Ultrasonication increases γ‐aminobutyric acid accumulation in coffee leaves and affects total phenolic content and angiotensin‐converting enzyme inhibitory activity

Regulation and mechanism of enzyme metabolism in germinated hemp seeds by ultrasound combined with exogenous calcium chloride treatment

γ-aminobutyric acid (GABA) plays an important role in anti-anxiety by inhibiting neurotransmitter in the central nervous system (CNS) of mammals, which is generated in the germinating seeds. The key enzymes activity of GABA metabolism pathway and nutrients content in hemp seeds during germination were studied after treated with ultrasound and CaCl2. The mechanism of exogenous stress on key enzymes in GABA metabolism pathway was investigated by molecular dynamics simulation. The results showed that ultrasonic combined with 1.5 mmol·L-1CaCl2 significantly increased the activities of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) in seeds, and promoted the conversion of glutamate to GABA, resulting in the decrease of glutamate content and the accumulation of GABA. Molecular dynamics simulations revealed that Ca2+ environment enhanced the activity of GAD and GABA-T enzymes by altering their secondary structure, exposing their hydrophobic residues. Ultrasound, germination and CaCl2 stress improved the nutritional value of hemp seeds.

Characterization of kombucha prepared from black tea and coffee leaves: A comparative analysis of physiochemical properties, bioactive components, and bioactivities

The utilization of coffee leaves in kombucha production has intrigued researchers; however, the lack of understanding regarding the characteristics of coffee leaf kombucha (CK) and its differentiation from black tea kombucha (BK) has impeded its application in the beverage industry. Therefore, this study aimed to characterize and compare the physiochemical properties, phytochemical compositions, antioxidant activity, and α-glucosidase inhibitory ability of kombucha prepared from the leaves of Coffea arabica (CK) and black tea (Camellia sinensis, BK) and their extracts (CT and BT). After fermentation, pH and the contents of total sugars, reducing sugars, and free amino acids of BK and CK were decreased, whereas the levels of total acids and organic acids, such as gluconic, lactic, and acetic acid were increased. Notably, the concentration of vitamin C in CK was 48.9% higher than that in BK. HPLC analysis exhibited that 5-caffeoylquinic acid in CT was significantly decreased by 48.0% in CK, whereas the levels of 3-caffeoylquinic acid and 4-caffeoylquinic acid were significantly increased after fermentation. The content of caffeine was significantly (p < 0.05) reduced by 9.5% and 22.0% in BK and CK, respectively, whereas the theobromine level was significantly increased in CK. Notably, CK has superior total phenolic and flavonoid contents and antioxidant activity than BK, whereas BK possesses higher α-glucosidase inhibitory capacity. Electronic nose analysis demonstrated that sulfur-containing organics were the main volatiles in both kombuchas, and fermentation significantly increased their levels. Our study indicates that coffee leaves are a promising resource for preparing kombucha. PRACTICAL APPLICATION: This article investigates the differences in physicochemical properties, bioactive constituents, antioxidant activity, and α-glucosidase inhibitory activity of kombucha preparation from black tea and coffee leaves. We have found that after fermentation BK had brighter soup color and higher α-glucosidase inhibitory capacity, whereas CK had higher levels of total phenols, flavonoids, vitamin C, and antioxidants and lower contents of sugars. This study provides valuable information for the preparation of CK with high-quality attributes and antioxidant activity.

Recent advances in the biosynthesis and industrial biotechnology of Gamma-amino butyric acid

GABA (Gamma-aminobutyric acid), a crucial neurotransmitter in the central nervous system, has gained significant attention in recent years due to its extensive benefits for human health. The review focused on recent advances in the biosynthesis and production of GABA. To begin with, the investigation evaluates GABA-producing strains and metabolic pathways, focusing on microbial sources such as Lactic Acid Bacteria, Escherichia coli, and Corynebacterium glutamicum. The metabolic pathways of GABA are elaborated upon, including the GABA shunt and critical enzymes involved in its synthesis. Next, strategies to enhance microbial GABA production are discussed, including optimization of fermentation factors, different fermentation methods such as co-culture strategy and two-step fermentation, and modification of the GABA metabolic pathway. The review also explores methods for determining glutamate (Glu) and GABA levels, emphasizing the importance of accurate quantification. Furthermore, a comprehensive market analysis and prospects are provided, highlighting current trends, potential applications, and challenges in the GABA industry. Overall, this review serves as a valuable resource for researchers and industrialists working on GABA advancements, focusing on its efficient synthesis processes and various applications, and providing novel ideas and approaches to improve GABA yield and quality.

Mechanistic study on the inhibition of α-amylase and α-glucosidase using the extract of ultrasound-treated coffee leaves

BACKGROUND

Our previous studies have shown that ultrasound-treated γ-aminobutyric acid (GABA)-rich coffee leaves have higher angiotensin-I-converting enzyme inhibitory activity than their untreated counterpart. However, whether they have antidiabetic activity remains unknown. In this study, we aimed to investigate the inhibitory activities of coffee leaf extracts (CLEs) prepared with ultrasound (CLE-U) or without ultrasound (CLE-NU) pretreatment on α-amylase and α-glucosidase. Subsequently, we evaluated the binding interaction between CLE-U and both enzymes using multi-spectroscopic and in silico analyses.

RESULTS

Ultrasound pretreatment increased the inhibitory activities of CLE-U against α-amylase and α-glucosidase by 21.78% and 25.13%, respectively. CLE-U reversibly inhibits both enzymes, with competitive inhibition observed for α-amylase and non-competitive inhibition for α-glucosidase. The static quenching of CLE-U against both enzymes was primarily driven by hydrogen bond and van der Waals interactions. The α-helices of α-amylase and α-glucosidase were increased by 1.8% and 21.3%, respectively. Molecular docking results showed that the key differential compounds, including mangiferin, 5-caffeoylquinic acid, rutin, trigonelline, GABA, caffeine, glutamate, and others, present in coffee leaves interacted with specific amino acid residues located at the active site of α-amylase (ASP197, GLU233, and ASP300). The binding of α-glucosidase and these bioactive components involved amino acid residues, such as PHE1289, PRO1329, and GLU1397, located outside the active site.

CONCLUSION

Ultrasound-treated coffee leaves are potential anti-diabetic substances, capable of preventing diabetes by inhibiting the activities of α-amylase and α-glucosidase, thus delaying starch digestion. Our study provides valuable information to elucidate the possible antidiabetic capacity of coffee leaves through the inhibition of α-amylase and α-glucosidase activities. © 2023 Society of Chemical Industry.

Proposing Signaling Molecules as Key Optimization Targets for Intensifying the Phytochemical Biosynthesis Induced by Emerging Nonthermal Stress Pretreatments of Plant-Based Foods: A Focus on γ-Aminobutyric Acid

Emerging evidence has confirmed the role of emerging nonthermal stressors (e.g., electromagnetic fields, ultrasonication, plasma) in accumulating bioactive metabolites in plant-based food. However, the signal decoding mechanisms behind NonTt-driven phytochemical production remain unclear, hindering postharvest bioactive component intensification. This study aims to summarize the association between signaling molecules and bioactive secondary metabolite production under nonthermal conditions, demonstrating the feasibility of enhancing phytochemical accumulation through signaling molecule crosstalk manipulation. Nonthermal elicitors were found to be capable of inducing stress metabolisms and activating various signaling molecules, similar to conventional abiotic stress. A simplified pathway model for nonthermally induced γ-aminobutyric acid accumulation was proposed with reactive oxygen species and calcium signaling being versatile pathways responsive to nonthermal elicitors. Manipulating signal molecules/pathways under nonthermal conditions can intensify phytochemical biosynthesis. Further research is needed to integrate signaling molecule responses and metabolic network shifts in nonthermally stressed plant-based matrices, balancing quality modifications and intensification of food functionality potential.

Coffee leaf extract exhibits anti-obesity property and improves lipid metabolism in high-fat diet-induced C57BL6 obese mice

In the present study, the effect of coffee leaf extract (CLE) on in vitro enzyme inhibition was studied. Furthermore, its impact on the high-fat diet (HFD)-induced obese mice (C57BL/6) at the levels of 100 and 200 mg/kg body weight along with positive control (orlistat) and the normal group maintained with starch-fed diet (SFD) was observed. CLE had significant α amylase and lipase enzyme inhibitory properties. In HFD-induced obese mice, treatment with CLE significantly reduced the body weight gain. The investigation demonstrated that CLE administration lowered blood glucose, total cholesterol, total triglycerides and LDL levels while increasing the HDL levels. It reduced the development of fatty liver by reducing hepatic fat accumulation and decreased the fat cell size in the adipose tissue. Further, CLE significantly increased the liver antioxidant enzyme activities and lowered the levels of hepatotoxicity markers in the serum when compared to the HFD-fed mice. The treatment also downregulated the mRNA expression of lipogenic transcription factors (SREBP-1c, CEBP-α) and enzymes (ACC, FAS) than HFD. Overall, the results indicate that coffee leaves have anti-obesity potential and can be used as functional ingredients in the development of innovative products for managing lifestyle disorders such as obesity.

Identification of differential volatile and non-volatile compounds in coffee leaves prepared from different tea processing steps using HS-SPME/GC-MS and HPLC-Orbitrap-MS/MS and investigation of the binding mechanism of key phytochemicals with olfactory and taste receptors using molecular docking

Tea processing steps affected the proximate composition, enzyme activity and bioactivity of coffee leaves; however, the effects of different tea processing steps on the volatiles, non-volatiles, color, and sensory characteristics of coffee leaves have yet been demonstrated. Here the dynamic changes of volatile and non-volatile compounds in different tea processing steps were investigated using HS-SPME/GC-MS and HPLC-Orbitrap-MS/MS, respectively. A total of 53 differential volatiles (alcohol, aldehyde, ester, hydrocarbon, ketone, oxygen heterocyclic compounds, phenol, and sulfur compounds) and 50 differential non-volatiles (xanthone, flavonoid, organic acid, amino acid, organic amine, alkaloid, aldehyde, and purine et al.) were identified in coffee leaves prepared from different processing steps. Kill-green, fermentation, and drying steps significantly influenced the volatiles; however, kill-green, rolling, and drying steps significantly affected the color of coffee leaves and their hot water infusion. The coffee leaf tea that was prepared without the kill-green process was found to have a more pleasant taste as compared to the tea that was prepared with the kill-green process. This can be attributed to the fact that the former contained lower levels of flavonoids, chlorogenic acid, and epicatechin, but had higher levels of floral, sweet, and rose-like aroma compounds. The binding interactions between the key differential volatile and non-volatile compounds and the olfactory and taste receptors were also investigated. The key differential volatiles, pentadecanal and methyl salicylate generate fresh and floral odors by activating olfactory receptors, OR5M3 and OR1G1, respectively. Epicatechin showed a high affinity to the bitter receptors, including T2R16, T2R14, and T2R46. Since the specific content of differential compounds in different samples varies greatly, the dose-effect and structure-function relationships of these key compounds and the molecular mechanism of the odor and taste of coffee leaf tea need to be further studied.

Ultrasonic treatment to enhance seed germination and vigour of wheat (Triticum durum) in association with γ-aminobutyric acid (GABA) shunt pathway

Treatments of wheat (Triticum durum L.) seeds with sonication or hydropriming may enhance seed germination and vigour in association with γ-aminobutyric acid (GABA). Therefore, the objective of this study is to examine the effect of sonication and hydropriming treatments on seed germination of wheat through the characterisation of seed germination performance, GABA shunt metabolite level (GABA, glutamate, and alanine), and the level of glutamate decarboxylase (GAD) mRNA transcription. Wheat seeds were exposed to three treatments for 0, 5, 10, 15, and 20min: (1) sonication with water; (2) sonication without water; and (3) hydropriming without sonication. Treated seeds were evaluated for germination percentage, mean time to germinate, germination rate index in the warm germination test, and seedling emergence and shoot length in the cold test. GABA shunt metabolites level (GABA, glutamate, and alanine), and the level of GAD mRNA transcription were measured for the seeds after treatments and for seedlings during germination and cold tests. Seeds treated with sonication or hydropriming treatments had a higher germination rate index (faster germination) in the standard germination test, and higher seedling emergence and shoot length in the cold test. Seeds treated with sonication or hydropriming treatments showed an enhancement in GABA shunt and their metabolites (alanine and glutamate), and GAD mRNA transcription level compared to untreated-control seeds. In conclusion, the sonication or hydropriming treatments significantly improved the germination performance of wheat and enhanced GABA metabolism to maintain the C:N metabolic balance, especially under cold stress.

The Effects of Gamma-Aminobuytric Acid (GABA) Enrichment on Nutritional, Physical, Shelf-Life, and Sensorial Properties of Dark Chocolate

Hypertension is the leading cause of cardiovascular disease and premature death worldwide. Gamma-aminobutyric acid (GABA) has potential in regulating hypertension. Cocoa beans are rich in GABA, but GABA is being destroyed during roasting of cocoa beans and chocolate production. This study aimed to develop GABA-enriched dark chocolate by partially replacing sugar syrup with pure GABA powder at concentrations of 0.05 (F1), 0.10 (F2), and 0.15% (F3). The chocolate samples were incorporated with GABA after the heating and melting process of cocoa butter to maintain the viability and functionality of the GABA in the final product. The effects of GABA enrichment on the quality of chocolate in terms of nutritional, physical, shelf-life, and sensorial properties were studied. The inclusion of 0.15% GABA significantly increased the GABA content and angiotensin-converting-enzyme (ACE) inhibitory effect of chocolate. The nutritional compositions of the control and GABA-enriched chocolates were almost similar. The addition of GABA significantly increased the hardness but did not affect the apparent viscosity and melting properties of chocolate. Accelerated shelf-life test results showed that all the chocolates stored at 20 and 30 °C were microbiologically safe for consumption for at least 21 days. Among the GABA-enriched chocolates, panellists preferred F2 the most followed by F3 and F1, owing to the glossiness and sweetness of F2. F3 with the highest GABA content (21.09 mg/100 g) and ACE inhibitory effect (79.54%) was identified as the best GABA-enriched dark chocolate.

Effects of hot-air drying on the bioactive compounds, quality attributes, and drying and color change kinetics of coffee leaves

Drying is a key step that affects the chemical composition and quality of tea. In the present study, we reported the impacts of drying temperature and time on drying and color change kinetics, phytochemical composition, antioxidant activity, and surface microstructure of coffee leaves during hot-air drying. The results showed that drying temperature was positively (p < 0.05) correlated with the drying rate (DR), color index a* and total color change ΔE, and total soluble sugar (TSS), while negatively correlated with color indexes b* and L*, soluble protein content, and the DPPH scavenging capacity. Drying time has similar impacts on the color indexes and soluble protein as drying temperature. The content of total free amino acid and TSS increased by 62.5% and 47.4%, respectively, when coffee leaves were dried at 160°C for 24 min, under which the total phenolic content and DPPH and ABTS scavenging capacities reached the maximum of 108.04 mg GAE/g, 515.07 µmol Trolox/g, and 606.70 µmol Trolox/g, respectively. Drying significantly decreased the contents of chlorogenic acids and mangiferin and antioxidant activity, while high-temperature short-time drying helped retain phenolic compounds in coffee leaves. The DR fitted Page kinetic model. The color changes fitted the first-order kinetic models and the activation energies ranged from 16.00 to 31.06 kJ·mol^-1 . Prolonged drying time caused serious wrinkles on the surface of coffee leaves and the stomata closed. PRACTICAL APPLICATION: Drying decreased soluble protein while increasing free amino acid and soluble sugar. High-temperature short-time drying helps retain phenolics in the coffee leaves. The color change of coffee leaves during drying follows first-order kinetic. Prolonged drying time resulted in loosened texture of coffee leaves. Our study suggested that drying coffee leaves at 160°C for 24 min results in the coffee leaf tea being of better quality.

Individual and synergistic effect of multi-frequency ultrasound and electro-infrared pretreatments on polyphenol accumulation and drying characteristics of edible roses

The freeze-dried (FD) edible roses with high content of bioactive substances and superior flavor have been favored by consumers. Nevertheless, the development of freeze-dried rose industry has been plagued by a long drying time and low efficiency. This study investigated the effects of ultrasonic pretreatment (UP) in multi-frequency modes and electro-infrared pretreatment (EIP) prior to FD on polyphenol accumulation and drying characteristics of roses. The mechanism was explored by the changes in microstructure, equivalent circuit parameters, and phenol identifications of rose. The results showed that the FD time of roses decreased by 26 % after ultrasonic-infrared sequential synergistic pretreatment (UP + EIP) due to the damage of cell membrane permeability from UP. The quality attributes of UP + EIP products including color, phenols, and antioxidant activity (DPPH and ABTS radical scavenging rates) remarkably improved. UP + EIP significantly (p < 0.05) increased the content of polyphenols, namely quercetin-3β-d-glucoside, phlorizin, procyanidin B₂, gallicacid, and rutin in the FD roses quantified by ultra-high performance liquid chromatography-quadrupole time of flight mass spectrometry (UPLC-qTOF-MS/MS). Therefore, UP + EIP is an effective pretreatment method for shortening FD time and producing high-quality FD rose products with enhanced polyphenol content.

Recent advances of γ-aminobutyric acid: Physiological and immunity function, enrichment, and metabolic pathway

γ-aminobutyric acid (GABA) is a non-protein amino acid which naturally and widely occurs in animals, plants, and microorganisms. As the chief inhibitory neurotransmitter in the central nervous system of mammals, it has become a popular dietary supplement and has promising application in food industry. The current article reviews the most recent literature regarding the physiological functions, preparation methods, enrichment methods, metabolic pathways, and applications of GABA. This review sheds light on developing GABA-enriched plant varieties and food products, and provides insights for efficient production of GABA through synthetic biology approaches.

Ultrasound accelerated γ-aminobutyric acid accumulation in coffee leaves through influencing the microstructure, enzyme activity, and metabolites

Gamma-aminobutyric acid (GABA) is a non-protein amino acid that possesses various physiological functions. Our previous study has shown that ultrasound increased GABA accumulation in coffee leaves. In this study, we aimed to uncover the GABA enrichment mechanism by investigating the surface microstructure, cellular permeability, enzyme activities, and metabolomics of coffee leaves under ultrasound treatment. The results showed that ultrasound increased the electrical conductivity and the activities of glutamate decarboxylase, γ-aminoaldehyde dehydrogenase, and diamine oxidase by 12.0%, 265.9%, 124.1%, 46.8%, respectively. Environmental scanning electron microscope analysis demonstrated an increased opening of stomata and the rougher surface in the leaves after ultrasound treatment. UPLC-qTOF-MS/MS-based untargeted metabolomics analysis identified 82 differential metabolites involved in various metabolism pathways. Our results indicated that ultrasound changed the surface microstructure of coffee leaves, thereby accelerating the migration of glutamate into the cells; activated related enzymes; regulated C/N metabolism pathways, which led to an increase of GABA.

Zinc oxide nanoparticles synthesized using coffee leaf extract assisted with ultrasound as nanocarriers for mangiferin

Plant extracts have been widely used to green synthesize zinc oxide nanoparticles (ZnO NPs); however, how the combination of ultrasound and coffee leaf extract (CLE) affects the structure characteristics and the yield of ZnO NPs remains unknown. In this study, we used CLE to green synthesize ZnO NPs with the help of ultrasound. The highest yield (43.59 ± 0.13%) of ZnO NPs was obtained under the optimal processing conditions of pH = 8.0, mass ratio of coffee leaves to C₄H₆O₄Zn•2H₂O = 1.71, ultrasound time = 10 min, ultrasound frequency = 28/40 kHz, ultrasound power = 180 W, and synthesis temperature = 30 °C. The as-synthesized ZnO NPs were characterized by UV–Vis, SEM, EDX, TEM, FTIR, XRD, and zeta potential analyses. SEM and TEM analyses revealed that ZnO NPs synthesized using ultrasound-assisted method were spherical with an average particle size of 8.29 ± 1.38 nm, which was smaller than ZnO NPs synthesized without ultrasound treatment (10.48 ± 1.57 nm) and the chemically synthesized ZnO NPs (17.15 ± 2.84 nm). HPLC analysis showed that the phenolic compounds in coffee leaves, especially 5-CQA, were the main reductants and chelating agents for ZnO NPs synthesis. The synthesized ZnO NPs were used to load mangiferin, which was control released under pH 7.4 over 132 h. Our study provides an easy and eco-friendly method using CLE assisted with ultrasound for green synthesis of ZnO NPs which can be used as nanocarriers to control release of mangiferin.

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Ultrasound increased the yield of ZnO NPs synthesized using coffee leaf extract.

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Ultrasound reduced the particle size and increased the stability of ZnO NPs.

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5-CQA was the main reductant for ZnO NPs synthesis.

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Caffeine and trigonelline were less potent reductants for ZnO NPs synthesis.

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Mangiferin loaded ZnO NPs can achieve long-term controlled release at pH 7.4.

The effects of ultrasonication on the phytochemicals, antioxidant, and polyphenol oxidase and peroxidase activities in coffee leaves

In the present study, we investigated the impacts of ultrasonic conditions on the phytochemical profiles, antioxidant activity, and polyphenol oxidase (PPO) and peroxidase (POD) activities in coffee leaves. Ultrasonic frequency, power, and time, pH, and incubation time affected PPO and POD differently, thus resulting in different ABTS scavenging capacity and phenolic content in coffee leaves. Triple-frequency (20/35/50 kHz) ultrasound significantly (P < 0.05) inhibited trigonelline, caffeine, mangiferin, rutin, chlorogenic acids, antioxidant activity, and PPO activity, while the single frequency of 35 kHz increased the phenolics compounds, which was associated with the lowest POD activity. Increasing the incubation time after ultrasonication gradually decreased phenolic compounds and antioxidant activities, however, POD activity followed a temporal pattern of first increase and then decrease. Our results showed that PPO and POD were temporally inactivated after ultrasonication, which leading to the continuous decrease of phenolics in coffee leaves.