Effects of acute intake of grape/pomegranate pomace dietary supplement on glucose metabolism and oxidative stress in adults with abdominal obesity.

A controlled acute, cross-over clinical study (NCT02710461) was performed in order to evaluate the effects on glucose metabolism of a grape/pomegranate pomace dietary supplement in subjects with abdominal obesity (aged 40-60, n = 20). A standard 75 g oral glucose tolerance test (OGTT) was administered alone, together with or 10 h after the consumption of 10 g of the dietary supplement, rich in both extractable (0.4 g) and non-extractable (1.4 g) polyphenols. The dietary supplement did not ameliorate glucose or insulin at any sampling time. No improvement in antioxidant capacity was observed in plasma or urine, concordant with no increased urine polyphenol excretion. A tendency towards improved insulin sensitivity was observed when the product was consumed 10 h before glucose solution. These results suggest that a single realistic dose of grape/pomegranate pomace is not able to clearly improve glucose metabolism; chronic intake remains to be evaluated.

A 6-week supplementation with grape pomace to subjects at cardiometabolic risk ameliorates insulin sensitivity, without affecting other metabolic syndrome markers.

Grape polyphenols have shown a promising role in the modulation of metabolic syndrome (MetS), mostly in animal models. However, clinical studies are scarce and they usually only consider a fraction of polyphenols, ignoring the non-extractable polyphenols (high molecular weight compounds or associated with macromolecules such as dietary fibre). This study aimed at evaluating the effect of grape pomace, rich in both extractable and non-extractable polyphenols, on markers of MetS. Fifty subjects (22 women) aged 20-65 with at least two MetS factors were randomly assigned to the product (daily dose of 8 g of dried grape pomace) or to the control group in a 6 week crossover design with a 4 week wash-out. Samples were collected at the beginning and at the end of both periods; half of the participants were subjected to an oral glucose tolerance test at the beginning and the end of the supplementation period. Grape pomace supplementation significantly improved fasting insulinaemia (p < 0.01), without affecting other cardiometabolic risk parameters. A tendency towards an improvement in postprandial insulinaemia was observed, particularly in those subjects with higher fasting insulin levels. Therefore, supplementation with grape pomace may be a strategy for improving insulin sensitivity in subjects at high cardiometabolic risk.

Fruit peels as sources of non-extractable polyphenols or macromolecular antioxidants: Analysis and nutritional implications.

Despite increasing interest in the relevance of non-extractable polyphenols (NEPP) or macromolecular antioxidants as food bioactive compounds, most studies on their presence in foods focus mainly on the edible part of specific fruits, but their potential presence in fruit peels is usually ignored. The aim of this study was to evaluate NEPP content in the peels from ten common fruits. The results showed that NEPP made up more than half of the total polyphenol contents in half of the studied samples. HPLC analysis showed that NEPP were constituted by phenolic acids, flavanols and flavonols. Also, it was found that peels accounted for >40% of total NEPP in the fruit in four of the samples analysed. These results should encourage both the use of fruit peels in the fruit industry as ingredients and the consumption of whole fruits given the significant presence of NEPP in fruit peels.

Comprehensive Characterization of Extractable and Nonextractable Phenolic Compounds by High-Performance Liquid Chromatography-Electrospray Ionization-Quadrupole Time-of-Flight of a Grape/Pomegranate Pomace Dietary Supplement.

Grape and pomegranate are rich sources of phenolic compounds, and their derived products could be used as ingredients for the development of functional foods and dietary supplements. However, the profile of nonextractable or macromolecular phenolic compounds in these samples has not been evaluated. Here, we show a comprehensive characterization of extractable and nonextractable phenolic compounds of a grape/pomegranate pomace dietary supplement using high-performance liquid chromatography-electrospray ionization-quadrupole time-of-flight (HPLC-ESI-QTOF) and matrix-assisted laser desorption/ionization (MALDI)-TOF techniques. The main extractable phenolic compounds were several anthocyanins (principally malvidin 3-O-glucoside) as well as gallotannins and gallagyl derivatives; some phenolic compounds were reported in grape or pomegranate for the first time. Additionally, there was a high proportion of nonextractable phenolic compounds, including vanillic acid, and dihydroxybenzoic acid. Unidentified polymeric structures were detected by MALDI-TOF MS analysis. This study shows that mixed grape and pomegranate pomaces are a source of different classes of phenolic compounds including a high proportion of nonextractable phenolic compounds.

Antioxidantes macromoleculares: importancia en salud y perspectivas / Macromolecular Antioxidants: Importance in Health and Perspectives

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Macromolecular Antioxidants and Dietary Fiber in Edible Seaweeds.

Seaweeds are rich in different bioactive compounds with potential uses in drugs, cosmetics and the food industry. The objective of this study was to analyze macromolecular antioxidants or nonextractable polyphenols, in several edible seaweed species collected in Chile (Gracilaria chilensis, Callophyllis concepcionensis, Macrocystis pyrifera, Scytosyphon lomentaria, Ulva sp. and Enteromorpha compressa), including their 1st HPLC characterization. Macromolecular antioxidants are commonly ignored in studies of bioactive compounds. They are associated with insoluble dietary fiber and exhibit significant biological activity, with specific features that are different from those of both dietary fiber and extractable polyphenols. We also evaluated extractable polyphenols and dietary fiber, given their relationship with macromolecular antioxidants. Our results show that macromolecular antioxidants are a major polyphenol fraction (averaging 42% to total polyphenol content), with hydroxycinnamic acids, hydroxybenzoic acids and flavonols being the main constituents. This fraction also showed remarkable antioxidant capacity, as determined by 2 complementary assays. The dietary fiber content was over 50% of dry weight, with some samples exhibiting the target proportionality between soluble and insoluble dietary fiber for adequate nutrition. Overall, our data show that seaweed could be an important source of commonly ignored macromolecular antioxidants.

Contribution of Macromolecular Antioxidants to Dietary Antioxidant Capacity: A Study in the Spanish Mediterranean Diet.

Epidemiological and clinical studies show that diets with a high antioxidant capacity, such us those rich in plant food and beverages, are associated with significant decreases in the overall risk of cardiovascular disease or colorectal cancer. Current studies on dietary antioxidants and dietary antioxidant capacity focus exclusively on low molecular weight or soluble antioxidants (vitamins C and E, phenolic compounds and carotenoids), ignoring macromolecular antioxidants. These are polymeric phenolic compounds or polyphenols and carotenoids linked to plant food macromolecules that yield bioavailable metabolites by the action of the microbiota with significant effects either local and/or systemic after absorption. This study determined the antioxidant capacity of the Spanish Mediterranean diet including for the first time both soluble and macromolecular antioxidants. Antioxidant capacity and consumption data of the 54 most consumed plant foods and beverages were used. Results showed that macromolecular antioxidants are the major dietary antioxidants, contributing a 61% to the diet antioxidant capacity (8000 µmol Trolox, determined by ABTS method). The antioxidant capacity data for foods and beverages provided here may be used to estimate the dietary antioxidant capacity in different populations, where similar contributions of macromolecular antioxidants may be expected, and also to design antioxidant-rich diets. Including macromolecular antioxidants in mechanistic, intervention and observational studies on dietary antioxidants may contribute to a better understanding of the role of antioxidants in nutrition and health.

Obtainment and characterization of a potential functional ingredient from olive.

Current olive oil production methods generate huge amounts of polluting waste, containing most of the health-related compounds in olive. Here, a new product is obtained from olive after pitting, drying and oil extraction, without generating waste. Its characterization showed the presence, within a single matrix, of more than 90% of the polyphenols present in olive, including hydroyxtyrosols (commonly not transferred to olive oil), dietary fiber, oleic acid and polyalcohols. This product is a potential new functional ingredient, consumption of which may lead to additive and/or synergic activities among its constituents; some of which already have approved health claims. Additionally, the olive oil obtained exhibits profiles of fatty acids and phenolic compounds similar to those of commercial olive oil. The procurement of this potential functional ingredient may represent a new approach to the revalorization of olive that additionally decreases waste.

Macromolecular antioxidants or non-extractable polyphenols in fruit and vegetables: Intake in four European countries.

Macromolecular antioxidants or non-extractable polyphenols are an emerging and ignored fraction of dietary antioxidants that present differential structural and physiological features as compared with the well-known extractable polyphenols. In this study, the macromolecular antioxidant content and profile were determined by the first time for the 24 most consumed fruit and vegetables in four European countries (France, Germany, The Netherlands and Spain). Results showed that macromolecular antioxidants, made up of hydolysable polyphenols and polymeric proanthocyanidins, are major contributors (mean value 57%) to the total polyphenol content of fruit and vegetables. Macromolecular antioxidant intake from fruit and vegetable determined in the four countries selected was about 200mg. Spain had the highest daily per capita macromolecular antioxidant intake from fruit, while The Netherlands had the highest intake derived from vegetables. Future studies of plant food macromolecular antioxidant analysis and of dietary intakes in different populations are needed to elucidate the contribution of these macromolecular antioxidants to the health effects associated with fruit and vegetable consumption, and with dietary antioxidant intake.

Regular consumption of an antioxidant-rich juice improves oxidative status and causes metabolome changes in healthy adults.

An improvement in oxidative status is associated with a reduction in the incidence of several chronic diseases. However, daily intake of antioxidants in Western diets is decreasing. This study evaluates the effect of daily consumption of an antioxidant-rich juice (ARJ) on oxidative status, cardiovascular disease risk parameters, and untargeted plasma and urine metabolomes. Twenty-eight healthy young adults participated in an 8-week clinical trial by drinking 200 mL of ARJ (pomegranate and grape) daily. At the end of the study, the subjects showed a significant decrease (-29%) in plasma lipid oxidation (malondialdehyde concentration), and a significant increase (+115%) in plasma antioxidant capacity. Plasma and urine metabolomes were also significantly modified and some ions modified in urine were identified, including metabolites of polyphenols, ascorbic acid and biliary acids. No significant changes were observed in lipid profile, inflammation, blood pressure or glycaemia. These results show that incorporating antioxidant-rich beverages into common diets may improve oxidative status in healthy subjects.

Non-extractable polyphenols, a major dietary antioxidant: occurrence, metabolic fate and health effects.

Current research on dietary antioxidants misses the so-called non-extractable polyphenols (NEPP), which are not significantly released from the food matrix either by mastication, acid pH in the stomach or action of digestive enzymes, reaching the colon nearly intact. NEPP, not detected by the usual analytical procedures, are made up of macromolecules and single phenolic compounds associated with macromolecules. Therefore, NEPP are not included in food and dietary intake data nor in bioavailability, intervention or observational studies. The present paper aims to provide an overview of dietary NEPP - nature, occurrence in diet, metabolic fate and possible health effects. NEPP are a relevant fraction of dietary polyphenols exerting their main biological action in the colon, where they are extensively fermented by the action of microbiota, giving place to absorbable metabolites. NEPP exhibit different potential health-related properties, in particular in relation to gastrointestinal health, such as increases in antioxidant and antiproliferative capacities, reduction of intestinal tumorigenesis and modification of gene expression, as observed in different animal models. Further research into NEPP may provide a better understanding of the health effects of dietary antioxidants.

Grape antioxidant dietary fiber inhibits intestinal polyposis in ApcMin/+ mice: relation to cell cycle and immune response.

Epidemiological and experimental studies suggest that fiber and phenolic compounds might have a protective effect on the development of colon cancer in humans. Accordingly, we assessed the chemopreventive efficacy and associated mechanisms of action of a lyophilized red grape pomace containing proanthocyanidin (PA)-rich dietary fiber [grape antioxidant dietary fiber (GADF)] on spontaneous intestinal tumorigenesis in the Apc(Min/+) mouse model. Mice were fed a standard diet (control group) or a 1% (w/w) GADF-supplemented diet (GADF group) for 6 weeks. GADF supplementation greatly reduced intestinal tumorigenesis, significantly decreasing the total number of polyps by 76%. Moreover, size distribution analysis showed a considerable reduction in all polyp size categories [diameter <1mm (65%), 1-2mm (67%) and >2mm (87%)]. In terms of polyp formation in the proximal, middle and distal portions of the small intestine, a decrease of 76, 81 and 73% was observed, respectively. Putative molecular mechanisms underlying the inhibition of intestinal tumorigenesis were investigated by comparison of microarray expression profiles of GADF-treated and non-treated mice. We observed that the effects of GADF are mainly associated with the induction of a G1 cell cycle arrest and the downregulation of genes related to the immune response and inflammation. Our findings show for the first time the efficacy and associated mechanisms of action of GADF against intestinal tumorigenesis in Apc(Min/+) mice, suggesting its potential for the prevention of colorectal cancer.

Concept and health-related properties of nonextractable polyphenols: the missing dietary polyphenols.

Most research studies in the field of dietary polyphenols or phenolic compounds use a chemical approach focusing exclusively on polyphenols extracted from plant foods with organic solvents. However, an appreciable part of polyphenols are not extracted with organic solvents and thus are ignored in biological, nutritional, and epidemiological studies. Recent studies have shown that these nonextractable polyphenols (NEPP) are a major part of total dietary polyphenols and that they exhibit a significant biological activity. A physiological approach is proposed on the basis that the bioavailability and health-related properties of polyphenols depend on their solubility in intestinal fluids, which is different from their solubility in organic solvents. This paper tries to clarify the concept of NEPP, distinguishing between chemical and physiological approaches and pointing out the main qualitative and quantitative differences between them. It is stressed that the literature and databases refer to only extractable polyphenols. Greater attention to NEPP may fill the current gap in the field of dietary polyphenols.

Improved procedure to determine non-extractable polymeric proanthocyanidins in plant foods.

Proanthocyanidins (PA) or condensed tannins, a major group of oligomeric and polymeric dietary polyphenols, have an essential role on the organoleptic and health-related properties of plant foods. Their content is usually determined by HPLC analysis of aqueous-organic extracts. However, appreciable amounts of polymeric PA that remain in the residues of extraction usually are not considered for the analysis. A complete quantification of PA requires an additional determination of these non-extractable PA (NEPA). The objective of this work was to develop a new procedure to determine the content of NEPA, based in depolymerization by butanolysis, which yields anthocyanidin monomers and xanthylium compounds. Samples and standard are treated with butanol/HCl with FeCl3 (100 °C, 60 min), and absorbances at 555 nm (anthocyanidins) and 450 nm (xanthylium compounds) are measured in the hydrolysates. NEPA content determined in some plant foods suggests that procedures based just on anthocyanidin concentration overestimate the actual content.

Metabolite production during in vitro colonic fermentation of dietary fiber: analysis and comparison of two European diets.

Metabolite production and antioxidant released during colonic fermentation of naturally occurring dietary fiber (DF) from two European diets (Mediterranean and Scandinavian) were determined. With this aim, DF and associated components were isolated from both whole diets, as well as from cereals and fruits and vegetables comprising the diets. DF was used as substrate for colonic fermentation in a dynamic in vitro model of the colon, samples were collected, and fermentation metabolites were analyzed. Statistical differences between samples were observed in the concentrations of short-chain fatty acids and ammonia and in the ratio acetate/propionate/butyrate. Whole grain cereal DF generated a larger amount of propionate than refined flour cereal DF. Fruit and vegetable DF generated higher amounts of butyrate than cereal DF. Most antioxidant compounds were released from DF during in vitro colonic fermentation. It is concluded that different sources of DF may play a specific role in health maintenance mediated by metabolites produced during colonic fermentation.

Beverages have an appreciable contribution to the intake of soluble dietary fibre: a study in the Spanish diet.

Beverages are generally not taken into account to determine the intakes of dietary fibre (DF) in diets. Soluble dietary fibre (SDF) content was determined in common alcoholic and non-alcoholic beverages - ranging from 0.18 g/l in white wine to 9.01 g/l in instant coffee - and their contribution to the DF intake in the Spanish Mediterranean diet was estimated as 2.13 g/person/day. It is concluded that beverages provide an appreciable amount of SDF in the diet, and the omission of its contribution may lead to underestimate DF intakes.

Dietary fiber as a carrier of dietary antioxidants: an essential physiological function.

The literature addresses dietary fiber (DF) and antioxidants (AOX) separately as nonrelated compounds. This paper proposes to show that DF and AOX could be approached jointly in nutrition and health studies because around 50% of the total dietary antioxidants, mainly polyphenolics, traverse the small intestine linked to dietary fiber. These antioxidants have received little attention so far. They release the fiber matrix in the colon by the action of the bacterial microbiota, producing metabolites and an antioxidant environment. The content of polyphenols associated with DF in different foods and their potential health-related properties, including animal experiments and human trials, are reviewed. It is concluded that the transportation of dietary antioxidants through the gastrointestinal tract may be an essential function of DF.

Conceptual study on maillardized dietary fiber in coffee.

There is a methodological and conceptual overlap between coffee melanoidins and dietary fiber. Green Uganda coffee beans were roasted in a range from 8.1 to 21.6% of weight loss to evaluate melanoidins and dietary fiber. Samples were characterized by color, moisture, solubility, water activity, carbohydrates, polyphenols, protein, soluble dietary fiber (SDF), and melanoidins content. Hydroxymethylfurfural and chlorogenic acids were also measured as chemical markers of the extent of roasting. Melanoidins rapidly increased from 5.6 (light roasting) to 29.1 mg/100 mg soluble dry matter (dark roasting). A melanoidins-like structure was already present in green coffee that might overestimate up to 21.0% of the melanoidins content as determined by colorimetric methods. However, its contribution is variable and very likely depends on the method of drying applied to green coffee. SDF content (mg/100 mg soluble dry matter) gradually increased from 39.4 in green coffee to 64.9 at severe roasting conditions due to incorporation of neoformed colored structures and polyphenols. Then, SDF progressively turns to a maillardized structure, which increased from 11.0 to 45.0% according to the roasting conditions. It is concluded that the content of coffee melanoidins includes a substantial part of dietary fiber and also that coffee dietary fiber includes melanoidins. A conceptual discussion on a new definition of coffee melanoidins as a type of maillardized dietary fiber is conducted.

Nonextractable polyphenols, usually ignored, are the major part of dietary polyphenols: a study on the Spanish diet.

SCOPE: Dietary polyphenols (PP) can be divided into two groups: extractable polyphenols (EPP) or compounds solubilized by aqueous organic solvents, and nonextractable polyphenols (NEPP) or compounds that remain in their corresponding extraction residues. Most studies on food polyphenols and dietary intakes address exclusively EPP. The objective of this work was to determine the actual amount of PP, including NEPP, in food and in a whole diet. METHODS AND RESULTS: HPLC-MS analyses were performed to identify EPP in methanol-acetone extracts and NEPP in the acidic hydrolyzates of their extraction residues in cereals, fruits, vegetables, nuts, and legumes. NEPP contents, estimated as hydrolyzable PP plus nonextractable proanthocyanidins (PA), ranged from 880 mg/100 g dry weight in fruits to 210 mg/100 g in cereals and were substantially higher than the contents of EPP. NEPP intake (day/person) in the Spanish diet (942 mg) is higher than EPP intake (258 mg) fruits and vegetables (746 mg) are the major contributors to the total PP intake (1201 mg). CONCLUSION: Non extractable polyphenols are the major part of dietary polyphenols. The knowledge of intakes and physiological properties of NEPP may be useful for a better understanding of the potential health effects of dietary PP.

Proanthocyanidin metabolites associated with dietary fibre from in vitro colonic fermentation and proanthocyanidin metabolites in human plasma.

Proanthocyanidins (PAs) or condensed tannins, a major group of dietary polyphenols, are oligomers and polymers of flavan-3-ol and flavan-3, 4-diols widely distributed in plant foods. Most literature data on PAs' metabolic fate deal with PAs that can be extracted from the food matrix by aqueous-organic solvents ( extractable proanthocyanidins). However, there are no data on colonic fermentation of non-extractable proanthocyanidins (NEPAs), which arrive almost intact to the colon, mostly associated to dietary fibre (DF). The aim of the present work was to examine colonic fermentation of NEPAs associated with DF, using a model of in vitro small intestine digestion and colonic fermentation. Two NEPA-rich materials obtained from carob pod (Ceratonia siliqua L. proanthocyanidin) and red grapes (grape antioxidant dietary fibre) were used as test samples. The colonic fermentation of these two products released hydroxyphenylacetic acid, hydroxyphenylvaleric acid and two isomers of hydroxyphenylpropionic acid, detected by HPLC-ESI-MS/MS. Differences between the two products indicate that DF may enhance the yield of metabolites. In addition, the main NEPA metabolite in human plasma was 3,4-dihydroxyphenyl acetic acid. The presence in human plasma of the same metabolites as were detected after in vitro colonic fermentation of NEPAs suggests that dietary NEPAs would undergo colonic fermentation releasing absorbable metabolites with potential healthy effects.