Tastes and structures of bitter peptide, asparagine-alanine-leucine-proline-glutamate, and its synthetic analogues

Measurement of degree of hydrolysis and molecular weight distribution of protein hydrolysates by liquid chromatography-mass spectrometry

Enzymatic hydrolysis of milk protein is an effective way to improve protein digestibility, to reduce their allergenicity and to produce peptides with better functionalities. Among the process, the degree of hydrolysis (DH) and molecular weight distribution (MWD) of protein hydrolysates are two important parameters that need to be monitored. In this work, a new method based on liquid chromatography-mass spectrometry (LC-MS) was developed for the first time to accurately detect the DH and the MWD of proteolytic peptides. With LC-MS, the content of free amine groups released during hydrolysis was acquired by direct analysis of free trinitrobenzene sulfonic acid (TNBS) for DH assay, overcoming the disadvantage of TNBS-based spectral method. Based on this method, the DH% values of five protein hydrolysis samples were determined and consistent with file specification values. Compared to the size-exclusion high-performance liquid chromatography (SE-HPLC) method, LC-MS was capable of measuring MWD (similar results with file specification values) while additionally providing precise molecular weight and amino acid sequence information for each proteolytic peptide. This method was characterized by its simplicity, accuracy, and reproducibility, making it a valuable technology for monitoring proteolysis and producing peptides with better functionality.

Identification, flavor characteristics and molecular docking of umami taste peptides of Xuanwei ham

To better understand the palatable properties of Xuanwei ham, the aqueous extract was isolated, analyzed and combin with sensory evaluation. Of umami-tasting activity and umami-enhancing impact, four new peptides (MDAIKKMQ, RKYEEVAR, YVGDEAQSKRG, and VNVDEVGGEALGR) were extracted and identified by ultrafiltration, gel separation, reverse performance liquid chromatography, and nano-LC-MS / MS. Sensory evaluation results showed that all of them had umami activity and enhanced umami taste, among which VNVDEVGGEALGR had the best effect. These peptides' umami taste thresholds ranged from 0.25 to 0.8 mg/mL. The MSG solution's umami taste threshold ranged from 0.125 to 0.5 mg/mL. Molecular docking results showed that the four umami peptides could be embedded into the binding pocket of the T1R3 cavity of the umami taste receptor T1R1/T1R3, wherein the binding sites Asp219, Asp150, and Thr179 may play crucial roles, and Glu222, Asp108, Glu217 and Glu148 play auxiliary roles. Hydrogen bonding and hydrophobic interactions were the most prominent interaction forces. This study helps to clarify the flavor characteristics of Xuanwei ham and could improve new processing technology.

Bitter Peptides in Fermented Soybean Foods - A Review

Fermented soybean foods with a long history are popular worldwide because of rich nutrition. However, many traditional fermented soybean foods have unacceptable bitterness, which mostly comes from the bitter peptides produced from the hydrolysis of soybean proteins. In this review, the bitter peptides in fermented soybean foods is briefly reviewed. The structural properties of bitter receptors and bitter peptides were reviewed. Bitterness is perceived through the binding between bitter compounds and specific sites of bitter receptors (25 hTAS2Rs), which further activate the downstream signal pathway mediated by G-protein. And it converts chemical signals into electrical signals, and transmit them to the brain. In addition, the influencing factors of bitter peptides in fermented soybean foods were summarized. The bitterness of fermented soybean foods primarily results from the raw materials, microbial metabolism during fermentation, unique techniques, and interactions of various flavor compounds. Moreover, the structure-bitterness relationship of bitter peptides was also discussed in this review. The bitterness degree of the bitter peptide is related to the polypeptide hydrophobicity, amino acids in the peptide, peptide molecular weight and polypeptide spatial structure. Studying the bitter peptides and their bitter characteristics in fermented soybean foods is beneficial for improving the sensory quality of fermented soybean foods and prompting more consumers accept them.

An overview of bitter compounds in foodstuffs: Classifications, evaluation methods for sensory contribution, separation and identification techniques, and mechanism of bitter taste transduction

The bitter taste is generally considered an undesirable sensory attribute. However, bitter-tasting compounds can significantly affect the overall flavor of many foods and beverages and endow them with various beneficial effects on human health. To better understand the relationship between chemical structure and bitterness, this paper has summarized the bitter compounds in foodstuffs and classified them based on the basic skeletons. Only those bitter compounds that are confirmed by human sensory evaluation have been included in this paper. To develop food products that satisfy consumer preferences, correctly ranking the key bitter compounds in foodstuffs according to their contributions to the overall bitterness intensity is the precondition. Generally, three methods were applied to screen out the key bitter compounds in foods and beverages and evaluate their sensory contributions, including dose-over-threshold factors, taste dilution analysis, and spectrum descriptive analysis method. This paper has discussed in detail the mechanisms and applications of these three methods. Typical procedures for separating and identifying the main bitter compounds in foodstuffs have also been summarized. Additionally, the activation of human bitter taste receptors (TAS2Rs) and the mechanisms of bitter taste transduction are outlined. Ultimately, a conclusion has been drawn to highlight the current problems and propose potential directions for further research.

Impact of Different Enzymatic Processes on Antioxidant, Nutritional and Functional Properties of Soy Protein Hydrolysates Incorporated into Novel Cookies

Soy protein concentrate (SPC) was hydrolyzed using several commercial food-grade proteases (Alcalase, Neutrase, papain, Everlase, Umamizyme, Flavourzyme) and their combination to obtain promising ingredients in the manufacture of functional bakery products. In all cases, the hydrolysis caused nutritional, sensory, and rheological changes in SPC, as well as protein structural changes like increased surface hydrophobicity and content of exposed SH groups with the magnitude of these changes depending on enzyme specificity. The hydrolysis with the combination of Neutrase and Flavourzyme (NeuFlav) increased essential amino acid content by 9.8% and that of Lys by 32.6% compared to SPC. This hydrolysate showed also significant antioxidant activities including ABTS and superoxide anion scavenging activity and metal-chelating ability. The addition of all hydrolysates in wheat flour decreased water adsorption and increased development time to some extent due to gluten network weakening, but also decreased the rate of starch retrogradation, contributing to the increase of the shelf-life of bakery products. The NeuFlav tasted less bitter than other hydrolysates, while E-nose provided a discrimination index of 93 between control and hydrolysates. It appeared that the addition of the NeuFlav hydrolysate in a cookie formulation improved protein content and nutritional quality and directed to its higher general consumer acceptability than cookies formulated with only wheat flour.

Characteristics of the enzyme-induced release of bitter peptides from wheat gluten hydrolysates

Bitter peptides in the enzymatic hydrolysates were prepared and purified from wheat gluten using aqueous ethanol solutions and macroporous resin, which has opened a new road for the extraction and separation of bitter peptides. This report contains the release regularity of bitter peptides and the factors affecting the change of bitter intensity during enzymatic hydrolysis, providing a scientific basis for the research on debitterizing method. In this study, the effects of different degrees of hydrolysis (DH) and enzyme active sites on the bitter peptide content and bitter taste thresholds were discussed. The relationship between amino acid composition, molecular weight distribution, surface hydrophobicity and bitter taste thresholds was extensively researched. The results showed the exposure of hydrophobic amino acids and the bitterness intensity of the hydrolysates increased as the DH increased, and the bitterness of wheat gluten hydrolysates (WGHs) hydrolyzed by Alcalase was stronger than that of Trypsin. According to correlation analysis, the proportion of total hydrophobic amino acid is the first factor that affects the sensory properties of bitter peptide, and the release content of bitter peptides and the content of total bitter amino acids are the second, following by the content of peptide in the molecular weight range of 500–1,000 Da and the surface hydrophobicity. The amino acid sequence of bitter peptides from WGHs were identified and predicted using high performance liquid chromatography-mass spectrometry (HPLC-MS/MS) and bioinformatics. It was found that the molecular weight of most of the peptides was below 1,500 Da, and the Q value was higher than 5.86 kJ/mol.

Modulation of Metabolome and Overall Perception of Pea Protein-Based Gels Fermented with Various Synthetic Microbial Consortia

Moving to a more sustainable food system requires increasing the proportion of plant protein in our diet. Fermentation of plant product could thus be used to develop innovative and tasty food products. We investigated the impact of fermentation by synthetic microbial consortia (SMC) on the perception of pea protein-based gels, giving possible keys to better understand the origin of sensory perception (e.g., beany, bitter). Two types of pea gels, containing (i) 100% pea proteins and (ii) 50% pea proteins/50% milk proteins, were fermented with three different SMC. Major species developing in both types of gels were Geotrichum candidum, Lactococcus lactis, and Lactobacillus rhamnosus. In pea gels, sensory analyses revealed that bitterness increased after fermentation, which could be due to hydrophobic amino acids resulting from protein hydrolysis, but also decreased pea note intensity in pea gels. In mixed gels, pea perception was similar whatever the SMC, whereas cheesy perception increased. Olfactometry experiments revealed that some specific “green” aroma compounds, responsible for green off-note, were suppressed/reduced by fermentation. The data presented investigated to which extent the design of SMC, together with gels composition (pea gels versus mixed gels), could modulate sensorial perception and drive consumer acceptability.

Research progress in the screening and evaluation of umami peptides

Umami is an important element affecting food taste, and the development of umami peptides is a topic of interest in food-flavoring research. The existing technology used for traditional screening of umami peptides is time-consuming and labor-intensive, making it difficult to meet the requirements of high-throughput screening, which limits the rapid development of umami peptides. The difficulty in performing a standard measurement of umami intensity is another problem that restricts the development of umami peptides. The existing methods are not sensitive and specific, making it difficult to achieve a standard evaluation of umami taste. This review summarizes the umami receptors and umami peptides, focusing on the problems restricting the development of umami peptides, high-throughput screening, and establishment of evaluation standards. The rapid screening of umami peptides was realized based on molecular docking technology and a machine learning method, and the standard evaluation of umami could be realized with a bionic taste sensor. The progress of rapid screening and evaluation methods significantly promotes the study of umami peptides and increases its application in the seasoning industry.

Manufacturing of Plant-Based Bioactive Peptides Using Enzymatic Methods to Meet Health and Sustainability Targets of the Sustainable Development Goals

Due to the rapid growth in the global population, the consumption of animal-based food products/food compounds has been associated with negative implications for food sustainability/security. As a result, there is an increasing demand for the development of plant-based food and compounds as alternatives. Meanwhile, a growing number of studies report the health benefits of food protein-based peptides prepared via enzymatic hydrolysis and exhibiting biological properties such as antioxidant, antihypertensive, anti-thrombotic, and antidiabetic activities. However, the inherent bitterness of some peptides hinders their application in food products as ingredients. This article aims to provide the latest findings on plant-based bioactive peptides, particularly their health benefits, manufacturing methods, detection and qualification of their bitterness properties, as well as debittering methods to reduce or eliminate this negative sensory characteristic. However, there is still a paucity of research on the biological property of debittered peptides. Therefore, the role of plant protein-derived bioactive peptides to meet the health targets of the Sustainable Development Goals can only be realised if advances are made in the industrial-scale bioprocessing and debittering of these peptides.

Identification and characterization of the main peptides in pea protein isolates using ultra high-performance liquid chromatography coupled with mass spectrometry and bioinformatics tools

Pea protein isolates are a source of high-quality plant proteins. However, from a sensory perspective, they are usually described as having strong beany and bitter notes, which arise from a complex mixture of volatiles, phytochemicals, and peptides. The aim of this study was to identify the main peptides in isolates and examine their correlations with sensory perceptions. Thus, 28 solutions containing different mixtures of pea protein fractions were assessed. Any peptides present were identified and characterized using ultra high-performance liquid chromatography-mass spectrometry. There were a total of 3,005 unique peptides representing various protein families; 1,640 and 275 peptides were correlated with broth and bitter attributes, respectively. In particular, 14 peptides with short sequences (<8 residues) were correlated with bitterness. These results show how key peptides in isolates may cause sensory perceptions.

Effect of microwave sterilization on maturation time and quality of low-salt sufu

The objective of this study was to reduce the microorganism number and salt content in pehtze by microwave sterilization. The maturation time and quality of low-salt sufu were evaluated. The microorganism inactivation rate, moisture content and water activity of the pehtze, which was used for the growth of the starter culture, showed that 4,250 W for 30 s was suitable for the preparation of low-salt sufu. With regard to the physicochemical properties of sufu, 120-day sufu samples obtained by traditional high-salt (14%) fermentation and 75-day sufu samples obtained by low-salt (4%) fermentation met the standard requirements. With regard to the sensory characteristics of sufu, the taste and after taste scores of 75-day low-salt sufu samples were significantly higher than those of 120-day high-salt sufu samples (p < .05).The overall acceptance score of low-salt sufu samples also was higher than that of high-salt sufu samples. The contents of free amino acids and the profiles of typical flavor compounds partly explained the sensory quality and shorter ripening time of sufu manufactured. The total biogenic amine contents were reduced by 46%.

Changes in the perception of bitter constituents in thermally treated yeast extract

BACKGROUND

Many studies have been performed over the past four decades to identify and quantify the odor-active key volatiles in yeast extract (YE) but knowledge of the nonvolatile taste compounds is still rather fragmentary. In particular, research on bitter peptides with various structures during the thermal treatment of YE is still scarce.

RESULTS

Compounds imparting a bitter taste to thermally treated YE were investigated using sensory-guided fractionation. This research found that when the treatment temperature reached 130 °C, bitter peptides were generated. Sensory evaluation of the purified, synthesized peptides revealed that four of these peptides showed a pronounced bitter taste with a taste dilution (TD) factor from 5 to 9. Guidance is provided for the production of bitter peptides in the flavor industry.

CONCLUSION

Based on results from previous work on umami peptides, and this study, keeping the thermal reaction temperature under 120 °C could maximize the umami flavor and control bitterness so that it remains in an acceptable range. © 2019 Society of Chemical Industry.

Enzymatic hydrolysis of lupin protein isolates-Changes in the molecular weight distribution, technofunctional characteristics, and sensory attributes

Enzymatic hydrolysis of lupin protein isolates (LPI; Lupinus angustifolius L.) was performed with nine different protease preparations to investigate their effect on technofunctionality, sensory properties, and the integrity of the proteins to estimate the reduction of the immunoreactivity. Alcalase 2.4 L, papain, and pepsin were most effective in the degradation of the α- and β-conglutin examined by SDS-PAGE analysis, although the degree of hydrolysis only slightly increased. The technofunctional properties of LPI-solubility, emulsifying, and foaming activity-were improved by most of the proteolytic enzymes with the most impressive increase from 980% foam activity for LPI up to 3,614% foam activity for pepsin hydrolysate. The formation of bitterness, most likely linked to generation of bitter peptides, was pronounced in the Alcalase hydrolysate, while the other hydrolysates did not show an extensive increase in bitterness compared to the LPI. Other sensory attributes of the hydrolysates-with the exception of Alcalase treatment-were also very similar to the LPI. The results of this study show the potential of enzymatic degradation of LPI to modify the IgE-reacting polypeptides and to improve the technofunctionality of the isolates and therefore their use as food ingredients.

Effect of harvest, drying and storage on the bitterness, moisture, sugars, free amino acids and phenolic compounds of jujube fruit (Zizyphus jujuba cv. Junzao)

BACKGROUND

The taste of dried jujube fruit when compared with fresh ones is less palatable, as it develops bitterness during drying and storage. Therefore, identifying the methods by which bitterness occurs is essential for developing strategies for processing and storage.

RESULTS

Bitterness in fresh jujube fruit was negligible; however, it increased by 0.9-, 1.5- and 1.8-fold during drying and storage over 6 and 12 months. The moisture significantly decreased during harvesting and drying. Free amino acids, except proline and tyrosine, significantly decreased during drying and storage. Fructose, glucose and sucrose hardly changed during harvest, drying and storage. Titratable acidity, total phenolic and total flavonoids contents were stable during harvest and drying, but increased upon storage. Additionally, protocatechuic and ellagic acids were not detected in fresh jujube fruit, however, were found to increase during drying and storage.

CONCLUSION

Bitterness in fresh jujube fruit tasted negligible because of meagre amount of phytochemicals, while the condensation effect of moisture reduction, the loss of free amino acids, and the formation of protocatechuic and ellagic acids could aggravate the bitterness of jujube fruit during drying and storage. © 2017 Society of Chemical Industry.

BitterDB: a database of bitter compounds

Basic taste qualities like sour, salty, sweet, bitter and umami serve specific functions in identifying food components found in the diet of humans and animals, and are recognized by proteins in the oral cavity. Recognition of bitter taste and aversion to it are thought to protect the organism against the ingestion of poisonous food compounds, which are often bitter. Interestingly, bitter taste receptors are expressed not only in the mouth but also in extraoral tissues, such as the gastrointestinal tract, indicating that they may play a role in digestive and metabolic processes. BitterDB database, available at http://bitterdb.agri.huji.ac.il/bitterdb/, includes over 550 compounds that were reported to taste bitter to humans. The compounds can be searched by name, chemical structure, similarity to other bitter compounds, association with a particular human bitter taste receptor, and so on. The database also contains information on mutations in bitter taste receptors that were shown to influence receptor activation by bitter compounds. The aim of BitterDB is to facilitate studying the chemical features associated with bitterness. These studies may contribute to predicting bitterness of unknown compounds, predicting ligands for bitter receptors from different species and rational design of bitterness modulators.