-ditertiarybutylphenol. In bulk menhaden oil, BHT was a more effective antioxidant than 4-hydroxymethyl-2,6-ditertiarybutylphenol while alpha-tocopherol was more effective than delta-tocopherol. In menhaden oil-in-water emulsions, BHT was a more effective antioxidant than 4-hydroxymethyl-2,6-ditertiarybutylphenol while delta-tocopherol was more effective than alpha-tocopherol. These results indicate that the surface activity and polarity of lipid-soluble antioxidants were not the only determinants of their antioxidant effectiveness in food lipids.     

Normal phase high-performance liquid chromatography method for the determination of tocopherols and tocotrienols in cereals

The eight vitamers of vitamin E (alpha-, beta-, gamma-, and delta-tocopherols and -tocotrienols) have different antioxidant and biological activities and have different distributions in foods. Some cereals, especially oat, rye, and barley, are good sources of tocotrienols. A fast procedure for the determination of tocopherols and tocotrienols (tocols) in cereal foods was developed. It involves sample saponification and extraction followed by normal phase high-performance liquid chromatography (HPLC). The results have been compared with those found by direct extraction without saponification. The method is sensitive and selective enough to be tested on a wide variety of cereal samples. The highest tocol levels were found in soft wheat and barley ( approximately 75 mg/kg of dry weight). beta-Tocotrienol is the main vitamer found in hulled and dehulled wheats (from 33 to 43 mg/kg of dry weight), gamma-tocopherol predominates in maize (45 mg/kg of dry weight) ), and alpha-tocotrienol predominates in oat and barley (56 and 40 mg/kg of dry weight, respectively).     

Comparison of two immunochemical methods with thin-layer chromatographic methods for determination of aflatoxins

Three different methods were compared for the determination of total flatoxins in corn and peanuts naturally contaminated with aflatoxins and in corn, peanuts, cottonseed, peanut butter, and poultry feed spiked with aflatoxins B1, B2, and G1. The 3 methods were an enzyme-linked immunosorbent assay (ELISA) screening test; a monoclonal antibody-affinity column-solid-phase separation method; and the AOAC official thin-layer chromatography (TLC) methods for all except poultry feed, for which Shannon's TLC method for mixed feed was used. The ELISA test is designed to provide only positive results for total aflatoxins at greater than or equal to 20 ng/g or negative results at less than 20 ng/g. The affinity column separation is coupled with either bromination solution fluorometry to estimate total aflatoxins or liquid chromatography (LC) to quantitate individual aflatoxins. Fluorodensitometry was used to determine aflatoxins in commodities analyzed by the TLC methods. The LC and TLC results were in good agreement for all the analyses. The results for the affinity column using bromination solution fluorometry were similar except those for cottonseed, which were about 60% higher. The ELISA screening method correctly identified naturally contaminated corn and peanut positive samples. No false positives were found for controls. The correct response for spiked corn, raw peanuts, peanut butter, and cottonseed at greater than or equal to 20 ng aflatoxins/g was about 90%. The correct response for spiked poultry feed at greater than or equal to 20 ng aflatoxins/g was about 50%.     

Effect of tocopherols in the antioxidative activity of oxidized lipid-amine reaction products

Phosphatidylethanolamine (PE), phosphatidylcholine (PC), lysine (Lys), and mixtures of them were tested for antioxidative activity in a tocopherol-stripped olive oil (TSO) and the same oil after addition of 250 microg of alpha-tocopherol g of oil/(tocopherol-added olive oil, TAO) to evaluate the role of tocopherol in the antioxidant activity of oxidized lipid-amine products. Neither PE nor PC nor Lys protected TSO when tested alone, but both PE and Lys increased the induction period (IP) of TAO. On the contrary, PE/Lys and PC/Lys mixtures, but not PC/PE mixtures, protected both TSO and TAO. These results were a consequence of both the formation of oxidized lipid-amine products, which were determined by gas chromatography-mass spectrometry after their conversion into volatile derivatives, and a synergism between alpha-tocopherol and the produced compounds. These results were confirmed by analyzing the antioxidative activity of two of the produced carbonyl-amine products: 6-amino-2-(1H-pyrrol-1-yl)hexanoic acid (1) and 2,3-dipalmitoylpropyl 2-(1H-pyrrol-1-yl)ethyl phosphate (2). The hydrophilic compound 1 was more antioxidant than the analogous lipophilic compound 2, and this antioxidative activity was observed in TAO and not in TSO. All these results suggested that antioxidative activity of carbonyl-amine products may be greatly increased with the addition of tocopherols, and those products derived from Lys are more antioxidant in bulk oils than those derived from PE.     

Enrichment of tocopherols and phytosterols in canola oil during seed germination

The effect of canola (Brassica napus L.) seed germination under illuminated and dark environments on the total concentration and the composition of tocopherols and phytosterols in seedlings and extracted oil were investigated. During the first 10 days of germination, a decrease in gamma-tocopherol was offset by an increase in alpha-tocopherol, indicating the interconversion of these isomers. From day 10 to day 20 under illumination, there was a net increase in alpha-tocopherol and total tocopherols suggesting the synthesis of new tocopherols, whereas there was no net increase in tocopherols in dark. Tocopherols were mainly concentrated in the leafy seedling tops rather than in the non-photosynthesizing bottoms, whereas phytosterols were equally distributed across both sections. The total tocopherol content of oil extracted from 20-day-old seedlings was 4.3- to 6.5-fold higher than that of intact seeds. On a dry seedling basis, the content and composition of phytosterols did not change significantly (p > 0.05) over the sprouting period, but the concentration of total phytosterols in the oil fraction increased 4.2- to 5.2-fold. The concentration of these valuable phytochemicals in the oil fraction is largely due to the depletion of oil reserves during germination, as well as the de novo synthesis of new alpha-tocopherol stimulated by the presence of light. Germination may represent a viable means to naturally concentrate these high-value constituents in canola oil, offering improvements in oil quality based on the nutritional value and oxidative protection offered by tocopherols and the health benefits provided by both tocopherols and phytosterols.     

Improvements to two routine methods for calcium carbonate determination in soils

Abstract

In the course of routine analytical work, wide discrepancies were noted between results from alternative, established procedures for measuring calcium carbonate (CaCO₃) in soils. In one procedure (Method I), the CaCO₃ content is calculated from the weight of CO₂ lost after treating a sample with excess hydrochloric acid. Results of an investigation using this procedure in our laboratory tended to be inaccurate and poorly reproducible. The method was therefore modified by using as the reaction vessel a plastic vial with pin‐holes in its lid, instead of a glass Erlenmeyer flask with a stopper removed at intervals, to let CO₂ escape. Further, the weighed soil sample was placed in a disposable cup inside the vial of acid, instead of being weighed and transferred. These modifications greatly improved accuracy and reproducibility of results obtained by Method I. In another procedure, the CaCO₃ content was calculated from the pH of a suspension of the soil in dilute acetic acid (Method II). This method tends to give results appreciably greater than zero for acidic soils containing no free lime. This undesirable tendency was reduced after Method II was modified by calibrating it against soils spiked with known amounts of CaCO₃, instead of against CaCO₃ alone. As a result of the modifications, agreement between results for soils analyzed by both methods was greatly improved. Method I is considered more suitable for soils with appreciable free lime, or for liming materials, and Method II for soils with low CaCO₃ content (.5% or less).     

Liquid chromatography-electrospray ionization-tandem mass spectrometry method for the determination of epoxidized soybean oil in food products

Epoxidized soybean oil (ESBO) is widely used as a plasticizer and stabilizer in such polymers [poly(vinyl chloride) in particular] commonly adopted for manufacturing of gaskets of the lids for glass jars and plastic films for food packaging. Human exposure to ESBO and its derivatives is likely to occur over a lifetime with a significant variation according to life stage. A reversed phase liquid chromatography interfaced with electrospray ion trap tandem mass spectrometry method for the determination of ESBO in foods was developed. A simple sample treatment procedure entailing the use of an extraction step with dichloromethane without any further cleanup was proved. Chromatographic separation was performed using two C18 columns with an aqueous acetic acid-acetone-acetonitrile mixture as the mobile phase under gradient conditions. The method was validated in terms of detection limits (4 mg kg(-1)), quantitation limits, linearity (established over 2 orders of magnitude), recovery (good mean recoveries, higher than 90% for all of the signals detected), precision (RSD% < 8), and trueness. The applicability of the method to the determination of ESBO in different food matrices (in particular those rich in edible oil) was demonstrated, and the performances were compared to those reachable by the commonly well-known gas chromatography-mass spectrometry procedure.     

Comparison of the Volhard and potentiometric methods for the determination of chloride in meat products: collaborative study

A collaborative study of the determination of chloride in meat products was conducted by the International Organization for Standardization (ISO) to compare the ISO 1841 method (Volhard titration) with the FAO/WHO Codex Alimentarius Committee method (potentiometric titration). Five canned luncheon meat products containing 0.25-2.0% sodium chloride at 4 different spiking levels were analyzed by 11 laboratories. The data were analyzed by ISO statistics (ISO 5725) and by AOAC statistics (Youden-Steiner), the major differences being in the rejection of outliers and in the statement of precision parameters. Good agreement was found between the mean chloride contents of the products as determined by both methods and with the added amounts, although statistically significantly higher sodium chloride recoveries were obtained with the potentiometric method. The within-laboratory variability (repeatability) is greater for the Volhard method, especially for chloride levels below 1.0%. Therefore it is proposed to set the lowest level of determination for the Volhard method at about 1.0% sodium chloride. The among-laboratories variability (reproducibility) of the potentiometric method was comparable with the results from the collaborative studies for chloride in cheese, giving acceptable values for relative standard deviations of 1.5-3.0% for meat products with 0.3-2.0% added sodium chloride. It is recommended that further work be conducted to reduce or eliminate the systematic error present with the potentiometric method as applied to meat and meat products.     

Automated methods for determination of fat and moisture in meat and poultry products: collaborative study

A collaborative study was conducted to compare automated methods for rapid determination of fat and moisture in meat and poultry products with the official AOAC solvent extraction and forced-air oven methods, respectively. Fourteen products were tested, with fat and moisture contents ranging from 2 to 43% and 44 to 74%, respectively. Eight of the collaborating laboratories analyzed the products by using a moisture/fat analyzer; 4 laboratories used the AOAC methods. Standard deviations for within-laboratory repeatability, between-laboratory reproducibility, and bias for each product indicated that the rapid methods were acceptable. The moisture/fat analyzer methods have been adopted official first action for fat and moisture analyses in meat and poultry products.     

Separation and determination of diesel contaminants in various fish products by capillary gas chromatography.

A semiquantitative capillary column gas chromatographic method is described for the determination of diesel fuel contamination in various canned seafood products. The diesel contaminants are separated from the fish sample by steam distillation, with little carry-over of interfering intrinsic materials such as fish oils. The diesel fuel is extracted from the condensate with n-hexane, and the extract is analyzed on an SPB-1 fused silica capillary column. The efficiency of recovery of diesel fuel added to canned seafood at levels of 40-400 ppt ranged from 72 to 102%. With the additional step of concentrating the hexane extract, the sensitivity of this procedure may be increased at least 10-fold. This procedure can detect the differences among diesel fuel grades No. 1, 2, and 5, and variations within diesel grade No. 2, and thus may be useful in determining the type of petroleum contaminants present in various canned fish products.     

Homogenization conditions affect the oxidative stability of fish oil enriched milk emulsions: lipid oxidation

In this study fish oil was incorporated into commercial homogenized milk using different homogenization temperatures and pressures. The main aim was to understand the significance of homogenization temperature and pressure on the oxidative stability of the resulting milks. Increasing homogenization temperature from 50 to 72 degrees C decreased droplet size only slightly, whereas a pressure increase from 5 to 22.5 MPa decreased droplet size significantly. Surprisingly, emulsions having small droplets, and therefore large interfacial area, were less oxidized than emulsions having bigger droplets. Emulsions with similar droplet size distributions, but resulting from different homogenization conditions, had significantly different oxidative stabilities, indicating that properties of significance to oxidation other than droplet size itself were affected by the different treatments. In general, homogenization at 72 degrees C appeared to induce protective effects against oxidation as compared to homogenization at 50 degrees C. The results thus indicated that the actual composition of the oil-water interface is more important than total surface area itself.     

Collaborative study for the comparison of two methods for the determination of total cholesterol in multicomponent foods.

The gas chromatographic method for determining total cholesterol in multicomponent foods, collaboratively studied by the AOAC in 1974 (Method 1), has been evaluated by 9 collaborating laboratories and compared with the Interim Methodology Instructions No. 2 modified method (Method 2). The 5 samples selected for collaboration were deviled ham sandwich spread, vegetable beef stew, frozen chicken pot pie, frozen fish sticks, and mayonnaise. The recovery data were obtained from a sample of wheat germ oil spiked with 0.297% cholesterol as cholesteryl palmitate. Collaborators performed 2 replicate analyses on all samples by both methods. The statistical evaluation of the results showed that Method 1 is superior to Method 2. Average recoveries from the spiked wheat germ oil samples were 91.4% (9 laboratories) and 85.8% (7 laboratories) with coefficients of variation of 12.5 and 14.4%, respectively. Based on the collaborative results and statistical evaluation, Method 1 has been adopted as official first action.