Metabolic discrimination of mango juice from various cultivars by band-selective NMR spectroscopy

Fresh Dual Presaturation Method for Analyzing H2O-Rich Samples Using Quantitative 1H NMR

A fresh dual presaturation (pre-SAT) method was developed to quantify analytes accurately near the suppressed water signal in ¹H NMR spectra obtained from H₂O-rich samples. The method includes an extra dummy pre-SAT with a suitable offset for each analyte signal in addition to the water pre-SAT. The residual HOD signal at 4.66 ppm was observed using D₂O solutions containing l-phenylalanine (Phe) or l-valine (Val) and an internal standard of 3-(trimethylsilyl)-1-propanesulfonic acid-d₆ sodium salt (DSS-d₆). When the HOD signal was suppressed using the conventional single pre-SAT method, the measured concentration of Phe from the NCH signal at 3.89 ppm decreased by a maximum of 48%, whereas the dual pre-SAT method gave a reduction in the Phe concentration measured from the NCH signal of less than 3%. The proposed dual pre-SAT method achieved accurate quantification of glycine (Gly) and maleic acid (MA) in a 10 vol % D₂O/H₂O solution. The measured concentrations of Gly of 513.5 ± 8.9 mg kg^-1 and MA of 512.2 ± 10.3 mg kg^-1 corresponded to sample preparation values of Gly of 502.9 ± 1.7 mg kg^-1 and MA of 506.7 ± 2.9 mg kg^-1 (the number after "±" indicates the expanded uncertainty (k = 2)).

Compositional Analysis of Four Kinds of Citrus Fruits with an NMR-Based Method for Understanding Nutritional Value and Rational Utilization: From Pericarp to Juice

Citrus is one of the most important economic crops and is widely distributed across the monsoon region. Citrus fruits are deeply loved by consumers because of their special color, fragrance and high nutritional value. However, their health benefits have not been fully understood, especially the pericarps of citrus fruits which have barely been utilized due to their unknown chemical composition. In the present study, the pericarp and juices of four typical varieties of citrus fruits (lemon, dekopon, sweet orange and pomelo) were analyzed by NMR spectroscopy combined with pattern recognition. A total of 62 components from the citrus juices and 87 components from the citrus pericarps were identified and quantified, respectively. The different varieties of the citrus fruits could be distinguished from the others, and the chemical markers in each citrus juice and pericarp were identified by a combination of univariate and multivariate statistical analyses. The nutritional analysis of citrus juices offers favorable diet recommendations for human consumption and data guidance for their potential medical use, and the nutritional analysis of citrus pericarps provides a data reference for the subsequent comprehensive utilization of citrus fruits. Our results not only provide an important reference for the potential nutritional and medical values of citrus fruits but also provide a feasible platform for the traceability analysis, adulteration identification and chemical composition analysis of other fruits.

Enhanced Bioactivity of Pomegranate Peel Extract following Controlled Release from CaCO3 Nanocrystals

Pomegranate peel extract is rich of interesting bioactive chemicals, principally phenolic compounds, which have shown antimicrobial, anticancer, and antioxidative properties. The aim of this work was to improve extract’ bioactivity through the adsorption on calcium carbonate nanocrystals. Nanocrystals revealed as efficient tools for extract adsorption reaching 50% of loading efficiency. Controlled release of the contained metabolites under acidic pH has been found, as it was confirmed by quantitative assay and qualitative study through NMR analysis. Specific functionality of inorganic nanocarriers could be also tuned by biopolymeric coating. The resulting coated nanoformulations showed a great antimicrobial activity against B. cinerea fungus preventing strawberries disease better than a commercial fungicide. Furthermore, nanoformulations demonstrated a good antiproliferative activity in neuroblastoma and breast cancer cells carrying out a higher cytotoxic effect respect to free extract, confirming a crucial role of nanocarriers. Finally, pomegranate peel extract showed a very high radical scavenging ability, equal to ascorbic acid. Antioxidant activity, measured also in intracellular environment, highlighted a protective action of extract-adsorbed nanocrystals twice than free extract, providing a possible application for new nutraceutical formulations.

Non-Invasive Methods for Predicting the Quality of Processed Horticultural Food Products, with Emphasis on Dried Powders, Juices and Oils: A Review

This review covers recent developments in the field of non-invasive techniques for the quality assessment of processed horticultural products over the past decade. The concept of quality and various quality characteristics related to evaluating processed horticultural products are detailed. A brief overview of non-invasive methods, including spectroscopic techniques, nuclear magnetic resonance, and hyperspectral imaging techniques, is presented. This review highlights their application to predict quality attributes of different processed horticultural products (e.g., powders, juices, and oils). A concise summary of their potential commercial application for quality assessment, control, and monitoring of processed agricultural products is provided. Finally, we discuss their limitations and highlight other emerging non-invasive techniques applicable for monitoring and evaluating the quality attributes of processed horticultural products. Our findings suggest that infrared spectroscopy (both near and mid) has been the preferred choice for the non-invasive assessment of processed horticultural products, such as juices, oils, and powders, and can be adapted for on-line quality control. Raman spectroscopy has shown potential in the analysis of powdered products. However, imaging techniques, such as hyperspectral imaging and X-ray computed tomography, require improvement on data acquisition, processing times, and reduction in the cost and size of the devices so that they can be adopted for on-line measurements at processing facilities. Overall, this review suggests that non-invasive techniques have the potential for industrial application and can be used for quality assessment.

Detecting Admixture to Mango Purée of the Alphonso Cultivar (Mangifera indica L. cv. Alphonso) by 1H-NMR Spectroscopy

Food authenticity is becoming increasingly important but challenges existing analytical methods. In this study, we analyze the mango cultivar Alphonso with regard to authenticity using 1H-NMR spectroscopy. This cultivar has been termed “the king of mangoes” due to its unique flavor. Regarding its metabolites however, little is known about unique constellations that allow for differentiation of the Alphonso cultivar. We find that the Alphonso cultivar is distinguished by high levels of niacin, trigonelline, and histidine but features relatively low levels of alanine. Furthermore, we develop a model based on the local outlier factor algorithm that effectively detects admixture of non-Alphonso cultivars to Alphonso purée. This task is highly challenging because we identified no metabolites that are unique or uniquely absent in the Alphonso cultivar compared to other mango cultivars analyzed in this study. Our model shows promising results on a test set: Admixtures consisting of 35% non-Alphonso and 65% Alphonso mango purée were uncovered with a sensitivity of 88%. At the same time, our model verified Alphonso samples with a good specificity of 86%.

Bioactivities of Phenolic Compounds from Kiwifruit and Persimmon

Fruit used in the common human diet in general, and kiwifruit and persimmon particularly, displays health properties in the prevention of heart disease. This study describes a combination of bioactivity, multivariate data analyses and fluorescence measurements for the differentiating of kiwifruit and persimmon, their quenching and antioxidant properties. The metabolic differences are shown, as well in the results of bioactivities and antioxidant capacities determined by ABTS, FRAP, CUPRAC and DPPH assays. To complement the bioactivity of these fruits, the quenching properties between extracted polyphenols and human serum proteins were determined by 3D-fluorescence spectroscopy studies. These properties of the extracted polyphenols in interaction with the main serum proteins in the human metabolism (human serum albumin (HSA), α-β-globulin (α-β G) and fibrinogen (Fgn)), showed that kiwifruit was more reactive than persimmon. There was a direct correlation between the quenching properties of the polyphenols of the investigated fruits with serum human proteins, their relative quantification and bioactivity. The results of metabolites and fluorescence quenching show that these fruits possess multiple properties that have a great potential to be used in industry with emphasis on the formulation of functional foods and in the pharmaceutical industry. Based on the quenching properties of human serum proteins with polyphenols and recent reports in vivo on human studies, we hypothesize that HSA, α-β G and Fgn will be predictors of coronary artery disease (CAD).

Understanding the Gastrointestinal Protective Effects of Polyphenols using Foodomics-Based Approaches

Plant polyphenols are rich sources of natural anti-oxidants and prebiotics. After ingestion, most polyphenols are absorbed in the intestine and interact with the gut microbiota and modulated metabolites produced by bacterial fermentation, such as short-chain fatty acids (SCFAs). Dietary polyphenols immunomodulatory role by regulating intestinal microorganisms, inhibiting the etiology and pathogenesis of various diseases including colon cancer, colorectal cancer, inflammatory bowel disease (IBD) and colitis. Foodomics is a novel high-throughput analysis approach widely applied in food and nutrition studies, incorporating genomics, transcriptomics, proteomics, metabolomics, and integrating multi-omics technologies. In this review, we present an overview of foodomics technologies for identifying active polyphenol components from natural foods, as well as a summary of the gastrointestinal protective effects of polyphenols based on foodomics approaches. Furthermore, we critically assess the limitations in applying foodomics technologies to investigate the protective effect of polyphenols on the gastrointestinal (GI) system. Finally, we outline future directions of foodomics techniques to investigate GI protective effects of polyphenols. Foodomics based on the combination of several analytical platforms and data processing for genomics, transcriptomics, proteomics and metabolomics studies, provides abundant data and a more comprehensive understanding of the interactions between polyphenols and the GI tract at the molecular level. This contribution provides a basis for further exploring the protective mechanisms of polyphenols on the GI system.

A review of fruit juice authenticity assessments: Targeted and untargeted analyses

Fruit juices are becoming more and more popular in the whole world. However, the increasing fruit juice fraud cases are undermining the healthy development of fruit juice industry. Fruit juice authenticity represents an important food quality and safety parameter. Many techniques have been applied in fruit juices authenticity assessment. The purpose of this review is to provide a research overview of the targeted and untargeted analyses of fruit authentication, and a method selection guide for fruit juice authenticity assessment. Targeted markers, such as stable isotopes, phenolics, carbohydrates, organic acids, volatile components, DNAs, amino acids and proteins, as well as carotenoids, will be discussed. And untargeted techniques, including liquid/gas chromatography-mass spectrometer, nuclear magnetic resonance, infrared spectroscopy, inductively-coupled plasma-mass spectrometry/optical emission spectrometer, fluorescence spectra, electronic sensors and others, will be reviewed. The emerging untargeted for novel targeted marker analysis will be also summarized.

NMR and Computational Studies as Analytical and High-Resolution Structural Tool for Complex Hydroperoxides and Diastereomeric Endo-Hydroperoxides of Fatty Acids in Solution-Exemplified by Methyl Linolenate

A combination of selective 1D Total Correlation Spectroscopy (TOCSY) and 1H-13C Heteronuclear Multiple Bond Correlation (HMBC) NMR techniques has been employed for the identification of methyl linolenate primary oxidation products without the need for laborious isolation of the individual compounds. Complex hydroperoxides and diastereomeric endo-hydroperoxides were identified and quantified. Strongly deshielded C-O-O-H 1H-NMR resonances of diastereomeric endo-hydroperoxides in the region of 8.8 to 9.6 ppm were shown to be due to intramolecular hydrogen bonding interactions of the hydroperoxide proton with an oxygen atom of the five-member endo-peroxide ring. These strongly deshielded resonances were utilized as a new method to derive, for the first time, three-dimensional structures with an assignment of pairs of diastereomers in solution with the combined use of 1H-NMR chemical shifts, Density Functional Theory (DFT), and Our N-layered Integrated molecular Orbital and molecular Mechanics (ONIOM) calculations.

Use of information dependent acquisition mass spectra and sequential window acquisition of all theoretical fragment-ion mass spectra for fruit juices metabolomics and authentication

INTRODUCTION

LC-MS based untargeted metabolomics are the main untargeted methods used for juice metabolomics to solve the authentication problem faced in fruit juice industry.

OBJECTIVES

To evaluate the performances of different untargeted metabolomics methods on fruit juices metabolomics and authentication, orange and apple fruit juices were selected for this study.

METHODS

IDA-MS and SWATH-MS based on UHPLC-QTOF were used for the metabolomics and authenticity determination of apple and orange juices, including the lab-made samples of oranges (Citrus sinensis Osb.) from Jiangxi Province, apples (Malus domestica Borkh) from Shandong Province, and different brands of commercial orange and apple juice samples from markets.

RESULTS

IDA-MS and SWATH-MS could both acquire numerous MS1 features and MS2 information of juice components, while SWATH-MS excels at the acquisition rate of MS2. Distinctive separation between authentic orange juice and not authentic orange juice could be seen from principal component analysis and hierarchical clustering analysis based on both IDA-MS and SWATH-MS. After analysis of variance, fold change analysis and orthogonal projection to latent structures discriminant mode, 53 and 46 potential markers were defined by IDA-MS and SWATH-MS (with 77.4% and 100% MS2 acquisition rate) separately. Subsequently, these potential markers were putatively annotated using general chemical databases with 6 more annotated by SWATH-MS. Furthermore, 7 of the potential markers, l-asparagine, umbelliferone, glucosamine, phlorin, epicatechin, phytosphingosine and chlorogenic acid, were identified with standards. For the consideration of model simplicity, two determined makers (umbelliferone and chlorogenic acid) were selected to construct the DD-SIMCA model in commercial samples because of their good correlation with apple adulteration proportion, and the sensitivity and specificity of the model were 100% and 95%.

CONCLUSION

SWATH-MS excels at the MS2 acquisition of juice components and potential markers. This study provides an overall performance comparison between IDA-MS and SWATH-MS, and guidance for the method selection on fruit juice metabolomics and juice authenticity determination. Two of the potential markers determined, umbelliferone and chlorogenic acid, could be used as apple juice indicators in orange juice.

Band-selective excitation NMR spectroscopy and quantitative time-domain analysis using Complete Reduction to Amplitude-Frequency Table (CRAFT) to determine distribution coefficients during drug development

A sensitive quantitative ¹ H NMR method for determining distribution or partition coefficients has been developed that is applicable to early drug discovery. After partitioning and equilibration, aliquots from each layer are analyzed using band-selective excitation ¹ H NMR spectroscopy in regions that are free of 1-octanol and water solvent signals. Signals are quantitated directly using CRAFT software, and their amplitudes are adjusted to correct for nonuniformity within the excitation band. Using this approach, the distribution coefficients for 20 drugs present at low concentrations were determined giving values that were in excellent agreement with literature values.

NMR-based metabolic profiling and comparison of Japanese persimmon cultivars

Persimmons are a traditional, autumnal, and healthy fruit commonly consumed in Japan and East Asia based on the saying, "a persimmon a day keeps the doctor away." The differences in metabolites among five major Japanese persimmon cultivars were investigated using a nuclear magnetic resonance (NMR)-based metabolomics approach. By using a broadband water suppression enhanced through T₁ effects (WET) method for the sensitive detection of minor metabolites, better discrimination among cultivars and more informative details regarding their metabolic differences have been achieved compared to those achieved in conventional ¹H NMR sequences. Among the nonastringent cultivars analyzed, the Taishu cultivar has the highest abundance of amino acids. The Matsumotowase-Fuyu cultivar contains ethyl-β-glycosides as characteristic components, which may relate to fruit softening. Citric acid concentration is higher in Maekawa Jiro than in other nonastringent cultivars. Among the two astringent cultivars analyzed, ethanol was significantly higher in Hiratanenashi than in Yotsumizo, which indicates different reactivity during deastringency treatments. The present study proposes an efficient and relatively quantitative metabolomics approach based on broadband WET NMR spectra.

Identification of metabolites in coriander seeds (Coriandrum Sativum L.) aided by ultrahigh resolution total correlation NMR spectroscopy

NMR is a fast method for obtaining a holistic snapshot of the metabolome and also offers quantitative information without separating the compounds present in a complex mixture. Identification of the metabolites present in a plant extract sample is a crucial step for all plant metabolomics studies. In the present work, we used various two dimensional (2D) NMR methods such as J-resolved NMR, total correlation spectroscopy (TOCSY), and heteronuclear single quantum coherence sensitivity enhanced NMR spectroscopy for the identification of 36 common metabolites present in Coriandrum sativum L. seed extract. The identified metabolites belong to the following classes: organic acids, amino acids, and carbohydrates. ¹ H NMR spectra of such complex mixtures in general display tremendous signal overlap due to the presence of a large number of metabolites with closely resonating multiplet signals. This signal overlapping leads to ambiguity in an assignment, and hence, identification of metabolites becomes tedious or impossible in many cases. Therefore, the utility of pure-shift proton spectrum along the indirect (F₁ ) dimension of the F₁ -PSYCHE-TOCSY spectrum is demonstrated for overcoming ambiguity in assignment of metabolites in crowded spectral regions from Coriandrum sativum L. seed extract sample. Because pure-shift NMR methods yield ultrahigh resolution spectrum (i.e., a singlet peak per chemical site) along one or more dimensions, such spectra provide better identification of metabolites compared with regular 2D TOCSY where signal overlap and peak distortions lead to ambiguity in the assignment. Nine metabolites were unambiguously assigned by pure-shift F₁ -PSYCHE-TOCSY spectrum, which was unresolved in regular TOCSY spectrum.

Metabolic profiling of natural and cultured Cordyceps by NMR spectroscopy

Cordyceps, a type of Chinese herbal medicine that exhibits anti-angiogenesis and tumor growth suppression effects, has recently gained increasing popularity. However, high-quality, natural Cordyceps, such as Ophiocordyceps sinensis, is very rare and difficult to obtain in large amounts. Cordyceps is cultured instead of harvested from natural sources, but the quality with respect to the ingredients has not been fully studied. In this study, we performed an NMR metabolic profiling of aqueous extracts of Cordyceps without any sample treatment to evaluate the proper species and medium and influence of two different disinfection methods. It was discovered that Cordyceps militaris fungus and silkworm chrysalis medium were suitable for cultivation of Cordyceps. Furthermore, cordycepin, a Cordyceps-specific functional compound, was produced at different growth stages during different cultivation processes, even at the mycelial stage, and was found at three times higher concentrations in cultured C. militaris compared to that in naturally occurring C. militaris.

1 H-NMR Based Metabolomics Profiling of Citrus Juices Produced in Veracruz, México

This study describes the ¹ H-NMR-based metabolomics profiling of juices from citrus fruits harvested in the state of Veracruz, México. The hydrophilic profile of commercial lemons (Agrio and Persian), tangerines (Fremont and Mónica), oranges (Valencia and Washington Navel), and grapefruits (Red Ruby and Rio Red) was determined. According to our results, 35 metabolites were identified in the ¹ H-NMR profiling. The statistical differences obtained by PCA and OPLS-DA revealed that specific amino acids, sugars, and organic acids were differential metabolites in the species and cultivars studied. High endogenous levels of sucrose (10-190 mM), α-glucose, β-glucose (α- and β-isomers, 40-205 mm), and fructose (36-170 mm) were detected in the juices of grapefruits, oranges, and tangerines, whereas citric acid (40-530 mm) was the principal organic acid in the juices of lemons. To calculate the specific amounts of metabolites from these species and their cultivars, the results were finely analyzed using the qNMR method. According to these calculations, Valencia oranges had the highest concentration of ascorbic acid (>2 mm). The described ¹ H-NMR method is highly reproducible, inexpensive, and highly robust in comparison to other analytical methods used to determine the hydrophilic profile of citrus juices.

Quality and Authenticity Control of Fruit Juices-A Review

Food fraud, being the act of intentional adulteration of food for financial advantage, has vexed the consumers and the food industry throughout history. According to the European Committee on the Environment, Public Health and Food Safety, fruit juices are included in the top 10 food products that are most at risk of food fraud. Therefore, reliable, efficient, sensitive and cost-effective analytical methodologies need to be developed continuously to guarantee fruit juice quality and safety. This review covers the latest advances in the past ten years concerning the targeted and non-targeted methodologies that have been developed to assure fruit juice authenticity and to preclude adulteration. Emphasis is placed on the use of hyphenated techniques and on the constantly-growing role of MS-based metabolomics in fruit juice quality control area.

1H NMR-based fingerprinting of eleven Mexican Capsicum annuum cultivars

Approximately 90% of the chili peppers consumed in the world are harvested in Mexico. The present article describes the untargeted ¹H NMR-based metabolomic profiling of 11 cultivars of Capsicum annuum species which are routinely consumed worldwide. The metabolomic fingerprinting detected via ¹H NMR contained 44 metabolites including sugars, amino acids, organic acids, polyphenolic acids and alcohols which were identified by comparison with the literature data, with Chenomx database and by 2D NMR. Statistical approaches based on principal component analysis (PCA) and linear discriminant analysis (LDA) were used to classify the Capsicum annuum cultivars according to their metabolite profile. LDA revealed metabolomic differences and similarities among Capsicum annuum cultivars, whereas hierarchical cluster analysis (HCA) significantly separated the cultivars according to the phylogenetic trees obtained. Substantial endogenous levels of free amino acids and carbohydrates were detected in all the studied cultivars but interestingly, Capsicum annuum cv. mirasol and C. annuum cv. chilaca contained almost three-fold more endogenous levels of vitamin C than the other cultivars. Considering that this antioxidant was found in crude aqueous extracts, its abundance could be directly proportional to its bioavailability for human nutrition. The results suggest that ¹H NMR is an effective method to determine differences among cultivars of the Capsicum annuum species.

Nuclear Magnetic Resonance (NMR) Spectroscopy in Food Science: A Comprehensive Review

Nuclear magnetic resonance (NMR) spectroscopy is a robust method, which can rapidly analyze mixtures at the molecular level without requiring separation and/or purification steps, making it ideal for applications in food science. Despite its increasing popularity among food scientists, NMR is still an underutilized methodology in this area, mainly due to its high cost, relatively low sensitivity, and the lack of NMR expertise by many food scientists. The aim of this review is to help bridge the knowledge gap that may exist when attempting to apply NMR methodologies to the field of food science. We begin by covering the basic principles required to apply NMR to the study of foods and nutrients. A description of the discipline of chemometrics is provided, as the combination of NMR with multivariate statistical analysis is a powerful approach for addressing modern challenges in food science. Furthermore, a comprehensive overview of recent and key applications in the areas of compositional analysis, food authentication, quality control, and human nutrition is provided. In addition to standard NMR techniques, more sophisticated NMR applications are also presented, although limitations, gaps, and potentials are discussed. We hope this review will help scientists gain some of the knowledge required to apply the powerful methodology of NMR to the rich and diverse field of food science.

Recent developments in the food quality detected by non-invasive nuclear magnetic resonance technology

Nuclear magnetic resonance (NMR) is a rapid, accurate and non-invasive technology and widely used to detect the quality of food, particularly to fruits and vegetables, meat and aquatic products. This review is a survey of recent developments in experimental results for the quality of food on various NMR technologies in processing and storage over the past decade. Following a discussion of the quality discrimination and classification of food, analysis of food compositions and detection of physical, chemical, structural and microbiological properties of food are outlined. Owing to high cost, low detection limit and sensitivity, the professional knowledge involved and the safety issues related to the maintenance of the magnetic field, so far the practical applications are limited to detect small range of food. In order to promote applications for a broader range of foods further research and development efforts are needed to overcome the limitations of NMR in the detection process. The needs and opportunities for future research and developments are outlined.

Real-Time Monitoring of Chemical Changes in Three Kinds of Fermented Milk Products during Fermentation Using Quantitative Difference Nuclear Magnetic Resonance Spectroscopy

Fermented milk products are rising in popularity throughout the world as a result of their health benefits, including improving digestion, normalizing the function of the immune system, and aiding in weight management. This study applies an in situ quantitative nuclear magnetic resonance method to monitor chemical changes in three kinds of fermented milk products, Bulgarian yogurt, Caspian Sea yogurt, and kefir, during fermentation. As a result, the concentration changes in nine organic compounds, α/β-lactose, α/β-galactose, lactic acid, citrate, ethanol, lecithin, and creatine, were monitored in real time. This revealed three distinct metabolic processes in the three fermented milk products. Moreover, pH changes were also determined by variations in the chemical shift of citric acid during the fermentation processes. These results can be applied to estimate microbial metabolism in various flora and help guide the fermentation and storage of various fermented milk products to improve their quality, which may directly influence human health.

Quantitation of Minor Components in Mango Juice with Band-Selective Excitation NMR Spectroscopy

¹H NMR-based metabolic analysis of foods has been widely applied. However, dynamic range problems frequently impede its application because foodstuffs are composed of various organic compounds in a wide range of concentrations. Band-selective excitation ¹H NMR spectroscopy has been found to be a useful tool for observing the minor components in foods. Because quantitative information is important for metabolic analysis of foods and complete metabolome data, quantitation with the band-selective excitation ¹H NMR method was carefully investigated in the present study. As a result, the concentrations of minor components in mango juice of the "Carabao" cultivar were successfully quantitated by band-selective excitation ¹H NMR using standard curves that exhibited good linearity. The band-selective excitation ¹H NMR technique was therefore effective for determining the concentrations of minor components in foods.

High Resolution NMR Spectroscopy as a Structural and Analytical Tool for Unsaturated Lipids in Solution

Mono- and polyunsaturated lipids are widely distributed in Nature, and are structurally and functionally a diverse class of molecules with a variety of physicochemical, biological, medicinal and nutritional properties. High resolution NMR spectroscopic techniques including 1H-, 13C- and 31P-NMR have been successfully employed as a structural and analytical tool for unsaturated lipids. The objective of this review article is to provide: (i) an overview of the critical 1H-, 13C- and 31P-NMR parameters for structural and analytical investigations; (ii) an overview of various 1D and 2D NMR techniques that have been used for resonance assignments; (iii) selected analytical and structural studies with emphasis in the identification of major and minor unsaturated fatty acids in complex lipid extracts without the need for the isolation of the individual components; (iv) selected investigations of oxidation products of lipids; (v) applications in the emerging field of lipidomics; (vi) studies of protein-lipid interactions at a molecular level; (vii) practical considerations and (viii) an overview of future developments in the field.

NMR-based metabolomics for simultaneously evaluating multiple determinants of primary beef quality in Japanese Black cattle

Analytical methodologies to comprehensively evaluate beef quality are increasingly needed to accelerate improvement in both breeding and post-mortem processing. Consumer palatability towards beef is generally attributed to tenderness, flavor, and/or juiciness. These primary qualities are modified by post-mortem aging and the crude content and fatty acid composition of intramuscular fat. In this study, we report a nuclear magnetic resonance (NMR)-based metabolic profiles of Japanese Black cattle to evaluate the compositional attributes of intramuscular fat and the long-term post-mortem aging. The unsaturation degree of triacylglycerol was estimated by the 1H NMR spectra and was correlated with the content ratio of unsaturated fatty acids (R 2 = 0.944) and the melting point of intramuscular fat (R 2 = 0.871). NMR-detected profiles of water-soluble metabolites revealed overall metabolic change (R 2 = 0.951) and several metabolites (R 2 > 0.818) linearly correlated with long-term aging duration, which can be used to evaluate the aging rate and aging duration of beef. This approach also provided the pH profile during aging, which is related to the water-holding capacity of beef. Thus, NMR-based metabolomics has the potential to evaluate multiple parameters related to the beef qualities of Japanese Black cattle.

1H NMR spectra dataset and solid-state NMR data of cowpea (Vigna unguiculata)

In this article the NMR data from chemical shifts, coupling constants, and structures of all the characterized compounds were provided, beyond a complementary PCA evaluation for the corresponding manuscript (E.G. Alves Filho, L.M.A. Silva, E.M. Teofilo, F.H. Larsen, E.S. de Brito, 2017) [3]. In addition, a complementary assessment from solid-state NMR data was provided. For further chemometric analysis, numerical matrices from the raw ¹H NMR data were made available in Microsoft Excel workbook format (.xls).

1H NMR and GC-MS based metabolomics reveal nano-Cu altered cucumber (Cucumis sativus) fruit nutritional supply

It is imperative to study the interaction of nanoparticles residuals with crop plants in agricultural soils, due to the increased application of nanotechnology in agriculture. So far, a few studies have focused on the impact of nanoparticles on fruit quality and nutritional supply. In this work, a thorough and comprehensive analysis of metabolite changes of cucumber fruits from plants under nano-Cu stress was possible through the use of both ¹H NMR and GC-MS. The results of supervised partial least-squares discriminant analysis from both platforms showed that cucumber fruit extracts samples were clearly grouped based on the nano-Cu level in soil. This indicates that the fruit metabolite profile was influenced by exposure to nano-Cu. GC-MS data showed concentrations of some sugars, organic acids, amino acids, and fatty acids were increased or decreased by nano-Cu. Several metabolites, such as methylnicotinamide (MNA), trigonelline, imidazole, quinolinate were only detected and quantified by ¹H NMR. Our results showed that combining the two platforms provided a comprehensive understanding about the metabolites (nutrient supply) changes in cucumber fruits impacted by exposure to nano-Cu.

Complex Mixture Analysis of Organic Compounds in Yogurt by NMR Spectroscopy

NMR measurements do not require separation and chemical modification of samples and therefore rapidly and directly provide non-targeted information on chemical components in complex mixtures. In this study, one-dimensional (¹H, (13)C, and (31)P) and two-dimensional (¹H-(13)C and ¹H-(31)P) NMR spectroscopy were conducted to analyze yogurt without any pretreatment. ¹H, (13)C, and (31)P NMR signals were assigned to 10 types of compounds. The signals of α/β-lactose and α/β-galactose were separately observed in the ¹H NMR spectra. In addition, the signals from the acyl chains of milk fats were also successfully identified but overlapped with many other signals. Quantitative difference spectra were obtained by subtracting the diffusion ordered spectroscopy (DOSY) spectra from the quantitative ¹H NMR spectra. This method allowed us to eliminate interference on the overlaps; therefore, the correct intensities of signals overlapped with those from the acyl chains of milk fat could be determined directly without separation. Moreover, the ¹H-(31)P HMBC spectra revealed for the first time that N-acetyl-d-glucosamine-1-phosphate is contained in yogurt.

NMR-based analysis of the chemical composition of Japanese persimmon aqueous extracts

Japanese persimmon (Diospyros kaki L.) is recognized as an outstanding source of biologically active compounds relating to many health benefits. In the present study, NMR spectroscopy provided a comprehensive metabolic overview of Japanese persimmon juice. Detailed signal assignments of Japanese persimmon juice were carried out using various 2D NMR techniques incorporated with broadband water suppression enhanced through T1 effects (BB-WET) or WET sequences, and 26 components, including minor components, were identified. In addition, most components were quantitatively evaluated by the integration of signals using conventional (1) H NMR and BB-WET NMR. This is the first detailed analysis combined with quantitative characterization of chemical components using NMR for Japanese persimmon. Copyright © 2015 John Wiley & Sons, Ltd.

Use of NMR-Based Metabolomics To Chemically Characterize the Roasting Process of Chicory Root

Roasted chicory root (Cichorium intybus) has been widely accepted as the most important coffee substitute. In this study, a nuclear magnetic resonance (NMR)-based comprehensive analysis was performed to monitor the substantial changes in the composition of chicory root during the roasting process. A detailed signal assignment of dried raw and roasted chicory roots was carried out using ¹H, ¹³C, ¹H-¹H DQF-COSY, ¹H-¹³C edited-HSQC, ¹H-¹³C CT-HMBC, and ¹H-¹³C HSQC-TOCSY NMR spectra. On the basis of the signal assignments, 36 NMR-visible components were monitored simultaneously during roasting. Inulins, sucrose, and most of the amino acids were largely degraded during the roasting process, whereas monosaccharides decreased at the beginning and then increased until the dark roasting stage. Acetamide, 5-hydroxymethylfurfural, di-d-fructose dianhydride, and norfuraneol were newly formed during roasting. Furthermore, a principal component analysis score plot indicated that similar chemical composition profiles could be achieved by roasting the chicory root either at a higher firepower for a shorter time or at a lower firepower for a longer time.

Selective One-Dimensional Total Correlation Spectroscopy Nuclear Magnetic Resonance Experiments for a Rapid Identification of Minor Components in the Lipid Fraction of Milk and Dairy Products: Toward Spin Chromatography?

We report a rapid, direct, and unequivocal spin-chromatographic separation and identification of minor components in the lipid fraction of milk and common dairy products with the use of selective one-dimensional (1D) total correlation spectroscopy (TOCSY) nuclear magnetic resonance (NMR) experiments. The method allows for the complete backbone spin-coupling network to be elucidated even in strongly overlapped regions and in the presence of major components from 4 × 10(2) to 3 × 10(3) stronger NMR signal intensities. The proposed spin-chromatography method does not require any derivatization steps for the lipid fraction, is selective with excellent resolution, is sensitive with quantitation capability, and compares favorably to two-dimensional (2D) TOCSY and gas chromatography-mass spectrometry (GC-MS) methods of analysis. The results of the present study demonstrated that the 1D TOCSY NMR spin-chromatography method can become a procedure of primary interest in food analysis and generally in complex mixture analysis.

Comprehensive NMR analysis of compositional changes of black garlic during thermal processing

Black garlic is a processed food product obtained by subjecting whole raw garlic to thermal processing that causes chemical reactions, such as the Maillard reaction, which change the composition of the garlic. In this paper, we report a nuclear magnetic resonance (NMR)-based comprehensive analysis of raw garlic and black garlic extracts to determine the compositional changes resulting from thermal processing. (1)H NMR spectra with a detailed signal assignment showed that 38 components were altered by thermal processing of raw garlic. For example, the contents of 11 l-amino acids increased during the first step of thermal processing over 5 days and then decreased. Multivariate data analysis revealed changes in the contents of fructose, glucose, acetic acid, formic acid, pyroglutamic acid, cycloalliin, and 5-(hydroxymethyl)furfural (5-HMF). Our results provide comprehensive information on changes in NMR-detectable components during thermal processing of whole garlic.

Dynamic metabolic and transcriptional profiling of Rhodococcus sp. strain YYL during the degradation of tetrahydrofuran

Although tetrahydrofuran-degrading Rhodococcus sp. strain YYL possesses tetrahydrofuran (THF) degradation genes similar to those of other tetrahydrofuran-degrading bacteria, a much higher degradation efficiency has been observed in strain YYL. In this study, nuclear magnetic resonance (NMR)-based metabolomics analyses were performed to explore the metabolic profiling response of strain YYL to exposure to THF. Exposure to THF slightly influenced the metabolome of strain YYL when yeast extract was present in the medium. The metabolic profile of strain YYL over time was also investigated using THF as the sole carbon source to identify the metabolites associated with high-efficiency THF degradation. Lactate, alanine, glutarate, glutamate, glutamine, succinate, lysine, trehalose, trimethylamine-N-oxide (TMAO), NAD(+), and CTP were significantly altered over time in strain YYL grown in 20 mM THF. Real-time quantitative PCR (RT-qPCR) revealed changes in the transcriptional expression levels of 15 genes involved in THF degradation, suggesting that strain YYL could accumulate several disturbances in osmoregulation (trehalose, glutamate, glutamine, etc.), with reduced glycolysis levels, an accelerated tricarboxylic acid cycle, and enhanced protein synthesis. The findings obtained through (1)H NMR metabolomics analyses and the transcriptional expression of the corresponding genes are complementary for exploring the dynamic metabolic profile in organisms.

NMR assignments and the acid-base characterization of the pomegranate ellagitannin punicalagin in the acidic pH-range

In exploring the capability of nuclear magnetic resonance (NMR) spectroscopy for pomegranate juice analysis, the eight aromatic singlet resonances of α- and β-punicalagin were clearly identified in the (1)H NMR spectra of juice samples. The four downfield resonances were found to be sensitive to small pH changes around pH 3.50 where the NMR spectra of the juice samples were recorded. To understand this unusual behavior, the (1)H and (13)C resonance assignments of the punicalagin anomers were determined in aqueous solution and pH titrations with UV and (1)H NMR detection carried out to characterize the acid-base properties of punicalagin over the pH range 2-8. Simultaneous fitting of all of the pH-sensitive (1)H NMR signals produced similar but significantly different pKa values for the first two deprotonation equilibria of the gallagic acid moiety of the punicalagin α- (pKa1 = 4.57 ± 0.02, pKa2 = 5.63 ± 0.03) and β- (pKa1 = 4.36 ± 0.01, pKa2 = 5.47 ± 0.02) anomers. Equivalent pKa values, (α : 6.64 ± 0.01, β : 6.63± 0.01) were measured for the third deprotonation step involving the ellagic acid group, in good agreement with a prior literature report. The punicalagin anomer equilibrium readjusts in parallel with the proton dissociation steps as the pH is raised such that β-punicalagin becomes the most abundant anomer at neutral pH. The unusual upfield shifts observed for the glucose H3 and H5 resonances with increasing pH along with the shift in the α/β anomer equilibrium are likely the consequence of a conformational rearrangement.

PGI chicory (Cichorium intybus L.) traceability by means of HRMAS-NMR spectroscopy: a preliminary study

BACKGROUND

Analytical traceability of PGI and PDO foods (Protected Geographical Indication and Protected Denomination Origin respectively) is one of the most challenging tasks of current applied research.

RESULTS

Here we proposed a metabolomic approach based on the combination of (1)H high-resolution magic angle spinning-nuclear magnetic resonance (HRMAS-NMR) spectroscopy with multivariate analysis, i.e. PLS-DA, as a reliable tool for the traceability of Italian PGI chicories (Cichorium intybus L.), i.e. Radicchio Rosso di Treviso and Radicchio Variegato di Castelfranco, also known as red and red-spotted, respectively. The metabolic profile was gained by means of HRMAS-NMR, and multivariate data analysis allowed us to build statistical models capable of providing clear discrimination among the two varieties and classification according to the geographical origin.

CONCLUSION

Based on Variable Importance in Projection values, the molecular markers for classifying the different types of red chicories analysed were found accounting for both the cultivar and the place of origin.

(13)C NMR-based metabolomics for the classification of green coffee beans according to variety and origin

(13)C NMR-based metabolomics was demonstrated as a useful tool for distinguishing the species and origins of green coffee bean samples of arabica and robusta from six different geographic regions. By the application of information on (13)C signal assignment, significantly different levels of 14 metabolites of green coffee beans were identified in the classifications, including sucrose, caffeine, chlorogenic acids, choline, amino acids, organic acids, and trigonelline, as captured by multivariate analytical models. These studies demonstrate that the species and geographical origin can be quickly discriminated by evaluating the major metabolites of green coffee beans quantitatively using (13)C NMR-based metabolite profiling.

NMR-based metabolic profiling of rice wines by F(2)-selective total correlation spectra

In this study, we performed NMR-based metabolic profiling of major rice wines (Japanese sake, Chinese Shaoxing wine, and Korean makgeolli). In the (1)H NMR spectra, the rice wines showed broad resonances in the region of about 7.9-9.0 ppm. These resonances showed many and complex correlations with approximately 0.5-4.5 ppm in the F(2)-selective TOCSY (total correlation spectroscopy) spectra, and these correlations were attributed mainly to peptides. These spectral patterns were characteristic of individual rice wines, and the combination of F(2)-selective TOCSY spectra and principal component analysis enabled us to classify the rice wine species. Furthermore, it also provided information about raw materials, namely, what type of koji (rice koji or wheat koji) was used. These spectra may be useful as a new "fingerprint" for quality control or food authentication.

Metabolomics in food science

Metabolomics, the newest member of the omics techniques, has become an important tool in agriculture, pharmacy, and environmental sciences. Advances in compound extraction, separation, detection, identification, and data analysis have allowed metabolomics applications in food sciences including food processing, quality, and safety. This chapter discusses recent advances and applications of metabolomics in food science.