Molecular simulation screening and sensory evaluation unearth a novel kokumi compound with bitter-masking effect: N-lauroyl-L-tryptophan

N-lauroyl-L-tryptophan (LT), which has the strongest potential flavor-presenting activity, was skillfully screened from numerous N-Lau-AAs docked to different taste receptors by molecular simulation techniques. Subsequently, LT was synthesized employing food-grade commercial enzymes and structurally characterized, the optimized yields of LT could reach 69.08%, 76.16%, and 50.40%, respectively. Sensory and E-tongue evaluations showed that LT at 1 mg/L significantly benefited the performance of different taste sensations and exhibited different bitter taste masking effects: L-Ile (68.42%), L-Trp (68.18%), D-salicylic acid (48.48%) and quinine (35.00%). The molecular docking results illustrated that LT had a high affinity for various taste receptors, dominated by hydrogen bonding and hydrophobic interactions. This work provided a rare systematic elucidation of the potential and mechanism of enzymatically synthesized LT in enhancing taste properties. It provides novel insights into the directions and strategies for the excavation and innovation of flavor enhancers and food flavors.

Synthesis, taste characteristics and taste mechanism of N-lactoyl leucine from soy sauce using sensory analysis and UPLC-MS/MS

Recently, amino acid derivatives gradually gained attention, but studies on N-lactoyl-leucine (Lac-Leu) and N-lactoyl-isoleucine (Lac-Ile) are limited. This study aims to explore the contributions of Lac-Leu and Lac-Ile to soy sauce. Lac-Leu and Lac-Ile were synthesized via enzymatic synthesis method catalyzed by Tgase. The mixed solutions containing Lac-Leu were found to have greater taste improvement than those containing Lac-Ile. Sensory evaluation indicated the sour, bitter, and astringent taste of Lac-Leu in water as well as its kokumi, astringent, and umami-enhancing taste in MSG solution. The taste threshold and umami-enhancing threshold of Lac-Leu measured by TDA and cTDA, respectively, were 0.08 mg/mL and 0.16 mg/mL. Molecular docking of Lac-Leu and Lac-Ile with the kokumi receptor CaSR and the umami receptors T1R1 and T1R3 indicated that Lac-Leu had higher affinities with receptors than Lac-Ile. These findings demonstrated the underlying contribution Lac-Leu made to soy sauce, indicating its potential to improve the flavor quality of soy sauce.

A Novel Compound with Kokumi Properties: Enzymatic Preparation and Taste Presentation Evaluation of N-Lauroyl Phenylalanine

To satisfy the demands of the food industry, innovative flavor enhancers need to be developed urgently to increase the food flavor. In our work, N-lauroyl phenylalanine (LP) was prepared from phenylalanine (l-Phe) and lauric acid (Lau) in water through the use of commercial enzymes (Promatex, Sumizyme FP-G, and Trypsin), and its flavor-presenting properties and mechanism were investigated. The highest LP yields obtained under one-factor optimized conditions were 61.28, 63.43, and 77.58%, respectively. Sensory assessment and an e-tongue test revealed that 1 mg/L LP enhanced the kokumi, saltiness, and umami of the simulated chicken broth solution and attenuated the bitterness of the l-isoleucine solution. The molecular simulation results suggested that the mechanisms of LP enhancement of kokumi and umami were related to hCaSR and hT1R1-hT1R3, and that hydrophobic forces and hydrogen bonds were involved in the binding of LP to taste receptors. The results implied that LP is a potential flavor enhancer for food applications.

Mechanisms of umami taste perception: From molecular level to brain imaging

Due to unique characteristics, umami substances have gained much attention in the food industry during the past decade as potential replacers to sodium or fat to increase food palatability. Umami is not only known to increase appetite, but also to increase satiety, and hence could be used to control food intake. Therefore, it is important to understand the mechanism(s) involved in umami taste perception. This review discusses current knowledge of the mechanism(s) of umami perception from receptor level to human brain imaging. New findings regarding the molecular mechanisms for detecting umami tastes and their pathway(s), and the peripheral and central coding to umami taste are reviewed. The representation of umami in the human brain and the individual variation in detecting umami taste and associations with genotype are discussed. The presence of umami taste receptors in the gastrointestinal tract, and the interactions between the brain and gut are highlighted. The review concludes that more research is required into umami taste perception to include not only oral umami taste perception, but also the wider "whole body" signaling mechanisms, to explore the interaction between the brain and gut in response to umami perception and ingestion.

Expression of umami-taste-related genes in the tongue: a pilot study for genetic taste diagnosis

OBJECTIVE

Expression of taste-related genes in the tongue was analysed to develop a technique for genetic diagnosis of umami taste disorders.

MATERIALS AND METHODS

Tissue samples were collected from healthy volunteers by scraping the foliate papillae of the tongue. Immunocytochemistry staining of gustducin, a taste-cell-specific G protein, and gene expression analysis by real-time polymerase chain reaction of β-actin, gustducin (GNAT3) and umami receptors (T1R1, T1R3 and mGluR1) were performed. Changes in umami receptor expression following application of umami substances onto the tongue were analysed.

RESULTS

Gustducin-positive cells were observed in the samples, indicating the presence of taste cells. Gene expression of β-actin, GNAT3, T1R1 and T1R3 was detected in all seven samples tested, while that of mGluR1 was detected in four samples. Sequence analysis by NCBI Blast showed that each polymerase chain reaction product had a 99% rate of identification of its target sequence. Stimulation of the tongue with monosodium glutamate significantly upregulated the gene expression levels of T1R1 and T1R3, indicating that this method can detect alterations in umami-related gene expression.

CONCLUSION

Evaluation of the expression of the umami receptor genes, T1R1 and T1R3, in the tongue may be clinically useful for objective genetic diagnosis of umami taste disorders.

Development of an umami taste sensitivity test and its clinical use

There is a close relationship between perception of umami, which has become recognized as the fifth taste, and the human physical condition. We have developed a clinical test for umami taste sensitivity using a filter paper disc with a range of six monosodium glutamate (MSG) concentrations. We recruited 28 patients with taste disorders (45–78 years) and 184 controls with no taste disorders (102 young [18–25 years] and 82 older [65–89 years] participants). Filter paper discs (5 mm dia.) were soaked in aqueous MSG solutions (1, 5, 10, 50, 100 and 200 mM), then placed on three oral sites innervated by different taste nerves. The lowest concentration participants correctly identified was defined as the recognition threshold (RT) for MSG. This test showed good reproducibility for inter- and intra-observer variability. We concluded that: (1) The RT of healthy controls differed at measurement sites innervated by different taste nerves; that is, the RT of the anterior tongue was higher than that of either the posterior tongue or the soft palate in both young and older individuals. (2) No significant difference in RT was found between young adults and older individuals at any measurement site. (3) The RT of patients with taste disorders was higher before treatment than that of the healthy controls at any measurement site. (4) The RT after treatment in these patients improved to the same level as that of the healthy controls. (5) The cutoff values of RT, showing the highest diagnostic accuracy (true positives + true negatives), were 200 mM MSG for AT and 50 mM MSG for PT and SP. The diagnostic accuracy at these cutoff values was 0.92, 0.87 and 0.86 for AT, PT and SP, respectively. Consequently, this umami taste sensitivity test is useful for discriminating between normal and abnormal umami taste sensations.

Umami flavour as a means of regulating food intake and improving nutrition and health

Diet and lifestyle have an impact on the burden of ill health and non-communicable ailments such as cardiovascular disease (including hypertension), obesity, diabetes, cancer and certain mental illnesses. The consequences of malnutrition and critical unbalances in the diet with regard to sugar, salt and fat are becoming increasingly manifest in the Western world and are also gradually influencing the general health condition for populations in developing countries. In this topical mini-review I highlight the lack of deliciousness and umami (savoury) flavour in prepared meals as a possible reason for poor nutritional management and excess intake of salt, fat and sugar. I argue that a better informed use of the current scientific understanding of umami and its dependence of the synergetic relationship between monosodium glutamate and certain 5'-ribonucleotides and their action on the umami taste receptors will not only provide better-tasting and more flavoursome meals but may also help to regulate food intake, in relation to both overeating and nutritional management of elderly and sick individuals.