Lea Lenhardt

Fluorescence spectroscopy coupled with PARAFAC and PLS DA for characterization and classification of honey

Fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) and Partial least squares Discriminant Analysis (PLS DA) were used for characterization and classification of honey. Excitation emission spectra were obtained for 95 honey samples of different botanical origin (acacia, sunflower, linden, meadow, and fake honey) by recording emission from 270 to 640 nm with excitation in the range of 240-500 nm. The number of fluorophores present in honey, excitation and emission spectra of each fluorophore, and their relative concentration are determined using a six-component PARAFAC model. Emissions from phenolic compounds and Maillard reaction products exhibited the largest difference among classes of honey of different botanical origin. The PLS DA classification model, constructed from PARAFAC model scores, detected fake honey samples with 100% sensitivity and specificity. Honey samples were also classified using PLS DA with errors of 0.5% for linden, 10% for acacia, and about 20% for both sunflower and meadow mix.

Authentication of the botanical origin of unifloral honey by infrared spectroscopy coupled with support vector machine algorithm

In recent years, the potential of Fourier-transform infrared spectroscopy coupled with different chemometric tools in food analysis has been established. This technique is rapid, low cost, and reliable and requires little sample preparation. In this work, 130 Serbian unifloral honey samples (linden, acacia, and sunflower types) were analyzed using attenuated total reflectance infrared spectroscopy (ATR-IR). For each spectrum, 64 scans were recorded in wavenumbers between 4000 and 500 cm−1 and at a spectral resolution of 4 cm−1. These spectra were analyzed using principal component analysis (PCA), and calculated principal components were then used for support vector machine (SVM) training. In this way, the pattern-recognition tool is obtained for building a classification model for determining the botanical origin of honey. The PCA was used to analyze results and to see if the separation between groups of different types of honeys exists. Using the SVM, the classification model was built and classification errors were acquired. It has been observed that this technique is adequate for determining the botanical origin of honey with a success rate of 98.6%. Based on these results, it can be concluded that this technique offers many possibilities for future rapid qualitative analysis of honey.

Discrimination Among Melanoma, Nevi, and Normal Skin by Using Synchronous Luminescence Spectroscopy

Novel optical spectroscopy and imaging methods may be valuable in the early detection of cancer. This paper reports differences in the luminescence responses of pigmented skin lesions (melanomas and nevi) and apparently normal non-pigmented human skin, based on analyses of synchronous luminescence spectroscopy measurements. Measurements were performed in the excitation range of 330–545 nm, with synchronous intervals varying from 30– 120 nm. Normal skin, nevi, and melanomas differ in the way they fluoresce, and these differences are more distinct in the synchronous fluorescence spectra than in the conventional emission and excitation spectra. The differences in the fluorescence characteristics of pigmented and normal skin samples were ascribed to differences in concentrations of endogenous fluorophores and chromophores. Principal component and linear discriminant analysis of the synchronous spectra measured at different synchronous intervals showed that the greatest variance among the sample groups was at the 70 nm interval spectra. These spectra were then used to create partial least squares discriminant analysis-based classification models. Evaluation of the quality of these models from the receiver operating characteristic curves showed they performed well, with a maximum value of 1 for the area under the curve for melanoma detection. Hence, synchronous luminescence spectroscopy coupled with statistical methods may be advantageous in the early detection of skin cancer.

Characterization of cereal flours by fluorescence spectroscopy coupled with PARAFAC

This paper presents parallel factor analysis (PARAFAC) of fluorescence of cereal flours. Excitation-emission matrices (EEMs) of different cereal flours (wheat, corn, rye, rice, oat, spelt, barley and buckwheat) were measured in a front-face configuration over the ultraviolet-visible spectral range. EEMs showed that flours strongly fluoresce in two spectral regions, where amino acids, tocopherols, pyridoxine and 4-aminobenzoic acid show intense emissions. 4-component PARAFAC was used to model flour fluorescence and to decompose EEMs into excitation and emission spectra of each component. PARAFAC also provided relative concentrations of these components. The largest differences between flours were found in the concentration levels of the first and third component. Finally, variations in concentrations of PARAFAC modelled components were analysed in relation to the botanical origin of flour samples.

Changes of Color and Fluorescence of Resin Composites Immersed in Beer

OBJECTIVE The aim of this study was to evaluate changes of color and fluorescence of resin based composite exposed to beer. MATERIALS AND METHODS 84 samples (13 mm in diameter and 1.5 mm thick) of microhybrid composite Gradia DirectTM extra bleach white were immersed in 5 different beers (dark and light) or distilled water. Color and fluorescence were measured prior and after 1-, 7-, and 14-day immersion by Spectrophotometer Thermo Evolution 600 and Fluorolog-3-221 spectrofluorometer. RESULTS Resin based composites changed color after immersion in beers of different types. Beers with higher optical absorption induced greater color changes. The fluorescence intensity of composites was decreased after immersion in beer, but the shape of fluorescence spectra was not changed. 14-day immersion in Bernard dark beer caused the greatest changes in optical properties of composite: ΔE*=9.0 and 57.6% reduced fluorescence. CONCLUSION Dark and light beers changed optical properties of resin based composite. The color change come exclusively from the change of chroma. CLINICAL SIGNIFICANCE To fully meet esthetic criteria when using dental materials in restoration it is crucial to match optical properties of teeth and dental restoration at the moment of placement, but also to keep the match over the time. Considering that staining in beer causes changes in color and fluorescence of composites and that discoloration is a frequent reason for replacement of composite restorations, the data and conclusions on discoloration of dental restorations caused by beer consumption should aid dental professionals when reaching for high esthetics of modern dentistry.(J Esthet Restor Dent 28:330-338, 2016).

Biophysical characterization of human breast tissues by photoluminescence excitation-emission spectroscopy

Abstract Fluorescence excitation-emission spectroscopy was used to investigate specimens of normal and malignant human breast tissues. Measurements were performed in two spectral regions: in the excitation range from 335nm to 400nm and emission range from 430nm to 625 nm, and in the excitation range from 400nm to 470nm and emission range from 500nm to 640 nm. It was found that fluorescence spectra are composed mainly of the emissions of extracellular proteins and that the differences in the intensity of their emissions reveal the changes in the tissue structure and morphology. These differences could be best observed in the emission spectra excited with 370 nm, 425nm and 455nm radiation. Statistical analysis revealed several spectral subregions that exhibited extremely significant statistical difference between normal and malignant breast tissues. The origin of these differences was elaborated, and prospects for optical diagnostics of breast cancer was discussed.

Discoloration of resin based composites in natural juices and energy drinks

Background/Aim. Discoloration of dental restorations makes them aesthetically unacceptable and is a frequent reason for replacement of composite restorations. The aim of this study was to evaluate changes of color and fluorescence of resin-based composites (RBCs) exposed to natural juices and energy drinks. Methods. Microhybrid composite Gradia Direct Extra Bleach White disc-shaped specimens (n = 35) were immersed in three different natural juices and four different energy drinks. Absorption spectra of natural juices and energy drinks, diffuse reflection and fluorescence of composite samples were measured prior and after sevenday immersion by spectrophotometer Thermo Evolution 600 and spectrofluorometer Fluorolog-3-221. Composite’s color was calculated from diffuse reflection spectra and expressed in CIELAB color space (Commission International de l’Eclairage). Results. All natural juices and energy drinks induced color change of resin based composites, but to the different extent. Only aronia and carrot juices induced total color change considerably higher than clinically acceptable threshold, 9.3 and 6.2, respectively. All energy drinks and aronia juice induced notable decrease in fluorescence; the highest change of 28% was evidenced in the case of aronia juice. Conclusion. Change of color and fluorescence will appear differently with various solutions due to different chemical composition and concentration of colorant species in different beverages. Solutions with higher optical absorption induced higher total color change. Discoloration of composites in aronia and carrot juices is similar to those earlier reported for red wine, tea and coffee.