A rapid method for the quantitative determination of short-chain free volatile fatty acids from cheese

The determination of free volatile fatty acids (FVFA) is of interest in the analysis of cheeses. As these compounds are components of taste and flavor, they give indications on metabolic reactions taking place during cheese ripening and can provide an evaluation of cheese defects and their causes. One of the most widely used methods for the determination of FVFA in cheese involves preliminary recovery from the matrix by steam distillation, followed by gas chromatography separation. Relatively high distillate volumes must be collected to achieve a quantitative yield of all the compounds of interest, so that, as a result, the solution is too diluted to achieve good instrumental sensitivity. In this paper, an alternative method for the determination of C2-C6 free carboxylic acids in cheeses involving the use of a Nukol capillary column and crotonic acid as internal standard is described. This method is quick and cheap, as the sample preparation is a simple extraction with water. The underivatized FVFA are then directly separated by gas chromatography. Using this method, all FVFA in cheeses can be quantified with good repeatability and excellent recovery.     

Development of a solid-phase extraction method for phenoxy acids and bentazone in water and comparison to a liquid-liquid extraction method

A rapid solid-phase extraction (SPE) method was developed for the determination of bentazone and the phenoxy acids 2,4-D, dichlorprop, MCPA, and mecoprop in Norwegian environmental water samples. Cartridges with a high-capacity cross-linked polystyrene-based polymer were used for off-line preconcentration. The effects of elution solvent, elution volume, sample volume, sorbent mass, pH, and flow rate on the recoveries of the pesticides were investigated using HPLC. Average recovery of >90% was achieved with 500 mg sorbents using 2 mL of methanol with 5% NH3 as elution solvent. The recoveries were independent of sample pH in the tested range of pH 1-7. Using a sample volume of 200 mL, the limits of determination for the phenoxy acids and bentazone are 0.02 microg/L. Sample volumes up to 2000 mL at a flow rate of 60 mL/min could be handled without any loss of analytes, which makes it possible to lower the limits of determination. The SPE method was compared to a routinely used liquid-liquid extraction method. Three different water matrices spiked at 1.0 and 0.05 microg/L were extracted, and the quantification was performed by GC-MS. Both methods permitted the determination of phenoxy acids and bentazone in distilled water, creek water, and well water down to a level of 0.05 microg/L with recoveries >80% for 200 mL samples. Important advantages of the SPE method compared to the liquid-liquid extraction method were the short extraction times, lack of emulsions, use of disposable equipment, and reduced consumption of organic solvents.     

Structure of humic acids isolated by sequential alkaline extraction from a typical chernozem

It was shown with the isolation of a humic acid (HA) preparation from a typical chernozem by sequential alkaline extraction as an example that the preparative yield of HAs decreased at each sequential extraction stage by 3–4 times. On the basis of studying the obtained preparations using elemental analysis, gel-penetration chromatography, and ¹³C NMR spectroscopy, the tendencies of the changes in the structural-group and molecular-weight compositions of the HAs from one extraction stage to the next one were revealed. The conclusion was drawn that a single extraction is sufficient for obtaining a representative HA sample.     

Dichloromethane as a solvent for lipid extraction and assessment of lipid classes and fatty acids from samples of different natures

The usefulness of the solvent mixture dichloromethane/methanol for lipid extraction and the determination of lipid classes and fatty acids in samples of different natures was conducted. Two different extraction methods were compared, one containing chloroform/methanol, another containing dichloromethane/methanol. Total lipid extraction showed some minor differences but no variation in the lipid classes. Regarding the fatty acid profile, in Echium virescens seeds, 17 major fatty acids could be identified and quantified, and all were equally extracted when either solvent system was employed. In Echium acanthocarpum hairy roots, 17 major fatty acids were quantified, showing some statistical differences for one cell line in favor of chloroform. The data obtained from the liquid nutrient medium were also comparable. The cod roe sample showed 31 major fatty acids, showing no statistical differences between the two solvent systems. Contrarily, the CH 2Cl 2 method was able to extract 31 main fatty acids found in European seabass dorsal muscle more efficiently than the CHCl 3 method. The results indicate that, for lipid extraction and fatty acid assessment, dichloromethane/methanol can readily replace the commonly employed chloroform/methanol, thus avoiding the major health, security, and regulatory problems associated with the use of chloroform.     

Effect of different extraction methods on fatty acids,volatile compounds,and physical and chemical properties of avocado (Persea americana Mill.) oil

Because Mexico is the number one producer of avocados in the world, this fruit has potential as a source for oil extraction. It is appropriate to further investigate the detailed changes that the oil undergoes when different extraction methods are applied. This research paper presents the study of the physical and chemical changes, the fatty acids profile, the trans fatty acid content, and the identification of volatile compounds of the oils from avocado pulp (Persea americana Mill.), obtained by four different extraction methods. The method with the greatest extraction yield was the combined microwave-hexane method. The amount of trans fatty acids produced in the microwave-squeezing treatment was <0.5 g/100 g. On the other hand, the amounts of trans fatty acids produced with the hexane and acetone treatments were 0.52 and 0.87 g/100 g, respectively. The method that caused the slightest modification to the oil quality was a novel combined extraction method of microwave-squeezing proposed by the authors.     

Effects of different chloroform stabilizers on the extraction efficiencies of phospholipid fatty acids from soils

Chloroform is commonly used as an organic solvent to extract phospholipid fatty acids from soil samples. However, the extraction efficiency of the fatty acids depends on the particular chloroform stabilizers used. The effect of chloroform stabilizers 2-methyl-2-butene and ethanol was investigated at different steps of the extraction procedure. Only the ethanol stabilized chloroform prevented the loss of certain phospholipid fatty acids. In particular, the unsaturated fatty acids 16:1ω7c, 16:1ω6c, 16:1ω5, 17:1ω8, 18:1ω7c, 18:1ω5, the fungal biomarker 18:2ω6,9 and the saturated fatty acid 17:0 were absent when chloroform stabilized with 2-methyl-2-butene was used. In addition, the total phospholipid fatty acid concentrations were also significantly reduced when chloroform stabilized with 2-methyl-2-butene was used. Thus, the proper choice of chloroform stabilizer for the analysis of phospholipid fatty acids is very important.     

Rapid extraction and analysis of volatile fatty acids in soil

Abstract

The concentrations of volatile fatty acids (VFA) in soils are important in studies involving phytotoxicity and fermentation processes. Concentrations of acetic, propionic, and butyric acids as low as 0.21, 0.14, and 0.10 mmol kg^‐1soil in water extracts were accurately determined. The extracts were filtered through 45 μm millipore disc filters and injected directly into a gas chromatograph following addition of purified formic acid. The formic acid eliminated ghosting of peaks. The gas chromatograph was equipped with a flame ionization detector and a 60/80 Carbopack C/0.3% Carbowax 20M/0.1% H₃PO₄packed precolumn (0.15 m) and column (1.83 m). The precolumn was changed after 150 to 200 sample injections when contaminated beyond acceptable limits. There was good separation of VFA with no interfering organic volatiles in extracts of soil containing glucose, cellulose or straw incubated anaerobically for as long as 4 weeks. The advantages of the procedure are relative rapidity and simplicity as well as improved sensitivity in measuring small quantities of volatile fatty acids in soil     

Modified method for the analysis of free fatty acids in fish

The objective of this study was the development of a method for the quantification of free fatty acids (FFA) using less aggressive reactants against the handler and the environment than those used in the classic method of Lowry and Tinsley. The modified procedure is a variation of the Lowry and Tinsley method employing cyclohexane in place of benzene. The use of benzene is prohibited in certain work processes and laboratories, and the competent authority in each country is actively promoting research into harmless or less harmful products that could replace benzene. A comparison with the traditional AOCS titration method for oil analysis was performed. FFA content in mackerel frozen at -10 degrees C was measured according to the three methods over a 12 month period. The results showed similar values, and good correlations were obtained.     

Quantification of individual phosphorus species in sediment: a sequential conversion and extraction method

Common sequential phosphorus (P) extraction methods are not specific to particular chemical species and have several limitations. This work presents the first chemical method for quantification of individual mineral and sorbed P species. It was developed by combining a conversion technique with a sequential extraction procedure. Mangrove sediments with different characteristics were incubated in pH‐adjusted 0.01 M CaCl₂ with and without reference material additions of octacalcium phosphate (Ca₈H₂(PO₄)₆·5H₂O; OCP), hydroxyapatite (Ca₅(PO₄)₃OH), strengite (FePO₄·2H₂O) or variscite (AlPO₄·2H₂O). The changes in soluble phosphate concentration were measured in the supernatant solution, while pH‐induced variations in P composition were determined by subsequent sequential extraction of the sediments. Dissolved phosphate concentration was controlled by adsorption below pH 7.8. Above this pH, soluble phosphate concentration was governed by OCP, which was qualitatively determined by plotting the experimental values of pH + pH₂PO₄ and pH – 0.5 pCa on a solubility diagram including the isotherms of known crystalline phosphate compounds. In contrast to the often‐predicted slow dissolution rate of crystalline phosphates in soils or sediments, drastic changes in P composition by dissolution, precipitation and adsorption processes were detected after 7 days. These were mainly not observed indirectly by changes in dissolved phosphate through adsorption effects, but were determined quantitatively by subsequent sequential extraction, thus enabling the quantification of individual species. Evaluation of the method was performed by standard addition experiments. Besides P species quantification, the method provides the means for other applications, such as the determination of P mineral dissolution kinetics in soils and sediments, the prediction of P composition in changing environmental settings and the refinement of theoretical models of phosphate solubility in soil and sedimentary environments.     

Development of a new HPLC method with precolumn fluorescent derivatization for rapid, selective and sensitive detection of triterpenic acids in fruits

Triterpenic acids are widespread in plants and have multiplicity of biological properties. Unfortunately the method for accurate analysis of these compounds remains poorly investigated. This study proposed a highly sensitive and selective precolumn derivatization method for accurate determination of five triterpenic acids (betulinic acid, betulonic acid, maslinic acid, ursolic acid and oleanolic acid) in fruits using acridone-9-ethyl-p-toluenesulfonate (AETS) as fluorescent labeling reagent by HPLC with fluorescence detection (FLD). Response surface methodology was employed to optimize the derivatization reaction, ensuring the sufficient labeling of the analyzed components. The rapid separation of five triterpenic acids could be achieved in as little as 16 min. This developed method offered the exciting detection limits of 1.68-2.04 ng/mL. When applied to several popular fruits in China, it revealed satisfactory applicability and reproducibility. This developed method also exhibits powerful potential for accurate detection of triterpenic acids from other foodstuffs and nature products.     

The carbon distribution among the functional groups of humic acids isolated by sequential alkaline extraction from gray forest soil

Preparations of humic acids (HAs) were isolated from a gray forest soil by sequential alkaline extraction. From a sample of 500 g, HA preparations of 2.24, 0.23, and 0.20 g were obtained from the first, second, and third alkaline extracts, respectively. The structure of the preparations was determined by ¹³C NMR spectroscopy. At each next extraction step, the portion of aliphatic fragments in the HA preparations increased and the content of aromatic structures decreased. The conclusion was drawn that a single extraction is sufficient for obtaining a representative HA sample.     

Development and validation of a spectrophotometric method for quantification of total glucosinolates in cruciferous vegetables

Given their putative role in chemoprevention, validated methods are needed for quantification of total glucosinolates. Based on the colorimetric reaction of ferricyanide with 1-thioglucose, released by alkaline hydrolysis of glucosinolates, we developed a simple and sensitive method for spectrophotometric quantification of total glucosinolates in cruciferous vegetables. Lyophilized and ground vegetables are extracted with 80% boiling methanol. Extracted glucosinolates are isolated using a strong anion exchange column and then hydrolyzed with 2 N NaOH to release 1-thioglucose. Ferricyanide is added, and the decrease in absorbance is measured at 420 nm, with final values adjusted for background. Recovery of internal standard (sinigrin) was 107%. Intra- and interassay coefficients of variation were 5.4% and 15.8%, respectively. Dose response was linear with sinigrin and amount of plant material extracted (R(2) ≥ 0.99). Using sinigrin, the lower limit of quantification was 0.6 mg. This straightforward method may be an alternative to time-consuming and costly chromatographic methods.     

A novel in situ water perfusion and extraction method for soil amino acid quantification

Classic methods of soil amino acid (SAA) determination involve field collection of soils and disturbance during storage, sieving, mixing and extraction in the laboratory. We describe a novel inexpensive method for extraction of SAA's in situ with minimal soil disturbance. In a comparison between methods of SAA extraction from a semiarid grassland site, glu-x and arginine were the dominant SAA nitrogen sources detected by the novel method while serine and glycine were the dominant SAA nitrogen sources detected using the classic method. The extraction method employed is likely to be useful for accurate determination of SAA availability to plants and soil microbes.     

Detection and quantification of protein residues in food grade amino acids and nucleic acids using a dot-blot fluorescent staining method

Food allergies represent an important health problem in industrialized countries, such that detection and quantitative analysis of the protein considered to be the main allergen is crucial. A dot-blot fluorescent staining method for the detection and quantitative analysis of protein residues in food grade amino acids and nucleic acids is presented. This method combines fluorescence staining with dot-blotting onto PVDF membrane. Several standard proteins, such as bovine serum albumin (66 kDa), lysozyme (14 kDa), ubiquitin (8.6 kDa), bovine insulin (5.7 kDa), and oxidized insulin B chain (3.5 kDa), were detectable at 0.1 ppm using SYPRO Ruby blot stain. Twenty-five different amino acids and two different nucleic acids of food grade were analyzed using this method combined with an internal standard addition method using BSA as an internal standard. All amino acids and nucleic acids were dissolved in 3.6% aqueous HCl and dot-blotted onto PVDF membrane before a large amount of amino acids and nucleic acid were removed. Protein residues and the internal standard protein immobilized on the membrane were stained using SYPRO ruby blot stain. The internal standard in all samples was detectable at 0.1 ppm. Samples were dissolved at 120 or 70 mg/mL, according to their solubility under acidic conditions. The detection limit of protein residues per weight was 0.8-1.4 ppm in amino acids and nucleic acids; residual protein was not detected in any sample.     

Application of FTIR spectroscopy for the quantification of sugars in mango juice as a function of ripening

FTIR-ATR spectroscopy and multivariate analysis were used for quantification of sugars in mango juices as a function of ripening. Calibration was based on sucrose/glucose/fructose mixtures, with six concentration levels and following a triangular experimental design. PLS1 regression of the spectra first derivatives gave the best results, enabling quantification of fructose, sucrose, and glucose with 1.4, 1.4, and 4.9% prediction errors, respectively. Throughout ripening, sucrose and fructose were accurately quantified by PLS-FTIR, whereas the accuracy of glucose determination decreased at later stages, when concentrations fell to 0.6-1.5 g/L. These results enabled a correlation with fruit ripening stage to be established. This may be particularly useful to detect over-ripening in fresh fruits, a period when other indicators (pH and % soluble solids (SS)) do not change significantly; this knowledge may help in predicting fruit stability to transport and storage. Similar information obtained for nonfresh juices (in which pH and %SS may be masked by additives), may help determine whether the source fruits had suitable ripening stages.     

A versatile targeted metabolomics method for the rapid quantification of multiple classes of phenolics in fruits and beverages

Compelling evidence of the health benefits of phenolic compounds and their impact on food quality have stimulated the development of analytical methods for the identification and quantification of these compounds in different matrices in recent years. A targeted metabolomics method has been developed for the quantification of 135 phenolics, such as benzoates, phenylpropanoids, coumarins, stilbenes, dihydrochalcones, and flavonoids, in fruit and tea extracts and wine using UPLC/QqQ-MS/MS. Chromatography was optimized to achieve separation of the compounds over a period of 15 min, and MRM transitions were selected for accurate quantification. The method was validated by studying the detection and quantification limits, the linearity ranges, and the intraday and interday repeatability of the analysis. The validated method was applied to the analysis of apples, berries, green tea, and red wine, providing a valuable tool for food quality evaluation and breeding studies.     

马铃薯生全粉中不饱和脂肪酸微波萃取工艺参数优化及应用

为了优化马铃薯生全粉不饱和脂肪酸的微波萃取工艺,该试验采用软件Design-Expert 8.05分析以及响应面法来优化马铃薯生全粉中不饱和脂肪酸微波萃取工艺,得出马铃薯生全粉中不饱和脂肪酸的萃取模型P=0.000 10.01,R2=0.939 8,并确定马铃薯生全粉中不饱和脂肪酸最佳萃取工艺:萃取温度81℃,萃取时间11 min,萃取溶剂中丙酮占比0.802 5,料液比3.25∶1,各因素对不饱和脂肪酸质量分数影响大小分别为:丙酮占比料液比萃取温度萃取时间,实测不饱和脂肪酸质量分数为1.081 mg/g和拟合方程的预测值1.084 mg/g基本一致。将该优化方案应用于热风干燥温度对马铃薯生全粉中不饱和脂肪酸含量影响的分析中,结果表明:随着干燥温度的升高,亚油酸质量分数显著增加(P0.05),总不饱和脂肪酸质量分数增加(P0.05)。优化试验为热风干燥条件对马铃薯品质影响的研究提供了理论依据。     

Development of a monoclonal antibody-based cELISA for the analysis of sulfadimethoxine. 2. Evaluation of rapid extraction methods and implications for the analysis of incurred residues in chicken liver tissue

Several rapid extraction methods were evaluated for use with a monoclonal antibody-based competitive inhibition ELISA (cELISA) to detect sulfadimethoxine (SDM) in chicken liver tissue. These methods included extraction of the samples with (1) aqueous buffer with or without ultrafiltration, (2) acetonitrile/water, (3) methanol/water, or (4) acetone. The organic extraction methods were evaluated with or without solvent evaporation prior to dilution into assay buffer for the cELISA. The aqueous-based extraction methods were compatible with the cELISA. However, of the organic extraction methods, only the acetone liver extract with solvent evaporation prior to analysis was compatible with the cELISA. The cELISA method coupled to aqueous- or acetone-based sample extraction as well as an HPLC method was evaluated for the analysis of chicken liver tissues fortified with SDM at levels from 0.2 to 0.025 ppm. Mean SDM recoveries for the HPLC method and for the cELISA method using samples prepared by aqueous extraction, aqueous extraction and ultrafiltration, or acetone extraction, evaporation, and reconstitution were 68.9, 95.7, 60.1, and 52.5%, respectively. For the analysis of samples obtained from an SDM incurred residue study, HPLC and cELISA analysis of the same organic extract gave results that were highly correlated (R(2) = 0.976; p < 0.0001). However, results obtained from the analysis of aqueous extracts by cELISA did not correlate well with those obtained by HPLC (R(2) = 0.61, p > 0. 0006). This was attributed to the coextraction of cross-reactive SDM-related residues that were not quantified by the HPLC method. The presence of these residues should be considered during data interpretation when ELISA methods coupled with rapid aqueous extraction of samples are used in SDM residue monitoring programs.     

Liquid chromatographic method for quantitative determination of free fatty acids in butter

A liquid chromatographic method has been developed for the determination of free fatty acids in butter. The fatty acids are converted to the p-bromophenacyl esters, via a crown ether-catalyzed reaction, without separation from the other butter components. The esters are separated on a C18-bonded silica column by using an acetonitrile-water solvent gradient and quantitated using the ester of heptadecanoic acid as internal standard. C16 and C18:1 co-elute in the acetonitrile-water system but are separated using an isocratic methanol-acetonitrile-water system. Limits of detection range from 7 ng for butyric acid to 45 ng for linoleic acid. The average coefficient of variation (n = 10) for 10 free fatty acids from a butter was 5.83%.     

Development of a rapid titration method for predicting optimal coagulant concentration for filled tofu

A rapid titration method was developed for predicting the optimal coagulant concentration for making filled tofu. Cooked soymilk (350 mL, 20 degrees C) in a 400 mL beaker was stirred by a magnetic stirrer to form a swirl. The quick-acting coagulant solution (20.0 Brix) was added into the soymilk at 1.0 mL/min. The swirl depth decreased when the soymilk viscosity increased as a result of increasing the concentration of coagulant in the soymilk. At a suitable stirrer speed, the swirl finally disappeared but the soymilk still maintained rotation, and then the swirl reappeared after around 1 min. The critical point of coagulant concentration (CPCC) was calculated on the basis of the volume of coagulant consumed to get the swirl to disappear. The influences of several factors on the CPCC were investigated, including coagulant addition rate, soymilk temperature, soymilk concentration, soymilk volume, stir bar length, and container size. For validation, 33 soybean samples were used to determine their CPCCs and make filled tofus. The results indicated that CPCC was a characteristic parameter of soymilk and could be used as an effective indicator for predicting optimal coagulant concentration.