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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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In the process of design and operation of sewerage system are used empirical formulas, which are in many cases, become obsolete and unusable when somebody can use nowadays modern technologies and materials. Therefore there is the possibility of using the mathematical models enormous importance for the enhanced environmental protection with the lowest operating and investment costs. In this modern method of analyzing of sewers has been designated as the first object, the object sedimentation tank. The purpose of the primary and secondary settling tank is to ensure the reduction of concentration the floating solids.

For the solution of research work has been chosen, after consultations with representatives of the Western Slovakia Water Company as interesting object of sedimentation tank located on the waste water treatment plant Nitra - Dolné Krškany.

Measurements on the object settlement tank situated at waste water treatment plant Nitra confirmed the expected speed parameters of the sewage in the tank. The velocity of wastewater is in the most cases very low, and even insignificant. However, finding that the sludge cloud has a non-standard form of a double wave gives the opportunity to optimize the operation of facilities sedimentation tank. The measured parameters are used as calibration parameters to input to the mathematical simulations, which are created by software ANSYS fluent.

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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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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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Nowadays most of the users needing geodetic accuracy use the Global Positioning System (GPS) with static measurements or with RTK (Real Time Kinematic) measurements. Few seconds are available to measure a detail point, therefore only the RTK method can satisfy the expectations. In this case (called observation space) the users require corrections from a base station. These corrections are available from the user’s own base station or they can be downloaded from the Internet if active permanent network is available in the area. There are many locations where kinematic data is recorded and have to be processed without owned base stations or without active permanent networks. For example, LEO (Low-Earth Orbit) satellite’s GPS receivers, ocean surface monitoring with GPS buoys or archaeological exploration in countries without geodetic base. This paper investigates the possibility of PPP (Precise Point Positioning) method processing kinematic data. It is known that the accuracy of this technique is enough in GIS (Geographic Information System) applications. To increase the accuracy and reach geodetic precision final orbits, clock data from the GPS satellites and receiver’s antenna calibration data are needed besides several additional parameters (called state space). The attainable accuracy will be determined after the examination of the results.

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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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