Antioxidant, antibacterial, and antibiofilm properties of polyphenols from muscadine grape (Vitis rotundifolia Michx.) pomace against selected foodborne pathogens

Mathematical modeling of the adsorption/desorption characteristics of anthocyanins from muscadine (Vitis rotundifolia cv. Noble) juice pomace on Amberlite FPX66 resin in a fixed bed column

BACKGROUND

Muscadine grape pomace, a by-product of juicing and wine-making, contains significant amounts of anthocyanin 3,5-diglucosides, known to be beneficial to human health.

RESULTS

The objective of this research was to use mathematical modeling to investigate the adsorption/desorption characteristics of these anthocyanins from muscadine grape pomace on Amberlite FPX66 resin in a fixed bed column. Anthocyanins were extracted using hot water and ultrasound, and the extracts were loaded onto a resin column at five bed depths (5, 6, 8, 10 and 12 cm) using three flow rates (4, 6 and 8 mL min^-1 ). It was found that adsorption on the column fitted the bed depth service time (BDST) model and the empty bed residence time (EBRT) model. Desorption was achieved by eluting the column using ethanol at four concentrations (25, 40, 55 and 70% v/v) and could be described with an empirical sigmoid model. The breakthrough curves of anthocyanins fitted the BDST model for all three flow rates with R² values of 0.983, 0.992 and 0.984 respectively. The EBRT model was successfully employed to find the operating lines, which allow for column scale-up while still achieving similar results to those found in a laboratory operation. Desorption with 40% (v/v) ethanol achieved the highest recovery rate of anthocyanins at 79.6%.

CONCLUSION

The mathematical models established in this study can be used in designing a pilot/industrial- scale column for the separation and concentration of anthocyanins from muscadine juice pomace. © 2018 Society of Chemical Industry.

HPLC-qTOF-MS/MS-Based Profiling of Flavan-3-ols and Dimeric Proanthocyanidins in Berries of Two Muscadine Grape Hybrids FLH 13-11 and FLH 17-66

FLH 13-11 FL and FLH 17-66 FL are two interspecific hybrid varieties of muscadine grape resulting from the cross of Vitis munsoniana (Simpson) ex Munson and V. rotundifolia. However, profiles of flavan-3-ols and proanthocyanidins in these two hybrids have not been characterized. Herein, we report the use of high-performance liquid chromatography-quadrupole, time-of-flight, tandem mass spectrometry (HPLC-qTOF-MS/MS) to characterize these two groups of metabolites in berries. Ripe berries collected from two consecutive cropping years were used to extract metabolites. Metabolites were ionized using the negative mode. Collision-induced dissociation was performed to fragmentize ions to obtain feature fragment profiles. Based on standards, MS features, and fragments resulted from MS/MS, four flavan-3-ol aglycones, 18 gallated or glycosylated conjugates, and eight dimeric procyanidins, were annotated from berry extracts. Of these 30 metabolites, six are new methylated flavan-3-ol gallates. Furthermore, comparative profiling analysis showed obvious effects of each cultivar on the composition these 30 metabolites, indicating that genotypes control biosynthesis. In addition, cropping seasons altered profiles of these metabolites, showing effects of growing years on metabolic composition. These data are informative to enhance the application of the two cultivars in grape and wine industries in the future.

Evaluation of phenolic compounds, antioxidant and antiproliferative activities of 31 grape cultivars with different genotypes

This study evaluated the total phenolic content, phenolic composition, antioxidant and in vitro antiproliferative properties of seeds and skins of 31 different grape cultivars. These properties of seeds and skins varied greatly among grape cultivars. European grapes had the highest values of phenolic compounds, antioxidant properties in seeds followed by Muscadine > American grapes > Oriental grapes. European grape seed extracts also were the strongest in inhibiting the growth of HepG2 cell, followed by American grapes > Muscadine > Oriental grapes. While these values of the Euro-Asian or Euro-American hybrids fell between the parents. However, the differences of these values in skin extracts among different grape cultivars were not significant. The antiproliferative activities were significantly correlated to the three antioxidant assays and the main phenolic compounds. PRACTICAL APPLICATIONS: This study presents phenolic compounds, antioxidant, and in vitro antiproliferative properties of seeds and skins of 31 different grape cultivars. The information is highly relevant to the ever-increasing need for natural sources of antioxidants or nutraceuticals among consumers. The study also provides information for grape geneticists to breed cultivars with higher nutritional value, and for food scientists to exploit the natural polyphenol antioxidants in various grape pomace.

Effect of resveratrol and Regrapex-R-forte on Trichosporon cutaneum biofilm

Microorganisms that cause chronic infections exist predominantly as surface-attached stable communities known as biofilms. Microbial cells in biofilms are highly resistant to conventional antibiotics and other forms of antimicrobial treatment; therefore, modern medicine tries to develop new drugs that exhibit anti-biofilm activity. We investigated the influence of a plant polyphenolic compound resveratrol (representative of the stilbene family) on the opportunistic pathogen Trichosporon cutaneum. Besides the influence on the planktonic cells of T. cutaneum, the ability to inhibit biofilm formation and to eradicate mature biofilm was studied. We have tested resveratrol as pure compound, as well as resveratrol in complex plant extract-the commercially available dietary supplement Regrapex-R-forte, which contains the extract of Vitis vinifera grape and extract of Polygonum cuspidatum root. Regrapex-R-forte is rich in stilbenes and other biologically active substances. Light microscopy imaging, confocal microscopy, and crystal violet staining were used to quantify and visualize the biofilm. The metabolic activity of biofilm-forming cells was studied by the tetrazolium salt assay. Amphotericin B had higher activity against planktonic cells; however, resveratrol and Regrapex-R-forte showed anti-biofilm effects, both in inhibition of biofilm formation and in the eradication of mature biofilm. The minimum biofilm eradicating concentration (MBEC₈₀) for Regrapex-R-forte was found to be 2222 mg/L (in which resveratrol concentration is 200 mg/L). These methods demonstrated that Regrapex-R-forte can be employed as an anti-biofilm agent, as it has similar effect as amphotericin B (MBEC₈₀ = 700 mg/L), which is routinely used in clinical practice.

Interaction of flavonols with human serum albumin: a biophysical study showing structure-activity relationship and enhancement when coated on silver nanoparticles

Binding affinities of flavonols namely quercetin, myricetin, and kaempferol to human serum albumin (HSA) were determined fluorimetrically and the order was observed to be myricetin > quercetin > kaempferol demonstrating structure-activity relationship. Quercetin-coated silver nanoparticles (AgNPs) show higher binding affinity to HSA compared to free quercetin with binding constants 6.04 × 10⁷ M^-1 and 4.2 × 10⁶ M^-1, respectively. Using site-specific markers it is concluded that free quercetin and that coated on AgNPs bind at different sites. Significant structural changes in circular dichroism (CD) spectra of HSA were recorded with quercetin-coated AgNPs compared to free quercetin. These results were further substantiated by time-resolved fluorescence spectroscopy where fluorescence life time of the tryptophan residue in HSA-quercetin-coated AgNPs complex decreased to 3.63 ns from 4.22 ns in HSA-quercetin complex. Isothermal calorimetric studies reveal two binding modes for quercetin-coated AgNPs and also higher binding constants compared to free quercetin. These higher binding affinities are attributed to altered properties of quercetin when coated on AgNPs enabling it to reach the binding sites other than site II where free quercetin mainly binds.

L. inermis-loaded nanofibrous scaffolds for wound dressing applications

Since ancient times, some herbal medicines have been extensively used for burn and wound treatments, showing preference to the common synthetic medications by virtue of having less side effects and faster healing rate. In this study, hybrid nanofibrous scaffolds of poly-l-lactic-acid (PLLA) and gelatin incorporated L. inermis were fabricated via electrospinning technique. Morphology and characteristics of the scaffolds were studied by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR), respectively. The release profile of the L. inermis from the nanofibers was also assessed in vitro. Moreover, the structural stability of the released L. inermis from the nanofibers was evaluated using high-performance liquid chromatography (HPLC). The nanofibers showed a gradual release of L. inermis up to two days while the intact structure was preserved. Furthermore, antibacterial assay demonstrated that L. inermis-loaded nanofibrous scaffolds could effectively kill E. coli and S. aureus within 2 h. Finally, biocompatibility of the nanofibers was proven on 3T3 fibroblasts. Therefore, the L. inermis loaded PLLA-Gelatin nanofibers showed a potential application as a wound dressing in order to control wound infections.

Preparation of a Smart and Portable Film for in Situ Sensing of Iron Microcorrosion

Corrosion of iron-containing materials, which presents serious economic and safety problems, normally begins with microcorrosion, which refers to the early stages of corrosion before visible changes appear on the surface. If microcorrosion could be detected and repaired immediately, corrosion damage could be greatly reduced. Current technology and materials, however, are not able to detect microcorrosion of iron in a cheap and convenient manner. Here, we have used a natural product, ellagic acid (EA), to fabricate an EA-functionalized poly(vinyl alcohol) (PVA) film (EAF) for in situ sensing of the initial stage of microcorrosion. EAF was able to effectively sense iron microcorrosion via an obvious color change. The film also had good long-term stability and mechanical strength. Since EAF can be easily prepared from inexpensive and green raw materials, the film opens up a new opportunity for the detection of iron microcorrosion.

Phytochemical profiles, and antimicrobial and antioxidant activities of greater galangal [Alpinia galanga (Linn.) Swartz.] flowers

Previous studies of galangal (Alpinia galanga) have focussed mostly on rhizomes but seldom on flowers. A comprehensive look at galangal flowers could reveal additional benefits. The chemical composition of galangal flowers was significantly (p < 0.05) different from that of galangal rhizome. Pentadecane and α-humulene were identified as major compounds of galangal flower essential oil. 1'-acetoxyeugenol acetate was identified as the highest compound in flowers and exhibited the strongest antimicrobial activity among all fractions, with MIC₅₀ values of 34 μg/ml against Staphylococcus aureus and 68 μg/ml against Listeria monocytogenes. Galangal flowers had a 3-fold higher total phenols content than had rhizomes (10.5 vs. 3.33 mg GAE/g powder). The antioxidant activities of different flower fractions varied from 2 to 4.45 mmol  trolox/g phenolics. These findings suggest that antimicrobial and antioxidant agents extracted from galangal flowers could potentially be utilized as natural food preservatives or as therapeutic agents.

Potential interactions among phenolic compounds and probiotics for mutual boosting of their health-promoting properties and food functionalities - A review

Several foods are rich sources of phenolic compounds (PC) and their beneficial effects on human health may be increased through the action of probiotics. Additionally, probiotics may use PC as substrates, increasing their survival and functionality. This review presents available studies on the effects of PC on probiotics, including their physiological functionalities, interactions and capability of surviving during exposure to gastrointestinal conditions and when incorporated into food matrices. Studies have shown that PC can improve the adhesion capacity and survival of probiotics during exposure to conditions that mimic the gastrointestinal tract. There is strong evidence that PC can modulate the composition of the gut microbiota in hosts, improving a variety of biochemical markers and risk factors for chronic diseases. Available literature also indicates that metabolites of PC formed by intestinal microorganisms, including probiotics, exert a variety of benefits on host health. These metabolites are typically more active than parental dietary PC. The presence of PC commonly enhances probiotic survival in different foods. Finally, further clinical studies need to be developed to confirm in vitro and experimental findings concerning the beneficial interactions among different PC and probiotics.

The antimicrobial effects of three phenolic extracts from Rosmarinus officinalis L., Vitis vinifera L. and Polygonum cuspidatum L. on food pathogens

In this study three phenolic extracts were examined, without volatile fraction, against common food pathogens. The samples, all suitable for food application, were from the leaves of Rosmarinus officinalis L., Vitis vinifera L., and the root of Polygonum cuspidatum L. The microorganisms tested were Escherichia coli O157:H7, Salmonella Enteritidis, Salmonella Typhi, Yersinia enterocolitica and Listeria monocytogenes, well-known as important food pathogens. The results demonstrated a microbicidal activity of all the tested compounds at different concentrations; the rosemary extract showed greater efficacy than the other compounds against the tested microorganisms. In particular, the best results were obtained with rosemary extract against E. coli O157:H7 and L. monocytogenes with values of 200 and 270 μg/mL, respectively. Our results show that rosemary extract, often present as a natural antioxidant in food, can also be proposed as a natural disinfectant in the food field.

Discovery and evaluation of the hybrid of bromophenol and saccharide as potent and selective protein tyrosine phosphatase 1B inhibitors

Protein tyrosine phosphatase 1B (PTP1B) is a key negative regulator of insulin signaling pathway. Inhibition of PTP1B is expected to improve insulin action. Appropriate selectivity and permeability are the gold standard for excellent PTP1B inhibitors. In this work, molecular hybridization-based screening identified a selective competitive PTP1B inhibitor. Compound 10a has IC50 values of 199 nM against PTP1B, and shows 32-fold selectivity for PTP1B over the closely related phosphatase TCPTP. Molecule docking and molecular dynamics studies reveal the reason of selectivity for PTP1B over TCPTP. Moreover, the cell permeability and cellular activity of compound 10a are demonstrated respectively.

Profile of Polyphenol Compounds of Five Muscadine Grapes Cultivated in the United States and in Newly Adapted Locations in China

Polyphenol compositions and concentrations in skins and seeds of five muscadine grapes (cv. “Noble”, “Alachua”, “Carlos”, “Fry”, and “Granny Val”) cultivated in the United States (Tallahassee-Florida, TA-FL) and South China (Nanning-Guangxi, NN-GX and Pu’er-Yunnan, PE-YN) were investigated, using ultra performance liquid chromatography tandem triple quadrupole time-of-flight mass spectrometry (UPLC Triple TOF MS/MS). Fourteen ellagitannins were newly identified in these muscadine grapes. The grapes grown in NN-GX accumulated higher levels of ellagic acid, methyl brevifolin carboxylate, and ellagic acid glucoside in skins, and penta-O-galloyl-glucose in seeds. In PE-YN, more flavonols were detected in skins, and higher contents of flavan-3-ols, ellagic acid, and methyl gallate were identified in seeds. Abundant seed gallic acid and flavonols were found among the grapes grown in TA-FL. Based on principal component analysis (PCA) of 54 evaluation parameters, various cultivars grown in different locations could be grouped together and vice versa for the same cultivar cultivated in different regions. This is the result of the interaction between genotype and environmental conditions, which apparently influences the polyphenol synthesis and accumulation.

Antibiofilm Activity of Plant Polyphenols

In the history of human medicine, antibiotics represent epochal examples of medical progress. However, with an approaching antibiotic crisis due to the emergence and extensive spread of antimicrobial resistance among bacterial agents, as well as to increasing number of patients with chronic and recalcitrant bacterial biofilm-associated infections, the naturally occurring molecules may become new sources of antibacterial and antibiofilm drugs for clinical usage. Polyphenols represent a class of plant natural products which are important in plant defense against microbial pathogens. The main focus of the review is on the antibiofilm activities of phenolic compounds against bacteria which play an essential role in medical device biofilm-associated infections. The other, not negligible part of the review is devoted to polyphenols’ activity against bacterial agents that cause dental caries and periodontal disease.

Applications of Wine Pomace in the Food Industry: Approaches and Functions

Winemaking generates large amounts of wine pomace, also called grape pomace. This by-product has attracted the attention of food scientists and the food industry, due to its high content in nutrients and bioactive compounds. This review mainly focuses on the different published approaches to the use of wine pomace and its functions in the food industry. Traditionally, wine pomace has been used to obtain wine alcohol, food colorings, and grape seed oil. More recently, research has focused in the production of other value-added products, such as extracts of bioactive compounds, mainly phenols, recovery of tartaric acid, and the making of flours. The most common functions associated with wine pomace products are their use as antioxidants, followed by their use as fortifying, coloring, and antimicrobial agents. These products have mainly been applied to the preparation of meat and fish products and to, a lesser extent, cereal products.

Microbicidal action of photoirradiated aqueous extracts from wine lees

Wine lees, a major waste product of winemaking, is a rich source of polyphenolic compounds. LED-light irradiation at 400-nm elicited microbicidal activity of aqueous extract from wine lees (WLE) against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans, in addition to reactive oxygen species (ROS) formation, including hydroxyl radical (·OH) and hydrogen peroxide (H2O2). Although treatment for 20 min of photoirradiation alone exerted bactericidal activity with a 2- to 3-log reduction, photoirradiated WLE for 20 min achieved a 5-log or greater reduction in viable S. aureus and P. aeruginosa cells. Regarding C. albicans, a 1-log reduction (90 % reduction) of viable cells was achieved by photoirradiated WLE for 40 min, whereas photoirradiation alone did not show any fungicidal effect. ROS analyses revealed that approximately 170 μM ·OH and 600 μM H2O2 were generated in photoirradiated WLE for 20 min. Because the bactericidal activity of photoirradiated WLE was abolished by ·OH scavengers, ROS, especially highly oxidative ·OH, may be responsible for the microbicidal activity of photoirradiated WLE. In addition to its microbicidal activity, WLE may act as an antioxidant as it exerted radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl, a stable free radical.

Assessment of total polyphenols, antioxidants and antimicrobial properties of aonla varieties

Phenolic content, antioxidant activities and antimicrobial activities of methanolic, ethanolic and ethyl acetate extracts of five different varieties of aonla (Emblica officinalis) fruits as well their powders were evaluated. Total polyphenolic content in fresh aonla fruit extracts varied from 70.6 to 159.4 mg GAE/g and their EC 50 (effective concentration) values for antioxidant activity ranged from 46.72 to 359.7 µg/ml. Significant varietal difference were observed in antioxidant activity of the extracts of fresh aonla fruit and powder. Among the variety analyzed, Desi variety exhibited significantly higher TPC (total polyphenol content) and antioxidant activity in fresh as well as dried form in all the extracts. Methanolic extracts of various varieties had maximum TPC and antioxidant activity. Variety NA-7 showed high TPC and antioxidant activity. Almost, similar trend was observed among the extracts of aonla powders for TPC and AOA (antioxidant activity). A high positive correlation coefficient existed between TPC and AOA of different aonla extracts. All the extracts analyzed, exhibited a strong antimicrobial potential against E. coli, Salmonella typhi, Staphylococcus aureus and Candida albicans. This study suggests aonla as potential natural source of antioxidants and antimicrobial agents.

Muscadine grape seed oil as a novel source of tocotrienols to reduce adipogenesis and adipocyte inflammation

Tocotrienols are unsaturated forms of vitamin E previously shown to reduce adipogenesis and adipose inflammation. In this study, muscadine grape seed oil (MGSO) was identified as a novel source of tocotrienols containing significant amounts of α- and γ-tocotrienol (T3) with minor seasonal changes. The aim of this study was to assess the anti-adipogenic and anti-inflammatory potential of MGSO by using primary human adipose-derived stem cells (hASCs). Differentiating hASCs were treated with MGSO and compared with rice bran and olive oil. Accumulation of triglyceride was significantly lower in MGSO-treated hASCs than rice bran and olive oils. A tocotrienol rich fraction (TRF) from MGSO was prepared by solid phase extraction and eluted with 15% 1,4-dioxane in hexane. The MGSO-derived TRF treatment significantly reduced mRNA and protein expression that are crucial to adipogenesis (e.g., PPARγ and aP2) in hASCs. Furthermore, TRF from MGSO markedly reduced LPS-induced proinflammatory gene expression in human adipocytes and cytokine secretion to the medium (IL-6 and IL-8). Collectively, our work suggests that MGSO is a stable and reliable natural source of T3 and MGSO may constitute a new dietary strategy to attenuate obesity and its associated adipose inflammation.

Genetic transformation of a fruit-specific, highly expressed stilbene synthase gene from Chinese wild Vitis quinquangularis

The stilbene synthase gene VqSTS6, from Chinese wild type Vitis quinquangularis accession Danfeng-2, increases the resveratrol content and pathogen resistance of transgenic plants of V. vinifera Thompson Seedless. This study successfully created transgenic plants of V. vinifera Thompson Seedless which overexpressed VqSTS6, cloned from Chinese wild type V. quinquangularis accession Danfeng-2. Western blot and qRT-PCR showed a variable range in transcript levels among transgenic lines. The resistance to powdery mildew (Uncinula necator) was particularly enhanced in lines most highly expressing VqSTS6. Compared with the non-transformed controls, trans-resveratrol and other stilbene compounds were significantly increased in the transgenic lines. The correlation between high resveratrol content and high pathogen resistance in transgenic grapes is discussed. We hypothesize that the fruit-specific, highly expressed gene VqSTS6 from Chinese wild V. quinquangularis accession Danfeng-2, is directly involved in the resveratrol synthesis pathway in grapes, and plays an important role in the plant's defense against pathogens. Genetic transformation of VqSTS6 explored the potential of the wild Chinese grape species for use in breeding, the results of which would raise both the disease resistance and the fruit quality of V. vinifera grapevines.

Screening of Anthocyanins and Anthocyanin-Derived Pigments in Red Wine Grape Pomace Using LC-DAD/MS and MALDI-TOF Techniques

Two phenolic extracts were made from a red wine grape pomace (GP) and fractionated first by sequential liquid-liquid extraction with organic solvents. The aqueous fraction was fractionated by low-pressure chromatography on Toyopearl HW-40 gel and on C18. Different fractions were obtained by sequential elution with aqueous/organic solvents, and then analyzed by liquid chromatography and mass spectrometry (LC-DAD/MS and MALDI-TOF). Over 50 anthocyanin-based pigments were detected by LC-DAD/MS in GP, mainly pyranoanthocyanins including A- and B-type vitisins and methylpyranoanthocyanins. The presence of oligomeric malvidin-3-O-coumaroylglucoside-based anthocyanins was also detected in GP using both LC-DAD/MS and MALDI-TOF.