Ottó Dóka

Correlation of trans-Lycopene Measurements by the HPLC Method with the Optothermal and Photoacoustic Signals and the Color Readings of Fresh Tomato Homogenates

The trans-lycopene content of fresh tomato homogenates was assessed by means of the laser photoacoustic spectroscopy, the laser optothermal window, micro-Raman spectroscopy, and colorimetry; none of these methods require the extraction from the product matrix prior to the analysis. The wet chemistry method (high-performance liquid chromatography) was used as the absolute quantitative method. Analytical figures of merit for all methods were compared statistically; best linear correlation was achieved for the chromaticity index a* and chroma C*.

Direct photothermal techniques for rapid quantification of total anthocyanin content in sour cherry cultivars

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.

Direct Measurement of Carbonate Content in Soil Samples by Means of CO Laser Infrared Photoacoustic Spectroscopy

CO laser infrared (IR) photoacoustic spectroscopy (PAS) at 1801 cm−1 was used to determine the content of carbonate in various soils. The PA signal is linearly proportional to the content of carbonate within the 0–30% (w/w) range; the 2% (w/w) limit of detection (LOD) is adequate for the application in practice.

Determination of sunset yellow in multi-vitamin tablets by photoacoustic spectroscopy and a comparison with alternative methods

Photoacoustic (PA) spectroscopy in the visible wavelength region was shown to be suitable for a direct (no preparatory steps involved) quantification of sunset yellow (E110) colour in effervescent multi-vitamin tablets. Measurements on powdered tablets containing E110 were performed at 480 nm at which wavelength this synthetic colour shows appreciable absorbance. The PA data obtained were compared to the results acquired by diffuse reflectance spectroscopy and conventional spectrophotometry. Intrinsic simplicity, ease of sampling and rapid response were the most important advantages of the PA technique. In terms of sensitivity the performance of the three methods were comparable.

Ultratraces of carotenes in tomato purées: HPLC-TLS study

The present study was designed to provide information about (i) the profile of carotene pigments and (ii) trace quantities of lycopene and β-carotene left in tomato purees. The ultrasensitive method comprising HPLC and thermal lens spectrometric (TLS) detection enabled us to detect as low as 0.3 and 1.1 ng ml−1 lycopene and β-carotene in puree extracts, respectively. Total concentration of β-carotene and lycopene (varying from 3 to 170 ng g−1) in the examined tomato purees may serve as an indicator of the carotene-specific antioxidative capacity of these products. Although conventional spectrophotometry can be used to rapidly assess the quality of products derived from tomatoes, a highly sensitive and selective method such as HPLC-TLS is needed for reliable analyses of samples such as, for example, those subjected to inappropriate storage and/or handling.

Photoacoustic study of airborne and model aerosols

Airborne particulates of either natural or anthropogenic origin constitute a significant portion of atmospheric pollution. Environmental xenobiotics, among which are polynuclear aromatic hydrocarbons (PAHs) and pesticides, often adsorb to aerosols and as such are transported through the atmosphere with the physicochemical properties of the aerosols determining the lifetime of these organic compounds. As an example, the resistance of some PAHs against the photolysis is explained by the effect of the aerosol’s “inner filter” that reduces the intensity of incident light reaching the mineral particles. On the other hand, some constituents of the aerosols can act as catalytic and/or stoichiometric reagents in atmospheric reactions on the solid surfaces. In the study described here the photoacoustic (PA) spectroscopy in the UV-Vis was used to investigate natural and model aerosols. The PA spectra obtained from coal and wood ashes and of Saharan sand, all three representatives of airborne aerosols, provide the evidence for the existence of the “inner filter.” Furthermore, valuable information about the different nature of the interaction between the model aerosols and adsorbed organics (e.g., PAH-pyranthrene and silica, alumina, and MgO) has been obtained. Finally, the outcome of the study conducted with powdered mixtures of chalk and black carbon suggests that the PA method is a candidate method for determination of carbon content in stack ashes.

Quantification of lycopene in the processed tomato-based products by means of the light-emitting diode (LED) and compact photoacoustic (PA) detector

The combined use of a high power light emitting diode (LED) and the compact photoacoustic (PA) detector offers the possibility for a rapid (no extraction needed), accurate (precision 1.5%) and inexpensive quantification of lycopene in different products derived from the thermally processed tomatoes. The concentration of lycopene in selected products ranges from a few mg to several tens mg per 100 g fresh weight. The HPLC was used as the well established reference method.

Determination of Free Fatty Acids in Cooking Oil: Traditional Spectrophotometry and Optothermal Window Assay

Abstract The concept of optothermal window (OW) (with 632.8 nm He‐Ne laser used as a radiation source), combined with copper soap based colorimetry, was proposed as a new analytical tool to determine total free fatty acid (FFA) content in thermally treated cooking oil. The results obtained were compared to those acquired by conventional spectroscopy; the correlation between the two methods is high for FFA concentrations exceeding 2 µmol/mL.

Assessing the Extent of Degradation in the UV Radiation and Heat-Catalyzed Oxidized Whole Milk Powder: The UV Photoacoustic and Diffuse Reflectance Spectroscopies versus the Peroxide Value

The extent of quality loss caused by enzymatic and nonenzymatic browning reactions in milk powders is usually assessed by the chemical methods, among which the determination of peroxide value (PV) is a widely used approach. In this paper, peroxide values obtained from deliberately oxidized (UV irradiation combined with the thermal stress) whole milk powders are compared to the results of photoacoustic spectroscopy (PAS) and diffuse reflectance spectrometry (DRS) in the ultraviolet and visible region. The same samples were also investigated by various methods in the near-infrared (NIR) region. The experimental data suggest a good degree of correlation between the PV and the PAS and DRS data collected at 335 nm.

The effect of the fat content on the thermal effusivity of foods: an inverse photopyroelectric study

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.