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The moisture content in materials has influence on their thermal, acoustic and mechanical properties, what has clear relation to their durability and service life. On this account, there is necessary to monitor liquid moisture content in building materials, and to know its influence on their behavior and performance. This information can find use already in the design of building structures as well in the restoration and reconstruction of existing buildings.In the presented paper, the problem of calibration of high frequency time domain reflectometry (TDR) method for moisture content measurement in porous building materials is studied. In this work there is focused on analysis of dielectric mixing models that can be used for calibration of dielectric moisture measurement methods. Experimentally accessed data were compared with the results of several mixing dielectric models like formulas developed by de Loor, Dobson, Polder and van Santen and Lichtenecker as well as Wiener’s and Hashin-Shtrikman’s bounds, which define a theoretical minimal and maximal value of permittivity for the given moisture content.On the basis of performed experiments and calculations, the suitable mixing models are identified and recommendations for their practical application are formulated.

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In the industrial practice Howard mould count (Howard, 1911) is used for the estimation of mould contamination of foods. It was developed originally for the investigation of mould contamination of tomato purée. It is also used nowadays for quality control purposes for other food products as well. Recently this constitutes the basis of the acceptance of the finished products in international trade. This technique demands experts with a lot of practice and morphological proficiency. The investigation makes use of eyes and so the tiredness of the investigator can cause uncertainties.The possibility of other methods for the determination of mould contamination of tomato purée was investigated to replace the Howard method. The NIR technique — as a rapid, non-destructive, reagentless and accurate method — was anticipated as a suitable method for the mentioned purpose. Canned tomato purée had been allowed to become mouldy then the sample was blended with non-mouldy samples in different ratio, so a series of tomato purées containing known amounts of mouldy purée was prepared. Howard mould counts and ergosterol content — another mould contamination relating value — was used as reference for NIR calibration.At quantitative investigation better results were obtained using ergosterol values. The best correlation coefficient (R=0.93) and the smallest standard error of calibration (SEC=0.008 mg g−1 ergosterol) was achieved with triangular smoothing and second derivation of the spectra. At qualitative investigation Polar Qualification System (PQS) was used. Clusters between samples with low and high ergosterol levels could be separated.

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Acta Alimentaria
Authors: J. Gajdoš Kljusurić, S. Djaković, I. Kruhak, K. Kovačević Ganić, D. Komes, and Ž. Kurtanjek

Briggs-Rauscher (BR) reaction is one of the most commonly studied oscillation reactions that has been applied for measurement of antioxidant activity of water-soluble substances. There is an immediate quenching of oscillations when free radicals are added from fruits or vegetables. The reaction is monitored potentiometrically and the inhibition time (IT), or time of no oscillations, is proportional to the concentration of antioxidants. pH of the BR reaction is about 2, which is similar to that of the fluids of the main digestive process (human stomach), giving in vitro information on antioxidant activity under “real digestion conditions”and can help in assessment of nutrition for the maintenance of health and prevention of diseases. Antioxidant activities of different concentrations of native Croatian red and white wines are analysed by the inhibition of BR reaction and determination of total phenols using gallic acid as the calibration standard is also carried out. Using mathematical models, relative antioxidant activities of antioxidants and amounts of total phenols are estimated. Second order polynomial calibration curve is estimated in the range of 150-2500 gallic acid equivalent (GAE mg l-1), with standard error of 84 GAE mg l-1.

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A modified QuEChERS method was developed and validated for determination of pesticide multi-residues in green tea by liquid chromatography tandem mass spectrometry. Lead acetate was first time used together with primary secondary amine and graphite carbon black to eliminate tannin, caffeine, and other pigments in tea and thus reduced the matrix effects. The method was compared to the original QuEChERS method as well as A.O.A.C. QuEChERS method. For accurate quantification, the matrix matched calibration technique was used. The method showed good performance in the concentration range from 0.01 to 1 mg kg–1. All pesticides could be quantified at and lower than 0.01 mg kg–1. Recoveries were from 70 to 120% and repeatabilities were <15% RSD depending on the compounds.

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Development of rapid methods is often needed for the in-line process control of the proximate composition (e.g. fat or moisture content) of meat in the meat processing plants. This paper reports on the continuous wave nuclear magnetic resonance (CW-NMR) technique applied for determining fat content in fresh meat. The interfering moisture content in meat was removed by microwave drying and the dried residue was transferred quantitatively into the NMR-tubes. The total analysis time was about 35 min. Experiments were performed with pork (with a fat content from 1.7% to 21%), beef (with a fat content from 1.0% to 16.1%), lard (rendered pork fat) and tallow (rendered beef fat) samples and with their combinations: lard-tallow, lard-lean pork, tallow-lean beef and lard-tallow-lean beef-lean pork. The regression (prediction) equations (NMR-signal vs. fat content determined with the Soxhlet reference method) of pork and beef did not differ significantly. However, there was a noticeable difference between the regression lines of pure lard and pure tallow. Moreover, the latter ones differed from the regression equations of pork, beef and of the various meat-fat combinations. The variability of the fatty acid composition of the fat also seems to influence the stability of the calibration curves, because the sensitivity of the CW-NMR signal to the fatty acid composition interferes with the quantitative determination of fat content in meat.

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Reliable determination of microbial or transgenic Cry toxins is an essential issue in food and feed analyses, and enzyme-linked immunosorbent assays (ELISAs) are the method of choice for quantifying these toxins currently in food and environmental analysis. Internal Quality Control (IQC) is an indispensable method to assess accuracy, precision, and reproducibility of analytical measurements. To assess the utility of the ELISA method, IQC was performed on EnviroLogix Cry1Ab/Cry1Ac QualiPlate ELISA with manufacturer supplied analytical standards. Applicability of negative and positive controls (C− and C+) was examined by Shewhart Control Charts for bias and Control Chart of the Range of Duplicates for precision. Linear regression (up to 5 ng ml−1 Cry1Ab concentration) of the commercial ELISA kit was compared to sigmoid calibration (up to 60 ng ml−1 Cry1Ab concentration). For immunoassay optimization process, possible matrix effects in different liquid and solid vertebrate tissues were examined by determination of the limit of detection values in these matrices.

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Experimental batches of chilled cutlets of pork have been stored aerobically and surface growth of bacteria was determined by standard aerobic spread-plate counts, and colony counts of pseudomonads on Cetrimid Agar simultaneously with detection times of respective stomached samples in triplicate using a Malthus Microbiological Analyzer at 30 °C, applying general impedance broth and Pseudomonas impedance medium, respectively. To study the effects of storage temperature on growth of spoilage bacteria, numerous samples were kept in successive experiments at 4, 8 or 12 °C. Parameters of the bacterial growth curves were estimated by curve fitting of the colony counts by DMfit programme package of the ComBase softwares, using Baranyi’s dynamic growth model. Linear correlations were found between the respective colony counts and the conductimetric detection times observed in periodic investigations during storage. According to these calibrations, the conductimetric method at 30 °C incubation is able to assess within 8 h whether a sample of pork cutlets contains greater or less than 10 7 CFU g −1 of psychrotrophic spoilage bacteria.

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The use of Fourier-transform near infrared spectroscopy (FT-NIR) to measure the content of protein, lipid and sugar contents of bakery products was investigated. The samples were dried, homogenized, sieved and measured in the wavelength range of 780–2500 nm. The calibration was based on partial least squares (PLS) regression with cross-validation. The performance of the final model was evaluated according to root mean square of cross-validation (RMSECV), root mean square error of estimation (RMSEE) and the determination coefficient (R2).The developed models use the ranges of 1100–1245 nm and 1590–2600 nm for protein determination, 1330–1840 nm and 2170–2350 nm for lipid, 1400–1630 nm, 2000–2170 nm and 2230–2570 nm for sugar determination, respectively. Protein, lipid and sugar could be determined directly with R2 values of 98.93, 99.07 and 98.81, and RMSECV values of 0.16 m/m%, 0.79 m/m% and 0.28 m/m%, respectively. It can be concluded that FT-NIR spectroscopy can be used for the routine determination of protein, lipid and sugar content of bakery products and it can contribute to the estimation of calorie content in a fast and non-destructive way.

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The feasibility of NIR spectroscopy for determining chemical composition of goose fatty liver was studied. The spectra of 50 fresh, homogenized liver samples (ether extract content EE=53.2, SD=4.87%) were taken between 1100 and 2500 nm in reflectance mode, then the chemical composition and the fatty acid profile was measured (gas chromatography). Calibration equations were developed using modified partial least-squares regression. The R 2 value in estimation of DM, CP and total EE were 0.72, 0.63 and 0.81, respectively. For the major fatty acids (oleic, palmitic and stearic acid, 51.4, 25.8 and 15.5% of total) the R² values were 0.94, 0.93 and 0.16. The estimation of the total saturated fatty acid (SAT) proportion and the so-called unsaturation index (UI) value was effective (R 2 =0.81 and 0.79, respectively). The paper demonstrates the usefulness of the NIRS method as a fast and solvent free alternative of liver qualification. For practical purposes a larger number of fatty liver samples are needed.

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The aim of this study was to adapt MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] colorimetric assay (MCA) (Wang et al., 2010) for determination of lactic acid bacteria cell count. Our study is helpful in developing protocols for measuring the viability of other lactic acid bacteria. We determined the cell concentration range which gives linear regression of CFU (colony forming units) and formazan production. In our experiment three authentic lactic acid bacteria strains were investigated: Lactobacillus rhamnosus VT1, L. plantarum 2142, and L. sakei DSM 2001. As data show beside the strain also the growth medium has influence on the MTT reduction activity, this means that for each special case separate calibration curve has to be prepared. Based on MTT reduction we also developed an improved microtiter plate assay which proved to be reliable for a rapid cell count determination. So our methods are only applicable for estimate cell number with fixed parameters, but under given circumstances they are fast and sensitive methods. With the modified methods we can rapidly measure the dehydrogenase enzyme activity of the lactic acid bacteria cells. With the microplate assay we can measure many conditions and strains at the same time.

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