Fluorescence spectroscopy: a rapid tool for analyzing dairy products

This paper gives a critical evaluation of the use of fluorescence spectroscopy for measuring chemical and physical changes in dairy products caused by processing and storage. Fluorescence spectroscopy is able to determine various properties of foods without use of chemicals and time-consuming sample preparation. This is shown by examples where the measurement of a given chemical parameter has been appropriately described and validated, as well as situations showing potential applications, but where further research and validation is required. The interpretation of fluorescence spectroscopic data is complex due to absorbance by other molecular groups, changes caused by variation in the sample matrix, etc. It is illustrated how advanced data analytical techniques are required to obtain optimal interpretation of the data. Even though the review focuses on examples from the dairy industry, the principles are broader and can be applied to other fields of food and agricultural research.     

ED-XRF as a tool for rapid minerals control in milk-based products

An ED-XRF method for the rapid determination of a series of analytes (phosphorus, sulfur, chlorine, potassium, calcium, iron, zinc) in milk-based products has been developed and validated. The investigated samples were commercial products obtained from various parts of the world. Reference values measured by inductively-coupled plasma-optical emission spectroscopy and by potentiometry for chloride were used to calibrate the ED-XRF. Calibrations were established with 30 samples, and validation was made using a second set of 30 samples. An evaluation of this alternative method was done by comparison with data from the reference methods. Pellets of 4 g were prepared under 2 tons of pressure. For each sample, 3 pellets were prepared and analyzed. Limits of quantification and repeatabilities were evaluated for the described analytes.     

Front-face fluorescence spectroscopy study of globular proteins in emulsions: displacement of BSA by a nonionic surfactant

The displacement of a globular protein (bovine serum albumin, BSA) from the surface of oil droplets in concentrated oil-in-water emulsions by a nonionic surfactant (polyoxyethylene sorbitan monolauarate, Tween 20) was studied using front-face fluorescence spectroscopy (FFFS). This method relies on measurement of the change in intensity (I(MAX)) and wavelength (lambda(MAX)) of the maximum in the tryptophan emission spectrum. A series of oil-in-water emulsions (21 wt % n-hexadecane, 0.22 wt % BSA, pH 7.0) containing different molar ratios of Tween 20 to BSA (R = 0-131) were prepared. As the surfactant concentration was increased, the protein was progressively displaced from the droplet surfaces. At R > or = 66, the protein was completely displaced from the droplet surfaces. There was an increase in both I(MAX) and lambda(MAX) with increasing Tween 20 concentration up to R = 66, which correlated with the increase in the ratio of nonadsorbed to adsorbed protein. In contrast, there was a decrease in I(MAX) and lambda(MAX) with Tween 20 concentration in protein solutions and for R > or = 66 in the emulsions, which was attributed to binding of the surfactant to the protein. This study shows that FFFS is a powerful technique for nondestructively providing information about the interfacial composition of droplets in concentrated protein-stabilized emulsions in situ. Nevertheless, in general the suitability of the technique may also depend on protein type and the nature of the physicochemical matrix surrounding the proteins.     

Ion-exchange chromatography as a tool for investigating vanadium speciation in sediments: preliminary studies

Journal of Soils and Sediments - We conducted this investigation in order to develop a simple method for the determination of bioavailable vanadium and its speciation within sediments. The...     

Interactions between bovine beta-lactoglobulin A and various bioactive peptides as studied by front-face fluorescence spectroscopy

Front-face fluorescence spectroscopy was used for the first time to study the interactions between bovine beta-lactoglobulin variant A (beta-Lg A) and various beta-Lg-derived bioactive peptides. Fluorescence spectra were recorded for beta-Lg A-peptide mixtures at 25 degrees C and pH 6.8 with an excitation wavelength of 290 nm to characterize the molecular environment of tryptophan (Trp) residues present in the protein but absent in the peptides. Spectra remained unchanged following addition of peptides beta-Lg f92-100 and beta-Lg f125-135, while Phe-Phe interaction between beta-Lg f69-83 molecules interfered with analysis. Addition of beta-Lg f102-105 produced a blue shift (3 nm) and a significant increase in fluorescence intensity, while addition of beta-Lg f142-148 also caused a significant increase in fluorescence intensity but accompanied by a red shift (3 nm). These results indicate that the polarity of the Trp environment in the beta-Lg A structure may be modified differently depending on the peptide added.     

C and N NMR spectroscopy as a tool in soil organic matter studies

Nuclear magnetic resonance (NMR) is a valuable tool for the characterization of soil organic matter and humification processes in soils. This review highlights soil organic matter studies based mainly on solid-state ¹³C and ¹⁵N NMR spectroscopy and some emerging applications, that may provide significant progress in our knowledge on soil organic matter. A major advantage of Nmr spectroscopy is that it can be used as a non-invasive method for solid soil samples or soil fractions. Although resolution is limited, one can obtain an overview on the organic matter structures present in the soil sample. Application of ¹³C and ¹⁵N NMR to soils has, for a long time, been confined to the study of bulk soils or humic extracts for structural characterization. The transformations of soil organic C and N are now being investigated after addition of ¹³C- and ¹⁵N-labelled parent materials to the soil and following their evolution in different C and N pools. With labelling techniques it is also possible to study the interaction of organic pollutants with soil organic matter. Contamination of a soil with man-made additives, such as soot or brown coal dust, can also be detected in soils or individual soil fractions.     

Synchronous fluorescence as a rapid method for the simultaneous determination of folic acid and riboflavin in nutritional beverages

A rapid synchronous spectrofluorimetric method was first developed for the simultaneous determination of folic acid and riboflavin in nutrimental beverages. Folic acid could be detected by using H(2)O(2) plus Cu(II) as oxidation system to produce pterine-6-carboxylic acid, which had strong fluorescence in aqueous solution, and riboflavin itself was obviously fluorescent. Various operational parameters were thoroughly discussed in terms of their effects on the fluorescence signals, including instrumental parameters, concentration of the oxidation system, and pH. Under optimum conditions, the calibration curves were linear in the ranges of 100-250 μg/L for folic acid and 1-250 μg/L for riboflavin, and the detection limits were 2.0 and 0.014 μg/L, respectively. In addition, this method was applied to the determination of folic acid and riboflavin in nutrimental beverages with satisfactory results.     

Multielement fingerprinting as a tool in origin authentication of PGI food products: Tropea red onion

Tropea red onion ( Allium cepa L. var. Tropea) is among the most highly appreciated Italian products. It is cultivated in specific areas of Calabria and, due to its characteristics, was recently awarded with the protected geographical indications (PGI) certification from the European Union. A reliable classification of onion samples in groups corresponding to "Tropea" and "non-Tropea" categories is now available to the producers. This important goal has been achieved through the evaluation of three supervised chemometric approaches. Onion samples with PGI brand (120) and onion samples not cultivated following the production regulations (80) were digested by a closed-vessel microwave oven system. ICP-MS equipped with a dynamic reaction cell was used to determine the concentrations of 25 elements (Al, Ba, Ca, Cd, Ce, Cr, Dy, Eu, Fe, Ga, Gd, Ho, La, Mg, Mn, Na, Nd, Ni, Pr, Rb, Sm, Sr, Tl, Y, and Zn). The multielement fingerprint was processed using linear discriminant analysis (LDA) (standard and stepwise), soft independent modeling of class analogy (SIMCA), and back-propagation artificial neural network (BP-ANN). The cross-validation procedure has shown good results in terms of the prediction ability for all of the chemometric models: standard LDA, 94.0%; stepwise LDA, 94.5%; SIMCA, 95.5%; and BP-ANN, 91.5%.     

Applicability of ground‐penetrating radar as a tool for nondestructive soil‐depth mapping on Pleistocene periglacial slope deposits

Soil depth plays a decisive role in determining soil properties in mountainous regions for ecological site assessment. To evaluate the use of ground‐penetrating radar (GPR) for fast and high‐resolution mapping within mountainous regions, we examined the possibilities and limitations of GPR to determine soil depth over bedrock and to delineate individual substrate layers formed during the Pleistocene in a periglacial environment (Pleistocene periglacial slope deposits, PPSD). Selected catenae in representative subregions of the study area (Dill catchment, SE Rhenish Massif, Germany) have been successfully mapped using GPR. A practicable method was developed using a 400 MHz antenna to reach a mean penetration depth of 1.5 m and to map different substrates and layers of PPSD based on calibrations of the GPR at soil pits along 12 catenae. Colluvium, the three types of PPSD layers, as well as the in situ bedrock could be distinguished in most sections of the GPR surveys. Characteristic GPR facies caused by intrinsic material properties of the different substrates, such as stone content and soil moisture content, could be distinguished in different geomorphologic and lithological settings. A layer‐based velocity distribution was determined for characteristic substrate layers at soil pits enabling us to considerably enhance the accuracy of soil‐depth prediction. Compared to traditionally surveyed soil profiles, our results demonstrate an accuracy of layer thickness surveying within a standard deviation of approx. 0.1 m. It is demonstrated that the combination of GPR with conventional soil‐pit mapping is an efficient and valid method to produce high‐resolution data of substrate distribution.     

Use of fourier transform near-infrared reflectance spectroscopy for rapid quantification of castor bean meal in a selection of flour-based products

Methodology was developed and evaluated for the rapid detection of castor bean meal (CBM) containing the toxic protein ricin by using Fourier transform near-infrared (FT-NIR) spectroscopy and multivariate techniques. The method is intended to be a prototype to develop a more general approach to detect food tampering. Measurements were made on an FT-NIR system using a diffuse reflection-integrating sphere. Flours spiked with caffeine, crystalline sugar, and corn meal, 1-20% w/w, were used as test articles to evaluate the methodologies. Food matrices (bleached flour, wheat flour, and blueberry pancake mix) spiked with CBM (0.5-8% w/w) were analyzed. Multiplicative scatter correction transformed partial least-squares regression models, using a specific NIR spectral region, predicted CBM contamination in foods with a standard error of cross-validation of <0.6% and a coefficient of determination (R(2)) of >94%. Models discriminated between flour samples contaminated with CBM and other protein sources (egg white, soybean meal, tofu, and infant formula). CBM had loading spectra with bands characteristic of amide groups (4880 and 4555 cm(-1)) and lipids (5800, 5685, 4340, and 4261 cm(-1)).     

FTIR spectroscopy can be used as a screening tool for organic matter quality in regenerating cutover peatlands

Vegetational changes during the restoration of cutover peatlands leave a legacy in terms of the organic matter quality of the newly formed peat. Current efforts to restore peatlands at a large scale therefore require low cost and high throughput techniques to monitor the evolution of organic matter. In this study, we assessed the merits of using Fourier transform infrared (FTIR) spectra to predict the organic matter composition in peat samples at various stages of peatland regeneration from five European countries. Using predictive partial least squares (PLS) analyses, we were able to reconstruct peat C:N ratio and carbohydrate signatures with reasonable accuracy, but not the micromorphological composition of vegetation remains. Despite utilising different size fractions, both carbohydrate (<200 μm fraction) and FTIR (bulk soil) analyses report on the composition of plant cell wall constituents in the peat and therefore essentially reveal the composition of the parent vegetational material. The accuracy of the FTIR-based PLS models for C:N ratios and carbohydrate signatures was adequate to allow for their use as initial screening tools in the evaluation of the present and future organic matter composition of peat during monitoring of restoration efforts.     

Excitation-emission fluorescence spectroscopy combined with three-way methods of analysis as a complementary technique for olive oil characterization

This paper shows the potential of excitation-emission fluorescence spectroscopy (EEFS) and three-way methods of analysis [parallel factor analysis (PARAFAC) and multiway partial least-squares (N-PLS) regression] as a complementary technique for olive oil characterization. The fluorescence excitation-emission matrices of a set of Spanish extra virgin, virgin, pure, and olive pomace oils were measured, and the relationship between them and some of the quality parameters of olive oils (peroxide value, K232, and K270) was studied. N-PLS was found to be more suitable than PARAFAC combined with multiple linear regression for correlating fluorescence and quality parameters, yielding better fits and lower prediction errors. The best results were obtained for predicting K270. EEFS allowed detection of extra virgin olive oils highly degraded at early stages (with high peroxide value) and little oxidized pure olive oils (with low K270). The proposed methodology may be used as an aid to analyze doubtful samples.     

Automated method for the determination of niacin and niacinamide in cereal products: collaborative study.

In a collaborative study, an automated method for the determination of niacin and niacinamide in cereal products was compared with the official final action microbiological (43.121-43.125) and chemical (43.044-43.046) methods. Ten samples of cereal products, including enriched flour, yeast-leavened baked products, fortified breakfast cereals, and baked pet food products, were submitted to 14 laboratories. Nine laboratories reported values by the automated method, 6 reported values by the microbiological method, and 7 reported values by the chemical method. The results from the microbiological method were not subjected to analysis of variance because of the unusually large between-laboratory variation. The between-laboratory coefficients of variation for the automated and chemical methods were 10.90 and 10.18%, on the basis of results from 7 and 4 laboratories, respectively. There was no significant (p greater than 0.05) difference between methods when results from the 4 laboratories who used both methods were compared. The automated chemical method has been adopted as official first action.     

Electron paramagnetic resonance (EPR) spectroscopy as a tool for the characterization of biochar from guava waste

Journal of Soils and Sediments - The ability of biochars prepared from pyrolysis of guava pulp and seed industrial wastes to form complexes with the ions vanadyl (VO2+), a Pearson hard acid, and...     

Using humic products as amendments to restore Zn and Pb polluted soil: a case study using rapid screening phytotest endpoint

Purpose

Heavy metal contamination is a priority issue affecting millions of hectares of soil throughout the world. One of the most promising, environmentally friendly, and cost-effective approaches to restore polluted soils could be applying organic amendments. We investigated the remediation potential of three types of humic products with regard to their effect on the bioavailability of Pb and Zn, content of nutrients, and the ability to mitigate acute phytotoxicity in contaminated soil.

Materials and methods

Spodosol samples were spiked with Pb (550 mg kg^?1) and Zn (880 mg kg^?1). Then, two different commercial humic products (from peat and lignosulfonate) and natural humic acids (from brown oxidized coal) were added in two doses to reach an equal content of carbon: a 10% increment and a 30% increment of the initial total organic carbon in the soil. After 30 days, the content of metals and nutrients (S, K, Na, Ca, Mn, P) was determined by the sequential extraction (i?H₂O, ii?NH₄COOH pH 4.8, iii–CH₃COOH). The effect of humic products on heavy metals bioavailability was evaluated using the calculated partition indexes. Seed germination and root elongation of Sinapis alba were also determined. Chemical and biochemical variables were aggregated by the principal component analysis.

Results and discussion

Humic products reduced the amount of bioavailable fractions of Pb and Zn in soils. The partition index, which quantitatively describes bioavailable fractions of the Zn and Pb in the soil, was 28–49% lower than in the spiked (Pb+Zn) control. The inhibition of root elongation and seed germination of mustard by Zn and Pb was significantly mitigated by humic products; in the soil test, the root length and seed germination were up to 36–87% higher than those of the Pb+Zn control and did not differ from those in the non-amended treatments. This effect may have been associated with the structural differences (H/C and O/C ratio) and content of nutrients (Na and K) in humic products.

Conclusions

Commercial humic products used in poor multi-contaminated soils can maintain plant growth by improving nutrient status due to heavy metals immobilization and can be a promising approach to remediate the soil contaminated with heavy metals at extremely high concentrations.

     

Quercetin exhibits a specific fluorescence in cellular milieu: a valuable tool for the study of its intracellular distribution

The elaboration of novel techniques for flavonoid intracellular tracing would elucidate the compounds' absorption and bioavailability and assist molecular and pharmacological approaches, as they are promising candidates for drug development. This study exploited the properties of quercetin (3,3',4',5,7-pentahydroxyflavone), found in high concentrations in the majority of edible plants. Through the use of UV-vis spectroscopy, confocal microscopy, and HPLC-ESI-MS, native quercetin, at physiologically relevant concentrations, was found to exhibit a specific fluorescence (488 nmex/500-540 nmem) upon internalization. This fluorescence shift is due to a non-covalent binding to intracellular targets (probably proteins) and compatible with the settings applied in confocal microscopy. This property provides a valuable, selective alternative technique for quercetin tracing in cellular systems, permitting the quantitative evaluation of its transit at pharmacologically relevant concentrations and the validation of a number of already described molecular functions.     

Fluorescence spectroscopy of sedimentary pore-water humic substances: a simple tool for retrospective analysis of lake ecosystems

Purpose

The feasibility of applying the method of single-scan fluorescence emission spectra of humic substances (HSs) without chemical pretreatments of sediment pore-water samples was tested to ascertain the past productivity and sources of organic matter of lakes.

Materials and methods

Sediment samples were collected from ten Estonian lakes (located between 57°36′ and 59°25′N and 22°12′ and 26°59′E) covering all levels of the trophic scale. The height (fluorescence intensity), location (fluorescence maximum) and shape (fluorescence index, the ratio of intensities at the emission wavelengths 450 and 500 nm) of the fluorescence emission spectrum at an excitation of 340 nm were under consideration.

Results and discussion

Pore-water humic substances (pwHSs) from sediments of eutrophic lakes had generally a high fluorescence intensity and fluorescence index and their fluorescence maximum was located at shorter wavelengths. Characteristic features of pwHSs from oligotrophic lakes were low fluorescence intensity, emission of maximum fluorescence at shorter wavelengths and high fluorescence index values. Pore-water humic substances from sediments of dystrophic lakes were characterized by a low fluorescence intensity and fluorescence index and their spectral peak was shifted to longer wavelengths. The study also demonstrated that a shift in the peak location of pwHSs fluorescence was accompanied with a change in the C/N ratios of sedimentary organic matter, and the alteration in the fluorescence index of pwHSs was synchronous with the changes in their molecular weight.

Conclusions

The obtained results suggest that fluorescence spectroscopy of pwHSs without using chemical pretreatments has a great potential in the reconstruction of past lake conditions.     

Using synchrotron transmission FTIR microspectroscopy as a rapid, direct, and nondestructive analytical technique to reveal molecular microstructural-chemical features within tissue in grain barley

The objective of this study was to use synchrotron transmission FTIR microspectroscopy as a rapid, direct, and nondestructive analytical technique to reveal molecular microstructural-chemical features within tissue in grain barley. The results showed that synchrotron transmission FTIR microspectroscopy could provide spectral, chemical, and functional group characteristics of grain barley tissue at ultrahigh spatial resolutions. The spatially localized structural-chemical distributions of biological components (lignin, cellulose, protein, lipid, and carbohydrates) and biological component ratios could be imaged. Such information on molecular microstructural-chemical features within the tissue can be used for plant breeding programs for selecting superior varieties of barley for special purposes and for prediction of grain barley quality and nutritive value for humans and animals.