Structural features,antioxidant and tyrosinase inhibitory activities of proanthocyanidins in leaves of two tea cultivars

In this study the structural features, antioxidant, and tyrosinase inhibitory activities of proanthocyanidins in leaves of two tea cultivars, namely Huangjingui and Qilan, were investigated. The matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and thiolysis-high performance liquid chromatography-electrospray ionization mass spectrometry analyses confirmed that these proanthocyanidins were built up a mixture of procyanidins, propelargonidins, and prodelphinidins, with the predominance of procyanidins. The proanthocyanidins in leaves of Huangjingui and Qilan cultivars exhibited potent antioxidant activities with IC₅₀ values of 87.36 ± 0.83 and 97.33 ± 0.61 µg/mL in 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay, 43.57 ± 0.25 and 55.01 ± 0.22 µg/mL in 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging assay, and with ferric reducing antioxidant power values of 4.83 ± 0.03 and 3.97 ± 0.02 mmol ascorbic acid equivalent/g in ferric reducing antioxidant power assay. It was also found that these proanthocyanidins had strong inhibition on tyrosinase activity with IC₅₀ values of 54.8 ± 1.27 and 20.0 ± 0.89 µg/mL for Huangjingui and Qilan cultivars, respectively. The results indicated that the proanthocyanidins in leaves of two tea cultivars could be considered as natural antioxidants and tyrosinase inhibitors applied in pharmaceutical and cosmetic industries in the future.     

对香豆酸、阿魏酸和低聚糖阿魏酸酯对酪氨酸酶的抑制效果

通过测定酶的稳态活力、迟滞时间和动力学参数,研究对香豆酸、阿魏酸及低聚糖阿魏酸酯对酪氨酸酶的抑制效果。结果表明,3种物质对酪氨酸酶单酚酶活性均有抑制作用,其中对香豆酸的抑制作用最强,其次为低聚糖阿魏酸酯和阿魏酸。对香豆酸、低聚糖阿魏酸酯和阿魏酸对单酚酶的IC_(50)值分别为0.75,3.20,9.30 mmol/L。对香豆酸和阿魏酸抑制二酚酶活性,IC_(50)值分别为4.3,12.7mmol/L;但低聚糖阿魏酸酯对二酚酶活力没有影响。对香豆酸能明显延长单酚酶反应的迟滞时间,阿魏酸影响很小,而低聚糖阿魏酸酯则缩短迟滞时间。动力学研究结果显示,阿魏酸和低聚糖阿魏酸酯对单酚酶的抑制作用表现为混合性抑制,而对香豆酸为竞争性抑制。     

A Novel Inhibitor Against Mushroom Tyrosinase with a Double Action Mode and Its Application in Controlling the Browning of Potato

In order to search for a new method for the anti-browning of food products, a novel hydroxypyridinone (HPO) derivative with a formyl group was evaluated for its anti-tyrosinase property. This compound was found to exhibit potent tyrosinase inhibition on the monophenolase activity of mushroom tyrosinase with an IC₅₀ value of 1.33 μM, indicating that this HPO derivative was 12-fold stronger than kojic acid (IC₅₀ 15.89 μM). This molecule can inhibit tyrosinase via two action modes, namely copper reduction and chelation, and the formation of a Schiff’s base with the amino group at the active site of the enzyme. A synergistic effect of these two action modes to enhance the inhibitory activity was observed. This compound was also investigated for the inhibitory effect on diphenolase activity of mushroom; the inhibitory mechanism was found to be reversible and of competitive-uncompetitive mixed-type inhibition. This hydroxypyridinone was demonstrated to effectively control the browning of vegetable products.     

Inhibitory effects of α-cyano-4-hydroxycinnamic acid on the activity of mushroom tyrosinase

The effects of α-cyano-4-hydroxycinnamic acid (HCCA) on the activity of mushroom tyrosinase have been studied. Results showed that HCCA could inhibit both the monophenolase activity and diphenolase activity of mushroom tyrosinase. For the monophenolase activity, the lag phase was obviously lengthened, and the steady-state activity of the enzyme decreased sharply. When the concentration of HCCA reached to 80 μM, the lag time was lengthened from 20 s to 150 s and the steady-state activity was lost by about 75%. The IC₅₀ value was estimated to be 48 μM. For the diphenolase activity, the inhibitory effect of HCCA was also dose-dependent and the IC₅₀ value was estimated to be 2.17 mM. The kinetic analyses showed that the inhibition of HCCA on the diphenolase activity was reversible and competitive with the inhibition constants (K_I) determined to be 1.24 mM.     

Tyrosinase inhibition by water and ethanol extracts of a far eastern sea cucumber, Stichopus japonicus

BACKGROUND: Tyrosinase plays a key role in hyperpigmentaion and enzymatic browning. The present study was aimed at investigating the inhibitory effects of water and 70% aqueous ethanol extracts of Stichopus japonicus, a sea cucumber long consumed as a tonic food and traditional medicine, on the diphenolase activity of tyrosinase. RESULTS: In the tyrosinase inhibition study, high‐performance liquid chromatography completely separated L ‐3,4‐dihydroxyphenylalanine and dopachrome from other compounds present in the extracts, and provided more reliable results than the commonly used spectrophotometry. The ethanol extract (IC₅₀ = 0.49–0.61 mg mL^?1) showed higher inhibitory activity than the water extract (IC₅₀ = 1.80–1.99 mg mL^?1). Enzyme inhibition by the extracts was reversible and of mixed type. For both extracts, the dissociation constants for binding to free enzyme were significantly smaller than those for binding to enzyme–substrate complex. Ethyl‐α‐D ‐glucopyranoside (IC₅₀ = 0.19 mg mL^?1), isolated for the first time from sea cucumber, and adenosine (IC₅₀ = 0.13 mg mL^?1), were identified as key tyrosinase inhibitors. CONCLUSION: The sea cucumber extracts were demonstrated to possess considerable inhibitory potency against the diphenolase activity of tyrosinase, suggesting that the sea cucumber may be a good source of safe and effective tyrosinase inhibitors. Copyright © 2011 Society of Chemical Industry     

Investigation of antibrowning activity of pine needle (Cedrus deodara) extract with fresh-cut apple slice model and identification of the primary active components

Cedrus deodara is a large evergreen tree of the family Pinaceae and widely distributed to the west of Himalayas. Its pine needles are consumed as a traditional food and perceived as a valuable source for bioactive compounds. A recent study has demonstrated Cedrus deodara pine needle extract (CDE) can inactivate tyrosinase. However, possible action mechanism and application of the extract have not been elucidated. In the present study, the application of CDE in food industry was explored using a fresh-cut apple slice model. Through evaluating the variation in a*, b* and L* values, the browning extent of apple slices was found to be inhibited by CDE. Moreover, in order to explore the antibrowning mechanism, we investigated the antioxidant and antibrowning capacities, total phenolic and flavonoid contents and the major bioactive constituents of the extract. It was found CDE showed strong antioxidant activity to scavenge ABTS (SC₅₀, 24.33 μg/mL) and DPPH (SC₅₀, 35.94 μg/mL) radicals, inhibited monophenolase (IC₅₀, 0.76 ± 0.08 mg/mL) and diphenolase (IC₅₀, 1.01 ± 0.09 mg/mL) activities and contained high content of phenolics (76.39 ± 2.27 mg gallic acid equivalent/g extract) and flavonoids (33.23 ± 3.25 mg rutin equivalent/g extract). Furthermore, according to the bioassay-guided isolation and the analysis of high-performance liquid chromatography–mass spectrometry and nuclear magnetic resonance, methylconiferin and ferulic acid-β-d-glucoside were determined to be the main active compounds. The current results provided the possible antibrowning mechanism of CDE and confirmed C. deodara pine needles might be a natural resource for preparing antibrowning agents of vegetables and fruits in food industry.     

Metabolite profiling and inhibitory properties of leaf extracts of Ficus benjamina towards α-glucosidase and α-amylase

The use of antioxidant-rich medicinal plants having the potential to reduce oxidative stress and postprandial hyperglycemic pressure is one of the most promising option for the management of diabetes. This study presents information on metabolite profiling and in vitro anti-diabetic effects of leaf extracts of Ficus benjamina. The DPPH (2, 2-diphenyl-1-picrylhydrazyl radicals) assay was performed to determine the in vitro antioxidant potential of the plant extracts. The anti-diabetic effects were investigated by evaluating inhibitory properties of F. benjamina leaf extracts towards carbohydrate hydrolyzing enzymes, i.e., α-glucosidase and α-amylase, whereas ¹H NMR and UHPLC-QTOF-MS/MS analytical methods were employed for metabolite profiling of F. benjamina leaf extracts. Among 40, 60, 80, and 100% ethanolic leaf extracts of F. benjamina, 80% ethanolic extract exhibited the highest antioxidant activity based upon its DPPH radical scavenging ability (IC₅₀ value: 63.71 ± 2.66 µg/mL). The 80% ethanolic leaf extract of F. benjamina also proved to be the most efficient α-glucosidase and α-amylase inhibitor with IC₅₀ values of 9.65 ± 1.04 µg/mL and 13.08 ± 1.06 µg/mL, respectively; these values were even better than acarbose with α-glucosidase inhibition activity (IC₅₀ = 116.01 ± 3.83 µg/mL) and α-amylase inhibition activity (IC₅₀ = 152.66 ± 7.32 µg/mL). Moreover, a total of 31 metabolites were identified in F. benjamina leaf extract, which may have the potential to contribute to its antioxidant and inhibitory properties against carbohydrate hydrolyzing enzymes. The findings of this study depict F. benjamina leaf extracts as a promising α-glucosidase and α-amylase inhibitor, and therefore, can be utilized for the development of anti-diabetic functional diets/nutra-pharmaceuticals.     

Inhibitory effects of 4-chlorosalicylic acid on mushroom tyrosinase and its antimicrobial activities

The inhibitory effects of 4-chlorosalicylic acid on the activity of mushroom tyrosinase have been investigated. The results showed that 4-chlorosalicylic acid could strongly inhibit both monophenolase activity and diphenolase activity. The IC₅₀ values were estimated as 1.89 mM and 1.10 mM for monophenolase and diphenolase activities, respectively. For the monophenolase activity, 4-chlorosalicylic acid could not only lengthen the lag time, but also decrease the steady-state rate. For the diphenolase activity, kinetic analyses showed that the inhibition by 4-chlorosalicylic acid was reversible and its mechanism was mixed-II type, which is different from salicylic acid. The inhibition constants (K_I and K_IS) were determined to be 1.51 mM and 0.82 mM, respectively. Furthermore, the antibacterial activity against Escherichia coli, Bacillus subtilis and Staphyloccocus aureus and antifungal activity against Aspergillus niger and Candida boidinii were investigated. The results showed that 4-chlorosalicylic acid was the most effective against E. coli with the MIC of 250 μg/ml and with the MBC of 500 μg/ml.     

Phenolic Compound Identification and Antioxidant Capacity of Alperujo Extracts from Region del Maule,Chile

This study was carried out to determinate phenolic, flavonoid content, and antioxidant capacity in methanolic extract from three Alperujo varieties. Alperujo Barnea showed the highest concentration of phenols and flavonoid. The greater hydroxytyrosol content was obtained in the same extract (4.93 ± 0.37 µg/mg extract), whereas the greater tyrosol content (0.23 ± 0.012 µg/mg extract) was found in Arbequina extract. These results were correlated with the greatest radical scavenging and the highest inhibition of lipoperoxidation process observed in Barnea extract (IC₅₀ of 27.9 ± 1.04 µg/mL; IC₅₀ 22.8 ± 3.5 µg/mL, respectively). In spite of differences, alperujo extracts exhibited notable antioxidant capacities.     

Mushroom tyrosinase inhibitory effects of isoflavones isolated from soygerm koji fermented with Aspergillus oryzae BCRC 32288

The inhibition of mushroom tyrosinase in soygerm koji, fermented with Aspergillus oryzae BCRC 32288, was investigated. A methanol extract of the soygerm koji was partitioned into hexane, ethyl acetate and water. The ethyl acetate extract showed potent anti-tyrosinase activity with an IC₅₀ value of 0.19 mg/ml. The active compounds were isolated by activity-guided silica gel column chromatography and high-performance liquid chromatography (HPLC) methods. Seven tyrosinase inhibitors were purified and identified as 6,7,4′-trihydroxyisoflavone, 7,8,4′-trihydroxyisoflavone, 5,7,8,4′-tetrahydroxyisoflavone, 7,4′-dihydroxyisoflavone (daidzein), 6-methoxy-7,4′-dihydroxyisoflavone (glycitein), 4′-hydroxyisoflavone-7-O-glucoside (daidzin), and 5,4′-dihydroxyisoflavone-7-O-glucoside (genistin) by comparing their mass, ¹H NMR, and ¹³C NMR spectral data with those in the literature. The purified seven isoflavones from fermented soygerm koji were divided into two groups, based on their inhibitory effects on mushroom tyrosinase. Five isolated isoflavones showed inhibitory activity against monophenolase activity of mushroom tyrosinase only, with IC₅₀ values of 0.009 ± 0.001 (6,7,4′-trihydroxyisoflavone), 0.203 ± 0.018 (daidzein), 0.218 ± 0.007 (glycitein), 0.267 ± 0.008 (daidzin), and 0.343 ± 0.013 (genistin) mM. The kinetic study indicated that the five inhibitors significantly lengthened the lag time of the monophenolase activity of tyrosinase and acted competitively for the l-tyrosine binding site of the enzyme. So, the five isoflavones were competitive inhibitors for the monophenolase activity of tyrosinase. The other two isoflavones, 7,8,4′-trihydroxyisoflavone and 5,7,8,4′-tetrahydroxyisoflavone, inhibited both monophenolase and diphenolase activities of tyrosinase. Moreover, pre-incubation of each of the two isoflavones with tyrosinase resulted in total irreversible inhibition of the enzyme activity, even at concentrations as low as of 10 μM. Hence, 7,8,4′-trihydroxyisoflavone and 5,7,8,4′-tetrahydroxyisoflavone were irreversible inhibitors of mushroom tyrosinase.     

白藜芦醇对酪氨酸酶体外抑制活性的动力学研究

在30℃,pH 6.8的Na2HPO4-NaH2PO4的缓冲体系中,采用酶促动力学方法,研究了白藜芦醇对酪氨酸酶单酚酶和二酚酶的抑制作用。结果表明,白藜芦醇对酪氨酸酶、单酚酶和二酚酶均有抑制作用,对单酚酶抑制活性的IC50值(抑制率达到50%时的白藜芦醇质量浓度)约为5.1mg/mL,对二酚酶抑制活性的IC50值约为5.6 mg/mL。此外,白藜芦醇可延长单酚酶的迟滞效应,8 mg/mL的白藜芦醇能使迟滞时间从22 s延长至62 s,而对二酚酶则无此迟滞作用。Lineweav-er-Burk图分析表明,白藜芦醇对酪氨酸酶的抑制作用为混合型抑制,对游离酶的抑制常数(KI)和对酶-底物络合物的抑制常数(KIS)分别为3.4 mg/mL和35.98 mg/mL。     

Inhibitory activities of hydroxyphenolic acid–amino acid conjugates on tyrosinase

The inhibitory effects of hydroxyphenolic acid–aromatic amino acid conjugates on the activity of mushroom tyrosinase were investigated. Amongst the hydroxyphenolic acid–amino acid derivatives, protocatechuic acid–amino acid amide (PA-AA-NH₂) showed highly increased tyrosinase inhibitory activity. The results show that it could strongly inhibit both the monophenolase and diphenolase activities of tyrosinase. The IC₅₀ values, inhibition type, and K_I values of these hydroxyphenolic acid derivatives (PA-F-NH₂, PA-W-NH₂, PA-Y-NH₂) were evaluated and compared. Kinetic analyses of PA-AA-NH₂ as a tyrosinase inhibitor revealed that it acted as a reversible mixed-? type inhibitor, possibly by chelating copper at the active site of tyrosinase. These results suggest that aromatic amino acid conjugation assisted PA in binding to the active site of mushroom tyrosinase where it interrupted access to the substrate.     

Inhibitory Mechanism and Kinetics Study of Apple Polyphenols on the Activity of Tyrosinase

Tyrosinase is the key enzyme in the biosynthesis of melanin. In order to investigate the effect of apple polyphenols on tyrosinase activity, the enzyme kinetic method was used. The concentration of apple polyphenols, which caused the tyrosinase activity to be lost by 50%, was 1.0 mg ml^?1 for monophenolase and 0.9 mg ml^?1 for disphenolase. When the concentration of apple polyphenols was 2.0 mg ml^?1, the lag time before reaction of monophenolase was extended from 1.2 to 4.5 min. Inhibition kinetics analysis suggested that apple polyphenols were reversible and mixed inhibitors for tyrosinase with an inhibition equilibrium constant 2.3 mmol l^?1. The results indicated that apple polyphenols were ideal tyrosinase inhibitors and could be used in food and cosmetics.     

雀嘴茶中三大酚类成分的抗氧化活性和酪氨酸酶抑制活性分析

为深入挖掘雀嘴茶的利用价值,本文以其中含量丰富的6’-O-咖啡酰熊果苷(CA)、β-熊果苷和绿原酸三大酚类成分为研究对象,对其抗氧化活性和酪氨酸酶抑制活性进行分析。结果表明,雀嘴茶三大酚类成分均表现出较好的抗氧化活性,6’-O-咖啡酰熊果苷(CA)、β-熊果苷和绿原酸清除DPPH自由基的IC₅₀值分别为13.56±0.14、104.41±6.52和8.42±0.21μg/mL,清除ABTS⁺自由基的IC₅₀值分别为18.01±0.06、50.60±1.25和26.93±0.38μg/mL,清除OH自由基的IC₅₀值为2.64±0.06、>10.00和<1.00 mg/mL,对铁离子总还原能力的强度依次为绿原酸>CA>β-熊果苷;雀嘴茶三大酚类成分对酪氨酸酶的抑制活性差异较大,CA对酪氨酸酶兼具单酚酶和二酚酶抑制作用,其IC₅₀值分别为1.114±0.035和95.198±1.117μmol/L,β-熊果苷仅有单酚酶抑制作用,IC₅₀...     

Polyphenol oxidase properties,anti-urease,and anti-acetylcholinesterase activity of Diospyros lotus L. (Plum Persimmon)

Diospyros lotus fruit polyphenol oxidase was purified using affinity chromatography, resulting in a 15-fold enrichment in specific activity. The purified enzyme, having 16.5 kDa molecular weight on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, exhibited the highest activity toward 4-methylcatechol. Maximum diphenolase activity was reached at pH 7.0 and 60°C in the presence of 4-methylcatechol. K_m and V_max values were calculated as 3.8 mM and 1250 U/mg protein, respectively. Ascorbic acid was a promising inhibitor with an IC₅₀ value of 0.121 µM. The activity of the purified enzyme was stimulated by Fe²⁺, Sr²⁺, Zn²⁺, and K⁺ and deeply inhibited by Hg²⁺, at 1 mM final concentration. Aqueous extract of Diospyros lotus L. fruit showed strong substantial urease and acetylcholinesterase inhibition, with IC₅₀ values of 1.55 ± 0.05 and 16.75 ± 0.11 mg/mL, respectively.     

Selective release of ACE-inhibiting tryptophan-containing dipeptides from food proteins by enzymatic hydrolysis

Enzymatic hydrolysis of hen egg white lysozyme led to hydrolysates with pronounced inhibition of angiotensin I-converting enzyme (ACE). Two dipeptides, alanyl-tryptophan (AW) and tryptophanyl-tryptophan (WW), were identified for the first time in lysozyme hydrolysates by LC–ESI-TOF-MS and quantified by RP-HPLC-UV/fluorescence. Hydrolysis conditions were established for enhanced release of ACE-inhibiting tryptophan-containing dipeptides from alpha-lactalbumin and hen egg white lysozyme. The highest ACE inhibition potency and release of tryptophan-containing dipeptides were observed for the hydrolysates prepared by chymotrypsin followed by thermolysin. All identified dipeptides showed a significant and competitive inhibitory effect on ACE activity (AW: IC₅₀ = 20 μmol/L; WW: IC₅₀ = 68 μmol/L, IW: IC₅₀ = 0.7 μmol/L, WL: IC₅₀ = 10 μmol/L) in vitro and proved to be moderate resistant towards simulated gastrointestinal digestion. Protein hydrolysates containing tryptophan-containing dipeptides are interesting candidates as ingredients for functional foods with possible blood pressure-lowering effect, but also as a good source for the amino acid tryptophan.     

ANTIFUNGAL,AFLATOXIN INHIBITORY AND FREE RADICAL‐SCAVENGING ACTIVITIES OF SOME MEDICINAL PLANTS EXTRACTS

ABSTRACT

The antifungal, aflatoxin inhibitory and antioxidant activity of methanol–aqueous extract (2:1) of 62 medicinal plants was explored. Based on the antifungal results, the extracts of 25 plants showed more than 50% antifungal activity and were further investigated for their aflatoxin inhibition and antioxidant properties. Methanol–aqueous extracts of Phyllanthus emblica and Terminalia chebula fruits caused 100% inhibition of aflatoxin production by the toxigenic strain of Aspergillus flavus in semisynthetic medium at 1 mg/mL. In addition, P. emblica (IC₅₀ = 4.1 µg/mL) and T. chebula (IC₅₀ = 6.9 µg/mL) fruits extracts exhibited strong antioxidant activity during the 2,2‐diphenyl‐1‐picrylhydrazyl radical‐scavenging assay in comparison with butylated hydroxytoluene (IC₅₀ = 8.1 µg/mL) and butylated hydroxyanisole (IC₅₀ = 6 µg/mL).

PRACTICAL APPLICATIONS

Based on the results of the present study, methanol–aqueous extracts of Phyllanthus emblica and Terminalia chebula, being endowed with strong antifungal, aflatoxin inhibitory and antioxidant activity, may be recommended as plant‐based preservatives for the enhancement of shelf life of food items and their protection from the undesirable harmful effects of molds, aflatoxin and free radical‐mediated damages.     

Antioxidant activity and acetylcholinesterase inhibition of field and in vitro grown <Emphasis Type="Italic">Musa</Emphasis> L. species

Bananas and plantains (Musa L. species) have medicinal applications against diseases such as hypoglycemia, hypertension, and neurological disorders, especially Alzheimer’s disease. The demand for these plants is growing very fast, resulting in a relatively heavy load on Musaceae genetic resources. The study evaluated and compared the acetylcholinesterase (AChE) inhibition and antioxidant activity of field and in vitro plant materials of nine accessions of Musa spp. consisting of Tropical Musa banana (TMb: TMb 106, TMb 145, TMb 8, TMb 82, TMb 55) and Tropical Musa plantain (TMp: TMp 116, TMp 24, TMp 36) from the International Institute of Tropical Agriculture and Musa sapientum (MS) from the University of Ibadan Botanical garden, Nigeria. Musa accessions were estimated onto Murashige and Skoog (MS) medium supplemented with 0.18 mg/L indole acetic acid (IAA) and 4.5 mg/L benzyl amino purine (BAP). The in vitro grown accessions behaved differently with TMb 8 having the highest average shoot length of 5.03?±?0.66 cm, and average number of leaves of 5.65?±?0.38 cm at the end of 6 weeks. Leaf extracts provide more quantity of phenolics, flavonoids and higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity than the fruit extracts. The AChEI activity of the field plants ranged from 60.54?±?0.54 to 98.46?±?0.09?% and in vitro plants from 61.88?±?0.11 to 76.60?±?0.34?% at 200 µg/mL. Crude methanol extract (CME) of the in vitro plants showed higher DPPH antioxidant activity than the field plants with IC₅₀ (extract concentration providing 50?% inhibition) values ranging from 9.57?±?0.24 to 48.37?±?0.62 µg/mL compared with CME of the field samples, which had IC₅₀ ranging from 75.86?±?1.76 to 162.20?±?3.77 µg/mL. Plant tissue culture can be a reliable alternative cultivation method for mass propagation and conservation of Musa species for the production of antioxidant and acetylcholinesterase metabolites.     

Angiotensin-I-converting enzyme inhibitory,antimicrobial, and antioxidant effect of bioactive peptides obtained from different varieties of common beans (Phaseolus vulgaris L.) with in vivo antihypertensive activity in spontaneously hypertensive rats

Peptides obtained from three varieties of common beans (Phaseolus vulgaris L.) named plus black (PB), azufrado higuera (AH) and pinto Saltillo (PS) presented antimicrobial, antioxidant and antihypertensive activities. Peptides were obtained from these common beans protein concentrates after treatment with Alcalase^® followed by ultrafiltration using 1-, 3- and 10-kDa molecular weight cutoff membranes. Antioxidant activity was determined by the 2,2′-azino-bis (3-etilbenzotiazolin-6-sulfonic) acid method and was expressed as Trolox equivalent antioxidant capacity (TEAC). The highest antioxidant activity (630, 550 and 517 mM TEAC/mg protein) was observed in the group of peptides with a molecular weight lower than 1 kDa (F < 1) from PB, AH and PS bean varieties, respectively. Antibacterial activity was determined as susceptibility test in which ten of twelve bacteria strains showed growth inhibition with the total hydrolysates (TH) and the peptidic fraction 3–10 kDa; subsequently, the minimum inhibitory concentration was determined with the standard microdilution assay in a 96-well plates in which the peptidic fraction F < 1 kDa presented antimicrobial activity against Shigella dysenteriae with the three beans varieties at 0.1, 0.4 and 0.3 mg/mL (for PB, AH and PS, respectively). Additionally to the antimicrobial and antioxidant activities, the TH of the PB and AH bean varieties presented high inhibition of the angiotensin-I-converting enzyme (ACE-I) (IC₅₀ = 4.34 ± 0.29 and 4.82 ± 1.59 μg/mL, respectively). And, when the peptidic fraction F3–10 kDa was tested, the AH variety showed a significant increase in the ACE-I capacity (IC₅₀ = 1.09 ± 0.04 μg/mL). Importantly, this peptidic fraction decreased the systolic blood pressure in a spontaneously hypertensive rat model after 2 h of administration by a single interperitoneally dose.     

Biological evaluation of coumarin derivatives as mushroom tyrosinase inhibitors

A series of coumarin derivatives were synthesised and their inhibitory effects on the diphenolase activity of mushroom tyrosinase were evaluated. The results showed that some of the synthesised compounds exhibited significant inhibitory activities. Especially, 2-(1-(coumarin-3-yl)ethylidene)hydrazinecarbothioamide bearing thiose-micarbazide group exhibited the most potent tyrosinase inhibitory activity with IC₅₀ value of 3.44 μM. The inhibition mechanism analysis of 2-(1-(coumarin-3-yl)-ethylidene)hydrazinecarbothioamide and 2-(1-(6-chlorocoumarin-3-yl)ethylidene)-hydrazinecarbothioamide demonstrated that the inhibitory effects of the compounds on the tyrosinase were irreversible. Preliminary structure activity relationships’ (SARs) analysis suggested that further development of such compounds might be of interest.