Colorimetric sensor arrays for the analysis of beers: a feasibility study

Eighteen commercial beers have been analyzed in both liquid and gas phases using colorimetric sensor arrays made from selected chemically responsive dyes printed on a hydrophobic membrane. Digital imaging of the dye array before and after exposure to the complex analytes in either the liquid phase or the head-gas provides a color change profile as a unique fingerprint for the specific analyte. The digital data libraries generated were analyzed using statistical and chemometric methods, including principal component analysis (PCA) and hierarchical clustering analysis (HCA). In either liquid- or gas-phase experiments, facile identification of specific beers was achieved using comparison of the color change profiles; using HCA statistical analysis the error rate of identification was <3%. Differentiation between even very similar beers proved to be straightforward. In addition, differentiation of pristine beer from the effects of watering or decarbonation proved to be possible. These results suggest that colorimetric sensor arrays may prove to be useful for quality assurance/quality control applications of beers and perhaps other beverages.     

Determinants of adolescents' soft drink consumption

OBJECTIVE: To identify determinants of adolescents' consumption of carbonated soft drinks (regular and diet), both of total consumption and of consumption at school. DESIGN/SETTING/SUBJECTS: Regular and diet soft drink consumption was measured by food frequency questions that were dichotomised. Several potential environmental and personal determinants of consumption were measured. A total of 2870 (participation rate: 85%) 9th and 10th graders, within 33 Norwegian schools, participated in the study. Multilevel logistic regression analyses were preformed for total soft drink consumption (twice a week or more vs. less) and for consumption at school (once a week or more vs. less). RESULTS: A total of 63% and 27% of the participants reported to drink respectively regular and diet soft drinks twice a week or more, and 24% and 8%, respectively, reported to drink soft drinks once a week or more at school. Preferences, accessibility, modelling and attitudes were the strongest determinants of both regular and diet soft drink consumption. In addition, gender, educational plans and dieting were related to both total soft drink consumption and consumption at school. Pupils with longer distance from school to shop and those in schools with rules concerning soft drink consumption tended to have lower odds of drinking both regular and diet soft drinks at school. CONCLUSION: This study shows that gender, educational plans, dieting, accessibility, modelling, attitudes and preferences all seem to be strong determinants of adolescents' soft drink consumption. Parents and the home environment appear as great potential intervention targets.     

Colorimetric method for field-screening above-tolerance parathion residues on and in citrus fruits

A colorimetric technique has been developed which is suitable for use as a field-screening method for detecting above-tolerance levels of parathion on and in citrus fruits. By using this method, a grower should be able to postpone harvesting a crop until parathion residues are below tolerance level, so that the crop is safe to market. The method depends on the reaction of parathion with 4-(p-nitrobenzyl)-pyridine. Parathion is extracted by mixing chopped citrus rind with acetone in a hand-operated homogenizer. The extract is partially cleaned by a partitioning step before final cleanup with a Sep-Pak Florisil cartridge. The colored reaction solution is read at 560 nm by using a portable, rechargeable spectrophotometer. A single test can be completed in about 75 min; the average time per test when several are conducted sequentially is considerably shorter. The analytical system responds readily to less than 5 ppm parathion on or in 1 g navel orange rind, which corresponds to less than 1 ppm in the whole fruit. The present U.S. tolerance for parathion on or in citrus is 1 ppm on a whole fruit basis. Preliminary work indicates that the method should also be suitable for apples.     

Automated Modification of the Molybdenum Blue Colorimetric Method for Phosphorus Determination in Soil Extracts

A flow injection analysis (FIA) method capable of automation for molybdate reactive phosphorus (P) determination in soil extracts is described. Results obtained using this method in three soil extracts [calcium chloride (CaCl₂), Olsen, and Mehlich I] were the same as those provided by the manual molybdate blue colorimetric method. Linear range extending to 2 mg P L^?1, detection limits ranging from 6 to 26 µg L^?1 depending on the soil extract, and accurate recoveries from P‐spiked samples were achieved. The sensitivity of the system was around 0.3 absorbance units per mg P L^?1, and the sampling frequency was 72 samples h^?1, higher than those described for most of the flow injection methods.     

Colorimetric Artificial Nose and Pattern Recognition Methods for the Concentration Analysis of NH3

An investigation was made to evaluate the capacity of a colorimetric artificial nose to detect toxic gas at low concentration. A low-cost and simple colorimetric sensor array for identification and quantification of NH₃ with different concentrations (30, 90, 150, and 210?ppb) were reported. Using porphyrin, porphyrin derivatives (mainly metalloporphyrins), and chemically responsive dyes as the sensing elements, the developed sensor array of artificial nose showed a unique pattern of colorific change upon its exposure to NH₃ with different concentrations. The dynamic responses of colorimetric sensor array to NH₃ and colorimetric sensor array to various NH₃ concentrations at the same time point showed that there was a positive relationship between the color change values of spots and contractions of NH₃. NH₃ with four concentrations were measured, and the response values at six different collection times were conducted by linear discrimination analysis (LDA) and artificial neural network (ANN). The four concentrations were discriminated completely by LDA. The response value of the colorimetric artificial nose at 0.4?min was optimum for discrimination. The method of ANN was performed and less than 5% of error by using T-S fuzzy neural network.     

Olfactory and quantitative analysis of aroma compounds in elder flower (Sambucus nigra L.) drink processed from five cultivars

Fresh elder flowers (Sambucus nigra L.) were extracted with an aqueous solution containing sucrose, peeled lemon slices, tartaric acid, and sodium benzoate to make elder flower syrup. Aroma compounds emitted from the elder flower syrup were collected by the dynamic headspace technique and analyzed by GC-FID and GC-MS. A total of 59 compounds were identified, 18 of which have not previously been detected in elder flower products. The concentrations of the identified volatiles were measured in five elder cultivars, Allesoe, Donau, Sambu, Sampo, and Samyl, and significant differences were detected among cultivars in the concentration levels of 48 compounds. The odor of the volatiles was evaluated by the GC-sniffing technique. cis-Rose oxide, nerol oxide, hotrienol, and nonanal contributed to the characteristic elder flower odor, whereas linalool, alpha-terpineol, 4-methyl-3-penten-2-one, and (Z)-beta-ocimene contributed with floral notes. Fruity odors were associated with pentanal, heptanal, and beta-damascenone. Fresh and grassy odors were primarily correlated with hexanal, hexanol, and (Z)-3-hexenol.     

Optical sensor for sulfur dioxide determination in wines

A method for the determination of free and total sulfur dioxide in wines, based on the use of an optical sensor that employs a dichlorobis(diphenylphosphino)methane dipalladium I complex [Pd(2)(dppm)(2)Cl(2)] immobilized in a PVC membrane plasticized with o-nitrophenyloctylether (o-NPOE) is described. A sensing membrane [4.2% Pd(2)(dppm)(2)Cl(2), 20.8% PVC, and 75% o-NPOE] was adapted to the tip of a bifurcated optical fiber bundle to perform reflectance measurements at 550 nm. The detection system consisted of two cells (40 mL), which hold the sample solution (plus reagents) and the optical sensor, respectively. For the determination of free SO(2), a wine sample was mixed with H(2)SO(4) solution in the sample cell, into which N(2) was bubbled, providing mixing of the solutions and conducting the SO(2) formed toward the detection cell. For determination of total SO(2), a KOH solution was mixed with the wine in the sample cell. Afterward, an H(2)SO(4) solution was added to the cell, and then N(2) was bubbled to conclude the measurement. Linear responses up to 50 and 150 mg L(-1) were obtained for free and total SO(2), with detection limits of 0.37 and 0.70 mg L(-1), respectively. The repeatability of the method was evaluated by carrying out 10 measurements using a single wine sample, providing relative standard deviation values of 2.2 and 2.5% for free and total SO(2), respectively. The sensing membrane prepared from 10 muL of the cocktail solution lasted for 80 measurements, whereas those prepared from 200 muL can be used for 250 measurements. The method was applied to free and total SO(2) determination in wines, and the results did not show significant difference from those obtained with the Ripper reference method at a confidence level of 95%.     

Colorimetric deoxyribonucleic acid hybridization assay for rapid screening of Salmonella in foods: collaborative study

A collaborative study was performed in 11 laboratories to validate a colorimetric DNA hybridization (DNAH) method for rapid detection of Salmonella in foods. The method was compared to the standard culture method for detection of Salmonella in nonfat dry milk, milk chocolate, soy isolate, dried whole egg, ground black pepper, and raw ground turkey. Samples inoculated with high (0.4-2 cells/g) and low (0.04-0.2 cells/g) levels of Salmonella and uninoculated control samples were included in each food group analyzed. There was no significant difference in the proportion of samples positive by DNAH and culture procedure for any of the 6 foods. The colorimetric DNA hybridization assay screening method has been adopted official first action as a rapid screening method for detection of Salmonella in all foods.     

Quantitative analysis of ginger components in commercial products using liquid chromatography with electrochemical array detection

For the first time, a sensitive reversed-phase HPLC electrochemical array method has been developed for the quantitative analysis of 8 major ginger components ([6]-, [8]-, and [10]-gingerol, [6]-, [8]-, and [10]-shogaol, [6]-paradol, and [1]-dehydrogingerdione) in 11 ginger-containing commercial products. This method was valid with unrivaled sensitivity as low as 7.3-20.2 pg of limit of detection and a range of 14.5-40.4 pg for the limit of quantification. The levels of 8 ginger components in 11 different commercial products were quantified by use of this method. The results found that both levels and ratios among the 8 compounds vary greatly in commercial products.     

Analysis of virgin olive oil volatiles by a novel electronic nose based on a miniaturized SAW sensor array coupled with SPME enhanced headspace enrichment

A novel electronic nose based on solid-phase microextraction (SPME) coupled with a surface acoustic wave (SAW) sensor array has been used to analyze different quality virgin olive oils. A mathematical model was designed with 37 samples to distinguish lampante from the other virgin olive oils categories (extra-virgin and virgin), because lampante-virgin olive oils cannot be consumed without a previous refining process. The model, successfully validated with a test set of 16 samples, was able to classify 90% of the samples correctly. Misclassifications were explained by SPME-HRGC analyses and a second sensory evaluation.     

Detection of soft wheat in semolina and durum wheat bread by analysis of DNA microsatellites

The aim of this work was to evaluate the analysis of DNA microsatellites for the detection of soft wheat (Triticum aestivum L.) in semolina and durum wheat bread (prepared from Triticum turgidum L. var. durum). The results enabled selection of an efficient D-genome-specific repetitive DNA sequence to detect common wheat in semolina and breads by qualitative PCR with a threshold of 3 and 5%, respectively, lowered to 2.5% by real-time PCR. This is of major importance for checking during production of some typical products recently awarded the European Protected Designation of Origin (PDO) mark such as Altamura bread, which should not contain soft wheat flour. The feasibility of quantification of common wheat adulteration in semolina using real-time PCR was also demonstrated.     

Plant Alkaline Fusion Technique Followed by Colorimetric Procedure for the Detection and Quantification of Total Silicon in Ornamental Plants

Silicon (Si)–determination procedures currently available require expensive equipment and must be modified to assess Si concentrations in plant tissues. A Si-determination procedure referred to as the plant alkaline fusion technique, or PAFT, was developed to assess total Si concentrations, specifically in plant tissue. The procedure consists of dry-ashing the plant material, alkaline fusion, solubilization of the fusion cake, dilution, and colorimetric determination to quantify total Si content. The fusion technique for solubilizing plant Si can be performed using sodium hydroxide (NaOH), nickel crucibles, and Bunsen burners. Silicon concentrations of two National Institute of Standards and Technology (NIST) standard reference materials (SRM) [pine needles (SRM 1575) and peach leaves (SRM 1547)], a rice straw standard (LSU#5), an NIST soil standard (SRM 2709), and five ornamental plant species were all assessed using the PAFT procedure, and then these values were compared to two different inductively coupled plasma–optical emission spectroscopy (ICP-OES) procedures conducted by independent laboratories. The PAFT Si determination procedure typically reported the greatest value or was within 15% of the two ICP-OES procedures while costing significantly less than both ICP-OES procedures.     

Evidence for recent acidification of lentic soft waters in the Netherlands

During 1983–1984 about 90% of the Dutch soft waters appeared to be acid, and 35% of them showed pH-values below 4.0. The alkalinity of most waters (70%) was less than 0.1 meq. L^?1. Evidence for recent acidification is derived from temporal trends in water quality, fish population status, shifts in aquatic biota and application of current empirical models for lake acidification. It has been concluded that at least 59% of the Dutch soft waters have been recently acidified. This is a conservative estimate. Depending on the criterion used for assessment of acidification this percentage might be as high as 96%.     

A qualitative colorimetric test for brominated vegetable oil in soft drinks

A simple and precise method of detecting brominated vegetable oil (BVO) in soft drinks is described. After extraction of BVO using diethyl ether, the concentrated ethereal solution was treated with a small quantity of zinc dust to convert the organic bromide to inorganic form; the solution was subsequently treated with lead dioxide to liberate bromine. The bromine evolved was detected by means of fluorescein-impregnated filter paper strip that turns pink because eosin is formed. The test can detect as low as 10 ppm (2 mg/200 ml) of BVO under experimental conditions. Gas chromatography was carried out on sodium methoxide derivatives prepared from ether extract for quantitation.     

Rapid discrimination of scented rice by solid-phase microextraction, mass spectrometry, and multivariate analysis used as a mass sensor

This study describes a new and suitable method for the rapid evaluation of rice (Oryza sativa, L.) aroma by analysis of the volatile fraction using solid-phase microextraction coupled with mass spectrometry (SPME/MS). The abundance list of unresolved mass fragments of the SPME extracted volatile fraction formed the "fingerprint" of a rice sample. Fingerprints of 61 rice samples were recorded in duplicate. Pollutants originating from the extraction system induce fingerprint background that could be lowered by careful cleaning of vials and caps and by exclusion of specific mass fragments. A good discrimination between scented and nonscented rice samples was obtained using the SIMCA procedure. Most of the discriminating mass fragments could be directly or indirectly assigned to potential aromatic molecules present in rice.     

Mass spectrometry based sensor strategies for the authentication of oysters according to geographical origin

This study was undertaken to investigate the relevance of using the pyrolysis-MS (Py-MS) technique to discriminate the production area of oysters harvested over two years and to assess from the data of the second year of harvest the potential of an alternative MS-based technique, the solid phase microextraction-MS (SPME-MS), to perform this discrimination. Oysters were harvested in various areas of France, and models of discrimination according to harvest season were built from Py-MS fingerprints and from virtual SPME-MS fingerprints obtained by summing the mass spectra generated by the SPME-GC-MS system. The treatment of the Py-MS data by a 21-12-3 artificial neural networks led to a correct classification of only 89.2% of the oyster samples according to shoreline. The misclassifications thus did not allow use of the Py-MS technique as a relevant tool for authentication of oyster origin. The assessment of the potential of the virtual SPME-MS fingerprints to discriminate the production area of oysters was undertaken on a part of the sample set. The virtual SPME-MS data were pretreated according to two methods, filtering of raw data (FRD) and comprehensive combinatory standard correction (CCSC), a recently developed chemometric method used for the correction of instrumental signal drifts in MS systems. The results obtained with the virtual SPME-MS fingerprints are promising because this technique, when the data were pretreated by the CCSC method, led to a successful discrimination of the oyster samples not only according to shoreline but also according to production region. This study confirms that an efficient correction method (CCSC) of instrumental drifts can considerably increase the discriminative information contained in the volatile fraction of food products.     

Cuban and Brazilian red propolis: botanical origin and comparative analysis by high-performance liquid chromatography-photodiode array detection/electrospray ionization tandem mass spectrometry

Chemical composition of propolis depends on the specificity of the local flora at the site of collection and thus on the geographic and climatic characteristics of this place. This paper describes a comparative analysis of Cuban red propolis (CRP), Brazilian red propolis (BRP), and Dalbergia ecastophyllum exudates (DEE) by high-performance liquid chromatography with diode-array detection and tandem mass spectrometry. The aim of this study was to investigate the overall chemical profile and the botanical origin of red propolis and to suggest similarities and differences between samples collected in different tropical regions. Isoliquiritigenin (1), liquiritigenin and naringenin (2 and 17), isoflavones (3-4 and 16), isoflavans (5-7 and 18), and pterocarpans (8-13) were detected in CRP, BRP, and DEE, whereas polyisoprenylated benzophenones (PPBs) guttiferone E/xanthochymol (14a,b) and oblongifolin A (15) were detected only in BRP. Pigments responsible for the red color of DEE and red propolis were also identified as two C30 isoflavans, the new retusapurpurin B (19) and retusapurpurin A (20). PPBs and pigments were isolated and unambiguously characterized by 1D and 2D NMR analysis. These results show that red propolis samples from different tropical zones have a similar chemical composition. DEE is the main red propolis source, but the presence of PPBs in BRP suggests the contribution of different botanical sources for Brazilian samples. This chemical information is important for quality control of red propolis and its commercial products and for biological study.