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.

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.

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.

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 purée were examined spectrophotometrically. Our results indicate that upon exposing unopened cans with double concentrated tomato purée to thermal treatments between 100 and 135 °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 °C. However, significant (20%) initial loss of lycopene content was induced by thermal treatment for 20 min at 100 °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 °C the content of lycopene was found to increase. All these results suggest simultaneous working of several mechanisms: possible auto-oxidation 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 °C obtained at different time points, confirmed severe isomerization in organic solvent and/or photo-oxidative degradation of lycopene.

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 (\(\Delta E^*\)).

Thermophysical properties of foods are of considerable relevance to food industry. The One among less explored thermophysical quantities is the thermal effusivity. In this paper the front variant of the photopyroelectric method was applied to determine thermal effusivity of both, fresh hen egg’s yolk and white as well as of their blends. The amount of egg yolk added to the blend affected the thermal effusivity of egg’s white. Thermal effusivity of mixtures containing pork meat and lard was also investigated. Addition of lard reduces significantly thermal effusivity of pork meat (the 1% increase of lard content leads to 6.93 Ws ½ m -2 K -1 drop of thermal effusivity).

This report is aimed at intra-laboratory and inter-laboratory comparison of the results obtained during spectrophotometric and HPLC analyses of lycopene, β-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.

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 %).

Ovo istraživanje opisuje promjene u profilu karotenskih sasstavnica u proizvodu od rajcice nakon toplinske obrade.

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 (s(y/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 s(y/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.

The front configuration photopyroelectric method has been used to determine, in a nondestructive fashion, thermal effusivity of the yolk and the white of eggs of several bird species as well as of the blends of a single egg yolk and egg white (also called liquid eggs) of different avian eggs. Statistically significant differences in thermal effusivity of egg whites were observed in ten out of twenty-one comparisons made. However, in the case of egg yolks, the differences were observed in twenty among twenty-one comparisons carried out. These observations are related to a varying fat content of egg yolk and a large amount of water found in egg white. The effusivity of the blends prepared from yolks and eggs varies because the contents of the yolk and white in avian eggs differ.

The spatial distribution pattern of silicon in the leaves of three species of Saccharum has been demonstrated by means of laser induced breakdown spectroscopy (LIBS). The in-situ point detection capability of LIBS was used to determine different elements in leaf samples. The concentrations of silicon and other elements in different parts of the leaves were estimated by measuring the intensities of their corresponding atomic lines. Silicon, deposited in the form of phytoliths, was also isolated by using the dry ash technique. LIBS observations showed that in all three Saccharum species, the concentration of silicon was highest in the midrib followed by that found in margin and vein areas. The concentration of silicon in S. officinarum is higher in comparison to S. spontaneum and S. bengalense. Furthermore, the concentration of silicon at the upper surface of the leaf was larger than at the lower surface. The LIBS spectra of Saccharum species also show the presence of spectral lines of Na, Mg, Ca, Fe, and K.

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 frequency-domain open photoacoustic cell (OPC) approach was used to determine room temperature thermal diffusivity of skins (pericarps) from the raw tomatoes (Lycopersicon esculetum Mill.) characterized by the three different stages of ripeness (from immature-green to a mature-red). Periodically interrupted 532 nm laser radiation was used to heat the dry tomato skins, typically 10 mm in diameter and up to 68 μm thick; the modulating frequency f varied from 8 to 150 Hz. Initially, a combined OPC-model that takes into account both, the thermoelastic bending and the effect of thermal diffusion (TD), has been applied. Preliminary results showed that until at least 40 Hz, the effect of TD dominates; above this value the combined model fits the experimental data only poorly. For this reason a less complex OPC-TD approach was applied to all investigated skins instead, which predicts an exponential decrease for the amplitude of measured photoacoustic signal S with increasing f. For a specimen that is simultaneously opaque and thermally thick, S depends on f as S∼exp(−b f1/2) where b is a fitting parameter. The S versus f plot enables one to deduce the numerical value for b which, on its turn allows for the assessment of skin’s thermal diffusivity α. Thermal diffusivities obtained for the immature green, orange, and red skins (periderms) are 9.9×10−8 m2 s−1, 7.2×10−8 m2 s−1, and 4.6×10−8 m2 s−1, respectively; the uncertainty was typically 5% of the measured value.

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-[(α-L-rhamnosyloxy) benzyl]} thiocarbamate and 2-acetoxy {4-[(2′,3′,4′-tri-O-acetyl-α-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.

The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (PAS) and of optothermal window (OW) method for quantification of total anthocyanin concentration (TAC) in five sour cherry varieties is compared to that of the spectrophotometry (SP). High performance liquid chromatography (HPLC) was used to identify and quantify specific anthocyanins. Both, PAS and OW are direct methods that unlike SP and HPLC obviate the need for the extraction of analyte. The outcome of the study leads to the conclusion that PAS and OW are both suitable for quick screening of TAC in sour cherries. The correlation between the two methods and SP is linear with R(2)=0.9887 for PAS and R(2)=0.9918 for OW, respectively. Both methods are capable of the rapid determination of TAC in sour cherries without a need for a laborious sample pretreatment.

The performance of various analytical methods is compared in terms of their potentiality to quantify the concentration of carotenoids in some foods accurately and rapidly. High performance liquid chromatography (HPLC) and spectrophotometry (SP), two absolute reference techniques, were used in parallel experiments. The emphasis is on the application of the new methods to significantly reduce the long analysis time (due to a laborious and costly extraction) characteristic for both HPLC and spectrophotometry. Among such direct quantification methods are colorimetry and a variety of novel photoacoustic (PA) and photothermal (PT) detection schemes that obviate the extraction step. The outcome of numerous studies shows a number of important advantages provided by these methods. Furthermore, the promising results suggest that the availability of practical, versatile, compact and affordable quality control instruments that offer a low-cost solution to routine analysis of specific carotenoids in some foods is within reach.