Colorimetric sensor array for soft drink analysis

Fourteen commercial soft drinks have been analyzed using colorimetric sensor arrays made from a set of 25 chemically responsive dyes printed on a hydrophobic membrane. Digital imaging of the dye array before and after immersion provides a color change profile as a unique fingerprint for each specific analyte. The digital data library generated was analyzed with statistical and chemometric methods, including principal component analysis (PCA) and hierarchical clustering analysis (HCA). Facile identification of all of the soft drinks was readily achieved using comparison of the color change profiles or a PCA score plot. Using a HCA dendrogram, the misclassification rate was <2%, and even very similar sodas were easily differentiated. In addition, the monitoring of soft drinks as they degas or upon dilution also proved to be possible. This work demonstrates the potential of our colorimetric sensor array technology for quality assurance/control applications of sodas and perhaps other beverages as well.     

Triacylglycerol analysis for the quantification of cocoa butter equivalents (CBE) in chocolate: feasibility study and validation

A new European legislation (2000/36/CE) has allowed the use of vegetable fats other than cocoa butter (CB) in chocolate up to a maximum value of 5% in the product. The vegetable fats used in chocolate are designated as cocoa butter replacements and are called cocoa butter equivalents (CBE). The feasibility of CBE quantification in chocolate using triacylglycerol (TAG) profiles was conducted by analyzing 55 samples of CBs and 31 samples of CBEs using a liquid chromatograph equipped with an evaporative light scattering detector (HPLC-ELSD). Statistical evaluation of the data obtained has been performed, and a simulation study has been carried out to assess the viability to use this method for quantifying the amount of CBE in real mixtures and in chocolates. The TAGs POP, POS, PLS, and the ratios POP/PLS, POS/PLP (P, palmityl; O, oleyl; S, stearyl; L, linoleyl) are particularly significant to discriminate between CB and CBE. Analysis of 50 mixtures between 5 different CBEs and 10 different CBs at 2 different concentration levels is presented. The data are visualized and interpreted. A mathematical model has been developed to assess the amount of CBE in real mixtures. This predictive model has been successfully applied and validated on dark chocolates including authorized CBE. The results are affected by +/-2.1% absolute average error. In particular, estimations between 10 and 20% of CBE show a very good match. On the other hand, values equal to or smaller than 5% show a larger prediction error (detection limit of the method). For the main purpose of this method (i.e., quantification of CBE at 5% max in chocolate, which represents about 15% of the total fat) this model shows very good results. For milk chocolate, the mathematical model can also be used if TAG are integrated from partition number (PN) 46 to 54. Consequently, the model proposed provides sufficient information to verify the real application of the European legislation.     

Potential of semiconductor sensor arrays for the origin authentication of pure Valencia orange juices.

Sensor array is a new method used in aroma analysis. This technique was employed for the differentiation of 49 pure Valencia orange juices from 5 different origins representative of the main culture areas of citrus according to their volatile organic fractions. An experimental design was used to set analytical factors, which control the generation of the static headspace; therefore, the preliminary optimization of analytical conditions allows the evaluation of the potential of such an apparatus in this kind of survey. Results obtained were then statistically treated by multivariate analyses such as principal component analysis and factorial discriminant analysis. Sensor arrays performed a good discrimination of the whole juices in classing them according to the origin of Valencia oranges used. A calibration of the sensors was then performed to build a database aiming to classify the juices according to the origin of oranges involved. New supplementary samples were then analyzed to assess the efficiency of the database. This technique coupled with other ones such as high-pressure liquid chromatography and gas chromatography may be a new tool for the investigation of adulteration detection due to the authentication of the origin of raw materials employed in the orange juice processes.     

基于聚苯胺的农用柔性低阻抗pH传感芯片设计与试验

商用玻璃pH电极应用于农业监测中存在探头易碎、接入阻抗大、易极化等问题,该研究利用喷墨打印技术制备了基于单壁碳纳米管介导质子酸掺杂聚苯胺柔性pH传感芯片,通过交流阻抗谱法比较分析了柔性芯片与商用电极在接入阻抗及电荷转移上的优势,系统测试了柔性pH芯片在灵敏度、响应时间、稳定性、重复性、抗干扰性、弯折影响等性能参数,验证了其在无土栽培生菜营养液pH值动态监测中的应用可行性。试验结果表明：柔性pH传感芯片电荷转移阻抗约为230.8 Ω,商用pH传感器达到9 879 Ω,两参数相差40倍以上,柔性pH传感器在频率全谱段皆表现出更为优越的仪器仪表阻抗匹配性能。在pH值2～10范围内,柔性pH传感芯片的灵敏度为–61.9 mV/pH,响应时间约为15 s,12 h内最大漂移不超过5.44 mV,重复性、抗干扰性指标理想,0°～120°弯折影响可忽略,温度变化40 ℃,柔性传感芯片所测pH值随温度漂移小于0.23,寿命达到14 d。连续10 d的水培生菜pH在线监测中,柔性芯片与商用电极一致性表现出良好,最大误差为0.12,可快速准确监测营养液pH值变化,具有良好农业应用前景。     

Reduction of persistent organic pollutants in fishmeal: a feasibility study

The dioxin, dioxin-like polychlorinated biphenyl (DL-PCB), fat, and dry matter partitioning during fishmeal production have been studied in pilot scale. Most of the dry matter and lipid content in the fishmeal could be ascribed to the press cake intermediate product. Dioxins and DL-PCBs are fat-soluble compounds, and the process partitioning is reflected by the fat partitioning data. Enzyme and heat treatment of the press cake and stickwater concentrate did not improve fat separation. Soybean oil extraction of the press cake reduced the dioxin and DL-PCB content by 97%. Less exchange of fatty acids was observed (56-72%). Combined with fat separation of the stickwater concentrate, the applied process conditions were able to give a fishmeal decontamination rate higher than hexane and isopropanol extraction of the fishmeal. Quantification of fat content based on chloroform/methanol extraction was found to be the best protocol to estimate fat partitioning and decontamination effects. The oil extraction process requires further optimization, but has several advantages compared to organic solvent extraction. These include easy implementation in an existing fishmeal processing line, use of a safe and nonflammable extraction medium, and expected lower investment and operation costs. A new integrated fishmeal and fish oil production and decontamination process line is proposed.     

Geographical classification of honey samples by near-infrared spectroscopy: a feasibility study

The potential of near-infrared (NIR) spectroscopy to determine the geographical origin of honey samples was evaluated. In total, 167 unfiltered honey samples (88 Irish, 54 Mexican, and 25 Spanish) and 125 filtered honey samples (25 Irish, 25 Argentinean, 50 Czech, and 25 Hungarian) were collected. Spectra were recorded in transflectance mode. Following preliminary examination by principal component analysis (PCA), modeling methods applied to the spectral data set were partial least-squares (PLS) regression and soft independent modeling of class analogy (SIMCA); various pretreatments were investigated. For unfiltered honey, best SIMCA models gave correct classification rates of 95.5, 94.4, and 96% for the Irish, Mexican, and Spanish samples, respectively; PLS2 discriminant analysis produced a 100% correct classification for each of these honey classes. In the case of filtered honey, best SIMCA models produced correct classification rates of 91.7, 100, 100, and 96% for the Argentinean, Czech, Hungarian, and Irish samples, respectively, using the standard normal variate (SNV) data pretreatment. PLS2 discriminant analysis produced 96, 100, 100, and 100% correct classifications for the Argentinean, Czech, Hungarian, and Irish honey samples, respectively, using a second-derivative data pretreatment. Overall, while both SIMCA and PLS gave encouraging results, better correct classification rates were found using PLS regression.     

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.     

Colorimetric characterization for comparative analysis of fungal pigments and natural food colorants

Exogenous pigments produced by ascomycetous filamentous fungi belonging to the genera Penicillium, Epicoccum, and Monascus, preselected based on chemotaxonomic knowledge, have been extracted and characterized by quantitative colorimetry. The color characteristics of the fungal extracts were compared to water soluble natural colorants derived from sources currently in use. The tested fungal extracts also included some commercially available Monascus colorants. The a values for the fungal extracts were found to be both positive and negative, the b values were found to be positive, while the hue angles of the fungal color extracts ranged from 40 to 110 indicating the color distribution of fungal extracts over the red-orange-yellow region of the CIELAB color space. The fungal extracts exhibited additional color hues in the red spectrum and similar hues in the yellow spectrum as compared to the reference natural colorants. They were also found to be similar or brighter in terms of chroma to some of the reference natural colorants. Principal component analysis was performed to group and distinguish different colors based on the a and b values. The fungal color extracts could be grouped in accordance with the similarity or difference in the color to those of the existing natural colorants. The diversity of colors was not only found among different fungal genera and/or species but also within the same species on changing the media. There was a marked change in the color composition of the extracts resulting in relatively different hues. Our results, thus, indicate that there exists pigment-producing genera of ascomycetous fungi other than Monascus that produce color shades in the red and the yellow spectra in addition or similar to reference colorants. These color shades could add to the color palette of the natural colorants currently in use. In addition, the multivariate approach in distinguishing and classifying the colorants was shown to be a very useful tool in colorimetric comparison of colorants.     

Authentication of organic feed by near-infrared spectroscopy combined with chemometrics: a feasibility study

Organic products tend to retail at a higher price than their conventional counterparts, which makes them susceptible to fraud. In this study we evaluate the application of near-infrared spectroscopy (NIRS) as a rapid, cost-effective method to verify the organic identity of feed for laying hens. For this purpose a total of 36 organic and 60 conventional feed samples from The Netherlands were measured by NIRS. A binary classification model (organic vs conventional feed) was developed using partial least squares discriminant analysis. Models were developed using five different data preprocessing techniques, which were externally validated by a stratified random resampling strategy using 1000 realizations. Spectral regions related to the protein and fat content were among the most important ones for the classification model. The models based on data preprocessed using direct orthogonal signal correction (DOSC), standard normal variate (SNV), and first and second derivatives provided the most successful results in terms of median sensitivity (0.91 in external validation) and median specificity (1.00 for external validation of SNV models and 0.94 for DOSC and first and second derivative models). A previously developed model, which was based on fatty acid fingerprinting of the same set of feed samples, provided a higher sensitivity (1.00). This shows that the NIRS-based approach provides a rapid and low-cost screening tool, whereas the fatty acid fingerprinting model can be used for further confirmation of the organic identity of feed samples for laying hens. These methods provide additional assurance to the administrative controls currently conducted in the organic feed sector.     

Colorimetric method for the determination of lipoxygenase activity

A colorimetic assay for lipoxygenase activity has been developed. The assay is based on the detection of the lipoxygenase reaction product, linoleic acid hydroperoxide, by the oxidative coupling of 3-methyl-2-benzothiazolinone (MBTH) with 3-(dimethylamino)benzoic acid (DMAB) in a hemoglobin-catalyzed reaction. This test reaction is rapid and sensitive, and it offers advantages over other methods for detecting lipoxygenase activity. The assay is capable of detecting activity in a number of crude vegetable homogenates and should be particularly useful where a rapid visual determination of lipoxygenase activity is desired.     

Contribution of 3-methylthiopropionaldehyde to the worty flavor of alcohol-free beers

Alcohol-free beers are usually criticized for two major defects: a lack of fruity aroma and a strong worty flavor. 3-Methylbutanal and 2-methylbutanal are described in the literature as being predominantly responsible for the worty taste. Although detected in large amounts in most malt and wort extracts, both compounds have proven unable to confer worty taste to beers. In this work, we extracted volatiles from wort with a Likens-Nickerson microextractor. The resulting extract had a strong worty aroma. Following GC/MS and GC/olfactometry analysis, 3-methylthiopropionaldehyde turned out to be the key feature since it remained the most organoleptically active compound through extract dilution. In vitro assays showed that 3-methylthiopropionaldehyde is a substrate for several Saccharomyces cerevisiae reducing enzymes. Screening of various strains led us to conclude that the higher the 3-methylbutanal reductase activity, the higher the 3-methylthiopropionaldehyde reductase activity. Monitoring of 3-methylthiopropionaldehyde concentration through an in vivo cold contact process has also been undertaken.     

Potentiality of red sorghum for producing stilbenoid-enriched beers with high antioxidant activity

trans-Piceid and trans-resveratrol were authenticated for the first time by high-resoution mass spectrometry in red sorghum grains. A 0.4-1 mg/kg amount of trans-piceid and up to 0.2 mg/kg trans-resveratrol were quantified by reversed phase high-performance liquid chromatography-atmospheric pressure chemical ionization(+)-tandem mass spectrometry. The white sorghum samples contained only traces of trans-piceid (up to 0.1 mg/kg), and trans-resveratrol was absent. In much lower amounts than procyanidins, stilbenoids are not able to contribute significantly to the exceptional antioxidant activity of red sorghum (ORAC, 83-147 μmol TE/g; AAPH, 0.61-1.79 min/mg kg(-1)). More than 10 mg/kg of total stilbenoids have been reported in some hop varieties. Yet, as hop is a minor wort ingredient as compared to cereals, red sorghum could be the main source of trans-piceid in beer. Hop remains, however, the single source of cis-piceid.     

Investigation of the beta-damascenone level in fresh and aged commercial beers

This study investigated the increase of beta-damascenone content during aging in a variety of commercial Belgian beers. Quantities detected in fresh beers were generally low (from 6 ng/g to 25 ng/g). After 5 days at 40 degrees C, the level increased (to as much as 210 ng/g) in most of the beers studied, according to the type of beer. Further experiments showed that wort initially contains large quantities of beta-damascenone (450 ng/g), but that degradation of the compound during fermentation accounts for the low concentrations observed in fresh beers. Production during beer aging can be partially explained by acid hydrolysis of glycosides.     

Sequential extraction and single-step cold-acid extraction: A feasibility study for use with freshwater-canal sediments

This investigation examines metal release from freshwater sediment using sequential extraction and single-step cold-acid leaching. The concentrations of Cd, Cr, Cu, Fe, Ni, Pb and Zn released using a standard 3-step sequential extraction (Rauret et al., 1999) are compared to those released using a 0.5 M HCl; leach. The results show that the three sediments behave in very different ways when subject to the same leaching experiments: the cold-acid extraction appears to remove higher relative concentrations of metals from the iron-rich sediment than from the other two sediments. Cold-acid extraction appears to be more effective at removing metals from sediments with crystalline iron oxides than the “reducible” step of the sequential extraction. The results show that a single-step acid leach can be just as effective as sequential extractions at removing metals from sediment and are a great deal less time-consuming.