Rapid and non-destructive prediction of methylxanthine and cocoa solid contents in dark chocolate by synchronous front-face fluorescence spectroscopy and PLSR

Leveraging infrared spectroscopy for cocoa content prediction: A dual approach with Kohonen neural network and multivariate modeling

People of all ages enjoy chocolate, and its popularity is attributed to its pleasant taste and aroma, as well as its associated health benefits. Produced through both artisanal and industrial processes, which involve harvesting, selecting, fermenting, roasting and grinding cocoa beans, chocolate has a diverse chemical composition. It contains stimulants for the central nervous system, including caffeine and theobromine, and antioxidants and flavonoids, some of which are associated with promoting cardiovascular health, circulatory function, alertness, and attention. This study aimed to use NIR spectroscopy to determine whether this technique can effectively quantify the percentage of cocoa present in commercial chocolates. In the exploratory analysis of the NIR spectra, conducted in the range of 900-1600 nm, it was observed that the cocoa percentage in the samples correlated most strongly with chemical groups exhibiting absorbance in the range of 900-1400 nm. Principal Component Analysis (PCA) exhibited good discriminatory ability between samples with different cocoa percentages. Kohonen neural networks have also been proven effective in processing high-dimensional nonlinear data and complementing PCA analysis in pattern recognition. Additionally, Principal Component Regression (PCR) was performed to evaluate the predictive capability of cocoa percentage based on NIR spectra, yielding an R2 value of 0.84. The study demonstrates that integrating the NIR spectra with PCA/PCR and KNN enables cocoa percentage identification, making it a valuable tool for chocolate quality control and authenticity assurance.

The Role of Near-Infrared Spectroscopy in Food Quality Assurance: A Review of the Past Two Decades

During food quality control, NIR technology enables the rapid and non-destructive determination of the typical quality characteristics of food categories, their origin, and the detection of potential counterfeits. Over the past 20 years, the NIR results for a variety of food groups-including meat and meat products, milk and milk products, baked goods, pasta, honey, vegetables, fruits, and luxury items like coffee, tea, and chocolate-have been compiled. This review aims to give a broad overview of the NIRS processes that have been used thus far to assist researchers employing non-destructive techniques in comparing their findings with earlier data and determining new research directions.

Enhancing grain drying methods with hyperspectral imaging technology: A visualanalysis

This study proposes a recognition model for different drying methods of grain using hyperspectral imaging technology (HSI) and multivariate analysis. Fresh harvested grain samples were dried using three different methods: rotating ventilation drying, mechanical drying, and natural drying. Hyperspectral images of the samples were collected within the 388-1065 nm band range. The spectral features of the samples were extracted using principal component analysis (PCA), while the texture features were extracted using second-order probability statistical filtering. Partial least squares regression (PLSR) drying models with different characteristics were established. At the same time, a BPNN (Back-propagation neural network, BPNN) based on spectral texture fusion features was established to compare the recognition effects of different models. Texture analysis indicated that the mean-image had the clearest contour, and the texture characteristics of mechanical drying were smaller than those of rotating ventilation drying and natural drying. The BPNN model established using spectral-texture feature variables showed the best performance in distinguishing grain in different drying modes, with a prediction model obtained based on the correlation coefficients of special variables. The spectral and texture feature values were fused for pseudo-color visualization expression, and the three drying methods of grain showed different colors. This study provides a reference for non-destructive and rapid detection of grain with different drying methods.

Front-face synchronous fluorescence spectroscopy: a rapid and non-destructive authentication method for Arabica coffee adulterated with maize and soybean flours

This article describes a novel front-face synchronous fluorescence spectroscopy (FFSFS) method for the fast and non-invasive authentication of ground roasted Arabica coffee adulterated with roasted maize and soybean flours. The detection was based on the different composition of fluorescent Maillard reaction products and caffeine in roasted coffee and cereal flours. For each roasted maize or soybean adulterant flour (5-40 wt%), principal component analysis coupled with linear discriminant analysis (PCA-LDA) was used for qualitative discrimination. Quantitative prediction models were constructed based on the combination of unfolded total synchronous fluorescence spectra and partial least square regression (PLSR), followed by fivefold cross-validation and external validation. The PLSR models produced suitable results, with the determination coefficient of prediction (R p 2) > 0.9, root mean square error of prediction (RMSEP) < 5%, relative error of prediction (REP) < 25% and residual predictive deviation (RPD) > 3. The limits of detection (LOD) were both 10% for roasted maize and soybean flours. Most relative errors for the prediction of simulated blind samples were between -30% and + 30%. The benefits of this strategy are simplicity, rapidity, and non-destructive detection. However, owing to the high similarity between roasted coffee and roasted cereal flours and the influence of the roasting degree on fluorescent Maillard reaction products, its application is limited to the preliminary screening of roasted coffee with the same roasting degree, adulterated with relatively large amounts of roasted cereal flours which are roasted to analogous color to the coffee.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00003-022-01396-8.

Cocoa extract with high content of flavan 3-ols, procyanidins and methylxanthines

The health benefits of cocoa depend on the flavan 3-ols, procyanidins, and methylxanthines, which decrease from the early stages of cocoa bean processing. The objective of this research was to obtain a cocoa extract high in these compounds with (-)-epicatechin as the primary reference. An evaluation of two pretreatments of cocoa beans with a control after harvesting was made: A (untreated/control), B (Frozen), and C (Polyphenol oxidase inhibition), all followed by dehydration at 45 °C until obtaining a cocoa powder. In terms of (-)-epicatechin content, the best pretreatment was put on to a hydroalcoholic extraction. Flavan 3-ols, procyanidins, methylxanthines, and total polyphenols content (TPC), were quantified in the cocoa powders and the hydroalcoholic extract. The results showed that the control (A), significantly conserves the (-)-epicatechin (24.964 ± 0.400 mg/g) ca. 7 times more than conventionally sun-dried and fermented beans (3.742 ± 1.977 mg/g) ca. The hydroalcoholic extraction increased the (-)-epicatechin ca. 3 times more based on pretreatment A (84.738 mg/g).

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%.

A preliminary study on the potential of front face fluorescence spectroscopy for the discrimination of Moroccan virgin olive oils and the prediction of their quality

This study examines the feasibility of using front face fluorescence spectroscopy (FFFS) to authenticate 41 virgin olive oil (VOO) specimens collected from 5 regions in Morocco (Fez/Meknes, Eastern, Northern, Beni-Mellal/Khenifra, and Marrakech/Safi) during 2 consecutive crop seasons (2015-2016 and 2016-2017). By jointly applying factorial discriminant analysis (FDA) to the emission spectra acquired after excitation at 270, 290, and 430 nm, clear discrimination between VOOs according to their geographic origin (96.72% correct classification) and variety (95.12% correct classification) was observed. This trend was confirmed following the application of partial least squares regression (PLSR) to the fluorescence spectra, where excellent prediction of free acidity (R2 = 0.98) and peroxide (R2 = 0.96) values and good prediction of k232 (R2 = 0.88), k270 (R2 = 0.88), and chlorophyll content (R2 = 0.89) values were observed.

Analysis of various solid samples by synchronous fluorescence spectroscopy and related methods: A review

This critical Review covers the literature reports on analysis of different types of solid samples by the synchronous fluorescence spectroscopy (SFS) and its varieties, which include synchronous phosphorescence spectroscopy and synchronous luminescence spectroscopy, in the three decades (1990-2019). Both the qualitative and quantitative spectroscopic analysis is described for a wide range of specimens. Their physical forms and chemical composition include: a) organic and inorganic analytes pre-concentrated from solution on matrices (beads, membranes, filters, disks, paper), b) natural and synthetic multi-component specimens of complex composition (biological tissues, soil, polymers) and c) inorganic and coordination compounds including porous materials and particularly metal-organic frameworks (MOFs). The comparison with the data obtained by "conventional" optical emission spectroscopy and other analytical techniques (when available) is presented. The specific advantages of the high-resolution varieties of the method, the first- and second-derivative solid-state synchronous fluorescence, luminescence, and phosphorescence spectroscopy are described. An attention is also paid to practical conditions of the typical tests, and the relevant experimental setups. The impetus is on the emerging capabilities of this highly promising method e.g. in-situ monitoring of chemical reactions, in-vivo diagnostics, surface reactions, and detection of the adsorbate. The existing challenges are analyzed, and the unexplored application "niches" to further develop this and the related analytical methods are revealed. 145 references, 9 Tables, 17 Figures and 1 Scheme.

Rapid in situ analysis of l-histidine and α-lactose in dietary supplements by fingerprint peaks using terahertz frequency-domain spectroscopy

A simple, green and nondestructive method based on terahertz fingerprint peaks has been developed for rapid in situ analysis of l-histidine and α-lactose in dietary supplements. Fingerprint absorption peaks of l-histidine and α-lactose located at 0.77 and 0.53 THz could be directly used for identification and quantitation of these analytes in commercial dietary supplements. Compared with the partial least squares regression model (PLSR), the linear least squares regression (LLSR) method based on peak areas presented better performance, with the linear correlation coefficients of 0.9899 and 0.9910 for l-histidine and α-lactose, respectively. Furthermore, analysis time per sample can be shortened to less than 1 min due to the narrower spectral acquisition region. The accuracies were 94.8-110% and 98.9-110%, comparable to those of ion chromatography for l-histidine and high-performance liquid chromatography for α-lactose. The results presented great potential of the developed method for rapid in situ analysis of nutrients in dietary supplements.

The dual functions of flavor and antioxidant potential of porcine bone marrow extract (PBME)

To improve and confirm the dual functions of flavor and antioxidant potential of porcine bone marrow extract (PBME). Response surface methodology and Box-Behnken design was employed to optimize the conditions for enzymatic hydrolysis of PBME. The optimal hydrolysis conditions were: hydrolysis time, 3h; temperature, 55 °C; substrate concentration, 375g/L; and amount of enzyme, 0.4%. L₁₆(3⁵) orthogonal experimental was utilized to obtain the optimal Maillard reaction conditions for PBME and enzymatic hydrolysate of PBME (EH-PBME). The optimal conditions for PBME were: components, 4% glucose, 2% xylose, 1.5% Tyr, 1.5% Ala, and 4% VB₁; reaction time, 40 min; and reaction temperature, 115 °C. The optimal conditions for EH-PBME were: components, 2% glucose, 2% xylose, 3% Ala, and 5% VB₁; reaction time, 40 min; temperature, 110 °C. The antioxidant activities for PBME, EH-PBME, Maillard reaction products of PBME (MPRs A) and Maillard reaction products of EH-PBME (MPRs B) were 50%, 86%, 84% and 41% respectively. The content of taste-active substances and volatile compounds were also determined. Finally, PLSR was employed to evaluate the correlation between flavor compounds and sensory data.