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.     

Antimicrobial activities of leptospermone isolated from Leptospermum scoparium seeds and structure–activity relationships of its derivatives against foodborne bacteria

Food Science and Biotechnology - This study was carried out to determine the antimicrobial activities of leptospermone isolated from Leptospermum scoparium and its derivatives against six foodborne...     

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.     

Production,structure–function relationships,mechanisms, and applications of antifreeze peptides

Growth of ice crystals can cause serious problems, such as frozen products deterioration, road damage, energy losses, and safety risks of human beings. Antifreeze peptides (AFPs), a healthy and effective cryoprotectant, have great potential as ice crystal growth inhibitors for a variety of frozen products. In this review, methods and technologies for the production, purification, evaluation, and characterization of AFPs are comprehensively summarized. First, this review describes the preparation of AFPs, including the methods of enzymatic hydrolysis, chemical synthesis, and microbial fermentation. Next, this review introduces the major methods by which to evaluate AFPs’ antifreeze activity, including nanoliter osmometer, differential scanning calorimetry, splat-cooling, the biovaluation model, and novel technology. Moreover, this review presents an overview of the molecular characteristics, structure–function relationships, and action mechanisms of AFPs. Furthermore, advances in the application of AFPs to frozen food, including frozen dough, meat products, fruits, vegetable products, and dairy, are summarized and holistically analyzed. Finally, challenges of AFPs and future perspectives on their use are also discussed. An understanding of the production, structure–function relationships, mechanisms and applications of AFPs provides inspiration for further research into the use of AFPs in food science and food nutrition applications.     

Evaluation of the structure–activity relationship of flavonoids as antioxidants and toxicants of zebrafish larvae

The antioxidant ability of an array of commercially available flavonoids was evaluated on the larvae of the zebrafish model organism, in order to find flavonoids with lower toxicities and higher radical oxygen-scavenging properties than flavone. Among the flavonoids tested, chrysin and morin possessed higher reactive oxygen species (ROS)-scavenging rates (−99% and −101%, respectively) and lower toxicity (LD₅₀ > 100 ppm). Zebrafish fins in the UVB + chrysin group were 6.30 times more likely to grow to normal fin size than those in the UVB-only control group, while zebrafish fins in the UVB + morin group were 11.9 times more likely to grow to normal fin size than those in the UVB-only control group. These results were analysed by the QSAR method and were in accordance with predicted values. A new 4′-fluoroflavone was synthesised. The ROS-scavenging rate of 4′-fluoroflavone was −54%, which corresponds well with the predicted value (−48%). We propose that a combination of QSAR prediction and the zebrafish model organism is efficient for evaluating new flavonoids.     

Biological activity of rice extract and the inhibition potential of rice extract,rice volatile compounds and their combination against α-glucosidase, α-amylase and tyrosinase

Rice is produced for consumption and traditional medicine. Rice is also used as an ingredient in cosmetic products. In this study, the author investigated the biological activity and inhibition potential against α-glucosidase, α-amylase and tyrosinase activity of rice extract (black rice [BR], red rice [RR] and white rice [WR]), rice volatile compounds, rice extract combined with volatile compounds, rice extract combined with standard inhibitors and volatile compounds combined with standard inhibitors. The results revealed that the free-radical scavenging capacity of rice extract is related to the phenolic content and flavonoids. BR showed the highest potential to inhibit α-glucosidase and α-amylase activity, whereas WR showed the highest potential to inhibit tyrosinase activity. Among rice volatile compounds, vanillin and vanillyl alcohol had the highest inhibition potential against α-glucosidase and α-amylase, respectively, whereas guaiacol had the highest inhibitory activity against tyrosinase. Molecular docking supported by the high binding efficiency was also obtained from vanillin and guaiacol when located at the active site of these enzymes. The combination of RR with acarbose (AB) had the highest inhibition potential and showed a synergic effect on both α-glucosidase and α-amylase. Interestingly, the combination of rice extract (BR, RR and WR) and vanillin and vanillyl alcohol had a synergic effect on α-amylase. Moreover, the combination of WR and vanillyl alcohol had the highest inhibition potential and showed a synergic effect on tyrosinase, whereas rice volatile compounds had a synergic effect on tyrosinase obtained from 2-pentylfuran/kojic acid (KA), vanillin/KA and vanillyl alcohol/KA.     

The effects of γ irradiation on the structure of apple pectin

The effects of γ irradiation on the mol. wts, viscosities and methoxyl contents of apple pectins were investigated at doses of 0–10 kGy. The apple pectins investigated were samples isolated in the laboratory before and after irradiation and an industrially purified apple pectin. No changes in mol. wts of the pectins were observed when whole apples were irradiated but decreases in viscosity and methoxyl content were observed at doses of 1 kGy. When isolated pectins were irradiated, reductions also in mol. wt were detected, at the same doses.     

Modifications of dietary flavonoids towards improved bioactivity: An update on structure–activity relationship

Over the past two decades, extensive studies have revealed that inflammation represents a major risk factor for various human diseases. Chronic inflammatory responses predispose to pathological progression of chronic illnesses featured with penetration of inflammatory cells, dysregulation of cellular signaling, excessive generation of cytokines, and loss of barrier function. Hence, the suppression of inflammation has the potential to delay, prevent, and to treat chronic diseases. Flavonoids, which are widely distributed in humans daily diet, such as vegetables, fruits, tea and cocoa, among others, are considered as bioactive compounds with anti-inflammatory potential. Modification of flavonoids including hydroxylation, o-methylation, and glycosylation, can alter their metabolic features and affect mechanisms of inflammation. Structure–activity relationships among naturally occurred flavonoids hence provide us with a preliminary insight into their anti-inflammatory potential, not only attributing to the antioxidant capacity, but also to modulate inflammatory mediators. The present review summarizes current knowledge and underlies mechanisms of anti-inflammatory activities of dietary flavonoids and their influences involved in the development of various inflammatory-related chronic diseases. In addition, the established structure–activity relationships of phenolic compounds in this review may give an insight for the screening of new anti-inflammatory agents from dietary materials.     

Antioxidant properties of resveratrol: A structure–activity insight

Resveratrol, a natural product, is known to affect a broad range of intracellular mediators. In the present study, we clarified the antioxidant activity of resveratrol by employing various in vitro antioxidant assays such as DPPH?, ABTS^?+, DMPD^?+, O₂^?? and H₂O₂ scavenging activities, total antioxidant activity, reducing abilities, and Fe²⁺ chelating activities. Resveratrol inhibited 89.1% of the lipid peroxidation of linoleic acid emulsion at 30 µg/mL concentration. On the other hand, BHA, BHT, α-tocopherol, and trolox exhibited inhibitions of 83.3, 82.1, 68.1, and 81.3% against peroxidation of linoleic acid emulsion at the same concentration, respectively. In addition, resveratrol had effective DPPH?, ABTS^?+, DMPD^?+, O₂^?? and H₂O₂ scavenging activities, reducing power, and Fe²⁺ chelating activities. The present study found that resveratrol had effective in vitro antioxidant and radical scavenging activity. It can be used in pharmacological and food industry due to its antioxidant properties.Industrial relevanceAntioxidants are often added to foods to prevent the radical chain reactions of oxidation and they act by inhibiting the initiation and propagation step leading to the termination of the reaction and delay the oxidation process. At the present time, the most commonly used antioxidants are BHA, BHT, propylgallate and tert-butyl hydroquinone. Besides that BHA and BHT are restricted by legislative rules because of doubts over their toxic and carcinogenic effects. Therefore, there is a growing interest on natural and safer antioxidants in food applications, and a growing trend in consumer preferences for natural antioxidants, all of which has given more impetus to explore natural sources of antioxidants. A variety of foods and beverages of vegetable origin contain several nonflavonoid classes of phenolic compounds synthesized by plants. Among them, resveratrol has been identified as the major active compound of stilbene phytoalexins and is presumed to be beneficial for human health. Resveratrol is naturally occurring in the fruits and leaves of edible plants, peanuts, mulberries, grapes and red wine. Resveratrol is currently in the limelight all over the world due to their beneficial effects on the human body. Resveratrol can be used for minimizing or preventing lipid oxidation in pharmaceutical products, retarding the formation of toxic oxidation products, maintaining nutritional quality and prolonging the shelf life of food products and pharmaceuticals instead of BHA and BHT and other antioxidant compounds because of their safer usage.     

Pro-oxidative effects of melanoidin–copper complexes on isolated and cellular DNA

High molecular weight Maillard reaction products (melanoidins) are described to possess metal-chelating properties. Whereas in food systems, this ability contributes to antioxidant properties, the consequences on biological systems are not quite clear. The study was aimed to evaluate the implication of metal complexation by melanoidins on DNA damage. Melanoidins prepared with d-glucose and different l-amino acids under water-free reaction conditions were charged with cupric ions. The effect on isolated DNA was investigated by the PM2 assay and on cellular systems in the human colon carcinoma cell line HCT-116 by alkaline unwinding. Independent of the amino acid composition, pure melanoidins (MW >14 kDa) did not cause significant DNA damage. By charging melanoidins with Cu²⁺ ions, a considerable DNA strand breaking activity was detectable, which was again amplified in an oxidative milieu (addition of hydrogen peroxide). Since Cu²⁺ normally does not provoke the formation of reactive oxygen species (ROS) via Fenton-type reaction, the results obtained have to be attributed to reducing properties of melanoidins. Thus, in melanoidin–copper complexes redox cycling may take place leading to Cu⁺ which subsequently undergoes Fenton-type and Haber–Weiss reactions. As a consequence, ROS are formed, which may explain the generation of DNA strand breaks.     

High pressure processing effects on the molecular structure of ovalbumin,lysozyme and β-lactoglobulin

Structural changes to the three sensitive food proteins, ovalbumin, β-lactoglobulin and lysozyme were examined following a series of high pressure processing experiments. The proteins prepared at specific pH were pressurized up to 600 MPa and held for periods of up to 30 min. Changes to the secondary and tertiary by examination of circular dichroism spectra revealed that the structure of the three proteins behaved differently to both the applied pressure and holding time. The notable effects were found to occur to both ovalbumin and β-lactoglobulin while lysozyme was found to be the most pressure resistant. For each of the proteins, it also appears that the processing conditions applied at specific pH act in combination to bring about structural change.     

Structure–antioxidant activity relationships of flavonoids isolated from different plant species

In the course of our phytochemical studies of different plants from developing countries we isolated and structurally characterized several flavonoid derivatives (compounds 1–26), both aglycones and glycosides, typical of the species investigated. The aim of this study was to evaluate varieties of medicinal plants that were growing in developing countries, known in traditional medicine as anti-inflammatory remedies, with respect to their flavonoidic isolated constituents, assuming that their anti-inflammatory activity could be explained, at least in part, by the presence of antioxidant principles. The antioxidant activities of compounds 1–26 were evaluated by measuring their ability to scavenge the radical cation 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS⁺) and the superoxide anion, to inhibit β-carotene oxidation in a lipid micelle system, and to inhibit xanthine oxidase activity, showing some structure–activity relationships.     

Extraction optimisation,antioxidant activity and inhibition on α-amylase and pancreatic lipase of polyphenols from the seeds of Syzygium cumini

The objectives of this study were to determine the optimal extraction conditions of polyphenols from Syzygium cumini seeds by response surface methodology and investigate their antioxidant activity and inhibition on α-amylase and pancreatic lipase. As results, the optimal extraction conditions in the ultrasonic extraction process which maximised total polyphenols content, minimised the IC₅₀ values of α-amylase and pancreatic lipase were determined as follows: extraction time 60 min, ethanol concentration 63% and solvent/solid ratio 44 mL g⁻¹. The main phenolic compounds in partially purified fraction of Syzygium cumini seeds were catechin, epicatechin, kaempferol, gallic, 5-caffeoylquinic, caffeic and ferulic acids. In addition, the partially purified fraction inhibited 87.66 ± 5.55 and 86.61 ± 3.15% of α-amylase and pancreatic lipase, respectively. The results suggested that Syzygium cumini seeds could be explored as a natural antioxidant and could be used as a source of highly antidiabetic and anti-obesity bioactive compounds.