Flavor Molecules Research Articles

RecipeDB: A Resource for Exploring Recipes

Cooking is the act of turning nature into the culture, which has enabled the advent of the omnivorous human diet. The cultural wisdom of processing raw ingredients into delicious dishes is embodied in their cuisines. Recipes thus are the cultural capsules that encode elaborate cooking protocols for evoking sensory satiation as well as providing nourishment. As we stand on the verge of an epidemic of diet-linked disorders, it is eminently important to investigate the culinary correlates of recipes to probe their association with sensory responses as well as consequences for nutrition and health. RecipeDB is a structured compilation of recipes, ingredients, and nutrition profiles interlinked with flavor profiles and health associations. The repertoire comprises of meticulous integration of over 1,18,000 recipes from cuisines across the globe (6 continents, 26 geo-cultural regions, and 74 countries), cooked using 268 processes (heat, cook, boil, simmer, bake, etc.), by blending over 20,262 diverse ingredients, which are further linked to their flavor molecules (FlavorDB), nutritional profiles (USDA), and empirical records of disease associations obtained from Medline (DietRx). This resource is aimed at facilitating scientific explorations of the culinary space (recipe, ingredient, cooking processes/techniques, dietary styles, etc.) to taste (flavor profile) and health (nutrition and disease associations) attributes seeking for divergent applications.

A Material Perspective of Wood, Smoke, and BBQ

For those of us who have attempted to barbecue (BBQ), wood matters. Smoking delicious meats is effectively a chemical process that involves control over combustion of organic materials. Here, we get joint insight from a local pitmaster and a materials scientist.

Molecular Dynamics Simulation on the Diffusion of Flavor, O2 and H2O Molecules in LDPE Film.

The diffusion of five flavor organic molecules, including D-limonene, myrcene, ethyl hexanoate, 2-nonanone, and linalool in low density polyethylene (LDPE) film were investigated by combined experimental and molecular dynamics (MD) simulation studies. The diffusion coefficients derived from the prediction model, experimental determination, and MD simulation were compared, and the related microscopic diffusion mechanism was investigated. The effects of the presence of the flavor organic molecules on the diffusion of O2 and H2O in polyethylene (PE) were also studied by MD simulation. Results show that: The diffusion of five flavor molecules in LDPE is well followed to Fick’s second law by the immersion experiment; MD simulation indicates the dual mode diffusion mechanism of the flavor molecules is in LDPE; the diffusion coefficients from MD simulation are close to those from the experimental determination, but are slightly larger than those values; the presence of the flavor organic molecules hinders the diffusion of O2 and H2O, which can be well explained from the fraction of free volume (FFV) and interaction energy calculation results derived from MD simulation.

Comparison of Differential Flavor Metabolites in Meat of Lubei White Goat, Jining Gray Goat and Boer Goat.

Flavor is one of the most important sensory characteristics of meat. The development of taste and aroma can be attributed to thousands of flavor molecules and precursors that are present in meat tissues. As a result, the identification of these flavor compounds and an improved understanding of their roles are necessary for improving the sensory quality and customer appeal of meat products. In the current study, we compared the metabolic profiles of meat specimens from the Lubei white goats (LBB), Boer goats (BE) and Jining grey goats (JNQ) by untargeted liquid chromatography-mass spectrometry. Our metabolomic data revealed that the three types of goat meat showed significantly different profiles of fatty acids, aldehydes, ketones, lactones, alkaloids, flavonoids, phenolics and drug residues, which could underpin the nuances of their flavors. Taken together, our results provided insights into the molecular basis for sensory variations between different goat meat products.

Nanoencapsulation of Hydrophobic Food Flavor Ingredients and Their Cyclodextrin Inclusion Complexes

Preservation of hydrophobic, volatile, food flavor ingredients during processing is a foremost concern for food manufacturers. Nanoencapsulation is a method, which enables achieving enhanced thermal stability, solubility, and antioxidant activity of flavors. Among the available techniques for nanoencapsulation, electrohydrodynamic technique and encapsulation of flavors in nanofibers give the opportunity to achieve enhanced efficiency and higher surface-to-volume ratio, with a more compact size equipment and a cost-effective process. Cyclodextrins have the potential to be used as nanocarriers with the capability to form complexes with various non-polar flavor molecules. The formed cyclodextrin inclusion complexes (ICs) can be included into biopolymers or can be electrospun to form a polymer-free nanofiber. Natural and modified types of cyclodextrins can be applied for encapsulation and development of inclusion complexes with flavor molecules. Higher thermal stability was achievable with γ-CD-ICs in most of the studied cases, due to larger size of the cavity, and higher strength of the formed complex. From the modified types of cyclodextrins, formed ICs of Mβ-CD showed higher stability, due to rigid structure of the molecule and HPβ-CD enabled achieving higher antioxidant properties, due to less strength of the formed complex and possibility for hydrogen donation. In comparison with polymeric nanofibers, polymer-free systems enabled higher loading of flavors. Concluding from the reported studies, electrospun nanofibers prepared from flavors and their CD-ICs can give the possibility to achieve higher thermal stability, enhanced solubility, antioxidant, and antibacterial properties together with prolonged shelf life of foods and can be applied in food processing and packaging.

Flavor-cyber-agriculture: Optimization of plant metabolites in an open-source control environment through surrogate modeling.

Food production in conventional agriculture faces numerous challenges such as reducing waste, meeting demand, maintaining flavor, and providing nutrition. Contained environments under artificial climate control, or cyber-agriculture, could in principle be used to meet many of these challenges. Through such environments, phenotypic expression of the plant—mass, edible yield, flavor, and nutrients—can be actuated through a “climate recipe,” where light, water, nutrients, temperature, and other climate and ecological variables are optimized to achieve a desired result. This paper describes a method for doing this optimization for the desired result of flavor by combining cyber-agriculture, metabolomic phenotype (chemotype) measurements, and machine learning. In a pilot experiment, (1) environmental conditions, i.e. photoperiod and ultraviolet (UV) light (known to affect production of flavor-active molecules in edible plants) were applied under different regimes to basil plants (Ocimum basilicum) growing inside a hydroponic farm with an open-source design; (2) flavor-active volatile molecules were measured in each plant using gas chromatography-mass spectrometry (GC-MS); and (3) symbolic regression was used to construct a surrogate model of this chemistry from the input environmental variables, and this model was used to discover new combinations of photoperiod and UV light to increase this chemistry. These new combinations, or climate recipes, were then implemented in the hydroponic farm, and several of them resulted in a marked increase in volatiles over control. The process also led to two important insights: it demonstrated a “dilution effect”, i.e. a negative correlation between weight and desirable chemical species, and it discovered the surprising effect that a 24-hour photoperiod of photosynthetic-active radiation, the equivalent of all-day light, induces the most flavor molecule production in basil. In this manner, surrogate optimization through machine learning can be used to discover effective recipes for cyber-agriculture that would be difficult and time-consuming to find using hand-designed experiments.

Beyond the Flavour: The Potential Druggability of Chemosensory G Protein-Coupled Receptors.

G protein-coupled receptors (GPCRs) belong to the largest class of drug targets. Approximately half of the members of the human GPCR superfamily are chemosensory receptors, including odorant receptors (ORs), trace amine-associated receptors (TAARs), bitter taste receptors (TAS2Rs), sweet and umami taste receptors (TAS1Rs). Interestingly, these chemosensory GPCRs (csGPCRs) are expressed in several tissues of the body where they are supposed to play a role in biological functions other than chemosensation. Despite their abundance and physiological/pathological relevance, the druggability of csGPCRs has been suggested but not fully characterized. Here, we aim to explore the potential of targeting csGPCRs to treat diseases by reviewing the current knowledge of csGPCRs expressed throughout the body and by analysing the chemical space and the drug-likeness of flavour molecules.

Citral Photodegradation in Solution: Highlighting of a Radical Pathway in Parallel to Cyclization Pathway.

Citral, a lemon flavor molecule often used in the beverage and fragrance industry, is known to be unstable under light irradiation. Its deterioration is considered to be an important issue for the stabilization of lemon-flavored drinks. The aim of this study is to understand the degradation mechanisms of citral under light irradiation with the variation of three parameters: the solvent (citrate buffer solution at pH 3 vs ethanol), the atmosphere (air vs N2), and the concentration of citral. The photodegradation has been studied using UV-visible spectroscopy after photolysis, nuclear magnetic resonance spectrometry, and electron spin resonance spectroscopy. To extend the investigation, molecular orbitals and bond dissociation energies have also been calculated. They give an insight into the light absorption properties and the possible cleavage of citral molecular bonds. In addition, UV-light absorption and radical scavenging activities of two additives, potassium sorbate and ascorbic acid, have been studied for the inhibition of the citral photodecomposition by UV-light irradiation. Both theoretical and experimental results highlight a new degradation pathway involving free-radical intermediates in parallel to the already reported cyclization one, which could be prevented by the addition of stabilizers such as ascorbic acid or sorbate.

Influence of Oxygen-Containing Sulfur Flavor Molecules on the Stability of β-Carotene under UVA Irradiation.

The influence of 11 kinds of oxygen-containing sulfur flavor molecules was examined on β-carotene stability under UVA irradiation in ethanol system. Both the effects of sulfides on dynamic degradation of β-carotene and the relation between structure and effect were investigated. The oxidation products of β-carotene accelerated by sulfides under UVA irradiation were also identified. The results indicated that the disulfides had more obvious accelerative effects on the photodegradation of β-carotene than mono sulfides. The degradation of β-carotene after methyl (2-methyl-3-furyl) disulfide (MMFDS), methyl furfuryl disulfide (MFDS) and bis(2-methyl-3-furyl) disulfide (BMFDS) exposure followed first-order kinetics. Furan-containing sulfides such as MMFDS and BMFDS showed more pronounced accelerative effects than their corresponding isomers. The oxidation products were identified as 13-cis-β-carotene, 9,13-di-cis-β-carotene and all-trans-5,6-epoxy-β-carotene. These results suggest that both the sulfur atom numbers and the furan group in oxygen-containing sulfides play a critical role in the photooxidation of β-carotene.

Dynamic flavor release from chewing gum: Mechanisms of release

Dynamic flavor release curves from chewing gum were measured using an Artificial Mouth coupled to the AFFIRM®. A flavor distribution model for chewing gum is proposed, where flavor is present as droplets in both the hydrophilic (water-soluble) and the hydrophobic (water insoluble) parts of the chewing gum and as molecularly dissolved in the hydrophobic part of the gum. During mastication, the flavor droplets in the water-soluble phase are released and responsible for an initial burst release. The flavor droplets captured in the gum-base are pushed towards the interface by mastication and are responsible for the subsequent release. The flavor molecules dissolved in the gum-base, released by diffusion, are only responsible for the release at very long time scales. It was found that the oil-water partition constant is an important parameter to explain the flavor release, where hydrophobic components show slower and longer release, while more hydrophilic components show more burst release.

Flavanols react preferentially with quinones through an electron transfer reaction, stimulating rather than preventing wine browning

Wine oxidation changes the chemistry, sensory profile and color of wines. In wine oxidation, phenolics are oxidized to quinones and these reactive compounds can be quenched by sacrificial nucleophiles, such as the A-ring on flavanoids, preventing oxidative damage from the loss of desirable flavor molecules. The “catechol” B-ring on flavanoids, in contrast, can be oxidized by quinones through electron transfer reactions that lead to flavanoid quinones, precursors of browning products. Here we compared the rate of flavanoids reacting by either nucleophilic quinone quenching, or by electron transfer to generate flavanoid quinones. Our approach is based on mathematical modeling of reaction data to derive the rate constants of reactions of A-ring quenching vs B-ring electron transfer with caffeic acid quinone, by fitting the predicted loss of precursors and the appearance of products (or derivatives) with experimental data collected by LC/MS. The rate constant of the electron transfer reaction of caffeic acid quinone towards 4-methyl-catechol was fast (k4MC = 3.43E-2 mLmol−1sec−1) but nucleophilic reactions with afzelechin (kAfz = 2.53E-3 mLmol−1sec−1) or malvidin-3-glucoside (kMal = 5.34E-3 mLmol−1sec−1), were much slower. No reaction was detected between caffeic acid quinone and isorhamnetin. Additionally, the electron transfer reaction rate of catechin and caffeic acid quinone was much faster at pH 7 (1.22E-02 mLmol−1sec−1) vs pH 3.5 (1.79E-03 mLmol−1sec−1). These results help explain why the reaction of catechin and caffeic acid quinone favors the formation of browning products, and more so at higher pH values. Furthermore, bisulfite reacted with quinones faster than the electron transfer reactions, preventing the browning observed in the reaction of catechin with caffeic acid quinone in the absence of bisulfite.

Saliva and Flavor Perception: Perspectives.

This paper reports the main trends and perspectives related to the current understanding of the relationships between saliva and flavor perception. Saliva is a key factor in flavor perception and controls the transport of flavor molecules to their receptors, their adsorption onto the mouth surfaces (i.e., oral mucosa), their metabolism by enzymatic modification, and the friction force in the oral cavity. The proteins in free saliva or in the mucosal pellicle contribute to flavor perception by interacting with or metabolizing flavor compounds. Most of these reactions were observed when using fresh whole saliva; however, they were absent or less frequently observed when using artificial saliva or depleted/frozen whole saliva. There is a need to better understand the role of protein aggregates in flavor perception. Within humans, there is great interindividual variation in salivary composition, which has been related to differences in flavor perception. However, the relative role of salivary proteins and the microbiota should be deeply investigated together with the impact of their composition on individual perception during life. Finally, future results must also consider cross-modal interactions at the brain level.

Isotopes could unmask truffle fraud

Alba white truffles, Tuber magnatum Pico, are among the priciest of delicacies, fetching almost $7,000 per kilogram last season and making them a target for fraud. A new method offers a way to distinguish bis(methylthio)methane—the key Alba white truffle flavor molecule—in real truffles from a synthetic version in food (Anal. Chem. 2018, DOI: 10.1021/acs.analchem.8b00386). Bis(methylthio)methane from natural truffles contains carbon-12 and carbon-13 in a ratio reflecting the environment in which the fungus grew. Meanwhile, the synthetic molecule’s ratio reflects its origins in petrochemical or plant-based feedstocks. Luigi Mondello of the University of Messina and his colleagues determined those relative amounts of 12C and 13C with an isotope ratio mass spectrometer, analyzing both synthetic bis(methylthio)methane and natural bis(methylthio)methane that evaporated from white truffles. The researchers then tested samples of commercial truffle-flavored foods including olive oil, pasta, and cheese. Those labeled as containing lower-quality truffles and added truffle aroma had the isotopic

Heterologous Protein Expression in Pichia pastoris: Latest Research Progress and Applications.

Pichia pastoris is a well-known platform strain for heterologous protein expression. Over the past five years, different strategies to improve the efficiency of recombinant protein expression by this yeast strain have been developed; these include a patent-free protein expression kit, construction of the P. pastoris CBS7435Ku70 platform strain with its high efficiency in site-specific recombination of plasmid DNA into the genomic DNA, the design of synthetic promoters and their variants by combining different core promoters with multiple putative transcription factors, the generation of mutant GAP promoter variants with various promoter strengths, codon optimization, engineering the α-factor signal sequence by replacing the native glutamic acid at the Kex2 cleavage site with the other 19 natural amino acids and the addition of mammalian signal sequence to the yeast signal sequence, and the co-expression of single chaperones, multiple chaperones or helper proteins that aid in recombinant protein folding. Publically available high-quality genome data from multiple strains of P. pastoris GS115, DSMZ 70382, and CBS7435 and the continuous development of yeast expression kits have successfully promoted the metabolic engineering of this strain to produce carotenoids, xanthophylls, nootkatone, ricinoleic acid, dammarenediol-II, and hyaluronic acid. The cell-surface display of enzymes has obviously increased enzyme stability, and high-level intracellular expression of acyl-CoA and ethanol O-acyltransferase, lipase and d-amino acid oxidase has opened up applications in whole-cell biocatalysis for producing flavor molecules and biodiesel, as well as the deracemization of racemic amino acids. High-level expression of various food-grade enzymes, cellulases, and hemicellulases for applications in the food, feed and biorefinery industries is in its infancy and needs strengthening.

Biochemical characterization of a key step involved in 2H4MB production in Decalepis hamiltonii

Decalepis hamiltonii is widely known for its flavour molecule 2-Hydroxy-4-Methoxy Benzaldehyde (2H4MB), a structural isomer of vanillin. As the biosynthetic pathway of 2H4MB is not known, we hypothesised 2H4MB origins could be from phenylpropanoid pathway (PPP). Accordingly, a study was conducted using PPP inhibitors (viz. piperonylic acid, MDCA and propanil) against in vitro root cultures of D. hamiltonii to find the branch of PPP which catalyses the 2H4MB formation. HPLC analysis was carried out to quantify 2H4MB levels in control and respective inhibitor treated root cultures in vitro. The results obtained revealed that piperonylic acid did not inhibit 2H4MB biosynthesis in the given period, whereas MDCA and propanil had the marked inhibitory effect. The inhibitory effect was evident with 13.2, 33.6 and 37.9% decrease in 2H4MB levels at 50, 100 and 150mM concentration of MDCA respectively in comparison with control roots. Similarly, the inhibitory effect of propanil on 2H4MB biosynthesis was obvious with 23.7, 49.5 and 57.9% decrease in 2H4MB levels at 50, 100 and 150μM concentration of inhibitor respectively when compared with control roots. Propanil showed a greater slow down effect on 2H4MB biosynthesis compared to MDCA. Incorporation of 0.1, 0.5 and 1.0mM ferulic acid as a precursor to in vitro root cultures of D. hamiltonii showed an increase in 2H4MB levels at the rate of 3.1, 107 and 94.1% respectively as quantified by HPLC analysis. However, ferulic acid in conjunction with propanil did not show any increase in 2H4MB levels. This clearly explains that ferulic acid is channelled through the 4-CL (4-coumarate CoA ligase) enzyme, where it would be converted to feruloyl-CoA and could be further converted to 2H4MB in D. hamiltonii.

Quantifying non-specific interactions between flavour and food biomolecules.

The ways in which flavour molecules interact with proteins in foods have an impact on flavour and aroma and on the (in)stability of the proteins. There is a long history of analysing these interactions using a "specific binding model" that gives values for the number of molecules, n, bound to the proteins with a binding constant Kb. However, recent progress in molecular thermodynamics forced us to reconsider this approach. In addition, there are a number of methods for determining these values and it is not at all clear whether the various assumptions behind the various methods allow legitimate comparisons between techniques. By adopting an assumption-free molecular thermodynamics approach, Kirkwood-Buff theory, we find that we gain a welcome universality, simplicity and deep understanding of what is happening at the molecular level. Here we look at three different methods for examining flavour-protein interactions (vapour pressure, dialysis equilibrium and melting temperature changes), show how historical data can be re-cast into the universal language of Kirkwood-Buff and provide a free, open-source app that can both re-analyze historical data and be a platform for analyzing fresh data. In each case, the fundamental theory is described along with a pragmatic implementation accepting the realities of experimentation. One key insight is that the n and Kb parameters of the classical binding models can be turned directly, via simple arithmetic, into the Kirkwood-Buff integrals that accurately capture non-specific flavour-protein interactions.

Flavor release from spray-dried amorphous matrix: Effect of lactose content and water plasticization

Glass-forming carbohydrates are widely used as matrix for encapsulation of nutrients and bioactive compounds. In this study, encapsulation systems with lactose/whey protein isolate (WPI) mixtures (4:1, 1:1, and 1:4), or WPI as wall materials and ethyl butyrate as core material were prepared by spray drying. The effects of lactose content and water plasticization on encapsulation efficiency and flavor release were investigated. Wall material consisting of lactose/WPI (4:1) mixture had significantly (P<0.05) higher encapsulation efficiency. The flavor retention in powders did not have significant decrease with equilibration at 0.33 aw, while it was dramatically decreased at 0.54 aw and 0.65 aw as a result of lactose crystallisation. Mechanical property study showed that the molecular mobility and free volume of encapsulation systems with higher lactose content increased more significantly with increasing water content, which accelerated the diffusion of flavor molecules. Those results may use in the assessment of protection and release characteristics of flavor components in formulated systems.

Investigation of plant sources of hydroperoxide lyase for 2(E)-hexenal production

Abstract 2(E)-hexenal is a green note flavour molecule that is widely used in various compositions of aromas, flavours and perfumery. As there is considerable demand for naturally produced aromas this article deals with some aspects of this C6-volatile production with regard to the selection of plant source material and reaction conditions. The following plants were tested for this purpose: runner bean (Phaseolus coccineus), common bean (Phaseolus vulgaris), three (Capsicum annuum) bell pepper varieties, garden cress (Lepidium sativum), green slicing cucumber (Cucumis sativa), mung beans (Vigna mungo) and brown lentils (Lens culinaris). Selection of source material was considered on the basis of 2(E)-hexenal yield and productivity. The common bean leafs were able to produce up to 35 mg of 2(E)-hexenal/kg fresh leaves.

Application of Sensory Evaluation, HS-SPME GC-MS, E-Nose, and E-Tongue for Quality Detection in Citrus Fruits.

In this study, electronic tongue (E-tongue), headspace solid-phase microextraction gas chromatography-mass spectrometer (GC-MS), electronic nose (E-nose), and quantitative describe analysis (QDA) were applied to describe the 2 types of citrus fruits (Satsuma mandarins [Citrus unshiu Marc.] and sweet oranges [Citrus sinensis {L.} Osbeck]) and their mixing juices systematically and comprehensively. As some aroma components or some flavor molecules interacted with the whole juice matrix, the changes of most components in the fruit juice were not in proportion to the mixing ratio of the 2 citrus fruits. The potential correlations among the signals of E-tongue and E-nose, volatile components, and sensory attributes were analyzed by using analysis of variance partial least squares regression. The result showed that the variables from the sensor signals (E-tongue system and E-nose system) had significant and positive (or negative) correlations to the most variables of volatile components (GC-MS) and sensory attributes (QDA). The simultaneous utilization of E-tongue and E-nose obtained a perfect classification result with 100% accuracy rate based on linear discriminant analysis and also attained a satisfying prediction with high coefficient association for the sensory attributes (R(2) > 0.994 for training sets and R(2) > 0.983 for testing sets) and for the volatile components (R(2) > 0.992 for training sets and R(2) > 0.990 for testing sets) based on random forest. Being easy-to-use, cost-effective, robust, and capable of providing a fast analysis procedure, E-nose and E-tongue could be used as an alternative detection system to traditional analysis methods, such as GC-MS and sensory evaluation by human panel in the fruit industry. Being easy-to-use, cost-effective, robust, and capable of providing a fast analysis procedure, E-nose and E-tongue could be used as an alternative detection system to traditional analysis methods for characterizing food flavors. Based on those results, one can draw a conclusion that the fusion system composed of E-tongue and E-nose could guarantee a satisfying result in the prediction of sensory attributes and volatile components for fruit quality profile.

Investigation of Evolutionary Events in Corynebacteriaceae Involving Prenyltransferases in Corynebacterium glutamicum

Terpenoids, a class of compounds with 30,000 unique structures, are known to include antitumor compounds, pigments, vitamins, antibiotics, and flavor molecules. Prenyltransferases are the primary enzyme responsible for assembling the carbon backbone of these compounds from five carbon isoprene units. Bioinformatic analysis has indicated that an evolutionary event has resulted in the acquisition of an additional prenyltransferase in Corynebacterium glutamicum (C. glutamicum) compared to the majority of the Corynebacteriaceae. This result suggests that C. glutamicum may produce a non‐essential terpenoid compound, or secondary metabolite. Sequencing has confirmed the successful cloning of the aforementioned genes. Present work includes expressing these genes in Escherichia coli, isolating the protein product, and assessing the function in vitro. This data will be used to expand our understanding of the evolutionary path of C. glutamicum compared to other members of the genus. Continuing work will shed light on the function of the third gene for C. glutamicum, and understanding the role of terpenoids in the family Corynebacteriaceae and greater Actinobacteria.