Antioxidant activity, total phenolics and flavonoids contents: Should we ban in vitro screening methods?

Protective effects of p-coumaric acid against oxidant and hyperlipidemia-an in vitro and in vivo evaluation

Dietary phenols are antioxidants with diverse physiological functions that are beneficial for human health. The objective of this research work was to investigate antioxidant activity of p-coumaric acid (p-CA) using four in vitro methods, the protective effects against oxidative stress in PC12 cells, and hypolipidemic effects on High fat-diet (HFD) mice model. The p-CA exhibited moderate antioxidant activity in the selected in vitro assay. The highest chelating activity of p-CA at 50 μg/mL was found to be 52.22%. Pretreatment with p-CA significantly enhanced cell viability of PC12 cell and suppressed AAPH-induced intracellular ROS generation and AAPH-induced LDH release. The hypolipidemic effects of p-CA (100 mg/kg BW) was directly linked to the increased expression of nuclear factor erythroid 2-related factor (Nrf2) by 2.0-fold, Glutathione peroxidase (Gpx) by 3.8-fold, Superoxide dismutase (SOD-1) by 1.6-fold, Heme oxygenase (HO-1) by 1.72-fold and NAD(P)H Quinone Dehydrogenase 1 (NQO-1) by 1.5-fold compared with HFD group. In addition to these effects, p-CA decreased total cholesterol and atherosclerosis index levels, and increased catalase (CAT) level in serum, total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-Px) levels in liver as compared HFD group. Administration of p-CA also promoted the recovery of hyperlipidemia steatohepatitis in mice by ameliorating lipid peroxidation. These results suggested that p-CA is a potent antioxidant with potential therapeutic efficacy for treating hyperlipidemia symptoms.

Anabasis aretioides Coss. & Moq. phenolic compounds exhibit in vitro hypoglycemic, antioxidant and antipathogenic properties

Background Based on our previous ethnobotanical survey, the non-investigated Saharan plant Anabasis aretioides Coss. & Moq., growing in the region of Errachidia, was selected for pharmacological investigation. In Moroccan traditional medicine, A. aretioides is being used for diabetes treatment. Thus, the current work aims at evaluating the antidiabetic, antioxidant, and antibacterial activities of the plant in relation to the digestive tract. Methods The different parts of the plant (aerial parts, roots, seeds) were extracted with methanol (MeOH) and screened in enzymatic assays for their inhibitory potential against α-amylase and α-glucosidase, as well as antioxidant and antibacterial activities. Furthermore, the phenolic compounds were analyzed using HPLC-DAD-QTOF-MS. Results The MeOH extracts of A. aretioides aerial parts, roots, and seeds, respectively, inhibited α-amylase (IC50 of 3148.07 μg/mL, 2440.20 μg/mL, 3395.71 μg/mL) and α-glucosidase (IC50 of 2940.59 μg/mL, 3521.81 μg/mL, 3393.83 μg/mL). Moreover, compared to aerial parts and seeds, the plant roots exhibited higher antioxidant capacity and a potent reducing power. In resazurin microplate assay, the plant parts displayed a minimal inhibitory concentration (MIC) ranging from 7.81 mg/mL to 31.25 mg/mL. Chemical analysis revealed 25 phenolic compounds, with chlorogenic acid as the main phenolic compound in the aerial parts, hesperidin in roots, and quercitrin in seeds. Conclusion Anabasis aretioides cited for treatment of diabetes shows promising antioxidant and antibacterial properties, as well as an ability to inhibit digestive enzyme, including α-amylase and α-glucosidase. Thus, our results explain in part the traditional use of this Saharan medicine and open doors for further in vivo mechanistic and functional studies.

Strawberry dietary fiber functionalized with phenolic antioxidants from olives. Interactions between polysaccharides and phenolic compounds

The interaction of strawberry cell wall with hydroxytyrosol (HT) and 3,4-dihydroxyphenylglycol (DHPG), two potent phenolic antioxidants naturally found in olive fruit with important biological properties, was investigated. The interaction occurred with drying and seemed to be more complex, strong and irreversible than a simple association. MALDI TOF-TOF analysis suggested covalent (ester bond) and non-covalent (strong hydrogen-bonding, mostly) interactions. The oxygen radical absorbance capacity (ORAC) assay confirmed that the phenols maintained partially their antioxidant activity after binding to the soluble dietary fraction. This soluble dietary fiber was obtained following digestion simulated in vitro with gastric and intestinal fluids. Although the antioxidant activity of HT and DHPG was affected by the dietary fiber interaction, this activity was restored when polysaccharide size was reduced by enzymatic treatment, suggesting that a similar process could occur in the colon. Thus, the use of this novel antioxidant-enriched soluble dietary fiber as a functional food ingredient could potentially promote intestinal health.

Evaluation of Antioxidant Capacity, Protective Effect on Human Erythrocytes and Phenolic Compound Identification in Two Varieties of Plum Fruit (Spondias spp.) by UPLC-MS

Plum edible part was used to obtained extracts by during a 4 h maceration process using three different solvents (ethanol, methanol and water) for the determination of total phenols and flavonoids, antioxidant capacity by (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hemolysis inhibition in human blood assays. Subsequently, phenolic compounds were identified using ultra-performance liquid chromatography (UPLC-MS). The results indicated that the ethanolic extract of plum fruit being a good source of phenolic (12–18 mg GAE/g FW) and flavonoids (2.3–2.5 mg QE/g FW) content in both varieties of plum. Also, the fruits proved a good source of antioxidants as measured by DPPH and ABTS; likewise, plum aqueous extracts showed the highest protective effect on human erythrocytes with 74.34 and 64.62% for yellow and red plum, respectively. A total of 23 bioactive compounds were identified by UPLC-MS, including gallic acid, rutin, resorcinol, chlorogenic acid, catechin, and ellagic acid, and the antioxidant capacity can be attributed to these species. The edible part of plum contains compounds of biological interest, suggesting that this fruit has antioxidant potential that can be exploited for various technologies.

Impact of conventional/non-conventional extraction methods on the untargeted phenolic profile of Moringa oleifera leaves

The impact of different extraction methods, namely maceration, homogenizer-assisted extraction, rapid solid-liquid dynamic extraction, microwave-assisted extraction and ultrasound-assisted extraction, on polyphenols of Moringa oleifera leaves was studied. The phenolic composition of alcoholic (methanol 100%) and hydroalcoholic (methanol/water 50:50, v/v) extracts was compared by using an untargeted metabolomics-based profiling approach followed by multivariate statistics. With this aim, ultra-high-pressure liquid chromatography coupled to a quadrupole-time-of-flight mass spectrometry was used to profile phenolic compounds under the different extraction conditions. Besides, the in vitro antioxidant activities of Moringa leaves were also investigated as ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC). The metabolomic approach allowed to putatively annotate 262 phenolic compounds. In particular, glycosidic forms of quercetin (i.e., quercetin 3-O-galactoside, quercetin 3-O-glucoside, and quercetin 4'-O-glucoside) were the most represented compounds among flavonoids. Furthermore, protocatechuic acid was found to be the most abundant hydroxybenzaldheyde derivative, while the isomeric forms of hydroxybenzoic acid characterized the phenolic acids class. Overall, the extractions in methanol 100% were found to be the most effective for phenolic compounds recovering, when compared with those in methanol/water (50:50, v/v). Homogenizer-assisted extraction of M. oleifera leaves using 100% methanol allowed extracting the highest amounts of polyphenols (35.19 mg/g) and produced the highest oxygen radical absorbance capacity (536.27 μmol Trolox Equivalents/g). The supervised orthogonal projection to latent structures discriminant analysis identified phenolic acids as the phenolic class mostly affected by the different extraction technologies. These findings demonstrate that each extraction method promoted the recovery of specific phenolic subclasses with different efficiencies.

Analytical Profiling of Proanthocyanidins from Acacia mearnsii Bark and In Vitro Assessment of Antioxidant and Antidiabetic Potential

The proanthocyanidins from ethanol extracts (80%, v/v) of Acacia mearnsii (A. mearnsii) bark on chemical-based and cellular antioxidant activity assays as well as carbolytic enzyme inhibitory activities were studied. About 77% of oligomeric proanthocyanidins in ethanol extracts of A. mearnsii bark were found by using normal-phase HPLC. In addition, HPLC-ESI-TOF/MS and MALDI-TOF/TOF MS analyses indicated that proanthocyanidins from A. mearnsii bark exhibited with a degree of polymerization ranging from 1 to 11. These results of combined antioxidant activity assays, as well as carbolytic enzyme inhibitory activities of proanthocyanidins from A. mearnsii bark, indicated an encouraging antioxidant capacity for the high polyphenol content and a potential for use as alternative drugs for lowering the glycemic response.

Opinion on the Hurdles and Potential Health Benefits in Value-Added Use of Plant Food Processing By-Products as Sources of Phenolic Compounds

Plant foods, their products and processing by-products are well recognized as important sources of phenolic compounds. Recent studies in this field have demonstrated that food processing by-products are often richer sources of bioactive compounds as compared with their original feedstock. However, their final application as a source of nutraceuticals and bioactives requires addressing certain hurdles and challenges. This review discusses recent knowledge advances in the use of plant food processing by-products as sources of phenolic compounds with special attention to the role of genetics on the distribution and biosynthesis of plant phenolics, as well as their profiling and screening, potential health benefits, and safety issues. The potentialities in health improvement from food phenolics in animal models and in humans is well substantiated, however, considering the emerging market of plant food by-products as potential sources of phenolic bioactives, more research in humans is deemed necessary.

Relevance and Standardization of In Vitro Antioxidant Assays: ABTS, DPPH, and Folin–Ciocalteu

Trolox, gallic acid, chlorogenic acid, caffeic acid, catechin, epigallocatechin gallate, and ascorbic acid are antioxidants used as standards for reaction with chromogenic radicals, 2,2-diphenyl-1-picrylhydrazyl (DPPH⋅) and 2,2′-azino-bis-3-ethylbenzotiazolin-6-sulfonic acid (ABTS⋅+), and Folin–Ciocalteu (FC) reagent. The number of exchanged electrons has been analyzed as function of method and solvent. A majority of compounds exchange more electrons in FC assay than in ABTS and DPPH assays. In reaction with chromogenic radicals, the largest number of electrons was exchanged in buffer (pH 7.4) and the lowest reactivity was in methanol (DPPH) and water (ABTS). At physiological pH, the number of exchanged electrons of polyphenols exceeded the number of OH groups, pointing to the important contribution of partially oxidized antioxidants, formed in the course of reaction, to the antioxidant potential. For Trolox, small impact on the number of exchanged electrons was observed, confirming that it is more suitable as a standard compound than the other antioxidants.

Impact of cooking and fermentation by lactic acid bacteria on phenolic profile of quinoa and buckwheat seeds

In this work, quinoa and buckwheat cooked seeds were fermented by two autochthonous strains of lactic acid bacteria isolated from the corresponding seeds, namely Lactobacillus paracasei A1 2.6 and Pediococcus pentosaceus GS·B, with lactic acid chemically acidified seeds as control. The impact of cooking and fermentation on the comprehensive phenolic profile of quinoa and buckwheat seeds was evaluated through untargeted ultra-high-pressure liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (UHPLC-QTOF-MS). Samples were analyzed also for in vitro antioxidant capacity (as FRAP and ORAC assays) and total phenolic content (TPC). The in vitro spectrophotometric assays highlighted that the microbial fermentation was more efficient in increasing (p < .05) the TPC and in vitro antioxidant potential in quinoa cooked seeds. However, an increase (p < .05) in TPC and ORAC radical scavenging was observed in both pseudocereals after the different cooking processes (i.e., boiling or toasting). The untargeted phenolic profiling depicted the comprehensive phenolic composition in these matrices. Raw seeds of both pseudocereals possessed a similar phenolic content (4.4 g kg^-1 equivalents; considering free and bound fractions). Besides, the metabolomics-based approach showed that all treatments (i.e., cooking and fermentation) induced the release of specific classes, namely phenolic acids and tyrosols. The PLS-DA multivariate approach identified in flavonoids the best markers allowing to discriminate the different treatments considered (i.e., cooking, chemical acidification and microbial fermentation). These findings support the use of cooking and microbial fermentation to ensure the health-promoting properties of non-wheat grains, such as buckwheat and quinoa.

Simultaneous LC-MS quantification of anthocyanins and non-anthocyanin phenolics from blueberries with widely divergent profiles and biological activities

A sensitive and straightforward LC-IT-TOF-MS method was validated for the profiling and simultaneous quantification of anthocyanins, flavan-3-ols, flavonols, phenolic acids, and resveratrol in blueberry genotypes with fruit color ranging from deep purple (Vaccinium angustifolium) to various shades of pink (crosses of V. corymbosum, V. darrowii, and V. ashei). Standard calibration curves were linear for all analytes with correlation coefficients >0.99. The relative standard deviation for intra- and inter-day precision was lower than 10%. The method allowed an easy and selective identification and quantification of phenolics in blueberries with divergent profiles. The in vitro antioxidant assay results were strongly correlated with total phenolics and total anthocyanin content. Lowbush blueberry extracts (50 μg/mL) reduced ROS and NO production, and inhibited the transcription of the proinflammatory cytokines IL-6β, COX2, iNOS, and IL-6 in the in vitro assays at much lower concentrations than pink fruited berries (250 μg/mL).

Edible nuts deliver polyphenols and their transformation products to the large intestine: An in vitro fermentation model combining targeted/untargeted metabolomics

The fate of polyphenols from edible tree nuts was investigated using a simulated in vitro intestinal fermentation system. The digested food matrix was fermented for 48 h and the changes in the phenolic profiles were evaluated by both untargeted UHPLC-QTOF and targeted UHPLC-Orbitrap mass spectrometry. The untargeted metabolomics approach allowed us to monitor the comprehensive changes in phenolic profiles from 0 up to 48 h of in vitro fermentation. Multivariate statistics (i.e., orthogonal projection to latent structures discriminant analysis) applied to this untargeted data allowed us to identify the most discriminating phenolic metabolites and to further understand the colonic transformation pathways involved. In particular, 13 putatively identified compounds derived from flavonoids, lignans and phenolic acids were found to have the highest discrimination potential. Six phenolic metabolites were then quantified by means of targeted metabolomics (using a UHPLC-Orbitrap). These metabolites included 3,4-dihydroxyphenylacetic acid, 4-hydroxybenzoic acid, hippuric acid, caffeic acid, protocatechuic acid and protocatechuic aldehyde. Using the targeted data, a clear matrix effect was observed over time, with an increase of some phenolic metabolites moving from 8 to 48 h of in vitro fermentation. Based on these data, catabolic pathways for colonic microbial degradation of flavonoids, hydroxycinnamic acids, tyrosols and lignans are proposed. Our findings show that edible tree nuts deliver polyphenols to the colon, where several microbial transformations occur that lead to smaller phenolic metabolites being observed. Furthermore, we found that the combined use of targeted and untargeted metabolomics can be particularly effective for investigating the fate of polyphenols in the large intestine.

Towards better quality criteria of European honeydew honey: Phenolic profile and antioxidant capacity

Concerning the particular nutritive value of honeydew honey compared to blossom honey, and small number of studies defining botanical origin of honeydew honey, comprehensive analysis of phenolic profile of 64 honeydew honey samples of specific botanical origin was performed. Two advanced techniques of liquid chromatography hyphenated with mass spectrometry were used for identification of a total of 52 compounds and quantification of 25 of them. Pattern recognition analysis applied on data on phenolic compounds content confirmed that quercetin, naringenin, caffeoylquinic acid, hydroxyphenylacetic acid, apigenin and genistein, could be considered as potential markers of botanical origin of honeydew honey. Spectroscopic and electrochemical approaches were applied for the evaluation of the antioxidant capacity. Quercus sps. samples, Quercus frainetto and Quercus ilex, showed high biological activity and specific chemical composition. Additionally, cyclic voltammetry profiles were used for characterization and natural clustering of honeydew honey for the first time.

Five-Golden-Flowers Tea: Green Extraction and Hepatoprotective Effect against Oxidative Damage

The consumption of herbal teas has become popular in recent years due to their attractive flavors and outstanding antioxidant properties. The Five-Golden-Flowers tea is a herbal tea consisting of five famous edible flowers. The effects of microwave-assisted extraction parameters on the antioxidant activity of Five-Golden-Flowers tea were studied by single-factor experiments, and further investigated using response surface methodology. Under the optimal parameters (53.04 mL/g of solvent/material ratio, 65.52 °C, 30.89 min, and 500 W), the ferric-reducing antioxidant power, Trolox equivalent antioxidant capacity, and total phenolic content of the herbal tea were 862.90 ± 2.44 µmol Fe2+/g dry weight (DW), 474.37 ± 1.92 µmol Trolox/g DW, and 65.50 ± 1.26 mg gallic acid equivalent (GAE)/g DW, respectively. The in vivo antioxidant activity of the herbal tea was evaluated on alcohol-induced acute liver injury in mice. The herbal tea significantly decreased the levels of aspartate aminotransferase, total bilirubin, and malonaldehyde at different doses (200, 400, and 800 mg/kg); improved the levels of liver index, serum triacylglycerol, and catalase at dose of 800 mg/kg. These results indicated its role in alleviating hepatic oxidative injury. Besides, rutin, chlorogenic acid, epicatechin, gallic acid, and p-coumaric acid were identified and quantified by high performance liquid chromatography (HPLC), which could contribute to the antioxidant activity of the herbal tea.

Effect of Different Cooking Methods on Polyphenols, Carotenoids and Antioxidant Activities of Selected Edible Leaves

This study aimed to evaluate the effect of cooking (boiling, steaming, and frying) on polyphenols, flavonoids, carotenoids and antioxidant activity of six edible leaves. The total antioxidant capacity of the fresh and cooked leaves was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and singlet oxygen scavenging assays. The results revealed that frying caused a reduction in major bioactives and antioxidant activities in all leafy vegetables tested. However, steamed and boiled leaves of C. auriculata and C. asiatica have shown greater levels of polyphenols, flavonoids, and antioxidant capacity compared with fresh leaves. Polyphenol and flavonoid contents of boiled S. grandiflora and G. lactiferum were higher than that of their fresh form. Boiled and steamed O. zeylanica and S. grandiflora have shown higher carotenoids. Boiled and steamed leaves of P. edulis have shown higher antioxidant activity. The impact of cooking on the changes in bioactive concentrations and antioxidant capacities are dependent on the species and the method of cooking.

Influence of different Agrobacterium rhizogenes strains on hairy root induction and analysis of phenolic and flavonoid compounds in marshmallow (Althaea officinalis L.)

Hairy roots were induced in Althea officinalis using Agrobacterium rhizogenes, strains A4, A13, ATCC15834, and ATCC15834(GUS). The leaf, petiole and shoot explants of marshmallow were used for the hairy roots induction. When hairy roots appeared, cultures were established in MS (Murashige and Skoog) liquid medium without growth regulators. Hairy roots in explants appeared 5-12 days after inoculation. Maximum transformation frequency of 83% was observed on shoot explants with ATCC15834 strain. Among the strains, ATCC15834(GUS) strain showed better potential in the mass production of hairy roots in the hormone-free liquid medium after 50 days of culturing. The highest total phenolic and flavonoids content was found at 1.57 ± 0.1 mg/g dry weight in A13 strain and 3.47 ± 0.3 mg/g in A4 strain, respectively. Secondary metabolite content of hairy roots was found to be strain-specific.

Gluten-free flours from cereals, pseudocereals and legumes: Phenolic fingerprints and in vitro antioxidant properties

The interest in gluten-free (GF) products increases together with the increase in gluten-sensitive people. However, GF foods might have decreased nutritional quality as compared to the gluten containing counterparts. In this work, an investigation of the phenolic and antioxidant profile in 18 GF flours belonging to legumes, cereals and pseudocereals was achieved. Significant differences could be observed across samples. Total phenolic content was highest in violet rice flours, whereas total anthocyanins were highest in violet, nerone, and black rice flours. FRAP and ORAC antioxidant activities were correlated to phenolic contents and found to be higher in violet rice flours. Metabolomics highlighted a wide diversity in phenolics, with flavonoids (197 compounds ascribable to anthocyanins, flavones, flavanones, isoflavonoids, flavonols, and flavanols), phenolic acids (74 compounds belonging to hydroxycinnamics, hydroxybenzoics, and hydroxyphenylacetics), and tyrosol derivatives the most represented. Finally, OPLS-DA multivariate statistics outlined flavonoids, furofurans and phenolic acids as the most discriminant phenolics.

Study of the Grape Cryo-Maceration Process at Different Temperatures

This research aimed to determine the effects of cryo-maceration at different temperatures on polyphenol content during the winemaking process of Chardonnay wine. Samples of Chardonnay grapes were subjected to rapid cooling processes by direct injection of liquid CO₂ to obtain final temperatures of 10.0, 8.0, 6.0 and 4.0 °C and yield different batches of grape mash. Subsequently, each batch underwent the winemaking process to produce four different wines. The wines obtained were characterized by chemical analyses. We observed higher extraction of polyphenolic compounds with low-temperature cold maceration, particularly when the temperature was reduced from 10.0 to 6.0 °C. Conversely, when the temperature was reduced below 6.0 °C, the increase in polyphenol content in wine was negligible, whereas CO₂ consumption increased. Furthermore, a numerical simulation was performed to determine the pipe length, L₀, after which the temperature was constant. This condition is very important because it guarantees that after the length L₀, the thermodynamic exchange between liquid CO₂ and is complete, eliminating the possibility of liquid CO₂ pockets in the cyclone.