Starch digested product analysis by HPAEC reveals structural specificity of flavonoids in the inhibition of mammalian α-amylase and α-glucosidases

Structure-function relationships in (poly)phenol-enzyme binding: Direct inhibition of human salivary and pancreatic α-amylases

(Poly)phenols inhibit α-amylase by directly binding to the enzyme and/or by forming starch-polyphenol complexes. Conventional methods using starch as the substrate measure inhibition from both mechanisms, whereas the use of shorter oligosaccharides as substrates exclusively measures the direct interaction of (poly)phenols with the enzyme. In this study, using a chromatography-based method and a short oligosaccharide as the substrate, we investigated the detailed structural prerequisites for the direct inhibition of human salivary and pancreatic α-amylases by over 50 (poly)phenols from the (poly)phenol groups: flavonols, flavones, flavanones, flavan-3-ols, polymethoxyflavones, isoflavones, anthocyanidins and phenolic acids. Despite being structurally very similar (97% sequence homology), human salivary and pancreatic α-amylases were inhibited to different extents by the tested (poly)phenols. The most potent human salivary α-amylase inhibitors were luteolin and pelargonidin, while the methoxylated anthocyanidins, peonidin and petunidin, significantly blocked pancreatic enzyme activity. B-ring methoxylation of anthocyanidins increased inhibition against both human α-amylases while hydroxyl groups at C3 and B3' acted antagonistically in human salivary inhibition. C4 carbonyl reduction, or the positive charge on the flavonoid structure, was the key structural feature for human pancreatic inhibition. B-ring glycosylation did not affect salivary enzyme inhibition, but increased pancreatic enzyme inhibition when compared to its corresponding aglycone. Overall, our findings indicate that the efficacy of interaction with human α-amylase is mainly influenced by the type and placement of functional groups rather than the number of hydroxyl groups and molecular weight.

Undescribed Cyclohexene and Benzofuran Alkenyl Derivatives from Choerospondias axillaris, a Potential Hypoglycemic Fruit

The fruit of Choerospondias axillaris (Anacardiaceae), known as south wild jujube in China, has been consumed widely in several regions of the world to produce fruit pastille and leathers, juice, jam, and candy. A comprehensive chemical study on the fresh fruits led to the isolation and identification of 18 compounds, including 7 new (1-7) and 11 known (8-18) comprised of 5 alkenyl (cyclohexenols and cyclohexenones) derivatives (1-5), 3 benzofuran derivatives (6-8), 6 flavonoids (9-14) and 4 lignans (15-18). Their structures were elucidated by extensive spectroscopic analysis. The known lignans 15-18 were isolated from the genus Choerospondias for the first time. Most of the isolates exhibited significant inhibitory activity on α-glucosidase with IC50 values from 2.26 ± 0.06 to 43.9 ± 0.96 μM. Molecular docking experiments strongly supported the potent α-glucosidase inhibitory activity. The results indicated that C. axillaris fruits could be an excellent source of functional foods that acquire potential hypoglycemic bioactive components.

Characterization of Various Noncovalent Polyphenol-Starch Complexes and Their Prebiotic Activities during In Vitro Digestion and Fermentation

This study explores the structural characterization of six noncovalent polyphenol-starch complexes and their prebiotic activities during in vitro digestion and fermentation. Ferulic acid, caffeic acid, gallic acid, isoquercetin, astragalin, and hyperin were complexed with sweet potato starch (SPS). The polyphenols exhibited high binding capacity (>70%) with SPS. A partial release of flavonoids from the complexes was observed via in vitro digestion, while the phenolic acids remained tightly bound. Molecular dynamics (MD) simulation revealed that polyphenols altered the spatial configuration of polysaccharides and intramolecular hydrogen bonds formed. Additionally, polyphenol-SPS complexes exerted inhibitory effects on starch digestion compared to gelatinized SPS, owing to the increase in resistant starch fraction. It revealed that the different complexes stimulated the growth of Lactobacillus rhamnosus and Bifidobacterium bifidum, while inhibiting the growth of Escherichia coli. Moreover, in vitro fermentation experiments revealed that complexes were utilized by the gut microbiota, resulting in the production of short-chain fatty acids and a decrease in pH. In addition, the polyphenol-SPS complexes altered the composition of gut microbiota by promoting the growth of beneficial bacteria and decreasing pathogenic bacteria. Polyphenol-SPS complexes exhibit great potential for use as a prebiotic and exert dual beneficial effects on gut microbiota.

Synergistic modification of ultrasound and bamboo leaf flavonoid on the rheological properties, multi-scale structure, and in vitro digestibility of pea starch

In this study, the effect of ultrasonic treatment (UT), bamboo leaf flavonoid (BLF), ultrasonic treatment prior to bamboo leaf flavonoid (UT-BLF), and bamboo leaf flavonoid prior to the ultrasonic treatment (BLF-UT) on the rheological properties, multi-scale structure, and digestibility of pea starch (PS) were investigated. The morphology and crystal structure of starch granules were destroyed by UT, thereby promoting starch retrogradation and digestion. The binding between BLF and starch through hydrophobic interactions and hydrogen bonds inhibited the interaction between starch molecular chains and impaired their double helix structure, thus effectively retarding starch retrogradation. The anti-digestibility of starch was enhanced after synergistic treatment. Compared with single treatment, synergistic treatment increased the ordered structure and gelatinization enthalpy of starch. In comparison with the UT-BLF group, the viscoelastic and thermal stability of BLF-UT group were improved with the increase in ordered structure. This study could provide valuable information for PS modification.

Theoretical Studies for the Discovery of Potential Sucrase-Isomaltase Inhibitors from Maize Silk Phytochemicals: An Approach to Treatment of Type 2 Diabetes

A theoretical analysis of the potential inhibition of human sucrase-isomaltase (SI) by flavonoids was carried out with the aim of identifying potential candidates for an alternative treatment of type 2 diabetes. Two compounds from maize silks, maysin and luteolin, were selected to be studied with the structure-based density functional theory (DFT), molecular docking (MDock), and molecular dynamics (MD) approaches. The docking score and MD simulations suggested that the compounds maysin and luteolin presented higher binding affinities in N-terminal sucrase-isomaltase (NtSI) than in C-terminal sucrase-isomaltase (CtSI). The reactivity parameters, such as chemical hardness (η) and chemical potential (µ), of the ligands, as well as of the active site amino acids of the NtSI, were calculated by the meta-GGA M06 functional in combination with the 6-31G(d) basis set. The lower value of chemical hardness calculated for the maysin molecule indicated that this might interact more easily with the active site of NtSI, in comparison with the values of the acarbose and luteolin structures. Additionally, a possible oxidative process was proposed through the quantum chemical calculations of the electronic charge transfer values (∆N) between the active site amino acids of the NtSI and the ligands. In addition, maysin displayed a higher ability to generate more oxidative damage in the NtSI active site. Our results suggest that maysin and luteolin can be used to develop novel α-glucosidase inhibitors via NtSI inhibition.

Inhibitory Mechanism of Quercimeritrin as a Novel α-Glucosidase Selective Inhibitor

In this study, 12 flavonoid glycosides were selected based on virtual screening and the literature, and Quercimeritrin was selected as the best selective inhibitor of α-glucosidase through in vitro enzyme activity inhibition experiments. Its IC50 value for α-glucosidase was 79.88 µM, and its IC50 value for α-amylase >250 µM. As such, it could be used as a new selective inhibitor of α-glucosidase. The selective inhibition mechanism of Quercimeritrin on the two starch-digesting enzymes was further explored, and it was confirmed that Quercimeritrin had a strong binding affinity for α-glucosidase and occupied the binding pocket of α-glucosidase through non-covalent binding. Subsequently, animal experiments demonstrated that Quercimeritrin can effectively control postprandial blood glucose in vivo, with the same inhibitory effect as acarbose but without side effects. Our results, therefore, provide insights into how flavone aglycones can be used to effectively control the rate of digestion to improve postprandial blood glucose levels.

Screening strategy for predominant phenolic components of digestive enzyme inhibitors in passion fruit peel extracts on simulated gastrointestinal digestion

BACKGROUND

The targeted biological activity of a natural product is often the result of the combined action of multiple functional components. Screening for predominant contributing components of targeting activity is crucial for quality evaluation.

RESULTS

Thirteen and nine phenolic compounds inhibiting α-glucosidase and α-amylase, respectively, were identified in the ethanol extracts of passion fruit peel through liquid chromatography-tandem mass spectrometry and multivariate analysis. Considering the different concentrations of components and their interactions, the role of the semi-inhibitory concentration (IC₅₀ ) in the dose-effect relationship is limited. We proposed the active contribution rate (ACR), which is the ratio of a single component concentration to its IC₅₀ in the whole, to assess the relative activity of each compound. Luteolin, quercetin, and vitexin exhibited a minimum IC₅₀ . Before the simulation of gastrointestinal digestion, quercetin, salicylic acid, and luteolin were identified as the dominant contributors to α-glucosidase inhibition according to ACR, while salicylic acid, 2,3-dihydroxybenzoic acid, and quercetin were identified as dominant contributors to α-amylase inhibition. After simulated digestion, the contents of all polyphenolic compounds decreased by various degrees. Salicylic acid, gentisic acid, and vitexin became the dominant inhibitors of α-glucosidase based on ACR (cumulative 57.96%), while salicylic acid and 2,3-dihydroxybenzoic acid became the dominant inhibitors of α-amylase (cumulative 84.50%).

CONCLUSION

Therefore, the ACR evaluation strategy can provide a quantitative reference for screening the predominant contributor components of a specific activity in complex systems. © 2022 Society of Chemical Industry.

Factors influencing the starch digestibility of starchy foods: A review

Starchy foods are a major energy source of the human diet, their digestion is closely related to human health. Most foods require lots of processing before eating, therefore, many factors can influence starch digestibility. The factors that affect the digestibility of starches have been widely discussed previously, but the extracted starches in those studies were different from those present within the actual food matrix. This review summarizes the factors influencing the starch digestibility in starchy foods. Endogenous non-starch components hinder the starch digestive process. Food ingredients and additives decrease starch digestibility by inhibiting the activity of digestive enzymes or hindering the contact between starch and enzymes. Storage induce the retrogradation of starch, decreasing the digestibility of foods. Therefore, preparing starchy foods with whole grains, processing them as little as possible, using food additives reasonably, and storage conditions may all be beneficial measures for the production of low GI foods.

Phytochemical profile and antioxidant capacity, α-amylase and α-glucosidase inhibitory activities of Oxalis pes-caprae extracts in alloxan-induced diabetic mice

Diabetes and its complications are closely correlated with chronic hyperglycemia, causing severe oxidative stress and leading to glycation reaction with formation of advanced glycation end products. However, medicinal plants are still a source of inspiration for the discovery of new treatments of several diseases, including diabetes. The present study was aimed to evaluate the antioxidant and antidiabetic properties of Oxalis pes-caprae flowers extract in alloxan-induced diabetic mice. The phytochemical and antioxidant activities of both aqueous and methanolic extracts were assessed by in-vitro testing such as free radical scavenging assays (DPPH and ABTS⁺), ferrous ions (Fe²⁺) chelating activity and reducing power assay. Additionally, the detection of Amadori products and advanced glycation end products was used to determine the antiglycation potential. α-glucosidase and α-amylase inhibitory assessment was employed to determine the antidiabetic effect, while alloxan-induced diabetic mice were used to measure the in-vivo activities of antioxidants and carbohydrates enzymes. The effect of the methanolic extract on body weight and blood glucose level of extract-treated diabetic mice were also investigated. Among the tested extract, the methanolic extract was the richest in phenolic compounds which is directly related with their remarkable antioxidant, enzyme inhibitory and antiglycation activity. The oral administration of the two doses of Oxalis pes-caprae flowers (150 mg/kg and 250 mg/kg) daily for 3 weeks resulted in hypoglycemic effect compared to the reference drug, glibenclamide (10 mg/kg). Furthermore, the extract was shown to significantly increase the activities of antioxidants and glycolysis enzymes in the liver, kidney and spleen of diabetic mice, compared to diabetic control group. Therefore, Oxalis pes-caprae extract effectively exhibited hypoglycemic and antidiabetic effects as indicated by in-vitro and in-vivo studies, confirming the protective effects on hyperglycemia and oxidative damage.

Molecular Characterization of Thymus capitellatus Extracts and Their Antioxidant, Neuroprotective and Anti-Proliferative Activities

Thymus capitellatus Hoffmanns & Link is an endemic species of the Iberian Peninsula listed as near-threatened, due to its restricted geographical distribution, occurring mainly in Portugal's mainland. In this work, we detail for the first time T. capitellatus extracts' phytochemical composition, as well as an evaluation of bioactivities to point out potential health benefits. Aqueous decoction (AD) and hydroethanolic (HE) extracts were obtained, both rich in flavonoids. However, quercetin-(?)-O-hexoside was identified as the main compound in T. capitellatus HE extract, while the phenolic acid rosmarinic acid was the main component of AD extracts. In addition, HE extract presents significant amounts of salvianolic acids and of the terpenoids oleanolic and ursolic acid. Both extracts showed antioxidant activity, evaluated by their capacity to scavenge ABTS and superoxide radicals, as well as an ability to prevent lipid peroxidation. AD extracts were also effective in scavenging hydroxyl and nitric oxide radicals. As potential functional foods, T. capitellatus extracts presented neuroprotective and anti-diabetic activity, in addition to time- and dose-dependent anti-proliferative activity against Caco-2 (colorectal adenocarcinoma) and HepG2 (hepatic carcinoma) cells. HE extract presented higher cytotoxicity than AD extract, and HepG2 cells were more resistant than Caco-2 cells. After 24 h exposure to HE extract, the IC₅₀ values were 330 μg/mL and 447 μg/mL for Caco-2 and HepG2 cells, respectively. T. capitellatus has potential as a functional food or as a source of bioactive molecules. These results also highlight the need to preserve species with as yet unknown molecular compositions and potential medicinal applications.

Measuring key human carbohydrate digestive enzyme activities using high-performance anion-exchange chromatography with pulsed amperometric detection

Carbohydrate digestion in the mammalian gastrointestinal tract is catalyzed by α-amylases and α-glucosidases to produce monosaccharides for absorption. Inhibition of these enzymes is the major activity of the drugs acarbose and miglitol, which are used to manage diabetes. Furthermore, delaying carbohydrate digestion via inhibition of α-amylases and α-glucosidases is an effective strategy to blunt blood glucose spikes, a major risk factor for developing metabolic diseases. Here, we present an in vitro protocol developed to accurately and specifically assess the activity of α-amylases and α-glucosidases, including sucrase, maltase and isomaltase. The assay is especially suitable for measuring inhibition by compounds, drugs and extracts, with minimal interference from impurities or endogenous components, because the substrates and digestive products in the enzyme activity assays are quantified directly by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD). Multiple enzyme sources can be used, but here we present the protocol using commercially available human α-amylase to assess starch hydrolysis with maltoheptaose as the substrate, and with brush border sucrase-isomaltase (with maltase, sucrase and isomaltase activities) derived from differentiated human intestinal Caco-2(/TC7) cells to assess hydrolysis of disaccharides. The wet-lab assay takes ~2-5 h depending on the number of samples, and the HPAE-PAD analysis takes 35 min per sample. A full dataset therefore takes 1-3 d and allows detection of subtle changes in enzyme activity with high sensitivity and reliability.

Changes in Phytochemical Profiles and Biological Activity of Olive Leaves Treated by Two Drying Methods

Olive leaves, which are the most abundant byproducts of the olive industry, offer multiple health benefits. The investigation of the phytochemical profiles and relevant biological activities is an essential step toward transforming these low-value byproducts into value-added ones. This study systematically investigated the phytochemical profiles, antioxidant capacity, and inhibition rates of olive leaves from four cultivars on the α-glucosidase, α-amylase, and angiotensin-converting enzyme (ACE). The leaves were prepared using two common drying methods, namely, hot air-drying and freeze-drying. A total of 33 bioactive compounds were identified in the olive leaves, namely, 19 flavonoids, 2 phenylethanoids, 2 coumarins, 2 hydroxycinnamic acids, 2 iridoids, and 6 triterpenic acids. Quantification of the bioactive compounds revealed high amounts of polyphenols, especially flavonoids [2,027–8,055 mg/kg dry weight (DW)], iridoids (566–22,096 mg/kg DW), and triterpenic acids (13,824–19,056 mg/kg DW) in the olive leaves. The hot air-dried leaves showed significantly (P < 0.05) higher iridoid (oleuropein and secoxyloganin) content than the fresh leaves, while freeze-drying resulted in significantly (P < 0.05) higher flavonoid aglycone and hydroxytyrosol content. Additionally, freeze-drying led to samples with the highest radical scavenging, α-amylase, α-glucosidase, and ACE inhibition abilities. The flavonoid (e.g., quercetin, luteolin, eriodictyol, kaempferol-7-O-glucoside, and luteolin-7-O-glucoside), hydroxytyrosol, and oleanolic acid contents in the olive leaves were positively correlated (P < 0.05) with their bioactive potentials.

Starch-digesting product analysis based on the hydrophilic interaction liquid chromatography coupled mass spectrometry method to evaluate the inhibition of flavonoids on pancreatic α-amylase

An accurate hydrophilic interaction liquid chromatography coupled mass spectrometry (HILIC-MS) method is presented to characterize starch digestion by α-amylase and measure the inhibition properties of flavonoids against α-amylase in vitro. Eleven products were found as 1 → 4 linkage glucose oligosaccharides with different degrees of polymerization (DPs) from 2 to 12. The products with DPs of 2, 3, 6, 7, and 9 had higher yields. The product with DP of 9 had the highest yields, which first increased and then decreased with the reaction time. Pelargonidin has the best inhibition activity on all enzyme products. The 3'-hydroxyl of B-ring enhanced the inhibition activity of flavonol and flavone but weakened that of anthocyanin. The C-ring 3-hydroxyl increased the inhibition effect of flavonol on maltose but decreased that on the products with higher DPs than flavone. The HILIC-MS method can provide more detailed information on enzyme products for the study of flavonoids inhibiting α-amylase.

Dietary starch is weight reducing when distally digested in the small intestine

Nowadays, carbohydrate-based foods have a negative consumer connotation and low carb diets have become a popular way to lose weight. Here, we show how digestible starch and flavonoids can be used as a dietary approach to manage food intake and weight gain through elevation of glucagon-like peptide-1 (GLP-1) secretion for gut-brain axis communication. This was achieved by extending the digestion of cooked starch to the distal small intestine using luteolin or quercetin as α-amylase-specific inhibitors with competitive inhibition mechanism. In a mouse model, extended and complete digestion produced a signature blunted glycemic profile that induced elevation of GLP-1 and positive regulation of hypothalamic neuropeptides with significantly reduced food intake and weight gain (p < 0.05). These findings represent a shift in paradigm of dietary carbohydrates from weight increasing to reducing, and have implications for industry and public health related to the design of carbohydrate-based foods/ingredients for managing obesity and diabetes.

Inhibitory properties of polyphenols in Malus "Winter Red" crabapple fruit on α-glucosidase and α-amylase using improved methods

To explore the inhibitory activity of polyphenols on α-glucosidase and α-amylase, 16 polyphenols were isolated, identified, and quantified in an edible Malus "Winter Red" crabapple fruit. The limitations of two traditional methods for α-glucosidase and α-amylase activity assay in vitro were assayed. An improved method based on an HPLC assay for α-glucosidase and a colorimetric method coupled with a custom-made mini-column for α-amylase were established. Compared with positive controls, acarbose and miglito, most polyphenols, especially the four aglycones (cyanidin, quercetin, phloretin, and 3-hydroxyphloretin) showed higher inhibition rates on α-glucosidase. None of the polyphenols showed higher inhibition rates on α-amylase than acarbose, but most, especially the four aglycones, showed higher inhibition rates on α-amylase than miglito. The Malus Winter Red fruit has great potential for postprandial blood glucose management as a potential diet therapy for diabetic patients.

Structural requirements of flavonoids for the selective inhibition of α-amylase versus α-glucosidase

In the present study, 14 structurally unique flavonoids were screened to systematically investigate structural requirements for selectively inhibiting human α-amylase versus α-glucosidase to obtain a slow but complete starch digestion for health benefit. The selective inhibition property of three flavonoids chosen against the two classes of starch digestive enzymes was confirmed through various analytical techniques - in vitro inhibition assay, fluorescence quenching, kinetic study, and molecular modeling. Considering the chemical structure of flavonoids, the double bond between C2 and C3 and OH groups at A5 and B3 are critical for the inhibition of α-amylase allowing flavonoids to lie parallel on the α-amylase catalytic active site, whereas the OH groups at B3 and C3 are important for α-glucosidase inhibition causing B-ring specific entry into the catalytic active site of α-glucosidase. Our findings provide insights into how to apply flavonoids to effectively control digestion rate for improving physiological responses.

Polyphenolic inhibition of enterocytic starch digestion enzymes and glucose transporters for managing type 2 diabetes may be reduced in food systems

With the current global surge in diabetes cases, there is a growing interest in slowing and managing diabetes and its effects. While there are medications that can be used, they have adverse side effects such as hypoglycemia and weight gain. To overcome these problems, bioactive compounds commonly found in fruits, vegetables and cereal grains are used to slow starch digestion and transport of simple sugars across the intestinal epithelia thereby reducing plasma blood glucose spike. These effects are achieved through inhibition of amylases, glucosidases and glucose transporters present in the gastrointestinal tract and brush boarder membrane. The extent of inhibition by polyphenols is dependent on molecular structure, doses and food matrix. Glycemic lowering effect of polyphenols have been demonstrated both in in vivo and in vitro studies. However, when these compounds are incorporated in food systems, they can interact with other polymers in the food matrix leading to lesser inhibition of digestion and/or glucose transporters compared to isolated or pure compounds as often witnessed in most in vitro studies.

Flavonoids as potential agents in the management of type 2 diabetes through the modulation of α-amylase and α-glucosidase activity: a review

Type 2 diabetes (T2D) is one of the most prevalent metabolic diseases worldwide and is characterized by increased postprandial hyperglycemia (PPHG). α-Amylase and α-glucosidase inhibitors have been shown to slow the release of glucose from starch and oligosaccharides, resulting in a delay of glucose absorption and a reduction in postprandial blood glucose levels. Since current α-glucosidase inhibitors used in the management of T2D, such as acarbose, have been associated to strong gastrointestinal side effects, the search for novel and safer drugs is considered a hot topic of research. Flavonoids are phenolic compounds widely distributed in the Plant Kingdom and important components of the human diet. These compounds have shown promising antidiabetic activities, including the inhibition of α-amylase and α-glucosidase. The aim of this review is to provide an overview on the scientific literature concerning the structure-activity relationship of flavonoids in inhibiting α-amylase and α-glucosidase, including their type of inhibition and experimental procedures applied. For this purpose, a total of 500 compounds is covered in this review. Available data may be considered of high value for the design and development of novel flavonoid derivatives with effective and potent inhibitory activity against those carbohydrate-hydrolyzing enzymes, to be possibly used as safer alternatives for the regulation of PPHG in T2D.

Identification of Dipeptidyl Peptidase-4 and α-Amylase Inhibitors from Melicope glabra (Blume) T. G. Hartley (Rutaceae) Using Liquid Chromatography Tandem Mass Spectrometry, In Vitro and In Silico Methods

The present study investigated the antidiabetic properties of the extracts and fractions from leaves and stem bark of M. glabra based on dipeptidyl peptidase-4 (DPP-4) and α-Amylase inhibitory activity assays. The chloroform extract of the leaves was found to be most active towards inhibition of DPP-4 and α-Amylase with IC₅₀ of 169.40 μg/mL and 303.64 μg/mL, respectively. Bioassay-guided fractionation of the leaves' chloroform extract revealed fraction 4 (CF4) as the most active fraction (DPP-4 IC₅₀: 128.35 μg/mL; α-Amylase IC₅₀: 170.19 μg/mL). LC-MS/MS investigation of CF4 led to the identification of trans-decursidinol (1), swermirin (2), methyl 3,4,5-trimethoxycinnamate (3), renifolin (4), 4',5,6,7-tetramethoxy-flavone (5), isorhamnetin (6), quercetagetin-3,4'-dimethyl ether (7), 5,3',4'-trihydroxy-6,7-dimethoxy-flavone (8), and 2-methoxy-5-acetoxy-fruranogermacr-1(10)-en-6-one (9) as the major components. The computational study suggested that (8) and (7) were the most potent DPP-4 and α-Amylase inhibitors based on their lower binding affinities and extensive interactions with critical amino acid residues of the respective enzymes. The binding affinity of (8) with DPP-4 (-8.1 kcal/mol) was comparable to that of sitagliptin (-8.6 kcal/mol) while the binding affinity of (7) with α-Amylase (-8.6 kcal/mol) was better than acarbose (-6.9 kcal/mol). These findings highlight the phytochemical profile and potential antidiabetic compounds from M. glabra that may work as an alternative treatment for diabetes.

Maltoheptaoside hydrolysis with chromatographic detection and starch hydrolysis with reducing sugar analysis: Comparison of assays allows assessment of the roles of direct α-amylase inhibition and starch complexation

The aim was to determine inhibition of human α-amylase activity by (poly)phenols using maltoheptaoside as substrate with direct chromatographic product quantification, compared to hydrolysis of amylose and amylopectin estimated using 3,5-dinitrosalicylic acid. Acarbose exhibited similar IC₅₀ values (50% inhibition) with maltoheptaoside, amylopectin or amylose as substrates (2.37 ± 0.11, 3.71 ± 0.12 and 2.08 ± 0.01 µM respectively). Epigallocatechin gallate, quercetagetin and punicalagin were weaker inhibitors of hydrolysis of maltoheptaoside (<50% inhibition) than amylose (IC₅₀: epigallocatechin gallate = 20.41 ± 0.25 µM, quercetagetin = 30.15 ± 2.05 µM) or amylopectin. Interference using 3,5-dinitrosalicylic acid was in the order punicalagin > epigallocatechin gallate > quercetagetin, with minimal interference using maltoheptaoside as substrate. The main inhibition mechanism of epigallocatechin gallate and punicalagin was through complexation with starch, especially amylose, whereas only quercetagetin additionally binds to the α-amylase active site. Interference is minimised using maltoheptaoside as substrate with product detection by chromatography, potentially allowing assessment of direct enzyme inhibition by almost any compound.

Antioxidant compounds from Banisteriopsis argyrophylla leaves as α-amylase, α-glucosidase, lipase, and glycation inhibitors

Banisteriopsis argyrophylla belongs to the Malpighiaceae family, which is a species from Cerrado, also known as "cipó-prata" or "cipó-folha-de-prata." Several species of this family present biological potential. This work reports the chemical identification of the ethanol extract (EE) and its fractions from B. argyrophylla leaves and shows the analysis of the antioxidant activity and inhibitory effects on activities of α-amylase, α-glucosidase and lipase, and non-enzymatic glycation. The ethyl acetate fraction (EAF) and n-butanol fraction (BF) showed antioxidant activity, with IC₅₀ values of 4.1 ± 0.1 and 4.8 ± 0.1 μg mL^-1, respectively, by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method, and IC₅₀ values of 6046.3 ± 174.2 and 6264.2 ± 32.2 µmol Trolox eq g^-1 by the oxygen radical absorbance capacity (ORAC) method. Furthermore, the DPPH method with these fractions presented electroactive species with antioxidant potential, as shown by the differential pulse voltammetry (DPV) method. The inhibitory effects of the EAF and BF were demonstrated by the following results: IC₅₀ of 5.1 ± 0.3 and 2.5 ± 0.2 μg mL^-1 for α-amylase, IC₅₀ of 1093.5 ± 26.0 and 1250.8 ± 21.9 μg mL^-1 for α-glucosidase, IC₅₀ of 8.3 ± 4.1 and 4.4 ± 1.0 μg mL^-1 for lipase, and IC₅₀ of 1.3 ± 0.1 and 0.9 ± 0.1 μg mL^-1 for glycation. Some bioactive compounds were identified by (-)-ESI-MS/MS, such as catechin, procyanidins, glycosylated flavonoids, kaempferol, and megastigmane glucosides. The antidiabetic activity of B.argyrophylla has been reported for the first time.

Inhibition of starch digestion by flavonoids: Role of flavonoid-amylase binding kinetics

In this study, kinetics of binding between α-amylase and green tea flavonoids were investigated by fluorescence quenching (FQ). Their effect on α-amylase inhibition was evaluated. Whereas epicatechin (EC) and epigallocatechin (EGC) exhibited slow binding kinetics (in the order of minutes), epicatechin gallate (ECG) and epigallocatechin gallate (ECGC) exhibited very rapid binding (in the order of seconds) with Human Salivary α-amylase (HSA) and Porcine Pancreatic α-amylase (PPA). EGCG reached maximum inhibition of HSA and PPA with short incubation time whereas maximum inhibition of HSA and PPA by EC was reached only after 45 to 60 min of incubation. Similar results with ECG and EGC, but not in line with FQ kinetics, highlighted possible interferences of starch-flavonoid interaction in the binding and inhibition process. These results suggest that incubation times of enzymes and flavonoids shall be evaluated prior to enzyme inhibition testing in order to ensure consistent and reliable results.

Evaluation of olive mill waste as substrate for carotenoid production by Rhodotorula mucilaginosa

The “alperujo” is a waste from the olive oil industry with great potential for valorization. It has a high organic load, with the presence of valuable compounds such as biophenols and sugars. The use of this waste can be thought of as a biorefinery from which different compounds of high added value can be obtained, whether they are present in the “alperujo” such as biophenols or can be generated from the “alperujo”. Therefore, the production of carotenoids by Rhodotorula mucilaginosa was evaluated using the liquid fraction of ‘alperujo’ (Alperujo Water, AW) or an aqueous extract (AE) of “alperujo” at different concentrations (5, 10, 20 and 30% w/V) as substrates. The AEs had an acidic pH, a total sugar concentration ranging from 1.6 to 7.6 g/L, a polyphenols content from 0.4 to 2.9 g/L and a significant amount of proteins (0.5–3 g/L). AW is similar in composition as 30% AE, but with a higher amount of total sugars. Rh. mucilaginosa was able to grow at the different mediums with consumption of glucose and fructose, a reduction in protein content and alkalinization of the medium. Maximum total carotenoid production (7.3 ± 0.6 mg/L) was achieved at AW, while the specific production was higher when the yeast grew at AW or at 30% AE (0.78 ± 0.06 and 0.73 ± 0.10 mg/g of biomass, respectively). Torulene and torularhodin were the main carotenoids produced. Polyphenol content did not change; thus, it is still possible to recover these compounds after producing carotenoids. These results demonstrate the feasibility of using alperujo-based mediums as cheap substrates to produce torularhodin and torulene and to include this bioprocess as a step in an integral approach for alperujo valorization.

UHPLC-ESI-QTOF-MS/MS characterization, antioxidant and antidiabetic properties of sorghum grains

The phenolic compounds composition, antioxidant and antidiabetic properties of eight brown sorghum genotypes were investigated. DPPH radical scavenging activity was highest in SOR 03, followed by SOR 11, SOR 08 and SOR 33. SOR 33, SOR 03, SOR 08, SOR 11 showed the highest ABTS radical scavenging activity. Furthermore, SOR 11, SOR 17 and SOR 33 exhibited significantly higher percentage inhibitory activity of α-glucosidase and α-amylase (IC₅₀ = 14.71, 32.98, 24.93 µg/ml and 27.6, 23.84, 45.01 µg/ml, respectively) compared to acarbose (IC₅₀ = 59.34 and 27.73 µg/ml, respectively). Similarly, SOR 17, SOR 11 and SOR 33 showed significantly potent inhibition of AGEs formation with IC₅₀ values of 14.19, 18.23 and 26.31 µg/ml, respectively, compared to aminoguanidine (AG) (52.30 µg/ml). Flavones, isoflavones and dihydroflavonols were the predominant flavonoids identified in SOR 11, SOR 17 and SOR 33 genotypes. Therefore, these sorghum grains are potential candidates for the development of functional foods.

Flavonoids in Decorticated Sorghum Grains Exert Antioxidant, Antidiabetic and Antiobesity Activities

Eight new genotypes of brown sorghum grain were decorticated and assessed for their antioxidant, antidiabetic and antiobesity activities in vitro. The DPPH and ABTS radical scavenging assays of the soluble fractions were evaluated, followed by digestive enzymes and advanced glycation end-products (AGEs) formation inhibition assays. DSOR 33 and DSOR 11 exhibited the highest DPPH (IC50 = 236.0 ± 1.98 µg/mL and 292.05 ± 2.19 µg/mL, respectively) and ABTS radical scavenging activity (IC50 = 302.50 ± 1.84 µg/mL and 317.05 ± 1.06 µg/mL, respectively). DSOR 17, DSOR 11 and DSOR 33 showed significantly higher inhibitory activity of both α-glucosidase and α-amylase (IC50 = 31.86, 35.10 and 49.40 µg/mL; and 15.87, 22.79 and 37.66 µg/mL, respectively) compared to acarbose (IC50 = 59.34 and 27.73 µg/mL, respectively). Similarly, DSOR 33, DSOR 11 and DSOR 17 showed potent inhibition of both AGEs and lipase with IC50 values of 18.25, 19.03 and 38.70 µg/mL; and 5.01, 5.09 and 4.94 µg/mL, respectively, compared to aminoguanidine (52.30 µg/mL) and orlistat (5.82 µg/mL). Flavonoids were the predominant compounds identified, with flavones being the major subclass in these three extracts. Our findings suggest that decorticated sorghum grains contain substantial amounts of flavonoids and could be promising candidates for the prevention and treatment of diabetes and obesity.

Inhibitory effect of chestnut (Castanea mollissima Blume) inner skin extract on the activity of α-amylase, α-glucosidase, dipeptidyl peptidase IV and in vitro digestibility of starches

This study aimed to investigate the inhibitory effect of chestnut inner skin extract (CISE) on the activity of postprandial blood sugar-related enzymes. In total, 12 flavonoids were identified by HPLC-TOF-MS. CISE showed strong and weak inhibition on α-amylase and α-glucosidase, with the IC₅₀ of 27.2 and 2.3 μg/mL, respectively. The inhibition modes of CISE against α-amylase and α-glucosidase were mixed-type and non-competitive type, respectively. Epicatechin gallate noncompetitively inhibited α-amylase, α-glucosidase and dipeptidyl peptidase IV (DPP-IV). Analysis by ultraviolet-visible spectroscopy, fluorescence spectroscopy and circular dichroism suggested that flavonoids altered the hydrophobicity and microenvironment of these enzymes. CISE decreased the starch bioavailability by reducing the enzymatic hydrolysis rate and increasing the fraction of undigested starch. The extract reduced the rapidly digestible starch and increased the resistant starch after incorporation into A-, B- or C- crystallinity starch. Thus, the chestnut inner skin is a useful resource for regulating postprandial blood sugar level.

Phenolic Profile, Antioxidant, and Antidiabetic Potential Exerted by Millet Grain Varieties

This study evaluated the potential antioxidant and antidiabetic properties in vitro of four millet grain varieties cultivated in South Korea. The free fractions were tested for their total antioxidant capacity using 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS⁺) and 2,2′-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays, followed by α-glucosidase, α-amylase, and advanced glycation endproducts (AGEs) formation inhibition assays. The total phenolics, flavonoids, and condensed tannins in the free fractions ranged from 107.8 to 136.4 mg ferulic acid equivalent (FAE)/100 g, 101.3 to 115.8 mg catechin equivalent (CE)/100 g, and 17.65 to 59.54 mg catechin equivalent (CE)/100 g, respectively. Finger Italian millet had the highest total phenolic content (136.4 mg FAE/100 g) and flavonoid content (115.8 mg CE/100 g). Barnyard and finger Italian millet showed the highest DPPH (IC₅₀ = 359.6 µg/mL and 436.25 µg/mL, respectively) and ABTS radical scavenging activity (IC₅₀ = 362.40 µg/mL and 381.65 µg/mL, respectively). Similarly, finger Italian millet also exhibited significantly lower IC₅₀ values for the percentage inhibition of α-glucosidase (18.07 µg/mL) and α-amylase (10.56 µg/mL) as compared with acarbose (IC₅₀ = 59.34 µg/mL and 27.73 µg/mL, respectively) and AGEs formation (33.68 µg/mL) as compared with aminoguanidine (AG) (52.30 µg/mL). All eight phenolic compounds identified in finger Italian millet were flavonoids, with flavanols being the predominant subclass. Taken together, millet flavonoids play important roles in the prevention and management of type 2 diabetes, and hence finger Italian millet has the potential to be developed as a functional food.

Starch Digestion Enhances Bioaccessibility of Anti-Inflammatory Polyphenols from Borlotti Beans (Phaseolus vulgaris)

The consumption of beans has been associated with chronic disease prevention which may be attributed to the polyphenols present in the seed coat and endosperm. However, their bioaccessibility is likely to be limited by interactions with bean matrix components, including starch, protein and fibre. The aim of this project was to evaluate the effect of domestic processing and enzymatic digestion on the bioaccessibility of polyphenols from Borlotti beans (Phaseolus vulgaris) and to test their anti-inflammatory properties in a macrophage cell model. In vitro digestion of cooked beans released twenty times more polyphenols (40.4 ± 2.5 mg gallic acid equivalents (GAE)/g) than domestic processing (2.22 ± 0.1 mg GAE/g), with starch digestion contributing to the highest release (30.9 ± 0.75 mg GAE/g). Fluorescence microscopy visualization of isolated bean starch suggests that polyphenols are embedded within the granule structure. LC-MS analysis showed that cooked Borlotti bean contain flavonoids, flavones and hydroxycinnamic acids, and cooked bean extracts exerted moderate anti-inflammatory effects by decreasing mRNA levels of IL1β and iNOS by 25% and 40%, respectively. In conclusion, the bioaccessibility of bean polyphenols is strongly enhanced by starch digestion. These polyphenols may contribute to the health benefits associated with bean consumption.