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Special Issue "Aquaphotomics - Exploring Water Molecular Systems in Nature"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Analytical Chemistry".

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 11691

Special Issue Editors

Prof. Dr. Roumiana Tsenkova
E-Mail Website
Guest Editor
Aquaphotomics Research Department, Graduate School of Agriculture Sciences Kobe University, Kobe 657-8501, Japan
Interests: aquaphotomics; water; light; spectroscopy; chemometrics; non-invasive biomeasurements; water molecular structure; water functionality
Prof. Dr. Jelena Muncan
E-Mail Website
Co-Guest Editor
Aquaphotomics Research Department, Graduate School of Agriculture Sciences Kobe University, Kobe 657-8501, Japan
Interests: aquaphotomics; water; light; spectroscopy; chemometrics; non-invasive bio measurements; water molecular structure; water functionality

Special Issue Information

Dear Colleagues,

Aquaphotomics as a new “omics” science was established in 2005, guided by the vision to explore the biological world and the aqueous systems using light–water interaction. In the past, water was seen as a passive element, an inert molecule, hindering useful spectral signals. A radical new approach in spectroscopy—using water–light interaction—opened a new door for the world of science. Water as an active factor, a biomolecule in its own right, one which builds miscellaneous structures leading to various functionalities, has been recognized and is slowly becoming a new interdisciplinary scientific platform connecting sciences and technology.

The mission of aquaphotomics is to understand the role of water, a simple but sophisticated molecule that connects everything with its rhythm and ability for self-organization. All spectroscopy techniques are crucially important for aquaphotomics, whether they cover visible light, infrared (IR), near-infrared (NIR), ultraviolet (UV), Raman, or Terahertz frequencies. The water spectra of the systems under various perturbations create a large ocean of data. Thanks to the advancement of computer science, data analysis, and new measurement technologies, in recent years, the spectral studies of water are expanding in a wide variety of disciplines, providing a common platform for diverse technological applications.

This Special Issue of Molecules is devoted to learning and spreading new knowledge regarding features and functionalities of this most incredibly versatile molecule, water, and the connections and networks it creates, from which different functionalities arise. In these unprecedented times of a worldwide pandemic, we hope that this Special Issue will, just like water, make connections and motivate many people to know more about life and the surrounding world, a paradigm shift that will change our collective attitude toward nature.

The Special Issue welcomes articles that examine the state of the art in water research using spectroscopy, water structure and science, spectral preprocessing and analysis, emerging areas of applications of aquaphotomics knowledge, and future directions of development. All scientists working in these emerging and promising fields of research are strongly encouraged to submit their original papers and review works for publication in this Special Issue.

Prof. Dr. Roumiana Tsenkova
Prof. Dr. Jelena Muncan
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2300 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • aquaphotomics
  • water
  • spectra
  • chemometrics
  • non-destructive measurements
  • biomeasurement
  • band assignment
  • functionality

Published Papers (13 papers)

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Research

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Article
Changes in Water Properties in Human Tissue after Double Filtration Plasmapheresis—A Case Study
Molecules 2022, 27(12), 3947; https://doi.org/10.3390/molecules27123947 - 20 Jun 2022
Viewed by 323
Abstract
Double-filtration plasmapheresis (DFPP) is a blood cleaning technique that enables the removal of unwanted substances from the blood. In our case study, we performed near-infrared (NIR) spectroscopy measurements on the human hand tissue before and after a specific DFPP treatment (INUSpheresis with a [...] Read more.
Double-filtration plasmapheresis (DFPP) is a blood cleaning technique that enables the removal of unwanted substances from the blood. In our case study, we performed near-infrared (NIR) spectroscopy measurements on the human hand tissue before and after a specific DFPP treatment (INUSpheresis with a TKM58 filter), along with NIR measurements of the substances extracted via DFPP (eluate). The spectral data were analyzed using the aquaphotomics approach. The analysis showed that the water properties in the tissue change after DFPP treatment, i.e., an increase in small water clusters, free water molecules and a decrease in hydroxylated water as well as superoxide in hydration shells was noted. The opposite effect was observed in the eluates of both DFPP treatments. Our study is the first that documents changes in water spectral properties after DFPP treatments in human tissue. The changes in tissue water demonstrated by our case study suggest that the positive physiological effects of DFPP in general, and of INUSpheresis with the TKM58 filter in particular, may be associated with improvements in water quality in blood and tissues. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Increase in the Intracellular Bulk Water Content in the Early Phase of Cell Death of Keratinocytes, Corneoptosis, as Revealed by 65 GHz Near-Field CMOS Dielectric Sensor
Molecules 2022, 27(9), 2886; https://doi.org/10.3390/molecules27092886 - 30 Apr 2022
Viewed by 577
Abstract
While bulk water and hydration water coexist in cells to support the expression of biological macromolecules, how the dynamics of water molecules, which have long been only a minor role in molecular biology research, relate to changes in cellular states such as cell [...] Read more.
While bulk water and hydration water coexist in cells to support the expression of biological macromolecules, how the dynamics of water molecules, which have long been only a minor role in molecular biology research, relate to changes in cellular states such as cell death has hardly been explored so far due to the lack of evaluation techniques. In this study, we developed a high-precision measurement system that can discriminate bulk water content changes of ±0.02% (0.2 mg/cm3) with single-cell-level spatial resolution based on a near-field CMOS dielectric sensor operating at 65 GHz. We applied this system to evaluate the temporal changes in the bulk water content during the cell death process of keratinocytes, called corneoptosis, using isolated SG1 (first layer of stratum granulosum) cells in vitro. A significant irreversible increase in the bulk water content was observed approximately 1 h before membrane disruption during corneoptosis, which starts with cytoplasmic high Ca2+ signal. These findings suggest that the calcium flux may have a role in triggering the increase in the bulk water content in SG1 cells. Thus, our near-field CMOS dielectric sensor provides a valuable tool to dissect the involvement of water molecules in the various events that occur in the cell. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Identification of Stingless Bee Honey Adulteration Using Visible-Near Infrared Spectroscopy Combined with Aquaphotomics
Molecules 2022, 27(7), 2324; https://doi.org/10.3390/molecules27072324 - 03 Apr 2022
Viewed by 985
Abstract
Honey is a natural product that is considered globally one of the most widely important foods. Various studies on authenticity detection of honey have been fulfilled using visible and near-infrared (Vis-NIR) spectroscopy techniques. However, there are limited studies on stingless bee honey (SBH) [...] Read more.
Honey is a natural product that is considered globally one of the most widely important foods. Various studies on authenticity detection of honey have been fulfilled using visible and near-infrared (Vis-NIR) spectroscopy techniques. However, there are limited studies on stingless bee honey (SBH) despite the increase of market demand for this food product. The objective of this work was to present the potential of Vis-NIR absorbance spectroscopy for profiling, classifying, and quantifying the adulterated SBH. The SBH sample was mixed with various percentages (10–90%) of adulterants, including distilled water, apple cider vinegar, and high fructose syrup. The results showed that the region at 400–1100 nm that is related to the color and water properties of the samples was effective to discriminate and quantify the adulterated SBH. By applying the principal component analysis (PCA) on adulterants and honey samples, the PCA score plot revealed the classification of the adulterants and adulterated SBHs. A partial least squares regression (PLSR) model was developed to quantify the contamination level in the SBH samples. The general PLSR model with the highest coefficient of determination and lowest root means square error of cross-validation (RCV2=0.96 and RMSECV=5.88 %) was acquired. The aquaphotomics analysis of adulteration in SBH with the three adulterants utilizing the short-wavelength NIR region (800–1100 nm) was presented. The structural changes of SBH due to adulteration were described in terms of the changes in the water molecular matrix, and the aquagrams were used to visualize the results. It was revealed that the integration of NIR spectroscopy with aquaphotomics could be used to detect the water molecular structures in the adulterated SBH. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Aquaphotomic, E-Nose and Electrolyte Leakage to Monitor Quality Changes during the Storage of Ready-to-Eat Rocket
Molecules 2022, 27(7), 2252; https://doi.org/10.3390/molecules27072252 - 30 Mar 2022
Viewed by 405
Abstract
The consumption of ready-to-eat (RTE) leafy vegetables has increased rapidly due to changes in consumer diet. RTE products are perceived as fresh, high-quality, and health-promoting. The monitoring of the RTE quality is crucial in relation to safety issues. This study aimed to evaluate [...] Read more.
The consumption of ready-to-eat (RTE) leafy vegetables has increased rapidly due to changes in consumer diet. RTE products are perceived as fresh, high-quality, and health-promoting. The monitoring of the RTE quality is crucial in relation to safety issues. This study aimed to evaluate the maintenance of RTE rocket salad freshness packed under modified atmospheres. A portable E-nose, the electrolyte leakage test (which measures the index of leaf damage—ILD), and NIR spectroscopy and Aquaphotomics were employed. Two trials were carried out, using the following gas mixtures: (A) atmospheric air (21% O2, 78% N2); (B) 30% O2, 70% N2; (C) 10% CO2, 5% O2, 85% N2. Samples were stored at 4 °C and analyzed at 0, 1, 4, 7, 11, and 13 days. ANOVA, PCA, PLS were applied for data processing. E-nose and ILD results identified the B atmosphere as the best for maintaining product freshness. NIR spectroscopy was able to group the samples according to the storage time. Aquaphotomics proved to be able to detect changes in the water structure during storage. These preliminary data showed a good agreement NIR/ILD suggesting the use of NIR for non-destructive monitoring of the damage to the plant membranes of RTE rocket salad. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Analysis of Vicinal Water in Soft Contact Lenses Using a Combination of Infrared Absorption Spectroscopy and Multivariate Curve Resolution
Molecules 2022, 27(7), 2130; https://doi.org/10.3390/molecules27072130 - 25 Mar 2022
Viewed by 641
Abstract
In this paper, we propose a new spectroscopic method to explore the behavior of molecules near polymeric molecular networks of water-containing soft materials such as hydrogels. We demonstrate the analysis of hydrogen bonding states of water in the vicinity of hydrogels (soft contact [...] Read more.
In this paper, we propose a new spectroscopic method to explore the behavior of molecules near polymeric molecular networks of water-containing soft materials such as hydrogels. We demonstrate the analysis of hydrogen bonding states of water in the vicinity of hydrogels (soft contact lenses). In this method, we apply force to hydrated contact lenses to deform them and to modulate the ratio between the signals from bulk and vicinal regions. We then collect spectra at different forces. Finally, we extracted the spectra of the vicinal region using the multivariate curve resolution-alternating least square (MCR-ALS) method. We report the hydration states depending on the chemical structures of hydrogels constituting the contact lenses. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Revealing the Effect of Heat Treatment on the Spectral Pattern of Unifloral Honeys Using Aquaphotomics
Molecules 2022, 27(3), 780; https://doi.org/10.3390/molecules27030780 - 25 Jan 2022
Viewed by 922
Abstract
In this study we aimed to investigate the effect of heat treatment on the spectral pattern of honey using near infrared spectroscopy (NIRS). For the research, sunflower, bastard indigo, and acacia honeys were collected from entrusted beekeepers. The honeys were not subject to [...] Read more.
In this study we aimed to investigate the effect of heat treatment on the spectral pattern of honey using near infrared spectroscopy (NIRS). For the research, sunflower, bastard indigo, and acacia honeys were collected from entrusted beekeepers. The honeys were not subject to any treatment before. Samples were treated at 40 °C, 60 °C, 80 °C, and 100 °C for 60, 120, 180, and 240 min. This resulted in 17 levels, including the untreated control samples. The 5-hydroxymethylfurfural (HMF) content of the honeys was determined using the Winkler method. NIRS spectra were recorded using a handheld instrument. Data analysis was performed using ANOVA for the HMF content and multivariate analysis for the NIRS data. For the latter, PCA, PCA-LDA, and PLSR models were built (using the 1300–1600 nm spectral range) and the wavelengths presenting the greatest change induced by the perturbations of temperature and time intervals were collected systematically, based on the difference spectra and the weights of the models. The most contributing wavelengths were used to visualize the spectral pattern changes on the aquagrams in the specific water matrix coordinates. Our results showed that the heat treatment highly contributed to the formation of free or less bonded water, however, the changes in the spectral pattern highly depended on the crystallization phase and the honey type. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Aquaphotomics Research of Cold Stress in Soybean Cultivars with Different Stress Tolerance Ability: Early Detection of Cold Stress Response
Molecules 2022, 27(3), 744; https://doi.org/10.3390/molecules27030744 - 24 Jan 2022
Viewed by 993
Abstract
The development of non-destructive methods for early detection of cold stress of plants and the identification of cold-tolerant cultivars is highly needed in crop breeding programs. Current methods are either destructive, time-consuming or imprecise. In this study, soybean leaves’ spectra were acquired in [...] Read more.
The development of non-destructive methods for early detection of cold stress of plants and the identification of cold-tolerant cultivars is highly needed in crop breeding programs. Current methods are either destructive, time-consuming or imprecise. In this study, soybean leaves’ spectra were acquired in the near infrared (NIR) range (588–1025 nm) from five cultivars genetically engineered to have different levels of cold stress tolerance. The spectra were acquired at the optimal growing temperature 27 °C and when the temperature was decreased to 22 °C. In this paper, we report the results of the aquaphotomics analysis performed with the objective of understanding the role of the water molecular system in the early cold stress response of all cultivars. The raw spectra and the results of Principal Component Analysis, Soft Independent Modeling of Class Analogies and aquagrams showed consistent evidence of huge differences in the NIR spectral profiles of all cultivars under normal and mild cold stress conditions. The SIMCA discrimination between the plants before and after stress was achieved with 100% accuracy. The interpretation of spectral patterns before and after cold stress revealed major changes in the water molecular structure of the soybean leaves, altered carbohydrate and oxidative metabolism. Specific water molecular structures in the leaves of soybean cultivars were found to be highly sensitive to the temperature, showing their crucial role in the cold stress response. The results also indicated the existence of differences in the cold stress response of different cultivars, which will be a topic of further research. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Raman Spectroscopy-Based Assessment of the Liquid Water Content in Snow
Molecules 2022, 27(3), 626; https://doi.org/10.3390/molecules27030626 - 19 Jan 2022
Viewed by 416
Abstract
In snow, water coexists in solid, liquid and vapor states. The relative abundance of the three phases drives snow grain metamorphism and affects the physical properties of the snowpack. Knowledge of the content of the liquid phase in snow is critical to estimate [...] Read more.
In snow, water coexists in solid, liquid and vapor states. The relative abundance of the three phases drives snow grain metamorphism and affects the physical properties of the snowpack. Knowledge of the content of the liquid phase in snow is critical to estimate the snowmelt runoff and to forecast the release of wet avalanches. Liquid water does not spread homogeneously through a snowpack because different snow layers have different permeabilities; therefore, it is important to track sudden changes in the amount of liquid water within a specific layer. We reproduced water percolation in the laboratory, and used Raman spectroscopy to detect the presence of the liquid phase in controlled snow samples. We performed experiments on both fine- and coarse-grained snow. The obtained snow spectra are well fitted by a linear combination of the spectra typical of liquid water and ice. We progressively charged snow with liquid water from dry snow up to soaked snow. As a result, we exploited continuous, qualitative monitoring of the evolution of the liquid water content as reflected by the fitting coefficient c. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Bovine Respiratory Syncytial Virus (BRSV) Infection Detected in Exhaled Breath Condensate of Dairy Calves by Near-Infrared Aquaphotomics
Molecules 2022, 27(2), 549; https://doi.org/10.3390/molecules27020549 - 16 Jan 2022
Cited by 1 | Viewed by 449
Abstract
Bovine respiratory syncytial virus (BRSV) is a major contributor to respiratory disease in cattle worldwide. Traditionally, BRSV infection is detected based on non-specific clinical signs, followed by reverse transcriptase-polymerase chain reaction (RT-PCR), the results of which can take days to obtain. Near-infrared aquaphotomics [...] Read more.
Bovine respiratory syncytial virus (BRSV) is a major contributor to respiratory disease in cattle worldwide. Traditionally, BRSV infection is detected based on non-specific clinical signs, followed by reverse transcriptase-polymerase chain reaction (RT-PCR), the results of which can take days to obtain. Near-infrared aquaphotomics evaluation based on biochemical information from biofluids has the potential to support the rapid identification of BRSV infection in the field. This study evaluated NIR spectra (n = 240) of exhaled breath condensate (EBC) from dairy calves (n = 5) undergoing a controlled infection with BRSV. Changes in the organization of the aqueous phase of EBC during the baseline (pre-infection) and infected (post-infection and clinically abnormal) stages were found in the WAMACS (water matrix coordinates) C1, C5, C9, and C11, likely associated with volatile and non-volatile compounds in EBC. The discrimination of these chemical profiles by PCA-LDA models differentiated samples collected during the baseline and infected stages with an accuracy, sensitivity, and specificity >93% in both the calibration and validation. Thus, biochemical changes occurring during BRSV infection can be detected and evaluated with NIR-aquaphotomics in EBC. These findings form the foundation for developing an innovative, non-invasive, and in-field diagnostic tool to identify BRSV infection in cattle. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Correction of Temperature Variation with Independent Water Samples to Predict Soluble Solids Content of Kiwifruit Juice Using NIR Spectroscopy
Molecules 2022, 27(2), 504; https://doi.org/10.3390/molecules27020504 - 14 Jan 2022
Viewed by 421
Abstract
Using the framework of aquaphotomics, we have sought to understand the changes within the water structure of kiwifruit juice occurring with changes in temperature. The study focuses on the first (1300–1600 nm) and second (870–1100 nm) overtone regions of the OH stretch of [...] Read more.
Using the framework of aquaphotomics, we have sought to understand the changes within the water structure of kiwifruit juice occurring with changes in temperature. The study focuses on the first (1300–1600 nm) and second (870–1100 nm) overtone regions of the OH stretch of water and examines temperature differences between 20, 25, and 30 °C. Spectral data were collected using a Fourier transform–near-infrared spectrometer with 1 mm and 10 mm transmission cells for measurements in the first and second overtone region, respectively. Water wavelengths affected by temperature variation were identified. Aquagrams (water spectral patterns) highlight slightly different responses in the first and second overtone regions. The influence of increasing temperature on the peak absorbance of the juice was largely a lateral wavelength shift in the first overtone region and a vertical amplitude shift in the second overtone region of water. With the same data set, we investigated the use of external parameter orthogonalisation (EPO) and extended multiple scatter correction (EMSC) pre-processing to assist in building temperature-independent partial least square regression models for predicting soluble solids concentration (SSC) of kiwifruit juice. The interference component selected for correction was the first principal component loading measured using pure water samples taken at the same three temperatures (20, 25, and 30 °C). The results show that the EMSC method reduced SSC prediction bias from 0.77 to 0.1 °Brix in the first overtone region of water. Using the EPO method significantly reduced the prediction bias from 0.51 to 0.04 °Brix, when applying a model made at one temperature (30 °C) to measurements made at another temperature (20 °C) in the second overtone region of water. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
Interactions of Linearly Polarized and Unpolarized Light on Kiwifruit Using Aquaphotomics
Molecules 2022, 27(2), 494; https://doi.org/10.3390/molecules27020494 - 13 Jan 2022
Viewed by 860
Abstract
Near infrared (NIR) spectroscopy is an important tool for predicting the internal qualities of fruits. Using aquaphotomics, spectral changes between linearly polarized and unpolarized light were assessed on 200 commercially grown yellow-fleshed kiwifruit (Actinidia chinensis var. chinensis ‘Zesy002’). Measurements were performed on [...] Read more.
Near infrared (NIR) spectroscopy is an important tool for predicting the internal qualities of fruits. Using aquaphotomics, spectral changes between linearly polarized and unpolarized light were assessed on 200 commercially grown yellow-fleshed kiwifruit (Actinidia chinensis var. chinensis ‘Zesy002’). Measurements were performed on different configurations of unpeeled (intact) and peeled (cut) kiwifruit using a commercial handheld NIR instrument. Absorbance after applying standard normal variate (SNV) and second derivative Savitzky–Golay filters produced different spectral features for all configurations. An aquagram depicting all configurations suggests that linearly polarized light activated more free water states and unpolarized light activated more bound water states. At depth (≥1 mm), after several scattering events, all radiation is expected to be fully depolarized and interactions for incident polarized or unpolarized light will be similar, so any observed differences are attributable to the surface layers of the fruit. Aquagrams generated in terms of the fruit soluble solids content (SSC) were similar for all configurations, suggesting the SSC in fruit is not a contributing factor here. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Article
NIRS and Aquaphotomics Trace Robusta-to-Arabica Ratio in Liquid Coffee Blends
Molecules 2022, 27(2), 388; https://doi.org/10.3390/molecules27020388 - 08 Jan 2022
Viewed by 535
Abstract
Coffee is both a vastly consumed beverage and a chemically complex matrix. For a long time, an arduous chemical analysis was necessary to resolve coffee authentication issues. Despite their demonstrated efficacy, such techniques tend to rely on reference methods or resort to elaborate [...] Read more.
Coffee is both a vastly consumed beverage and a chemically complex matrix. For a long time, an arduous chemical analysis was necessary to resolve coffee authentication issues. Despite their demonstrated efficacy, such techniques tend to rely on reference methods or resort to elaborate extraction steps. Near infrared spectroscopy (NIRS) and the aquaphotomics approach, on the other hand, reportedly offer a rapid, reliable, and holistic compositional overview of varying analytes but with little focus on low concentration mixtures of Robusta-to-Arabica coffee. Our study aimed for a comparative assessment of ground coffee adulteration using NIRS and liquid coffee adulteration using the aquaphotomics approach. The aim was to demonstrate the potential of monitoring ground and liquid coffee quality as they are commercially the most available coffee forms. Chemometrics spectra analysis proved capable of distinguishing between the studied samples and efficiently estimating the added Robusta concentrations. An accuracy of 100% was obtained for the varietal discrimination of pure Arabica and Robusta, both in ground and liquid form. Robusta-to-Arabica ratio was predicted with R2CV values of 0.99 and 0.9 in ground and liquid form respectively. Aquagrams results accentuated the peculiarities of the two coffee varieties and their respective blends by designating different water conformations depending on the coffee variety and assigning a particular water absorption spectral pattern (WASP) depending on the blending ratio. Marked spectral features attributed to high hydrogen bonded water characterized Arabica-rich coffee, while those with the higher Robusta content showed an abundance of free water structures. Collectively, the obtained results ascertain the adequacy of NIRS and aquaphotomics as promising alternative tools for the authentication of liquid coffee that can correlate the water-related fingerprint to the Robusta-to-Arabica ratio. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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Review

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Review
Chemometrics: An Excavator in Temperature-Dependent Near-Infrared Spectroscopy
Molecules 2022, 27(2), 452; https://doi.org/10.3390/molecules27020452 - 11 Jan 2022
Cited by 1 | Viewed by 2708
Abstract
Temperature-dependent near-infrared (NIR) spectroscopy has been developed and taken as a powerful technique for analyzing the structure of water and the interactions in aqueous systems. Due to the overlapping of the peaks in NIR spectra, it is difficult to obtain the spectral features [...] Read more.
Temperature-dependent near-infrared (NIR) spectroscopy has been developed and taken as a powerful technique for analyzing the structure of water and the interactions in aqueous systems. Due to the overlapping of the peaks in NIR spectra, it is difficult to obtain the spectral features showing the structures and interactions. Chemometrics, therefore, is adopted to improve the spectral resolution and extract spectral information from the temperature-dependent NIR spectra for structural and quantitative analysis. In this review, works on chemometric studies for analyzing temperature-dependent NIR spectra were summarized. The temperature-induced spectral features of water structures can be extracted from the spectra with the help of chemometrics. Using the spectral variation of water with the temperature, the structural changes of small molecules, proteins, thermo-responsive polymers, and their interactions with water in aqueous solutions can be demonstrated. Furthermore, quantitative models between the spectra and the temperature or concentration can be established using the spectral variations of water and applied to determine the compositions in aqueous mixtures. Full article
(This article belongs to the Special Issue Aquaphotomics - Exploring Water Molecular Systems in Nature)
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