Open air calibration with temperature compensation of a luminescence quenching-based oxygen sensor for portable instrumentation

This report addresses the task of calibrating an optical sensor for oxygen determination. Detailed analyses of the functional dependences from our measurement system results have been carried out with the additional aim of temperature compensation. As a result, an empirical calibration function has been successfully derived for the luminescent quenching-based oxygen sensor included in a self-designed portable instrument. This function also compensates for the temperature influence on the quenching luminescence process in the range from 0 to 45 degrees C. Moreover, the calibration procedure is extremely simple because only a single standard is needed. In fact, the oxygen measurement system can be calibrated with exposure to an open air atmosphere, and therefore, neither laboratory standards nor trained personnel are required. The method has been applied to a set of 11 units of the mentioned sensor (up to 24% oxygen concentration) giving an overall deviation between our calibrated system results and the laboratory standards of 0.3% oxygen concentration (calculated with 95% confidence level). The proposed calibration function has shown itself to be applicable for different sensing film thicknesses and luminophore concentrations using the same fittings parameter. Additionally, this function has been successfully applied to other oxygen dyes. Good agreement has also been found when the performance of the instrument was compared to a commercially available portable instrument based on an electrochemical sensor. We believe that this work could be an interesting finding for spreading the use of optical sensors for atmospheric oxygen determination in commercial measurement equipment for different purposes in confined working atmospheres, such as mines, undergrounds, warehouses, vehicles, and ships.     

Effect of storage time on sensory and instrumental properties of skim‐milk yoghurt obtained with microbial transglutaminase

Not many studies have examined changes in microbial transglutaminase (MTG) yoghurts during storage. In this work, yoghurts manufactured with skimmed milk and treated with MTG were evaluated in refrigerated storage for 35 days. Instrumental measurements showed that firmness, consistency and pH values in MTG yoghurt experienced a significant increase with the storage time. However, sensory measurements showed that MTG yoghurts were not affected significantly by storage time. Acid taste scores only increased significantly with storage time in the control samples. Microbial transglutaminase treatment showed a positive effect on textural properties and allowed syneresis to be prevented completely during storage.     

Vanadium-ceria catalysts for H2S abatement from biogas to feed to MCFC

Vanadium-based catalysts supported on ceria were studied for the direct and selective oxidation of H₂S to sulphur and water at low temperature.Catalysts with two vanadium loading (20–50 wt% of V₂O₅) were prepared, characterized and tested at temperature of 150–200 °C in order to identify the best catalytic formulation. The most promising catalyst was the sample with the 20 wt% of V₂O₅ that showed 99% of sulphur selectivity and equilibrium H₂S conversion at 150 °C.The effect of the components of a typical biogas stream (CH₄, CO₂ and H₂O) was studied at 150 °C in order to investigate the possible formation of secondary products such COS, CS₂. No significant effect was observed in terms of H₂S conversion (99%) and selectivity to SO₂ (<1%) by adding CH₄ and CO₂ to the feed stream. Furthermore, the effect of the H₂S inlet concentration, temperature, contact time and molar feed ratio (O₂/H₂S) were also investigated at a reaction temperature of 80 °C.Finally, time on stream tests of 30 h were performed at 80 and 120 °C, in order to examine the catalyst stability.     

Contribution to the experimental review of the colorimetric standard observer

The color‐matching functions of six observers have been measured in the range of 400–700 nm in intervals of 10 nm using two modified Donaldson‐type colorimeters at a luminance of 4.5 cd/m². A statistical study has been carried out to determine the interobserver variability (in our results), and the results of other authors using various representational color systems have been compared with ours. The most important findings are that, although a common mathematical mean cannot be found, the shape of the curves for the color‐matching functions obtained in our laboratory for all the observers is very close to that of other authors, thereby implying that the overall color response of the human visual system is similar in all observers. In addition, the results show that, for the long wavelengths (around 600 nm), a great amount of desaturant primary (460 nm) is necessary, indicating possible rod intrusion under our experimental conditions. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 377–388, 1999     

Phenolic characterisation of red grapes autochthonous to Andalusia

Twenty six phenolic compounds in wine grapes were identified and quantified in five winegrape varieties using the complementary information from high-performance liquid chromatography coupled to diode array and fluorescence detectors, and mass spectrometry in both positive and negative mode. Fourteen different anthocyanins were identified in these grapes. In all varieties, malvidin-3-glucoside and its derivatives, mainly p-coumaroyl derivatives, were the major compounds. Seven flavonols were detected, most as quercetin and myricetin derivatives, and few qualitative differences were found among varieties. Total hydroxycinnamic content was rather low in all varieties. Lastly, catechin and epicatechin were detected in both skin and seed; differences in respect of the content in the seeds can be attributed to differences in the number and weight of seed per berry in each variety. The results of the characterisation can be used to select winemaking techniques aimed at improving the quality of the final wine.     

Short communication: Detection of human Torque teno virus in the milk of water buffaloes (Bubalus bubalis)

Forty-four raw milk and 15 serum samples from 44 healthy water buffaloes reared in Caserta, southern Italy, the most important region in Europe for buffalo breeding, were examined to evaluate the presence of Torque teno viruses (TTV) using molecular tools. Furthermore, 8 pooled pasteurized milk samples (from dairy factories having excellent sanitary conditions) and 6 Mozzarella cheese samples were also tested. Four of the cheese samples were commercial Mozzarella cheese; the remaining 2 were prepared with TTV-containing milk. Human TTV were detected and confirmed by sequencing in 7 samples of milk (approximately 16%). No TTV were found in serum, pooled pasteurized milk, or Mozzarella cheese samples. The samples of Mozzarella cheese prepared with TTV-containing milk did not show any presence of TTV, which provides evidence that standard methodological procedures to prepare Mozzarella cheese seem to affect viral structure, making this food fit for human consumption. The 7 TTV species from water buffaloes were identified as genotypes corresponding to the tth31 (3 cases), sle 1981, sle 2031, and NLC030 (2 cases each) human isolates. Although cross-species infection may occur, detection of TTV DNA in milk but not in serum led us to believe that its presence could be due to human contamination rather than a true infection. Finally, the mode of transmission of TTV has not been determined. Contaminated of the food chain with TTV may be a potential risk for human health, representing one of the multiple routes of infection.     

Nondestructive direct determination of heroin in seized illicit street drugs by diffuse reflectance near-infrared spectroscopy

A new method has been developed for the fast and nondestructive direct determination of heroin in seized street illicit drugs using partial least-squares regression analysis of diffuse reflectance near-infrared spectra. Data were obtained from untreated samples placed in standard glass chromatography vials. A heterogeneous population of 31 samples, previously analyzed by a reference method, was employed to build the calibration model and to have a separated validation set. Based on the use of zero-order data for a calibration set of 21 samples, after standard normal variate and quadratic linear removed baseline correction (detrending), in the wavelength range from 1111 to 1647 nm, 8 PLS factors were enough to obtain a root-mean-square error of prediction of 1.3% w/w, with a quality coefficient of 10% for the estimation of the accuracy error in the prediction of heroin concentration in unknown samples and a residual predictive deviation of 5.4.     

Unsupervised illuminant estimation from natural scenes: an RGB digital camera suffices

A linear pseudo-inverse method for unsupervised illuminant recovery from natural scenes is presented. The algorithm, which uses a digital RGB camera, selects the naturally occurring bright areas (not necessarily the white ones) in natural images and converts the RGB digital counts directly into the spectral power distribution of the illuminants using a learning-based spectral procedure. Computations show a good spectral and colorimetric performance when only three sensors (a three-band RGB camera) are used. These results go against previous findings concerning the recovery of spectral reflectances and radiances, which claimed that the greater the number of sensors, the better the spectral performance. Combining the device with the appropriate computations can yield spectral information about objects and illuminants simultaneously, avoiding the need for spectroradiometric measurements. The method works well and needs neither a white reference located in the natural scene nor direct measurements of the spectral power distribution of the light.     

Polyphenolic fractions improve the oxidative stability of microencapsulated linseed oil

The main objective of this study was to evaluate the effect of incorporating polyphenolic‐enriched fractions from murta leaves on the oxidative stability of linseed oil microencapsulated by spray drying. For this purpose, polyphenol‐enriched fractions from murta leaves were separated by gel permeation chromatography and chemically characterized. The oxidative stability of microencapsulated linseed oil (MLO) with antioxidants was evaluated in storage conditions at 25°C for 40 days. The antioxidant effects of the polyphenolic fractions and commercial antioxidants (BHT and trolox) on microencapsulated oil were evaluated by the value of conjugated dienes, peroxide, and p‐anisidine. In the initiation step of the oxidation, no significant oxidation delay (p>0.05) in MLO containing fractions F₆, F₈, or BHT and trolox was observed. However, in the termination step of the oxidation, the addition of fractions F₆, F₈, and BHT and trolox decreases significantly (p ≤ 0.05) the rancidity in MLO. Furthermore, the results of this study demonstrated the importance of the addition of natural antioxidants such as fractions of murta leaf extract in microencapsulated linseed oil to increase its resistance to oxidation. Practical applications: For incorporating linseed oil, a source of omega‐3 fatty acids, in the diet it is necessary to protect it against oxidative rancidity, the main cause of deterioration that affects food with a high unsaturated fat content. Microencapsulation is effective in retarding or suppressing the oxidation of unsaturated fatty acids and natural plants extracts are effective in inhibiting the lipid oxidation of microencapsulated oil. The use of process technology and a natural additive is expected to increase storage stability and enable its use in dry foods such as instant products. Linseed oil can be used in human nutrition as well as in animal feed as a replacement for fish oil.     

In vitro and in vivo antioxidant activity of musts and skin extracts from off-vine dried Vitis vinifera cv. “Tempranillo” grapes

The phenolic composition and antioxidant activity of musts and skin extracts from Tempranillo grapes dried for variable lengths of times were examined here. Both were found to increase in the grape must with increasing drying time, but the opposite trend was observed in the skin extracts. The antioxidant activity of the must and skin was largely due to anthocyanins. Also, the anthocyanins fraction exhibited the highest antioxidant activity per gram of phenolic compound in the musts and skin extracts at the end of the drying process, polymeric pigments and high-molecular-weight procyanidins were also prominent in this respect. In vivo antioxidant activity in terms of protein oxidation and survival of Saccharomyces cerevisiae cells previously incubated with 10 μg/mL of polyphenols from the musts and skins and exposed to hydrogen peroxide was also measured. Both extracts exerted a protective effect against oxidative stress, the effect increasing with increasing dehydration time and being somewhat higher for skin than for must. Thus, must and skin from dehydrated grapes possess antioxidant properties, which allow the latter, a by-product of sweet wine, to be used as a natural source of antioxidants.