Preparation, receptors, bioactivity and bioavailability of γ-glutamyl peptides: A comprehensive review

Gamma-glutamylation of beef protein hydrolysates to improve its overall taste and functions of gastro-intestinal hormone (CCK and GLP-1) pro-secretion and anti-inflammation

γ-Glutamylation of beef protein hydrolysate (BPH) by L-glutaminase was carried out to improve the taste, as well as enhance the stimulating effect of gastrointestinal hormone (CCK and GLP-1) secretion and the anti-inflammatory property. Results of sensory evaluation showed that the kokumi taste, umaminess, saltiness of the γ-glutamylated product (γ-GBPH) were significantly higher (p < 0.05), whilst the bitterness was remarkably decreased (p < 0.05) than that of BPH. γ-GBPH had a better promoting effect (p < 0.05) on CCK and GLP-1 secretion and a higher inhibition (p < 0.05) on TNF-α and IL-8 production than BPH in vitro cell experiments. In γ-GBPH, 15 γ-Glutamylated amino acids (γ-[Glu](n =1/2)-AAs) and 10 γ-Glutamyl-tripeptide (γ-Glu-AA-AAs) were synthesized from the bitter amino acids and bitter peptides, respectively, and their total production yield was 140.01-170.46 mg/g and 149.06 mg/g, respectively. The synthesized γ-Glu-AA-AAs entered the binding pocket of the calcium-sensitive receptor (CaSR), and they all interacted with three reported amino acid residues (Ser147, Ala168, and Ser170) of CaSR.

Food-derived peptides unleashed: emerging roles as food additives beyond bioactivities

Innovating food additives stands as a cornerstone for the sustainable evolution of future food systems. Peptides derived from food proteins exhibit a rich array of physicochemical and biological attributes crucial for preserving the appearance, flavor, texture, and nutritional integrity of foods. Leveraging these peptides as raw materials holds great promise for the development of novel food additives. While numerous studies underscore the potential of peptides as food additives, existing reviews predominantly focus on their biotic applications, leaving a notable gap in the discourse around their abiotic functionalities, such as their physicochemical properties. Addressing this gap, this review offers a comprehensive survey of peptide-derived food additives in food systems, accentuating the application of peptides' abiotic properties. It furnishes a thorough exploration of the underlying mechanisms and diverse applications of peptide-derived food additives, while also delineating the challenges encountered and prospects for future applications. This well-time review will set the stage for a deeper understanding of peptide-derived food additives.

Synthesis of taste active γ-glutamyl peptides with pea protein hydrolysate and their taste mechanism via in silico study

Pea (Pisum sativum L.) protein hydrolysate (PPH) has a bitter taste, which has limited its use in food industry. γ-Glutamylation is used to debitter PPH. Results showed that the bitterness of PPH was decreased significantly due to the formation of γ-glutamyl peptides, including 16 γ-[Glu](n=1/2)-amino acids (AAs) and 8 newly discovered γ-glutamyl tripeptides (γ-Glu-Asn-Phe, γ-Glu-Leu-Val, γ-Glu-Leu-Tyr, γ-Glu-Gly-Leu, γ-Glu-Gly-Phe, γ-Glu-Gly-Tyr, γ-Glu-Val-Val, and γ-Glu-Gln-Tyr). Their total production concentrations were 27.25 μmol/L and 77.76 μmol/L, respectively. The γ-Glu-AA-AAs presented an umami-enhancing, salty-enhancing, and kokumi taste when their concentration reached 1.67 ± 0.20 ∼ 2.07 ± 0.20, 1.65 ± 0.25 ∼ 2.29 ± 0.45 and 0.68 ± 0.19 ∼ 1.03 ± 0.22 mmol/L, respectively. The γ-Glu-AA-AAs exhibited a kokumi taste by entering the Venus flytrap (VFT) of the calcium-sensing receptor and interacting with Ser147, Ala168, and Ser170. γ-Glu-AA-AAs can enhance the umaminess of Monosodium Glutamate (MSG) as they can enter the binding pocket of the taste receptor type 1 subunit 3 (T1R3)-MSG complex.

Preparation of Glutamine-Enriched Fermented Feed from Corn Gluten Meal and Its Functionality Evaluation

China faces a persistent deficiency in feed protein resources. Enhancing the utilization efficiency of indigenous feed protein resources emerges as a viable strategy to alleviate the current deficit in protein feed supply. Corn gluten meal (CGM), characterized by a high proportion of crude protein and glutamine, is predominantly employed in animal feed. Nonetheless, the water-insolubility of CGM protein hampers its protein bioavailability when utilized as feed material. The aim of this study was to augment protein bioavailability, liberate glutamine peptides from CGM, and produce glutamine-enriched CGM fermented feed. We executed a co-fermentation protocol using Bacillus subtilis A5, Lactobacillus 02002, and acid protease to generate the CGM fermented feed. Subsequent in vivo experiments with broilers were conducted to assess the efficacy of the fermented product. The findings revealed that the soluble protein, glutamine, small peptides, and lactic acid contents in the fermented feed increased by 69.1%, 700%, 47.6%, and 125.9%, respectively. Incorporating 15% and 30% CGM fermented feed into the diet markedly enhanced the growth performance and intestinal health of broilers, positively modulated the cecal microbiota structure, and augmented the population of beneficial bacteria, specifically Lactobacillus. These results furnish both experimental and theoretical foundations for deploying CGM fermented feed as an alternative protein feed resource.

Derivation of Kokumi γ-Glutamyl Peptides and Volatile Aroma Compounds from Fermented Cereal Processing By-Products for Reducing Bitterness of Plant-Based Ingredients

Current food production methods and consumption behaviours are unsustainable and contribute to environmental harm. One example is food waste-around 38% of food produced is wasted each year. Here, we show that two common food waste products, wheat bran and brewer's spent grain, can successfully be upcycled via miso fermentation. During the fermentation process, kokumi γ-glutamyl peptides, known to increase mouthfulness, are produced; these include γ-ECG (oxidized), γ-EVG, γ-EV, γ-EE, γ-EF, and γ-EL. The profiles of kokumi peptides and volatile aroma compounds are correlated with koji substrate, pH, and enzymatic activity, offering straightforward parameters that can be manipulated to increase the abundance of kokumi peptides during the fermentation process. Correlation analysis demonstrates that some volatile aroma compounds, such as fatty acid ethyl esters, are correlated with kokumi peptide abundance and may be responsible for fatty, greasy, and buttery aromas. Consumer sensory analysis conveys that the bitter taste of vegetables, such as that in endives, can be dampened when miso extract containing kokumi peptides is added. This suggests that kokumi peptides, along with aroma volatile compounds, can enhance the overall flavour of plant-based products. This study opens new opportunities for cereal processing by-product upcycling via fermentation, ultimately having the potential to promote a plant-based diet.

The maca protein ameliorates DSS-induced colitis in mice by modulating the gut microbiota and production of SCFAs

Maca is a functional food with anti-inflammatory activity, and it is rich in protein. Currently, inflammatory bowel disease (IBD) is a common gastrointestinal disease. However, there is little research focusing on the effect of maca protein (MCP) on IBD. In this study, we extracted MCP from maca root and explored its effect and mechanism on improving dextran sodium sulfate (DSS)-induced IBD in mice. The results indicated that MCP intervention alleviated the clinical symptoms and colon tissue damage of mice with DSS-induced colitis and inhibited the expression of inflammatory factors. Moreover, it can modulate the gut microbiota composition in mice with DSS-induced colitis. The regulation is achieved by reducing the relative abundance of the IBD-exacerbating key bacterial genera: Lachnospiraceae_NK4A136_group, Bacteroides, Desulfovibrio, Prevotella, Helicobacter and Sutterella, while increasing the relative abundance of the IBD-alleviating key bacterial genera: norank_f_Muribaculaceae, Lactobacillus, Oscillospira, Akkermansia and Bifidobacterium. MCP can also promote the production of short-chain fatty acids (SCFAs). The further western blotting results indicated that MCP can regulate the Treg/Th17 immune balance in mice with colitis via the SCFAs-GPR41/43/HDAC1 signaling pathway. Overall, MCP can alleviate colitis by comprehensively regulating the gut microbiota and inflammatory response. It may be a promising functional component that reduces the risk of colitis by maintaining intestinal health.

Recent advances in taste transduction mechanism, analysis methods and strategies employed to improve the taste of taste peptides

Taste peptides are oligopeptides that enhance both aroma and taste of food, and they are classified into five categories based on their taste characteristics: salty, sour, umami, sweet, bitter, and kokumi peptide. Recently, taste peptides have attracted the attention of several fields of research in food science and commercial applications. However, research on taste receptors of taste peptides and their taste transduction mechanisms are not clearly understood and we present a comprehensive review about these topics here. This review covers the aspects of taste peptides perceived by their receptors in taste cells, the proposed transduction pathway, as well as structural features of taste peptides. Apart from traditional methods, molecular docking, peptidomic analysis, cell and animal models and taste bud biosensors can be used to explore the taste mechanism of taste peptides. Furthermore, synergistic effect, Maillard reaction, structural modifications and changing external environment are employed to improve the taste of taste peptides. Consequently, we discussed the current challenges and future trends in taste peptide research. Based on the summarized developments, taste peptides derived from food proteins potentially appear to be important taste substances. Their applications meet the principles of "safe, nutritious and sustainable" in food development.

Streamlined Efficient Synthesis and Antioxidant Activity of γ-[Glutamyl](n≥1)-tryptophan Peptides by Glutaminase from Bacillus amyloliquefaciens

As a group of naturally occurring peptides in various foods, γ-glutamyl peptides possess a unique Kokumi taste and health benefits. However, few studies have focused on the functionality of γ-glutamyl peptides. In this study, the γ-[glutamyl] _{(n=1, 2, 3)}-tryptophan peptides were synthesized from a solution of glutamine (Gln) and tryptophan (Trp) employing L-glutaminase from Bacillus amyloliquefaciens. Four different γ-glutamyl peptides were identified from the reaction mixture by UPLC-Q-TOF-MS/MS. Under optimal conditions of pH 10, 37 °C, 3 h, 0.1 mol/L Gln: 0.1 mol/L Trp = 1:3, and glutaminase at 0.1% (m/v), the yields of γ-l-glutamyl-l-tryptophan (γ-EW), γ-l-glutamyl-γ-l-glutamyl-l-tryptophan (γ-EEW) and γ-l-glutamyl-γ-l-glutamyl-γ-l-glutamyl-l-tryptophan (γ-EEEW) were 51.02%, 26.12% and 1.91% respectively. The antioxidant properties of the reaction mixture and the two peptides (γ-EW, γ-EEW) identified from the reaction media were further compared. Results showed that γ-EW exhibited the highest DPPH^•, ABTS^•+ and O₂^•--scavenging activity (EC₅₀ = 0.2999 mg/mL, 67.6597 μg/mL and 5.99 mg/mL, respectively) and reducing power (EC₅₀ = 4.61 mg/mL), while γ-EEW demonstrated the highest iron-chelating activity (76.22%). Thus, the synthesized mixture may be used as a potential source of antioxidant peptides for food and nutraceutical applications.

New Insight into the Substrate Selectivity of Bovine Milk γ-glutamyl Transferase via Structural and Molecular Dynamics Predictions

Bovine milk γ-glutamyltransferase (BoGGT) can produce γ-glutamyl peptides using L-glutamine as a donor substrate, and the transpeptidase activity is highly dependent on both γ-glutamyl donors and acceptors. To explore the molecular mechanism behind the donor and acceptor substrate preferences for BoGGT, molecular docking and molecular dynamic simulations were performed with L-glutamine and L-γ-glutamyl-p-nitroanilide (γ-GpNA) as donors. Ser450 is a crucial residue for the interactions between BoGGT and donors. BoGGT forms more hydrogen bonds with L-glutamine than γ-GpNA, promoting the binding affinity between BoGGT and L-glutamine. Gly379, Ile399, and Asn400 are crucial residues for the interactions between the BoGGT intermediate and acceptors. The BoGGT intermediate forms more hydrogen bonds with Val-Gly than L-methionine and L-leucine, which can promote the transfer of the γ-glutamyl group from the intermediate to Val-Gly. This study reveals the critical residues responsible for the interactions of donors and acceptors with the BoGGT and provides a new understanding of the substrate selectivity and catalytic mechanism of GGT.

Potential of Food Protein-Derived Bioactive Peptides against Sarcopenia: A Comprehensive Review

Sarcopenia is an age-related progressive muscle disorder characterized by accelerated loss of muscle mass, strength, and function, which are important causes of physiological dysfunctions in the elderly. At present, the main alleviating method includes protein supplements to stimulate synthesis of muscle proteins. Food protein-derived peptides containing abundant branched-chain amino acids have a remarkable effect on the improvement of sarcopenia. Understanding the underlying molecular mechanism and clarifying the structure-activity relationship is essential for the mitigation of sarcopenia. This present review recaps the epidemiology, pathogenesis, diagnosis, and treatment of sarcopenia, which facilitates a comprehensive understanding of sarcopenia. Moreover, the latest research progress on food-derived antisarcopenic peptides is reviewed, including their antisarcopenic activity, molecular mechanism as well as structural characteristics. Food-derived bioactive peptides can indeed alleviate/mitigate sarcopenia. These antisarcopenic peptides play a pivotal role mainly by activating the PI3K/Akt/mTOR and MAPK pathways and inhibiting the ubiquitin-proteasome system and AMPK pathway, thus promoting the synthesis of muscle proteins and inhibiting their degradation. Antisarcopenic peptides alleviate sarcopenia via specific peptides, which may be absorbed into the circulation and exhibit their bioactivity in intact forms. The present review provides a theoretical reference for mitigation and prevention of sarcopenia by food protein-derived bioactive peptides.

Isolation, identification and sensory evaluation of kokumi peptides from by-products of enzyme-modified butter

BACKGROUND

Enzyme-modified butter is used as a common raw material to obtain a natural milk flavor. Butter protein is a by-product in butter processing that can be used as substrate to produce taste-active peptides, which can create additional value and new application opportunities, making the method more environmentally friendly.

RESULTS

Putative kokumi peptides from hydrolysates of protein by-products were isolated by gel filtration chromatography and reversed-phase high-performance liquid chromatography. The isolated peptide fraction with the most pronounced kokumi taste was screened by sensory evaluation and electronic tongue analysis. Eleven peptides were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Six peptides were synthesized to verify their taste characteristics. Five synthetic peptides (FTKK, CKEVVRNANE, EELNVPG, VPNSAEER and YPVEPFTER) showed different intensity levels of kokumi taste. Of these peptides, the decapeptide CKEVVRNANE had the highest kokumi intensity.

CONCLUSION

The newly identified kokumi peptides increased the kokumi taste intensity and showed some synergistic effect with umami taste. Both termini of the peptides seem to play an important role in taste characteristic. Glu residue at both termini can increase the kokumi taste intensity. This work indicated that it was feasible to produce kokumi peptides by enzymatic hydrolysis of the protein by-products of butter. © 2022 Society of Chemical Industry.

Production of Corn Protein Hydrolysate with Glutamine-Rich Peptides and Its Antagonistic Function in Ulcerative Colitis In Vivo

Ulcerative colitis is a typical chronic inflammatory disease of the gastrointestinal tract, which has become a serious hazard to human health. The purpose of the present study was to evaluate the antagonistic effect of corn protein hydrolysate with glutamine-rich peptides on ulcerative colitis. The sequential hydrolysis of corn gluten meal by Alcalase and Protamex was conducted to prepare the hydrolysate, and then the mouse ulcerative colitis model induced by dextran sulfate sodium was applied to evaluate its biological activities. The results indicated that the hydrolysate significantly improved weight loss (p < 0.05), reduced the colonic shortening and the disease activity index, diminished the infiltration of inflammatory cells in the colonic tissue, and reduced the permeability of the colonic mucosa in mice. In addition, the hydrolysate decreased the contents of pro-inflammatory factors IL-1β, IL-6, and TNF-α, increased the anti-inflammatory factor IL-10 and oxidative stress markers GSH-Px and SOD in the animal tests. Moreover, the hydrolysate also regulated the abundance and diversity of the intestinal microbiota, improved the microbiota structure, and increased the content of beneficial bacteria including Lactobacillus and Pediococcus. These results indicated that the hydrolysate might be used as an alternative natural product for the prevention of ulcerative colitis and could be further developed into a functional food.

Protein Hydrolysates from Pleurotus geesteranus Modified by Bacillus amyloliquefaciens γ-Glutamyl Transpeptidase Exhibit a Remarkable Taste-Enhancing Effect

Long-term high salt intake exerts a negative impact on human health. The excessive use of sodium substitutes in the food industry can lead to decreased sensory quality of food. γ-Glutamyl peptides with pronounced taste-enhancing effects can offer an alternative approach to salt reduction. However, the content and yield of γ-glutamyl peptides in natural foods are relatively low. Enzyme-catalyzed synthesis of γ-glutamyl peptides provides a feasible solution. In this study, Pleurotus geesteranus was hydrolyzed by Flavourzyme to generate protein hydrolysates. Subsequently, they were modified by Bacillus amyloliquefaciens γ-glutamyl transpeptidase to generate γ-glutamyl peptides. The reaction conditions were optimized and their taste-enhancing effects were evaluated. Their peptide sequences were identified by parallel reaction monitoring with liquid chromatography-tandem mass spectrometry and analyzed using molecular docking. The optimal conditions for generation of γ-glutamyl peptides were a pH of 10.0, an enzyme condition of 1.2 U/g, and a reaction time of 2 h, which can elicit a strong kokumi taste. Notably, it exhibited a remarkable taste-enhancing effect for umami intensity (76.07%) and saltiness intensity (1.23-fold). Several novel γ-glutamyl peptide sequences were found by liquid chromatography-tandem mass spectrometry, whereas the binding to the calcium-sensing receptor was confirmed by molecular docking analysis. Overall, γ-glutamyl peptides from P. geesteranus could significantly enhance the umami and salt tastes, which can serve as promising taste enhancers.

Global Metabolomics of Fireflies (Coleoptera: Lampyridae) Explore Metabolic Adaptation to Fresh Water in Insects

Aquatic insects are well-adapted to freshwater environments, but metabolic mechanisms of such adaptations, particularly to primary environmental factors (e.g., hypoxia, water pressure, dark light, and abundant microbes), are poorly known. Most firefly species (Coleoptera: Lampyridae) are terrestrial, but the larvae of a few species are aquatic. We generated 24 global metabolomic profiles of larvae and adults of Aquatica leii (freshwater) and Lychnuris praetexta (terrestrial) to identify freshwater adaptation-related metabolites (AARMs). We identified 110 differentially abundant metabolites (DAMs) in A. leii (adults vs. aquatic larvae) and 183 DAMs in L. praetexta (adults vs. terrestrial larvae). Furthermore, 100 DAMs specific to aquatic A. leii larvae were screened as AARMs via interspecific comparisons (A. leii vs. L. praetexta), which were primarily involved in antioxidant activity, immune response, energy production and metabolism, and chitin biosynthesis. They were assigned to six categories/superclasses (e.g., lipids and lipid-like molecules, organic acids and derivatives, and organoheterocyclic compound). Finally, ten metabolic pathways shared between KEGG terms specific to aquatic fireflies and enriched by AARMs were screened as aquatic adaptation-related pathways (AARPs). These AARPs were primarily involved in energy metabolism, xenobiotic biodegradation, protection of oxidative/immune damage, oxidative stress response, and sense function (e.g., glycine, serine and threonine metabolism, drug metabolism-cytochrome P450, and taste transduction), and certain aspects of morphology (e.g., steroid hormone biosynthesis). These results provide evidence suggesting that abundance changes in metabolomes contribute to freshwater adaptation of fireflies. The metabolites identified here may be vital targets for future work to determine the mechanism of freshwater adaptation in insects.

Peptide profile of Parmigiano Reggiano cheese after simulated gastrointestinal digestion: From quality drivers to functional compounds

Time of ripening has a strong impact on shaping the valuable and recognizable characteristics of long-ripened types of cheese such as Parmigiano Reggiano (PR) due to the interrelationship between microbiota and proteolysis that occurs during ripening. The derived peptide profile is linked to cheese quality and represents the canvas for enzymes upon digestion, which could be responsible for the release of potentially bioactive peptides (BPs). In this study, we aimed at investigating the presence of BP in 72 PR cheese samples of different ripening times, from curd to 24 months of ripening, produced in six different dairies, and following their fate after simulated gastrointestinal digestion. A small number of peptide sequences sharing 100% similarity with known antimicrobial, antioxidant, and ACE-inhibitor sequences were found in PR cheeses, while a higher number of potential BPs were found after their simulated gastrointestinal digestion, in different amounts according to ripening time. Taking advantage of the complex organization of the sampling plan, we were able to follow the fate of peptides considered quality drivers during cheese ripening to their release as functional compounds upon digestion.

Comprehensive Review of γ-Glutamyl Peptides (γ-GPs) and Their Effect on Inflammation Concerning Cardiovascular Health

γ-Glutamyl peptides (γ-GPs) are a group of peptides naturally found in various food sources. The unique γ-bond potentially enables them to resist gastrointestinal digestion and offers high stability in vivo with a longer half-life. In recent years, these peptides have caught researchers' attention due to their ability to impart kokumi taste and elicit various physiological functions via the allosteric activation of the calcium-sensing receptor (CaSR). This review discusses the various food sources of γ-glutamyl peptides, different synthesis modes, allosteric activation of CaSR for taste perception, and associated multiple biological functions they can exhibit, with a special emphasis on their role in modulating chronic inflammation concerning cardiovascular health.

An updated review of functional properties, debittering methods, and applications of soybean functional peptides

Soybean functional peptides (SFPs) are obtained via the hydrolysis of soybean protein into polypeptides, oligopeptides, and a small amount of amino acids. They have nutritional value and a variety of functional properties, including regulating blood lipids, lowering blood pressure, anti-diabetes, anti-oxidant, preventing COVID-19, etc. SFPs have potential application prospects in food processing, functional food development, clinical medicine, infant milk powder, special medical formulations, among others. However, bitter peptides containing relatively more hydrophobic amino acids can be formed during the production of SFPs, seriously restricting the application of SFPs. High-quality confirmatory human trials are needed to determine effective doses, potential risks, and mechanisms of action, especially as dietary supplements and special medical formulations. Therefore, the physiological activities and potential risks of soybean polypeptides are summarized, and the existing debitterness technologies and their applicability are reviewed. The technical challenges and research areas to be addressed in optimizing debittering process parameters and improving the applicability of SFPs are discussed, including integrating various technologies to obtain higher quality functional peptides, which will facilitate further exploration of physiological mechanism, metabolic pathway, tolerance, bioavailability, and potential hazards of SFPs. This review can help promote the value of SFPs and the development of the soybean industry.

Enzymatic hydrolysis and microbial fermentation: The most favorable biotechnological methods for the release of bioactive peptides

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Peptide release methods influence its bioactivity by generating different sequences.

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The absorption, toxicity and taste of peptides is influenced by the production method.

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The most used methods are enzymatic hydrolysis and microbial fermentation.

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The most used methods are biotechnological and differ in their process.

Bioactive peptides are biomolecules derived from proteins. They contain anywhere from 2 to 20 amino acids and have different bioactivities. For example, they have antihypertensive activity, antioxidant activity, antimicrobial activity, etc. However, bioactive peptides are encrypted and inactive in the parental protein, so it is necessary to release them to show their bioactivity. For this, there are different methods, where biotechnological methods are highly favorable, highlighting enzymatic hydrolysis and microbial fermentation.

The choice of the method to be used depends on different factors, which is why it is essential to know about the process, its principle, and its advantages and disadvantages. The process of peptide release is critical to generate various peptide sequences, which will produce different biological effects in the hydrolysate. This review focuses on providing extensive information on the enzymatic method and microbial fermentation to facilitate selecting the method that provides the most benefits.