Search

The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (LPAS) and colorimetric method for quantification of anthocyanin (E163) in commercially available hard boiled candies are compared to that of the spectrophotometry (SP). Both LPAS and colorimetry are direct methods that unlike SP do not require the extraction of the analyte or some additional sample treatment. Results indicate that LPAS and colorimetry are both suitable for quickly screening content of anthocyanin in hard boiled candies. The correlation between the two methods and spectrophotometry is linear with R2 = 0.9989 for LPAS and R2 = 0.9570 for colorimetry.

A relatively novel approach for easy and quick determination of rutin in buckwheat grain is suggested. The rutin content of the grain in seven common buckwheat (Fagopyrum esculentum) and six Tartary buckwheat (Fagopyrum tataricum) varieties was investigated by means of UV photoacoustic spectroscopy and HPLC as reference method. The lowest content was found in ‘Botan’ and ‘Bamby’ varieties, while the highest values were obtained in the variety ‘Emka’. Rutin content in grain of all Tartary buckwheat varieties was two orders of magnitude higher than in the other varieties. Rutin content in F. esculentum ranges between 9 and 36 mg/100 g dry weight as compared to 921 to 2 132 mg/100 g dry weight in F. tataricum. The UV photoacoustic spectroscopy data show rather good correlations of R2=0.977 and R2=0.980 with values obtained by HPLC data for all measured samples. Therefore, UV photoacoustic spectroscopy can be a cheap and quick method for determining rutin content in buckwheat grain.

Carotenes, found in a diversity of fruit-containing foods, are important sources of antioxidants; a good example is apricot jam. In the study described in this paper, both the total carotenoid content (TCC) as well as the content of $$\upbeta $$ -carotene in six different apricot jams were quantified using traditional (UV–VIS) spectrophotometry (SP), high-performance liquid chromatography (HPLC), laser photoacoustic spectroscopy (LPAS), and the optothermal window (OW) method. Unlike SP and HPLC, LPAS and the OW methods require the minimum of sample preparation and only a one time calibration step which enables practically direct quantification of the TCC. Results were verified versus data obtained with SP as the reference technique. It was shown that LPAS and the OW method (at 473 nm) provide satisfactory results with $$R^{2}=0.9884$$ and 0.9766 for LPAS and OW, respectively.

This report adds to the ongoing vivid dispute on the fate of carotenes in tomato upon thermal processing. Although many papers dealing with changes in the raw tomatoes during industrial treatment have already appeared, data on the fate of finished, processed tomato products when they are additionally heated (e.g., when used in the household) is scarce. In this study, effects of heating and storage on a commercial, double concentrated tomato pur ee were examined spectrophotometrically. Our results indicate that upon exposing unopened cans with double concentrated tomato pur ee to thermal treatments between 100 and 135 ^o C during specific time intervals spectral profile of lycopene remained preserved. Likewise, a slight hypsochromic shift of lycopene peak III did not occur up to 135 ^o C. However, significant (20%) initial loss of lycopene content was induced by thermal treatment for 20 min at 100 ^o C. During the more intensive treatments that followed the lycopene content was first leveling off and then slightly increased. After storage of thermally treated samples at - 18 ^o C the content of lycopene was found to increase. All these results suggest simultaneous working of several mechanisms: possible autooxidation and isomerization processes of carotenes taking place, in addition to the Maillard reaction and enhanced extractability of carotenes at increased temperatures. Results acquired from hexane solutions of samples treated at temperatures of 120 and 135 ^oC obtained at different time points, confirmed severe isomerization in organic solvent and/or photo-oxidative degradation of lycopene.

Laser photoacoustic spectroscopy (PAS) and colorimetry have been used to rapidly and accurately determine the content of fat-free cocoa solids in dark chocolates. Both techniques are inexpensive and require only a one-time calibration step versus a method capable of absolute concentration measurement (for example HPLC). Once the response of PAS and/or colorimetry has been obtained, the content of fat-free cocoa solids in dark chocolates can be determined directly (i.e. without any sample preparation including the process of extraction) from the calibration curves and the experimentally measured microphone signal (in PAS studies) and colorimetric indices L* and ΔE* (in colorimetric investigations). Both colorimetric indices and PA signals correlate positively with the content of fat-free cocoa solids. The correlation is highly linear over a wide concentration range (25–50 %).

This paper reports, the Laser Induced Breakdown Spectroscopy (LIBS) studies and structure elucidation of compounds isolated from the fruit extract of Moringa oleifera and also deals with their possible effects on some bacterial strains viz. Staphylococcus aureus, Klebsiella pneumonia, Escherichia coli and Pseudomonas aeruginosa. The extract was found to be active against all four microorganisms used. Extent of inhibitory effect of extract was assessed at different concentrations of 25, 50, 75 mg/ml by measuring diameter of inhibition zone (DIZ). Our results clearly showed that the 75 mg/ml concentration of the extract had 14, 12 and 18 mm of the DIZ against Staphylococcus aureus, Klebsiella pneumonia and Pseudomonas aeruginosa and 14 mm with 50 mg/ml concentration against Escherichia coli. The results were compared with the standard antibiotic ‘ampicillin’ of 1 mg/ml concentration. LIBS was recorded with high power pulsed laser beam from Nd: YAG Laser (Continuum Surelite III-10), focused on the surface of the material, which was in liquid form, to generate plasma on the surface of the sample. LIBS data clearly demonstrate the presence of trace elements, magnesium and iron, in high concentration in the extract. Whereas, from the phytochemical profile reveals the presence of two new compounds, S-ethyl-N-{4-[(a-L-rhamnosyloxy) benzyl]} thiocarbamate and 2-acetoxy {4-[(2',3',4'-tri-O-acetyl-a-L-rhamnosyloxy) benzyl]} acetonitrile as the major constituents. This study is the first report on synergetic effect of the phytoconstituents and certain set of elements present in their defined role in bacterial management against different bacterial strains.

Photopyroelectric (PPE) methods belong to the class of photothermal techniques and provide the means for determining some thermal properties of foods in a relatively fast and simple way. In particular, the inverse variant of the photopyroelectric method, abbreviated IPPE, was used here to determine thermal effusivity (also called heat penetration coefficient) of the sour cream and mayonnaise as a function of their fat content. In the sour cream the latter varied from 12 to 31 g/100 g as compared to 27 to 80 g/100 g range in mayonnaise; for both samples the effusivity decreased linearly with the increasing fat content. Each additional gram of fat in 100 g sour cream or mayonnaise resulted in 11.13 and 12.11 Ws1/2m-2K-1 drop in effusivity. Good agreement between the experimentally obtained data and the calculated effusivity was observed if both, the composition and the thermal properties of individual constituents of sour cream were known.

The performance of the newly proposed laser-based optothermal window (OW) method and colorimetry for quantification of trans -lycopene in 10 watermelon homogenates has been evaluated. Reverse phase HPLC served as an established reference method. Both, OW and colorimetry are direct methods as they, contrary to the HPLC, obviate the need for extraction, which leaves homogenization of the sample as the only preparatory step prior to the analysis itself. The evaluation of analytical performance of each method leads to the conclusion that the OW method and colorimetry are both suitable for quick screening of the trans -lycopene concentration of red-fleshed watermelon homogenates. Linear correlation is highest ( R = 0.917) for the laser-based OW method. This detection concept offers an additional but very unique advantage. By virtue of the operational principle of the OW method, it is possible to avoid the effect of saturation, a phenomenon known to cause difficulties when interpreting data collected by other analytical methods.

The scientific evaluation of the antidiabetic efficacy of aqueous extract of Trichosanthes dioica fruits on streptozotocin-induced diabetic rats is being presented. The graded doses of the extract, viz., 500, 750, 1,000, and 1,250 mg/kg body weight (bw), were administered orally, and it was observed that the blood glucose concentration decreased in a dose-dependent manner. The dose of 1,000 mg/kg bw showed the maximum fall of 23.8% and 19.1% in blood glucose level (BGL) during fasting BGL and glucose tolerance test (GTT) studies, respectively, of nondiabetic rats. Whereas in the case of subdiabetic and mild diabetic models, the same dose showed reduction in BGL of 22.0% and 31.4% during GTT. The study also involves the first use of laser-induced breakdown spectroscopy as a sensitive analytical tool to detect the elemental profile responsible for the antidiabetic activity of aqueous extract of T. dioica fruits that exhibits the antidiabetic activity. High intensities of Ca, Mg, and Fe indicate large concentrations of these elements in the extract, since according to Boltzmann’s distribution law, intensities are directly proportional to concentrations. The higher concentrations of these glycemic elements, viz. Ca, Mg, and Fe, are responsible for the antidiabetic potential of T. dioica as well as other plant already reported by our research group.

Gold nanoparticles were synthesized by laser ablation of a gold metallic disc at wavelengths of 532 nm and 355 nm with 7 ns pulse duration in the pure water. The colloidal gold nanoparticles were characterized by ultraviolet-visible absorption spectroscopy, transmission electron microscopy, and fluorescence spectrometry. The presence of a surface plasmon resonance peak around ∼ 524 nm indicates the formation of gold nanoparticles. The formation efficiencies of gold nanoparticles in colloids were found to increase when ablating the gold metallic disc with a laser having a longer wavelength. The size distributions of the gold nanoparticles thus produced were measured by transmission electron microscopy. A reduction in mean diameter of the particles was observed with a decrease in the laser wavelength under the irradiation at a high fluence of 25 mJ/pulse. The fluorescence spectroscopy demonstrated that these gold nanoparticles are fluorescent, showing a strong blue emission intensity at 458 nm.

Colloidal silver nanospheres, nanorings, and nanonetworks were synthesized by the nanosecond pulsed laser ablation of a silver metal plate in a pure distilled water (at room temperature) using the fundamental (1064 nm), second harmonic (532 nm), and third harmonic (355 nm) wavelengths of the Nd:YAG laser, respectively. The products were characterized by means of both transmission electron microscopy (TEM) and optical absorption spectroscopy. The TEM data show the formation of silver nanospheres, nanorings, and nanonetworks. On the other hand, optical spectra reveal the occurrence of the red shift of the peak associated with the surface plasmon resonance (SPR) of silver nanorings and nanonetworks. A possible explanation for the formation of above stated silver nanostructures is being discussed.

Carotenes found in a diversity of fruits and vegetables are among important natural antioxidants. In a study described in this paper, the total carotenoid content (TCC) in seven different products derived from thermally processed tomatoes was determined using laser photoacoustic spectroscopy (LPAS), infrared lock- in thermography (IRLIT), and near-infrared spectroscopy (NIRS) combined with chemometrics. Results were verified versus data obtained by traditional VIS spectrophotometry (SP) that served as a reference technique. Unlike SP, the IRLIT, NIRS, and LPAS require a minimum of sample preparation which enables practically direct quantification of the TCC.

The availability of thermo-physical data of foods and their constituents is of general importance to food industry. The thermal effusivity e is one among the relevant thermodynamical quantities. The latter is normally calculated from the relationship e = (κρc)½, where c is specific heat, ρ is the density, and κ is the thermal conductivity. The necessity for performing the time consuming independent measurements of these three quantities is the major reason that the existing database with effusivity of foods is not very wide. This paper describes the application of the inverse photopyroelectric (IPPE) technique that allows the determination of effusivity from a single measurement. This approach was used to directly measure thermal effusivity of fresh egg yolk, egg white, and white/yolk blends. In addition, thermal effusivity of rehydrated egg powders (white, yolk, and the whole egg powder) has been measured and compared to that of the fresh hen egg. In case of the egg white, effusivity of rehydrated egg powders was practically the same as that of the fresh egg. However, the difference in effusivity between fresh egg yolk and rehydrated egg yolk, and between the blend of fresh egg and the rehydrated whole egg power was significant. Finally, thermal effusivity of rehydrated egg yolk, egg white, and the whole egg powder was determined as a function of dilution factor.

The back photopyroelectric (PPE) configuration, with opaque sample and thermally thick sample and sensor, was applied in order to obtain room temperature values of the thermal diffusivity of some liquid mixtures. The methodology is based on a sample's thickness scan, and not on a frequency scan as is usually the case. The possibility of precisely controlling the sample's thickness variation leads to very accurate and reproducible values for the thermal diffusivity. The method is proposed as an alternative for evidencing molecular associations in binary liquid mixtures.

Direct and reliable spectrophotometric method for assaying total carotenes (TC) in margarines with the minimum of sample manipulation is proposed. For the first time saponification step used in determination of carotenes in margarines was omitted leading to a substantial cost saving and reduction of time needed to complete the analysis. The resulting analytical procedure is characterized in details in terms of the figures of merit. The method is sensitive, precise and accurate; for both, standard additions and calibration in soybean oil, recovery ranges between 98 and 102%. For the most accurate analyses the approach of standard additions is preferred but for quick routine analyses this latter can be replaced by the calibration in soybean oil. Limit of detection value (LOD = 3S.D.B/a, where S.D.B is the standard deviation of the blank, “a” is the slope of calibration line) as low as 12 μg TC/100 g was achieved in soybean oil enabling the sensitive detection. Concentration of TC in margarines declared as being coloured with β-carotene (carotene) ranges between 0.3 and 0.9 mg/100 g while in carrot extract-coloured margarine TC is 0.2 mg/100 g.

The photopyroelectric (PPE) method, in both front and back configuration, was used to measure the thermal effusivity and diffusivity of several tomato puree concentrates. These results were used to construct a calibration curve which was used at a later stage to determine dry matter content of tomato puree concentrates. The phase transition investigations showed that the freezing point is dependent on the dry matter content, indicating that the water in these foods is not free.

This study reports on the first use of the "optothermistor" as a novel, precise, fast, and low-cost detector of lycopene in a wide range of commercially available processed-tomato products. The quantitative performance of the new device was evaluated by comparing data obtained to that acquired by conventional methods, namely, absorption spectrophotometry and high-performance liquid chromatography (HPLC) ; the linear correlation was high (R = 0.98). The variation of data obtained with the optothermistor in a series of consecutive measurements performed with the same loading of the sample was better than 1%. However, the repeatability (RSD 0.5-9.0%, n = 3-5) achieved with the optothermistor by independent analyses (multiple loading) is comparable to that of HPLC and spectrophotometry. Results of the studies performed on the 19 products derived from tomatoes demonstrated that the optothermistor is suitable for selective, accurate, precise, and simple determination of lycopene (range = 7-75 mg/100 g of product weight) without the need for a sample pretreatment step. The estimated sensitivity of the present optothermistor is 2 mg of lycopene/100 g of product.

A new photothermal method suitable for direct, accurate and highly reproducible quantitative measurements of lycopene in tomato products has been introduced. The intrinsic precision of the method is typically better than 0.2%; the repeatability of determination is comparable to that of high-performance liquid chromatography, with 0.86% least overall error.

CO2-laser photothermal radiometry (PTR) was demonstrated to be suitable for the non-destructive and non-contact characterization (both optical and thermal) of solid phase agricultural commodities (fresh vegetables, fruits) and confectionery products (candy). Proper interpretation of PTR signals enable one to calculate two parameters, i.e. the well known thermal effusivity e ( e= λρc p , where λ and ρcp are the thermal conductivity and the volume specific heat, respectively) and a newly introduced physical quantity termed ‘initial heating coefficient’ chi (χ=β/(ρcp), β is the absorption coefficient). Obtained values for e are in a good agreement with data reported in the literature. PTR enables one to rapidly determine e via a single measurement. As opposed to this, the knowledge of two out of three thermophysical parameters (thermal diffusivity, thermal conductivity and volume specific heat) is a condition sine qua non for determining effusivity in the conventional manner.

Photoacoustic (PA) spectroscopy in the ultraviolet and visible was demonstrated to be a suitable tool for direct determination of total phenolic content in red sorghum flours. The PA spectra obtained feature two characteristic peaks: the first centered at 285 nm is due to the aromatic amino acids, while the second one at 335 nm is associated with the total phenolic content. The outcome of the PA study was compared with the results obtained by a conventional, tedious Folin-Ciocalteau chemical method. Statistical analysis indicates no significant difference between the two methods used in this study.

Several physical techniques were used to study the extent of spoilage in apple juice deliberately inoculated with yeast (concentration of Saccharomyces cerevisiae ranged from 25 cells mL(-1) to 2.5 x 10(6) cells mL(-1), respectively) and their performance compared in terms of detection limit achieved. The optical methods used in this investigation rely on the measurement of either absorption [as is the case for classical spectrophotometry (SP) and the so called optothermal window (OW), a variant of a photothermal method], or scattering [examples are turbidimetry (TB), laser scattering (SC), and laser speckle fluctuation (SF)]. It is shown that the presence of yeast increases both optical absorption and scattering. The most favorable detection limit (25 cells mL(-1)) and a highest (nearly 10(4)) dynamic range, combined with a good linearity, were obtained with the experimental set-up for SC. In addition, the extent of correlation between different methods was determined using two markedly different reference substances, i.e., (i) the mixture of apple and blackcurrant juices, representing a strongly absorbing sample, and (ii) diluted (dilution factor of 103) milk as a strong scatterer. Finally, one has monitored the progress of a spontaneous spoilage process in the inoculated juices stored at 5degreesC under aerobic conditions.

Detecting early ageing stages of seeds in storage is of great concern to vegetable seed companies. Despite their reliability conventional germination tests are destructive and time consuming. One alternative towards assessing the quality of seed is to monitor the concentration of certain volatiles (acting as biological markers) evolved from the seeds; examples are ethanol (EtOH), acetaldehyde, ethane, methanol, etc. Most of the presently used methods have only moderate insensitivity and are therefore not suitable for the on-line measurements. In this work CO laser photoacoustic spectroscopy (LPAS) was used to investigate the on-line evolution of EtOH and acetaldehyde from the imbibed nonaged and aged seeds of cabbage. The overall performance of LPAS was superior to that of Fourier transform infrared and of gas chromatography.

The optothermal window detection method at 488 nm was used to monitor on-line the concentration of trans-ß-carotene that was added to several vegetable oils after treating them at 200 °C in the presence of air for varying amounts of time. Results obtained for extra virgin oil show a direct proportionality between the rate constant describing the disappearance of trans-ß-carotene and the duration of thermal treatment. The rate constant for the decay of trans-ß-carotene in oils treated under identical conditions was also dependent on the type of oil. Trends and individual data are discussed in the light of a possible application of the method for the determination of the oxidative stability of vegetable oils.

The concept of OW (with 632.8 nm He–Ne laser), combined with colorimetry based on a reaction of anthrone-sulphuric acid, was proposed as a new tool for determination of lactose in raw milk. Data obtained from various milk samples by OW colorimetry were compared to those acquired from the MilkoScan analyser; the correlation between the two methods is high.

Carotenoids are important antioxidants found in various foods including those for nutrition of infants. In this investigation, the total carotenoid content (TCC) of nine different commercially available baby foods was quantified using colorimetric index a * obtained via reflectance colorimetry (RC) and by laser photoacoustic spectroscopy (LPAS) at 473 nm. The latter requires a minimum of sample preparation and only a one time calibration step which enables practically direct quantification of TCC. Results were verified versus UV–Vis spectrophotometry (SP) as the reference technique. It was shown that RC and LPAS (at 473 nm) provide satisfactory results for a *, R 2 = 0.9925 and R 2 = 0.9972, respectively. Other color indices do not show a correlation with TCC. When determining the TCC in baby foods containing tomatoes, it is necessary to select a different analytical wavelength to compensate for the effect of lycopene’s presence in the test samples.

Cocoa is a very important ingredient in the food industry and largely consumed worldwide. In this investigation, colorimetry and photoacoustic spectroscopy were used to directly assess the content of cocoa powder in cakes; both methods provided satisfactory results. The calibration curve was constructed using a series of home-made cakes containing varying amount of cocoa powder. Then, at a later stage, the same calibration curve was used to quantify the cocoa content of several commercially available cakes. For self-made cakes, the relationship between the PAS signal and the content of cocoa powder was linear while a quadratic dependence was obtained for the colorimetric index $$L^*$$ (brightness) and total color difference ( $$\Delta E^*$$ ).

This research study demonstrates that thermal lens spectrometry (TLS) combined with efficient isocratic HPLC separation provides an excellent analytical means to profile and quantify carotenes in fish body oils and possibly also in vegetable oils. In particular, a highly sensitive, selective, simple and rapid method for the determination of ultratraces of beta-carotene in fish oil-based supplementary drugs has been proposed. The analyte could be determined reliably and precisely in the presence of a complex matrix including other fat-soluble vitamins (A, D and E), polyunsaturated fatty acids, sterols and other pigments by matrix-matched calibration in cod liver oil. The suitability of the method is also evidenced by favourable analytical figures of merit for beta-carotene such as a linearity range of 1-120 ng ml(-1), LOD of 0.58 ng ml(-1), recovery of 101.4+/-3.3% and measurement repeatability of 4.1%.

The temperature dependence of thermal diffusivity of the low density polyethylene (LDPE) and polyvinyl chloride (PVC) packaging foils was determined using the photopyroelectric (PPE) approach in the standard configuration. Glassy phase transitions observed in foils within the -30°C to 70°C range cause a 7 to 20% increase in values of thermal diffusivity for these test materials. The results obtained by the PPE approach were confirmed by differential scanning calorimetry.

The photopyroelectric (PPE) method is proposed as a new technique for thermal characterisation of fruit juices. By combining different geometries and experimental conditions, the PPE method was shown capable of providing temperature-dependent (between 0 and 70 °C) values of thermophysical parameters (thermal diffusivity, thermal effusivity, thermal conductivity and volume specific heat) for juices having different Brix index. The computer-controlled PPE cell allowed stable temperature variation rates and continuous signal acquisition. The experimental data were used to develop empirical models and hence prediction equations for all the thermal parameters. © 1999 Society of Chemical Industry

The optothermal window (OW) in conjunction with a low-power infrared source was used at 4 μm wavelength to measure the concentration of D2O needed to determine the total body water (TBW) in human subjects. The 30 ppmv D2O detection limit is comparable to that obtainable by infrared transmission (IRT) spectroscopy but can be further enhanced. Low cost and ease of sampling and operation are other advantages of the novel method.

Photopyroelectric (PPE) study of some saturated (C5: 0, and C23: 0) and unsaturated (C18: 2 and C18: 3) free fatty acids was performed in a temperature range that included their melting points. The standard PPE configuration was used consistently during the experiment; the special PPE case requests thermally thick sample and sensor and optically opaque sample. For those fatty acids for which literature data on volume-specific heat were available (C18: 2, C18: 3), the behaviour around the melting point of all static and dynamic thermal parameters (specific heat, thermal conductivity, diffusivity and effusivity) was obtained. Since no data for volume-specific heat of C5: 0 and C23:0 were found in the literature, only the temperature behaviour of the thermal diffusivity was obtained for these specimens.

Thermal lens spectrometry (TLS) was applied for the detection of beta-cryptoxanthin, alpha-carotene, trans-beta-carotene, and lycopen in blood plasma. This combined high-performance liquid chromatography-TLS (HPLC-TLS) method was validated by comparison with HPLC-UV-Vis analysis of blood plasma under identical chromatographic conditions and by comparing the results obtained from an independent, standard HPLC procedure for determination of carotenoids in blood plasma samples. The results demonstrated good agreement with the target values for carotenoids in an in-laboratory control sample and confirmed the accuracy of the HPLC-TLS technique. Limits of detection for blood plasma samples were 70 pg/ml for beta-cryptoxanthin, 85 pg/ml for alpha-carotene, 100 pg/ml for trans-beta-carotene, and 120 pg/ml for lycopen. This represents a 100-fold improvement compared to the HPLC analysis with UV-Vis detection.

A simple pyroelectric sensor is presented for on-line monitoring of Rayleigh-Benard -Marangoni convective instabilities in methanol, ethanol and isopropanol aqueous solutions, caused by alcohol evaporation from the free surface of the liquid. The signals measured at the liquid-substrate interface represent thermal fluctuations of the order of 10−2 K, having a frequency spectrum between 0.08 Hz and 0.4 Hz. The numerical estimation of the Rayleigh and Marangoni numbers leads to the conclusion that the latter is dominant in the conditions of the experiment. The amplitude and duration of the thermal noise are investigated as a function of alcohol concentration. An attempt is made to determine characteristic invariant quantities.

Optothermal window spectroscopy at CO2 laser infrared wavelengths was used to detect the extent of adulteration of extra-virgin olive oil by sunflower and safflower oils. A good linearity between the strength of optothermal signal and the concentration of each adulterating compound was found. Predicted limits of detection presently attainable by this new method are 6 (w/w) and 4.5% (w/w) for extra-virgin olive oil adulterated with safflower oil and sunflower oil, respectively, and were confirmed experimentally; the corresponding relative errors were 0.3 and 0.18%. Interference effects are comparable to those encountered in other spectroscopic methods at the same wavelength.

The operational principle and the first application of a novel infrared differential thermal lens spectrometer for optical studies of liquid samples is described. Compared to a conventional double-beam (pump/probe) configuration, the instrumental setup described here offers the possibility to substantially reduce (as much as 30 times) the background signal caused by the absorption of solvent, and hence to achieve improved limits of detection (LOD). Differential thermal lens spectrometry (TLS) with a CO laser as the excitation source was applied to detect tuberculostearic acid and the insecticide Carbaryl, both extracted into CCl4; the corresponding LOD are 200 μg/L and 150 μg/L, respectively. Results of preliminary studies also suggest the potential use of differential TLS for detection of citric acid dissolved in water.

Introduction Fruits and vegetables used in various processed products, as well as in fresh market sales, are expected to comply with the certain quality standards. However. quality is everything but a single parameter state and, therefore, a variety of subjective and objective measurements are usually performed. In particular, the firmness and maturity are considered important attributes to the quality of fruits and vegetable crops. Presently. these parameters are usually determined either destructively (by a pressure tester) or by means of ultrasound; a development of alternative methods has been strongly encouraged in the recent years.

The potential of photothermal beam deflection spectrometry (PTDS), photoacoustic spectroscopy (PAS) and photothermal radiometry (PTR) for the characterization of thin-layer chromatography (TLC) plates with respect to the surface and in-depth distribution of different compounds inside the sorbent was investigated. Photothermal measurements of TLC chromatograms of the Camag III test dye mixture demonstrate that accurate and comparable values for thermal diffusivity of spots in chromatograms and of the sorbent can be obtained by PTDS and PAS. PAS has been demonstrated to be the most reliable and least time-consuming among the three investigated techniques. Differences observed between the PAS signal and the phase-frequency scans obtained from the spots of the same compound on different TLC plates could be due to the irreproducibility of chromatogram development or the inhomogeneousness in different TLC plates.

The back and front photopyroelectric configurations were combined in order to obtain room temperature values of the thermal parameters of some margarines present on the Romanian market. The back configuration (with thermally thick sample and sensor) allows the direct and absolute measurement of the thermal diffusivity. The thermal effusivity was obtained in the front configuration (with thermally thin and optically opaque sensor and thermally thick sample).

The optothermal window method, a variant of photoacoustic spectroscopy, was used at 10 μm wavelength to explore its feasibility for direct investigation of aqueous solutions of lactose and corn sta...

This report is aimed at intra-laboratory and inter-laboratory comparison of the results obtained during spectrophotometric and HPLC analyses of lycopene, beta-carotene and total carotenoids in tomato products and yellow maize flours/grits. Extensive statistical analyses are performed in order to identify the main sources of uncertainties which may occur when using: (i) different techniques/methods/approaches in the same/different laboratories, in various food samples, and (ii) to indicate the facts/conditions under which the biases between results may remain unidentified after applying statistical testing. Our data points to the inertness of t-test to detect significance of differences, particularly at low R values: in general, the higher correlation coefficient, the higher is sensitivity of statistical testing, especially of the paired t-test. Therefore, simple deviation of relationship line slope from unity could be used as additional evaluation parameter. This adds to reliable and objective quality assurance of foods in regard to carotenoids.

Photoacoustic spectroscopy (PAS) and reflectance colorimetry are suggested as new tools for the analysis of total carotenoids in lyophilized apricot powders. The data obtained by these two techniques from seven apricot cultivars were compared to those acquired by spectrophotometry and high-performance liquid chromatography (HPLC). Best correlations were found between the total carotenoid (TC) content (obtained by VIS spectrophotometry: 1.2–3.4 mg per 100 g of fresh mass) and colorimetric index a* (a* represents the redness of the investigated sample), as well as either argon-ion laser- or xenon-lamp-based PAS. In all three cases linear correlations were comparable. However, according to the sensitivity and precision data, expressed via limit of detection (LOD) and measurement repeatability, the Xe-lamp-based PAS is a preferred approach, followed by colorimetric index a* and Ar-ion laser PAS. Both PAS methods exhibit practically the same Pearson's correlation coefficient (R=0.987 and R=0.991) values. Nevertheless, residual sum of squares (RSS) and residual standard deviation of the linear regression (sy/x) differ markedly. For Xe-lamp-based PAS these parameters were much lower than in the case of Ar-ion laser PAS. Likewise, analysis imprecision amounted to relative standard deviation (RSD) of 1–3 % for Xe-lamp PAS and 2–6 % for Ar-ion laser PAS. On the other hand, as expected, the calibration sensitivity achieved for the PAS signal induced by an Ar-ion laser at 481 nm was substantially higher than that of a Xe-lamp at 470 nm. Nevertheless, according to much lower sy/x, the corresponding LOD for Xe-lamp PAS was still two times lower than that of Ar-ion-based laser PAS (0.59 vs. 1.10 mg per 100 g). Unlike this, Ar-ion laser PAS showed more favourable instrumental precision and standard error of the weighed mean when compared to the Xe-lamp PAS (0.1–0.6 and 0.1–0.3 % vs. 0.5–8.0 and 0.4–1.7 %, respectively). As far as colorimetric indices are concerned, only a* proved to be analytically useful; excellent R but rather modest RSS and sy/x resulted in LOD value of 0.70 mg per 100 g and acceptable analysis imprecision of up to 3 %. The outcome of this research provides sufficient amount of evidence that analytical methods such as reflectance colorimetry and PAS without the use of any chemicals are feasible for reliable quantification of total carotenoids in freeze-dried apricot homogenates., Fotoakustična spektroskopija (PAS) i refleksna kolorimetrija predložene su kao nove metode određivanja udjela ukupnih karotenoida u liofiliziranom prahu marelice. Rezultati dobiveni ispitivanjem sedam kultivara marelice ovim dvjema tehnikama uspoređeni su s onima dobivenim konvencionalnom vidljivom spektrofotometrijom i tekućinskom kromatografijom visoke djelotvornosti (HPLC). Najbolje su korelacije dobivene između udjela ukupnih karotenoida (vidljivom je spektrofotometrijom utvrđen udjel od 1,2 do 3,4 mg u 100 g svježe mase) i kolorimetrijskog indeksa a* (parametar crvenila ispitanog uzorka), te metodom PAS s argonskim laserom ili ksenonskom lampom kao izvorom zračenja. U sva su tri slučaja dobivene usporedljive linearne korelacije. Međutim, s obzirom na osjetljivost i preciznost rezultata izraženih pomoću granice detekcije i ponovljivosti mjerenja, najboljom se pokazala metoda PAS sa ksenonskom lampom, zatim kolorimetrijski indeks a* i naposljetku metoda PAS s argonskim laserom. Obje su metode PAS imale podjednake Pearsonove koeficijente korelacije (R=0,987 i R=0,991). Ipak, rezidualna suma kvadrata (RSS) i rezidualna standardna devijacija linijske regresije (sy/x) značajno su se razlikovale. Za metodu PAS sa ksenonskom lampom ovi su parametri bili znatno manji nego za metodu PAS s argonskim laserom. Također, nepreciznost je metode izražena pomoću relativne standardne devijacije (RSD) bila od 1 do 3 % za metodu PAS sa ksenonskom lampom i od 2 do 6 % za metodu PAS s argonskim laserom. S druge je pak strane, kao što je i bilo očekivano, kalibracijska osjetljivost postignuta za signal PAS induciran argonskim laserom pri 481 nm bila znatno niža od one dobivene ksenonskom lampom pri 470 nm. Ipak, zahvaljujući bitno nižoj vrijednosti sy/x, granica detekcije metode PAS sa ksenonskom lampom (0,59 mg u 100 g) bila je dvostruko manja od one metode PAS s argonskim laserom (1,10 mg u 100 g). Nasuprot tomu, metoda PAS s argonskim laserom imala je bolju preciznost instrumenta (nepreciznost mjerenja od samo 0,1-0,6 %) i standardnu pogrešku ponderirane sredine (0,1-0,3 %), u usporedbi s metodom PAS sa ksenonskom lampom (0,5-8,0 % odnosno 0,4-1,7 %). Među kolorimetrijskim indeksima samo je indeks a* bio koristan za analizu; odlične vrijednosti R, ali skromne vrijednosti RSS i sy/x rezultirale su granicom detekcije od 0,70 mg u 100 g i prihvatljivom nepreciznošću mjerenja od najviše 3 %. Rezultati ovog istraživanja pokazuju da se analitičke tehnike, poput refleksne kolorimetrije i fotoakustične spektroskopije mogu primijeniti za pouzdano određivanje udjela ukupnih karotenoida u liofiliziranim homogenatima marelice, i to bez uporabe reagenasa.

The standard (SPPE) and inverse (IPPE) photopyroelectric configurations were combined in order to obtain room temperature values of the thermal parameters for various types of food products. The SPPE configuration (with thermally thick sample and sensor) allows the direct and absolute measurement of the thermal diffusivity. The thermal effusivity was obtained in the inverse configuration (with thermally thin and optically opaque sensor and thermally thick sample). The static (volume specific heat) and dynamic (thermal conductivity, diffusivity and effusivity) thermal parameters for a variety of liquid and pasty products such as oils, margarine, butter, creams, mustard, ketchup and juices are reported.

Four techniques, i.e., gas-liquid chromatography, gas-liquid chromatography + thin-layer chromatography, and two spectroscopic methods, Fourier transform infrared spectroscopy and optothermal window, a variant of the open photoacoustic cell, were intercompared to determine their potential to detect the total trans fatty acid content in margarine. At the same time, this study represents a first application of the optothermal window technique at long wavelengths (10 μm). The total trans fatty acid data obtained by different methods show good mutual agreement. Besides offering several attractive advantages above conventional methods, the optothermal window also proved suitable for measuring total trans fatty acid content as low as 2%.

The technique of photothermal beam deflection has been used to determine the thermal diffusivity of beans with varying levels of hydration. A strong relationship between the water content and measured thermal diffusivity was observed. The technique was also tried on other kinds of agricultural produce but was found to be unsuitable for non-destructive testing in most cases.