Front-face Fluorescence Research Articles

Determination of Adulteration of Chicken Meat into Minced Beef Mixtures using Front Face Fluorescence Spectroscopy Coupled with Chemometric.

The objective of this study was to explore the potential of front face fluorescence spectroscopy (FFFS) as rapid, non-destructive and inclusive technique along with multi-variate analysis for predicting meat adulteration. For this purpose (FFFS) was used to discriminate pure minced beef meat and adulterated minced beef meat containing (1%, 2%, 3%, 4%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%) of chicken meat as an adulterant in uncooked beef meat samples. Fixed excitation (290 nm, 322 nm, and 340 nm) and fixed emission (410 nm) wavelengths were used for performing analysis. Fluorescence spectra were acquired from pure and adulterated meat samples to differentiate pure and binary mixtures of meat samples. Principle component analysis, partial least square regression and hierarchical cluster analysis were used as chemometric tools to find out the information from spectral data. These chemometric tools predict adulteration in minced beef meat up to 10% chicken meat but are not good in distinguishing adulteration level from 1% to 5%. The results of this research provide baseline for future work for generating spectral libraries using larger datasets for on-line detection of meat authenticity by using fluorescence spectroscopy.

Texture staling of pound cakes assessed by front face fluorescence spectroscopy in tandem with chemometric analysis.

Two vegetal oils have been selected for the formulation of pound cakes, rapeseed oil (RO) and palm oil (PO). The freshness of these products has been monitored during 58 days of storage. The RO pound cakes of 58 days as well as PO pound cakes presented higher values (p < .05) of hardness (N), Young's modulus (N.cm-2 ) and compressive stress (N.cm-2 ) than those aged of 5 days. For both vitamin A and tryptophan spectra, the maximum of fluorescence intensity varied according to the aging period. For both RO and PO recipes, lipid oxidation indicators (peroxide value, para-anisidine value, and total oxidation value [TOTOX]) were interestingly correlated to Young's modulus (R2 =0.99) as well as compressive stress (R2 =0.99), using polynomial model. The application of partial least squares regression to the vitamin A spectra provided excellent predictive results for both compressive stress (R2 = 0.99) and TOTOX (R2 =0.99). Good results were observed for tryptophan spectra for the prediction of TOTOX (R2 = 0.77). Thus, the use of front face fluorescence spectroscopy may provide rapid and accurate results for the monitoring of pound cakes freshness throughout storage.

Tryptophan front-face fluorescence and functional properties of whey: A preliminary study

This study investigated the potential of front-face fluorescence spectroscopy to predict the functional properties of whey. Whey has a commercial interest due to its excellent nutritional value and versatile functional properties. However, its attributes depend dramatically on heat treatment, which may alter its suitability for different food applications. Tryptophan front-face fluorescence of whey and its functional properties, i.e., foaming, gel-forming, and emulsifying properties, were evaluated after milk heat treatment (at 80 °C with seven holding times) to detect correlations between tryptophan fluorescence and functional parameters and generate predictive models. Whey samples were obtained by isoelectric precipitation of caseins from reconstituted skim milk powder enriched with whey protein isolate. As expected, heat treatments induced an increase in whey protein denaturation, as well as a decrease in total whey protein concentration and tryptophan fluorescence intensity. Gel-forming and emulsifying properties of whey significantly correlated with the maximum intensity of tryptophan (P < 0.001). Concerning foaming properties, only the foam stability index revealed a weak correlation with tryptophan maximum intensity (P < 0.05). Consequently, models presented strong significances (P < 0.001). Specifically, using only tryptophan fluorescence allowed successful prediction of emulsifying properties but was not enough for foaming and gel forming properties.

Noninvasive diagnosis of type 2 diabetes mellitus by hair analysis using laser-induced breakdown spectroscopy (LIBS)

Currently, the reference method for diagnosing the pathology of diabetes is the measurement of glycated hemoglobin HbA1c. As a major public health problem, as categorized by the World Health Organization, the need to develop new techniques that are more accessible, especially for developing countries, is necessary. The objective of this work is to propose a new technique based on laser-induced breakdown spectroscopy (LIBS) using the essential minerals calcium, sodium, magnesium, and zinc in hair as biomarkers for the screening of type 2 diabetes. The study involved 130 women: 24 were classified as low-level diabetics with a glycated hemoglobin HbA1c <7% and 56 were classified as high-level diabetics with an HbA1c >7% after clinical tests were performed at the Habib Thameur Hospital in Tunis. The other 50 women were healthy and used as controls. The correlation of the mineral concentrations in the hair with the values of glycated hemoglobin allow an economical and rapid detection of the disease. The results showed a strong negative correlation between the levels of calcium, magnesium, and zinc with the HbA1c values and a strong positive correlation between the intensity of the sodium lines and HbA1c. These results allowed the discrimination of the three groups in the cohort, offering a new approach to quickly classify the patients involved in a screening campaign. In addition, the strong correlation between laser-induced breakdown spectroscopy (LIBS) and the front face fluorescence spectroscopy (FFFS), previously applied on the same samples, may help identify the source of the fluorescence spectra. All of these results support the use of LIBS upon hair to evaluate minerals as effective biomarkers for the detection of type II diabetes to be a promising approach.

Non-invasive and rapid diagnosis of type 2 diabetes mellitus based on the analysis of hair by front-face fluorescence spectroscopy.

Rapid and early detection of pathologies for screening purposes is not always easy with traditional methods. New low-cost optical techniques that are suitable for preventive detection and, more specifically, for developing countries must be developed. The objective of this work is to propose UV-VIS fluorescence of hair as a promising technique for a simple and rapid preliminary diagnosis of type II diabetes. In this work, we analyzed 130 hair samples taken from volunteers of different ages at the Habib Thameur Hospital in Tunis, Tunisia. These samples were analyzed clinically beforehand, and 50 were classified as healthy acting as a control, 24 were classified as low-level diabetics with a glycated hemoglobin A1C (HbA1c) <7%, and the other 56 were classified as high-level diabetics having an HbA1c >7%. The fluorescence of the patients' hair led to several interesting results. Indeed, a clear discrimination was obtained not only between the healthy and patients with a disease, but also a discrimination between diabetics with low levels and high levels or diabetics with and without complication. Also, a strong correlation between fluorescence spectra and glycated HbA1c for the diabetic population was clearly established. A linear discriminant analysis shows that it is possible to predict the status of test patients after having trained a fraction of the population. All these results show the ability of the front-face fluorescence (FFF) technique to detect disease and predict advanced states simply by capturing the fluorescence of the hair illuminated by a single LED. This work shows for the first time, to our knowledge, the capability of the FFF technique on hair samples for the diagnosis of diabetes.

Animal Species Authentication in Dairy Products.

Milk is one of the most important nutritious foods, widely consumed worldwide, either in its natural form or via dairy products. Currently, several economic, health and ethical issues emphasize the need for a more frequent and rigorous quality control of dairy products and the importance of detecting adulterations in these products. For this reason, several conventional and advanced techniques have been proposed, aiming at detecting and quantifying eventual adulterations, preferentially in a rapid, cost-effective, easy to implement, sensitive and specific way. They have relied mostly on electrophoretic, chromatographic and immunoenzymatic techniques. More recently, mass spectrometry, spectroscopic methods (near infrared (NIR), mid infrared (MIR), nuclear magnetic resonance (NMR) and front face fluorescence coupled to chemometrics), DNA analysis (real-time PCR, high-resolution melting analysis, next generation sequencing and droplet digital PCR) and biosensors have been advanced as innovative tools for dairy product authentication. Milk substitution from high-valued species with lower-cost bovine milk is one of the most frequent adulteration practices. Therefore, this review intends to describe the most relevant developments regarding the current and advanced analytical methodologies applied to species authentication of milk and dairy products.

Front-Face Fluorescence Spectroscopy and Feature Selection for Fruit Classification Based on N-CovSel Method

Internal disorder is a major problem in fruit production and is responsible for considerable economical losses. Symptoms are not externally visible, making it difficult to assess the problem. In recent years, 3D fluorescence spectroscopy has been used to reveal features of interest in agronomical field, such as plant stress and plant infection. Such technique could provide useful information regarding changes that occur at the tissue level, in order to distinguish spectral differences between healthy and disordered fruits. This paper introduces the use of the new three-way feature extraction N-CovSel method, compared to the commonly used N-PLS-DA method. These approaches were used upon front-face fluorescence spectra of 27 fruit pulp and skin samples, by analysing excitation wavelengths ranging from 250 to 650 nm, and emission wavelengths varying from 290 to 800 nm. N-CovSel method was applied to identify the most relevant features on: 1) excitation-emission wavelength couples, 2) excitation wavelengths whatever the emission wavelengths and 3) emission wavelengths whatever the excitation wavelengths. Discriminant analysis of the selected features were performed across classes. The constructed models provided key features to differentiate healthy fruits from disordered ones. These results highlighted the capability of N-CovSel method to extract the most fitted features for enhanced fruit classification using front-face fluorescence spectroscopy. They revealed characteristic fluorophores involved in the structural modifications generated by the physiological disorder studied. This paper provides preliminary results concerning the suitability of N-CovSel method for the desired application. Further investigations could be performed on intact fresh fruits in a non-destructive way, allowing an earlier and faster detection of the internal disorder for in-field or industrial applications.

Prediction of riboflavin and ascorbic acid concentrations in skimmed heat-treated milk using front-face fluorescence spectroscopy

The objective of this work was to obtain degradation kinetic models of riboflavin and ascorbic acid, and to evaluate the potential of front-face fluorescence (FFF) spectroscopy to predict their concentration in milk after thermal processing. A factorial design with three temperatures (70, 80 and 90 °C) and nine times (from 0 to 60 min) of heat treatment was used. Degradation kinetics of both vitamins were of first order. Predictive kinetic models using the Arrhenius equation had a variability coefficient of 2.26 and 3.64% for riboflavin and ascorbic acid, respectively. With fluorescent predictors such as tryptophan, Maillard compounds and riboflavin, prediction models with coefficients of variation smaller than 3.57% for riboflavin and ranging from 4.24 to 14.25% for ascorbic acid were obtained. In conclusion, FFF is a viable alternative to predict riboflavin and ascorbic acid content of milk which could allow in-line monitoring and control of thermal damage.

Japanese dace (Tribolodon hakonensis) fish freshness estimation using front-face fluorescence spectroscopy coupled with chemometric analysis

Although fish and its related products are good sources of protein and unsaturated fatty acids, like omega-3 in the human diet, their shelf-life is limited by biochemical and microbial changes. In this study, a front-face fluorescence spectroscopy technique was used to acquire Excitation-emission matrices (EEM) to monitor Japanese dace (Tribolodon hakonensis) fish freshness degradation during storage. EEM of Japanese dace fish parts (intact eyeball and surface-containing scales), excitation from 220 to 585 nm and emissions from 250 to 600 nm, were measured at different times during storage. To simplify the acquired complex spectra datasets from each fish part, the variables were reduced to those that were only significant/important (those with higher positive or negative correlation) for K value prediction, and as an index of freshness. Partial least square regression (PLSR) results demonstrated that combining the fluorescence EEM of the eyeball and surface-containing scales the best monitoring of fish freshness; excitation at 280 and 350 nm for both the eyeball and surface-containing scales, with 2.84 and 0.96 as RMSE and R2, respectively. These findings demonstrate that multiple excitation fluorescence approaches can be convenient for the freshness evaluation of fish.

A non-invasive and rapid diagnosis of type 2 diabetes Mellitus based on the analysis of hair by Front Face Fluorescence Spectroscopy (FFFS)

A non-invasive and rapid diagnosis of type 2 diabetes Mellitus based on the analysis of hair by Front Face Fluorescence Spectroscopy (FFFS)

Early diagnosis of dental pathologies by front face fluorescence (FFF) and laser-induced breakdown spectroscopy (LIBS) with principal component analysis (PCA)

In dentistry, the early detection of lesions is not always obvious with traditional methods. It is necessary to develop new techniques, especially optical approaches, which are rapid for preventive detection. These developments are needed especially for developing countries. The objective of this work is to show how to take advantage of the decrease in fluorescence intensity associated with demineralization and to promote this technique for clinical use. For this purpose, front face fluorescence (FFF) based on the direct measurement of fluorescence was used. This study shows that it is possible to assess the presence of deposits and plaque by refining the discoloration of the areas. These analyses were reinforced by laser-induced breakdown spectroscopy (LIBS) to better understand the fluorescence changes with the mineral and trace element concentrations. The results demonstrate that fluorescence is suitable to estimate the onset of mineral loss in surface lesions. Indeed, the obtained results highlight the mineral loss in enamel surface lesions. The strong correlations between variations of certain regions of the fluorescence spectra with the intensities of calcium and phosphorus, obtained by LIBS, show the evolution of the deficiencies of these two elements from white to darker areas.

Characterization of activated sludge in wastewater treatment processes using front-face excitation–emission matrix (FF-EEM) fluorescence spectroscopy

The novel front-face fluorescence excitation–emission matrix (FF-EEM) spectroscopy was applied to in situ and online analyze the activated sludge from wastewater treatment processes to probe its biomass and bioactivity.

Multiblock Analysis Applied to Fluorescence and Absorbance Spectra to Estimate Total Polyphenol Content in Extra Virgin Olive Oil.

A fast and easy methodology to estimate total polyphenol content in extra virgin olive oil was developed by applying the chemometric multiblock method sequential and orthogonalized partial least squares (SO-PLS) in order to combine front-face emission fluorescence spectra (270 nm excitation wavelength) and absorbance spectra. The hypothesis of this work stated that inner-filter effects in fluorescence spectra that would reduce the estimation performance of a single block model could be overcome by incorporating the absorbance spectral information of the compounds causing them. Different spectral preprocessing algorithms were applied. Double cross-validation with 50 iterations was implemented to improve the robustness of the obtained results. The PLSR model on the single block of fluorescence raw spectra achieved an RMSEP of 177.11 mg·kg−1 as the median value, and the complexity of the model was high, as the median value of latent variables (LVs) was eight. Multiblock SO-PLS models with pretreated fluorescence and absorbance spectra provided better performance, although artefacts could be introduced by transformation. The combination of fluorescence and absorbance raw data decreased the RMSEP median to 134.45 mg·kg−1. Moreover, the complexity of the model was greatly reduced, which contributed to an increase in robustness. The median value of LVs was three for fluorescence data and only one for absorbance data. Validation of the methodology could be addressed by further work considering a higher number of samples and a detailed composition of polyphenols.

3D front face fluorescence spectroscopy as a tool for monitoring the oxidation level of edible vegetable oil during storage at 60 °C

Fluorescence landscapes with excitation wavelengths varying between 280 and 400 nm, and emission wavelengths in the range of 300–650 nm were scanned directly on oil samples throughout storage in capped and uncapped flasks for 15 days at 60 °C. PARAFAC analysis of the fluorescence landscapes showed the presence of three fluorophores in the edible oils, which are strongly dependent on the storage conditions. The fluorescence spectra were resolved into excitation and emission profiles of the pure fluorescent compounds, which are ascribed to be oxidation products and vitamin E. The complexity of edible oil data sets was suitable for PARAFAC modelling. Problems with scattering were encountered, the use of missing values was tackled before obtaining a validated model with a criterion of similarity measurements of splits reaching the 83.8% and this allowed us to start getting through the model of interpretation.

Direct quantification of red wine phenolics using fluorescence spectroscopy with chemometrics

Phenolic compounds are secondary metabolites known to play crucial roles in important chemical reactions impacting the mouthfeel, colour and ageing potential of red wine. Their complexity has resulted in a number of advanced analytical methods, which often prevent routine phenolic analysis in winemaking. Fluorescence spectroscopy could be an alternative to current spectrophotometric techniques and its combination with chemometrics was investigated for its suitability in directly quantifying phenolic content of unaltered red wine and fermenting samples. Front-face fluorescence was optimised and used to build predictive models for total phenols, total condensed tannins, total anthocyanins, colour density and polymeric pigments. Machine learning algorithms were used for model development. The most successful models were built for total phenols, total condensed tannins and total anthocyanins with coefficient of determination (R2cal) and RMSECV of 0.81, 0.89, 0.80 and 5.71, 104.03 mg/L, 60.67 mg/L, respectively. The validation results showed R2val values of 0.77, 0.8 and 0.77, and RMSEP values of 7.6, 172.37 mg/L and 76.57 mg/L, respectively. A novel approach for the classification of South African red wine cultivars based on unique fluorescent fingerprints was also successful with an overall cross validation score of 0.8. The best classification ability (validation score = 0.93) was shown for the data set containing only fermenting wines for the most widely represented cultivars (>20 samples). This approach may provide a useful tool for authentication and quality control by regulatory bodies.

Changes in Hydrophobic Interactions among Gluten Proteins during Dough Formation

In this study, changes in hydrophobic interactions among gluten proteins were analyzed during dough mixing. Size-exclusion high-performance chromatography and two-dimensional fluorescence difference gel electrophoresis were performed on proteins extracted with 1-propanol by weakening the hydrophobic interaction. The amount of proteins extracted with 30% 1-propanol increased from the start of mixing to peak consistency, suggesting that the hydrophobic interactions among the strongly aggregated proteins weakened and resulted in disaggregation. The amount of proteins extracted with 10% 1-propanol decreased during hydration, indicating that these proteins aggregated through relatively weak hydrophobic interactions. The proteins that extractability decreased were mainly low molecular weight glutenin, α-gliadin, and γ-gliadin. The amount of monomeric proteins extracted with 30% 1-propanol decreased after peak consistency. The decreased protein was mainly ω-gliadin, indicating that ω-gliadin aggregated with other proteins through hydrophobic interactions. A front-face fluorescence analysis was performed on the dough with the addition of 8-anilino-1-naphthalenesulfonic acid or thioflavin T. The fluorescence intensity increased as a result of exposure to the hydrophobic groups of the gluten proteins and the formation of protein aggregates during dough mixing. These results indicate the importance of hydrophobic interactions in dough formation.

Classification of sea bream (Sparus aurata) fillets subjected to freeze-thaw cycles by using front-face fluorescence spectroscopy

The most common frauds carried out in different points of fish and fish product supply chain concern the selling of freeze-thaw fish as fresh fish. Moreover, fluctuation of temperature during the storage process, transportation, and sale modified the fish quality and increased the frozen-thawed cycles. In this study, front face fluorescence spectroscopy (FFFS) was used to determine the effect of freeze-thaw cycles on the quality of sea bream fillets. The application of factorial discriminant analysis (FDA) to the concatenated fluorescence spectra allowed to distinguish clearly between the numbers of freeze-thaw cycles applied to sea bream fillets since correct classification rate amounting to 91.67% was observed, regardless of the initial raw quality. This could be explained by changes in the tertiary structure of tryptophan and the oxidation state of NADH. The obtained result was confirmed following the application of partial least square regression (PLSR) since an excellent prediction of the number of freeze-thaw cycles was obtained (R 2 = 0.99; RPD = 7.13). Therefore, FFFS could be used as a rapid screening technique to detect with high accuracy between fresh, once and twice freeze-thaw sea bream fillets. • Fluorescence spectroscopy allowed the classification of sea bream fillets based on the number of freeze-thaw cycles. • Factorial discriminant analysis allowed fillets discrimination according to freeze-thaw cycles. • High predictive accuracy of freeze-thaw cycles was obtained by partial least square regression. • Fluorescence spectroscopy could be used for differentiating sea bream fillets subjected to freeze-thaw cycles.

Front Face Fluorescence Spectroscopy Combined with PLS‐DA Allows to Monitor Chemical Changes of Edible Vegetable Oils during Storage at 60 °C

AbstractIn this work, front‐face fluorescence spectroscopy coupled with chemometric tools are used for the monitoring of rapeseed, sunflower, extra virgin olive, and linseed oil. The oil samples are heated at 60 °C for up to 15 days. The fluorescence excitation spectra are scanned in the range of 270–420 nm and 250–310 nm after emission wavelength set at 450 and 330 nm, respectively. The primary and secondary lipid oxidation products are also determined on the same oil samples. By applying partial least square discriminant analysis (PLS‐DA) to each spectral collection obtained after emission set at 450 and 330 nm, clear discrimination of edible oil samples according to their botanical types, and sometimes aging, is obtained.Practical Applications: This study shows that oxidation of rapeseed, sunflower, extra virgin olive, and linseed oil monitored different trends due to their difference in composition. The presented results demonstrated the capability of the front‐face fluorescence spectroscopy to differentiate four vegetable oils contained in capped and uncapped flasks indicating the evolution of primary and secondary indicators of oxidation during the storage period. The technology can be exploited at the industrial level for monitoring in a non‐destructive manner the level of oxidation of edible oil.

Front-face synchronous fluorescence spectroscopy for rapid and non-destructive determination of free capsanthin, the predominant carotenoid in chili (Capsicum annuum L.) powders based on aggregation-induced emission

Capsanthin is the major natural carotenoid pigment in red chili pepper possessing important bioactivity. Its conventional determination method is high performance liquid chromatography (HPLC) with complex and tedious sample pretreatment. In this study, synchronous front-face fluorescence spectroscopy (FFFS) was applied for the fast and non-invasive detection of free capsanthin in chili powders. Although capsanthin was only weak fluorescent in solution state, it showed strong fluorescence in two separated regions in front-face geometry which could also be clearly observed in chili powders. The mechanisms of these emissions are revealed to be aggregation-induced emission (AIE) and J-aggregate formation (JAF). The free capsanthin in 85 chili powder samples were determined by HPLC as in the range of 0.6–3.0 mg/g. The total synchronous FFFS spectra of these samples were scanned. Simple first-order models were built by partial least square regression (PLSR), and were validated by 5-fold cross-validation and external validation. The coefficients of determination (R2) were higher than 0.9, and the root mean square errors (RMSE) were less than 0.2 mg/g. The relative error of prediction (REP) was 9.9%, and the residual predictive deviation (RPD) was 3.7. The method was applied for the estimation of free capsanthin in several real-world samples with satisfactory analytical results. The average relative error to HPLC reference values was −11.8%.

Effect of pH on heat-induced interactions in high-protein milk dispersions and application of fluorescence spectroscopy in characterizing these changes

This study investigated casein-whey protein interactions in high-protein milk dispersions (5% protein wt/wt) during heating at 90°C for 1.5 to 7.5 min at 3 different pH of 6.5, 6.8, and 7.0, using both conventional methods (gel electrophoresis, physicochemical properties) and fluorescence spectroscopy. Conventional methods confirmed the presence of milk protein aggregates during heating, similar to skim milk. These methods were able to help in understanding the denaturation and aggregation of milk proteins as a function of heat treatment. However, the results from the conventional methods were greatly affected by batch-to-batch variations and, therefore, differentiation could be drawn only in nonheated samples and samples heated for a longer duration. The front-face fluorescence spectroscopy was found to be a useful tool that provided additional information to conventional methods and helped in understanding differences between nonheated, low-, and high-heated samples, along with the type of sample used (derived from liquid or powder milk protein concentrates). At all pH values, tryptophan maxima in nonheated samples derived from powdered milk protein concentrates presented a blue shift in comparison to samples derived from liquid milk protein concentrates, and tryptophan maxima in heated samples presented a red shift. With the heating of the sample, Maillard emission and excitation spectra also showed increases in the peak intensities from 408 to 432 and 260 to 290 nm, respectively. As the level of denaturation increased with heating, a marked differentiation can be seen in the principal component analysis plots of tryptophan, Maillard emission, and excitation spectra, indicating that the front-face fluorescence technique has a potential to monitor and classify samples according to milk protein interactions as a function of pH and heat exposure. Overall, it can be said that the pattern of protein-protein interactions in high-protein dispersions was similar to the observation reported in skim milk systems, and fluorescence spectroscopy with chemometrics can be used as a rapid, nondestructive, and complementary method to conventional methods for following heat-induced changes.