On the human taste perception: Molecular-level understanding empowered by computational methods

Multi-omic applications for understanding and enhancing tropical fruit flavour

Consumer trends towards nutrient-rich foods are contributing to global increasing demand for tropical fruit. However, commercial cultivars in the breeding pipeline that are tailored to meet market demand are at risk of possessing reduced fruit flavour qualities. This stems from recurrent prioritised selection for superior agronomic traits and not fruit flavour, which may in turn reduce consumer satisfaction. There is realisation that fruit quality traits, inclusive of flavour, must be equally selected for; but currently, there are limited tools and resources available to select for fruit flavour traits, particularly in tropical fruit species. Although sugars, acids, and volatile organic compounds are known to define fruit flavour, the specific combinations of these, that result in defined consumer preferences, remain unknown for many tropical fruit species. To define and include fruit flavour preferences in selective breeding, it is vital to determine the metabolites that underpin them. Then, objective quantitative analysis may be implemented instead of solely relying on human sensory panels. This may lead to the development of selective genetic markers through integrated omics approaches that target biosynthetic pathways of flavour active compounds. In this review, we explore progress in the development of tools to be able to strategically define and select for consumer-preferred flavour profiles in the breeding of new cultivars of tropical fruit species.

Role of taste receptors in salty taste perception of minerals and amino acids and developments in salt reduction strategies: A review

Salt (sodium chloride) plays a key role in maintaining the textural, microbiological, and sensorial aspects of the foods. However high dietary salt intake in the population has led to a series of health problems. Currently manufacturers are under pressure to reduce the sodium levels in foods without compromising the consumer experience. Because of the clean salty taste produced by sodium chloride, it has been challenging for the food industry to develop a suitable salt substitute. Studies have shown that different components within a food matrix can influence the perception of saltiness. This review aims to comprehend the potential synergistic effect of compounds such as minerals and amino acids on the perception of saltiness and covers the mechanism of perception where relevant to taste resulting from sodium ions and other metallic ions (such as K, Mg, Ca), as well as various amino acids and their derivatives. Finally, the review summarizes various salt reduction strategies explored by researchers, government organizations and food industry, including the potential use of plant-based extracts.

Integrated virtual screening coupled with sensory evaluation identifies N-succinyl-L-tryptophan as a novel compound with multiple taste enhancement properties

N-Succinyl amino acids (N-Suc-AAs) are garnering attention for their potential as taste-active compounds. The intricate variety of N-Suc-AAs presented considerable challenges in identifying those with taste-active properties. Consequently, we employed structure-based virtual screening to pinpoint taste-active N-Suc-AAs, revealing N-succinyl-L-tryptophan (ST) as a compound with high affinity for different taste receptors. Following this discovery, ST was synthesized through an enzymatic process, achieving a yield of 40.2%, with its structure verified via NMR spectroscopy. Sensory evaluation alongside electronic tongue assessments indicated that ST at a concentration of 1 mg/L significantly enhances umami, kokumi, and saltiness intensities, while concurrently mitigating bitterness from various bitter compounds, whilst itself remaining tasteless. Additionally, time-intensity (TI) results elucidated a marked augmentation in umami duration and a notable diminution in bitterness duration for solutions imbued with 1 mg/L ST. Molecular docking study suggested ST interacted with diverse taste receptors as an agonist or antagonist, primarily through hydrogen bonds and hydrophobic interactions. This study marked the inaugural report on the enzymatic synthesis of ST and its efficacy in improving taste characteristics, underscoring the importance of ST in improving sensory qualities of food products and fostering innovation within the seasoning industry.

Machine learning approaches to predict TAS2R receptors for bitterants

Bitter taste involves the detection of diverse chemical compounds by a family of G protein-coupled receptors, known as taste receptor type 2 (TAS2R). It is often linked to toxins and harmful compounds and in particular bitter taste receptors participate in the regulation of glucose homeostasis, modulation of immune and inflammatory responses, and may have implications for various diseases. Human TAS2Rs are characterized by their polymorphism and differ in localization and function. Different receptors can activate various signaling pathways depending on the tissue and the ligand. However, in vitro screening of possible TAS2R ligands is costly and time-consuming. For this reason, in silico methods to predict bitterant-TAS2R interactions could be powerful tools to help in the selection of ligands and targets for experimental studies and improve our knowledge of bitter receptor roles. Machine learning (ML) is a branch of artificial intelligence that applies algorithms to large datasets to learn from patterns and make predictions. In recent years, there has been a record of numerous taste classifiers in literature, especially on bitter/non-bitter or bitter/sweet classification. However, only a few of them exploit ML to predict which TAS2R receptors could be targeted by bitter molecules. Indeed, the shortage and incompleteness of data on receptor-ligand associations in literature make this task non-trivial. In this work, we provide an overview of the state of the art dealing with this specific investigation, focusing on three ML-based models, namely BitterX (2016), BitterSweet (2019) and BitterMatch (2022). This review aims to establish the foundation for future research endeavours focused on addressing the limitations and drawbacks of existing models.

Progress in Multisensory Synergistic Salt Reduction

Excessive salt intake, primarily from sodium chloride prevalent in modern food processing, poses a significant public health risk associated with hypertension, cardiovascular diseases and stroke. Researchers worldwide are exploring approaches to reduce salt consumption without compromising food flavor. One promising method is to enhance salty taste perception using multisensory synergies, leveraging gustatory, olfactory, auditory, visual, tactile and trigeminal senses to decrease salt intake while preserving food taste. This review provides a comprehensive overview of salt usage in foods, mechanisms of salty taste perception and evaluation methods for saltiness. Various strategies for reducing salt consumption while maintaining food flavor are examined, with existing salt reduction methods' advantages and limitations being critically analyzed. A particular emphasis is placed on exploring the mechanisms and potential of multisensory synergy in salt reduction. Taste interactions, olfactory cues, auditory stimulation, visual appearance and tactile sensations in enhancing saltiness perception are discussed, offering insights into developing nutritious, appealing low-sodium foods. Furthermore, challenges in current research are highlighted, and future directions for effective salt reduction strategies to promote public health are proposed. This review aims to establish a scientific foundation for creating healthier, flavorful low-sodium food options that meet consumer preferences and wellness needs.

Building a Kokumi Database and Machine Learning-Based Prediction: A Systematic Computational Study on Kokumi Analysis

Kokumi is a subtle sensation characterized by a sense of fullness, continuity, and thickness. Traditional methods of taste discovery and analysis, including those of kokumi, have been labor-intensive and costly, thus necessitating the emergence of computational methods as critical strategies in molecular taste analysis and prediction. In this study, we undertook a comprehensive analysis, prediction, and screening of the kokumi compounds. We categorized 285 kokumi compounds from a previously unreleased kokumi database into five groups based on their molecular characteristics. Moreover, we predicted kokumi/non-kokumi and multi-flavor compositions using six structure-taste relationship models: MLP-E3FP, MLP-PLIF, MLP-RDKFP, SVM-RDKFP, RF-RDKFP, and WeaveGNN feature of Atoms and Bonds. These six predictors exhibited diverse performance levels across two different models. For kokumi/non-kokumi prediction, the WeaveGNN model showed an exceptional predictive AUC value (0.94), outperforming the other models (0.87, 0.90, 0.89, 0.92, and 0.78). For multi-flavor prediction, the MLP-E3FP model demonstrated a higher predictive AUC and MCC value (0.94 and 0.74) than the others (0.73 and 0.33; 0.92 and 0.70; 0.95 and 0.73; 0.94 and 0.64; and 0.88 and 0.69). This data highlights the model's proficiency in accurately predicting kokumi molecules. As a result, we sourced kokumi active compounds through a high-throughput screening of over 100 million molecules, further refined by toxicity and similarity screening. Lastly, we launched a web platform, KokumiPD (https://www.kokumipd.com/), offering a comprehensive kokumi database and online prediction services for users.

Novel kokumi peptides from yeast extract and their taste mechanism via an in silico study

Yeast extract, a widely utilized natural substance in the food industry and biopharmaceutical field, holds significant potential for flavor enhancement. Kokumi peptides within yeast extracts were isolated through ultrafiltration and gel chromatography, followed by identification using liquid chromatography tandem mass spectrometry (LC-MS/MS). Two peptides, IQGFK and EDFFVR, were identified and synthesized using solid-phase methods based on molecular docking outcomes. Sensory evaluations and electronic tongue analyses conducted with chicken broth solutions revealed taste thresholds of 0.12 mmol L-1 for IQGFK and 0.16 mmol L-1 for EDFFVR, respectively, and both peptides exhibited kokumi properties. Additionally, through molecular dynamics simulations, the binding mechanisms between these peptides and the calcium-sensing receptor (CaSR) were explored. The findings indicated stable binding of both peptides to the receptor. IQGFK primarily interacted through electrostatic interactions, with key binding sites including Asp275, Asn102, Pro274, Trp70, Tyr218, and Ser147. EDFFVR mainly engaged via van der Waals energy and polar solvation free energy, with key binding sites being Asp275, Ile416, Pro274, Arg66, Ala298, and Tyr218. This suggests that both peptides can activate the CaSR, thereby inducing kokumi activity. This study provides a theoretical foundation and reference for the screening and identification of kokumi peptides, successfully uncovering two novel kokumi peptides derived from yeast extract.

Identifying the structures and taste characteristics of two novel Maillard reaction products in tea

Maillard reaction products (MRPs) produced during thermal processing of tea are intimately related to its flavor. Our recent work revealed that both levels of l-theanine and d-galacturonic acid in tea leaves decreased dramatically during drying, whereas the specific MRPs from l-theanine and d-galacturonic acid remain elusive. Here, the MRPs formed from l-theanine and d-galacturonic acid were investigated and their taste characteristics and the involved mechanisms were explored. Two novel MRPs from l-theanine and d-galacturonic acid were identified as 1-(1-carboxy-4-(ethylamino)-4-oxobutyl)-3-hydroxypyridin-1-ium (MRP 1) and 2-(2-formyl-1H-pyrrole-1-yl) theanine (MRP 2). MRP 1 and MRP 2 accumulated in dark tea and black tea and were associated with sour (threshold, 0.25 mg/mL) and astringent tastes and an umami taste (threshold, 0.18 mg/mL), respectively. Molecular docking revealed that the taste characteristics of MRPs may be due to strong binding to umami taste receptor proteins (CASR, T1R1/T1R3) and the sour taste protein OTOP1 via hydrogen bonds and hydrophobic interactions.

Gentiopicroside-An Insight into Its Pharmacological Significance and Future Perspectives

Gentiopicroside (GPS) is a leading component of several plant species from the Gentianaceae botanical family. As a compound with plenty of biological activities and a component of herbal drugs, GPS has an important role in the regulation of physiological processes in humans. The results of recently published scientific studies underline a meaningful role of this molecule as an active factor in metabolic pathways and mechanisms, which may have an influence in the treatment of different diseases, including digestive tract disorders, malignant changes, neurological disorders, microbial infections, bone formation disorders, inflammatory conditions, and others. This review aims to collect previously published reports on the biological properties of GPS as a single compound that were confirmed by in vitro and in vivo studies, and to draw attention to the newly discovered role of this bitter-tasting secoiridoid. Thanks to these properties, the research on this substance could be revisited.

Kokumi-Enhancing Mechanism of N-l-lactoyl-l-Met Elucidated by Sensory Experiments and Molecular Simulations

Recent research indicates that N-lactoyl amino acid derivatives have the potential as kokumi substances, with their kokumi profile closely linked to that of amino acids. This study aimed to explore the unexplored effects resulting from the introduction of lactate groups into l-Methional (l-Met), a prevalent flavor compound found in foods, such as tomatoes, known for its ability to activate the monosodium glutamate response. N-l-Lac-l-Met was enzymatically synthesized using food grade, and its taste profile and underlying mechanisms were investigated. The structure of N-l-Lac-l-Met was determined by high-performance liquid chromatography (HPLC)-mass spectrometry (MS)/MS. Sensory evaluation revealed the presence of astringency, kokumi, and bitterness of N-l-Lac-l-Met. In a stimulated broth, N-l-Lac-l-Met exhibited enhanced umami and kokumi taste perception compared to l-Met while demonstrating good stability within pH 5 to 9. A molecular simulation and quantum mechanics analysis indicated that the formation of an amide bond played a crucial role in the kokumi-enhancing effect of N-l-Lac-l-Met, specifically by increasing its affinity with umami receptors T1R1-T1R3 and a kokumi receptor CaSR. These findings established the relationship between amide bond formation and the kokumi-enhancing effect of N-l-Lac-l-Met, presenting its potential application as the kokumi substance in the food industry.

Sweet Taste Receptors and Associated Sweet Peptides: Insights into Structure and Function

Long-term consumption of a high-sugar diet may contribute to the pathogenesis of several chronic diseases, such as obesity and type 2 diabetes. Sweet peptides derived from a wide range of food sources can enhance sweet taste without compromising the sensory properties. Therefore, the research and application of sweet peptides are promising strategies for reducing sugar consumption. This work first outlined the necessity for global sugar reduction, followed by the introduction of sweet taste receptors and their associated transduction mechanisms. Subsequently, recent research progress in sweet peptides from different protein sources was summarized. Furthermore, the main methods for the preparation and evaluation of sweet peptides were presented. In addition, the current challenges and potential applications are also discussed. Sweet peptides can stimulate sweetness perception by binding sweet taste receptors T1R2 and T1R3 in taste buds, which is an effective strategy for reducing sugar consumption. At present, sweet peptides are mainly prepared artificially by synthesis, hydrolysis, microbial fermentation, and bioengineering strategies. Furthermore, sensory evaluation, electronic tongues, and cell models have been used to assess the sweet taste intensity. The present review can provide a theoretical reference for reducing sugar consumption with the aid of sweet peptides in the food industry.

Basic sensory properties of essential oils from aromatic plants and their applications: a critical review

With higher standards in terms of diet and leisure enjoyment, spices and essential oils of aromatic plants (APEOs) are no longer confined to the food industry. The essential oils (EOs) produced from them are the active ingredients that contribute to different flavors. The multiple odor sensory properties and their taste characteristics of APEOs are responsible for their widespread use. The research on the flavor of APEOs is an evolving process attracting the attention among scientists in the past decades. For APEOs, which are used for a long time in the catering and leisure industries, it is necessary to analyze the components associated with the aromas and the tastes. It is important to identify the volatile components and assure quality of APEOs in order to expand their application. It is worth celebrating the different means by which the loss of flavor of APEOs can be retarded in practice. Unfortunately, relatively little research has been done on the structure and flavor mechanisms of APEOs. This also points the way to future research on APEOs.Therefore, this paper reviews the principles of flavor, identification of components and sensory pathways in humans for APEOs. Moreover, the article outlines the means of increasing the efficiency of using of APEOs. Finally, with respect to the sensory applications of APEOs, the review focuses on the practical application of APEOs in food sector and in aromatherapy.

Discovery of N-l-Lactoyl-l-Trp as a Bitterness Masker via Structure-Based Virtual Screening and a Sensory Approach

N-Lactoyl-amino acid derivatives (N-Lac-AAs) are of increasing interest as potential taste-active compounds. The complexity and diversity of N-Lac-AAs pose a significant challenge to the effective discovery of taste-active N-Lac-AAs. Therefore, a structure-based virtual screening was used to identify taste-active N-Lac-AAs. Virtual screening results showed that N-lactoyl-hydrophobic amino acids had a higher affinity for taste receptors, specifically N-l-Lac-l-Trp. And then, N-l-Lac-l-Trp was synthesized in yields of 22.3% by enzymatic synthesis in the presence of l-lactate and l-Trp, and its chemical structure was confirmed by MS/MS and one-dimensional (1D) and two-dimensional (2D) NMR. Sensory evaluation revealed that N-l-Lac-l-Trp had a significant taste-masking effect on quinine, d-salicin, caffeine, and l-Trp, particularly l-Trp and caffeine. N-l-Lac-l-Trp had a better masking effect on the higher concentration of bitter compounds. It reduced the bitterness of caffeine (500 mg/L) and l-Trp (1000 mg/L) by approximately 20 and 26%, respectively. The result of the ligand-receptor interaction and a quantum mechanical analysis showed that N-l-Lac-l-Trp increased the binding affinity to the bitter receptor mainly through hydrogen bonding and lowering the electrostatic potential.

Toward a general and interpretable umami taste predictor using a multi-objective machine learning approach

The umami taste is one of the five basic taste modalities normally linked to the protein content in food. The implementation of fast and cost-effective tools for the prediction of the umami taste of a molecule remains extremely interesting to understand the molecular basis of this taste and to effectively rationalise the production and consumption of specific foods and ingredients. However, the only examples of umami predictors available in the literature rely on the amino acid sequence of the analysed peptides, limiting the applicability of the models. In the present study, we developed a novel ML-based algorithm, named VirtuousUmami, able to predict the umami taste of a query compound starting from its SMILES representation, thus opening up the possibility of potentially using such a model on any database through a standard and more general molecular description. Herein, we have tested our model on five databases related to foods or natural compounds. The proposed tool will pave the way toward the rationalisation of the molecular features underlying the umami taste and toward the design of specific peptide-inspired compounds with specific taste properties.

Insights into the flavor perception and enhancement of sodium-reduced fermented foods: A review

Salt (sodium chloride, NaCl) is a vital ingredient in fermented foods, which affects their safety, texture, and flavor characteristics. Recently, the demand for reduced-sodium fermented foods has increased, as consumers have become more health-conscious. However, reducing sodium content in fermented foods may negatively affect flavor perception, which is a critical quality attribute of fermented foods for both the food industry and consumers. This review summarizes the role of salt in the human body and foods and its role in the flavor perception of fermented foods. Current sodium reduction strategies used in the food industry mainly include the direct stealth reduction of NaCl, substituting NaCl with other chloride salts, and structure modification of NaCl. The odor-induced saltiness enhancement, application of starter cultures, flavor enhancers, and non-thermal processing technology are potential strategies for flavor compensation of sodium-reduced fermented foods. However, reducing sodium in fermented food is challenging due to its specific role in flavor perception (e.g., promoting saltiness and volatile compound release from food matrices, inhibiting bitterness, and changing microflora structure). Therefore, multiple challenges must be addressed in order to improve the flavor of low-sodium fermented foods. Future studies should thus focus on the combination of several strategies to compensate for the deficiencies in flavor resulting from sodium reduction.

Taste GPCRs and their ligands

Taste GPCRs are expressed in taste buds on the tongue and play a key role in food choice and consumption. They are also expressed extra-orally, with various physiological roles that are currently under study. Unraveling the roles of these receptors relies on the knowledge of their ligands. Combining sensory, cell-based and computational approaches enabled the discovery of numerous agonists and several antagonists. Here we provide a short overview of taste receptor families, main recent methods for ligands discovery, and current sources of information about known ligands. The future directions that are likely to impact the taste GPCR field include focus on ligand interactions with naturally occurring polymorphisms, as well as harnessing the power of CryoEM and of multiple signaling readout techniques.