More than 500 phenolic compounds have been reported as present in foodstuffs, and their intake has been related to the prevention of several chronic diseases. Most of the literature on phenolic ...compounds focuses on those present in the supernatant of aqueous-organic extractions: extractable phenolics. Nevertheless, significant amounts of phenolic compounds remain in the solid residues after such extractions. These nonextractable phenolics are mostly proanthocyanidins, phenolic acids, and hydrolyzable tannins that are closely associated with the food matrix. Studies of this fraction of dietary phenolic compounds are scarce, and the few there are usually refer to particular types of phenolics rather than to the fraction as a whole. The present review reports the state-of-the-art methods that currently exist for analyzing nonextractable phenolic compounds in foods.
The effects of temperature (50–200 °C) and contact time (5–30 min) on the pressurized hot water extraction of deodorized thyme were explored for antioxidant activity, polyphenol profiles, and total ...antioxidants. Six not previously reported polyphenolic compounds were identified in thyme. An inverse correlation was found between the antioxidant activity and total antioxidants with the amount and diversity of polyphenols. The highest total extract yield and antioxidant activity were obtained at 200 °C, although maximum polyphenol extraction yields of hydroxycinnamic acids, flavones, flavonols/flavanones, and total polyphenols were detected at 100 °C and 5 min. Higher temperatures and longer exposure times reduced extract polyphenol diversity. Dihydroxyphenyllactic acid was the only phenolic compound for which extraction yield increased with temperature, probably as a product of the thermal degradation of rosmarinic acid. Consequently, for extracting phenolics from thyme, 100 °C and 5 min would be appropriate operating conditions, whereas antioxidant-active nonphenolic compounds were favored at higher temperatures and exposure times.
A preliminary approximation to characterizes the banana culture by‐products, like banana flowers and banana pseudo‐stem, including a comprehensive analysis of the phenolic compounds by HPLC‐MS was ...performed in this study. The results suggest that both materials showed to have a potential for their use as novel food ingredients.
Abstract Objective The objective of the study was to evaluate the effects of a grape product rich in dietary fiber and natural antioxidants on cardiovascular disease risk factors. Methods A ...randomized, controlled parallel-group trial was carried out. Thirty-four non-smoking (21 normocholesterolemic and 13 hypercholesterolemic) adults were supplemented for 16 wk with 7.5 g/d of grape antioxidant dietary fiber, a natural product containing 5.25 g of dietary fiber and 1400 mg of polyphenols. Nine non-supplemented non-smokers were followed as a control group. Fasting blood samples, blood pressure, and anthropometric readings were obtained at baseline and at week 16. Subjects were allowed to consume their regular diet, which was monitored weekly. Results Grape antioxidant dietary fiber (7.5 g/d) reduced significantly ( P < 0.05) total cholesterol (9%), low-density lipoprotein cholesterol (9%), and systolic and diastolic blood pressures (6% and 5% respectively). Greater reductions in total cholesterol (14.2%) and low-density lipoprotein cholesterol (11.6%, P < 0.05) were observed in hypercholesterolemic subjects. No changes were observed in the control group. There was a reduction of 2.5 points in the Framingham Global Risk Score in the supplemented group. A significant reduction in triacylglycerol concentration took place in the supplemented hypercholesterolemic subjects (18.6%, P < 0.05). Conclusion Grape antioxidant dietary fiber showed significant reducing effects in lipid profile and blood pressure. The effects appear to be higher than the ones caused by other dietary fibers, such as oat fiber or psyllium, probably due to the combined effect of dietary fiber and antioxidants.
Grape pomace was extracted with pressurized hot water at laboratory scale before and after fermentation to explore the effects of fermentation and extraction temperature (50-200 °C) and time (5 and ...30 min) on total extracted antioxidant levels and activity and to determine the content and recovery efficiency of main grape polyphenols, anthocyanins, and tannins. Fermented pomace yielded more total antioxidants (TAs), antioxidant activity, and tannins, than unfermented pomace but fewer anthocyanins. Elevating the extraction temperature increased TA extraction and antioxidant activity. Maximum anthocyanin extraction yields were achieved at 100 °C and at 150 °C for tannins and tannin-anthocyanin adducts. Using higher temperatures and longer extraction times resulted in a sharp decrease of polyphenol extraction yield. Relevant proanthocyanidin amounts were extracted only at 50 and 100 °C. Finally, TA recovery and activity were not directly related to the main polyphenol content when performing pressurized hot water grape pomace extraction.
The comparison between antioxidant capacity values reported by different laboratories is quite difficult because of substantial differences in sample preparation, extraction of antioxidants and ...expression of results. An updated methodology to determine of antioxidant capacity in plant foods, oils and beverages – including extraction of antioxidants, measurement of antioxidant capacity and expression of results – is presented. During sample preparation, loss of antioxidants in drying and milling steps must be minimized. Antioxidant capacity is determined in aqueous-organic extracts (combining at least two extraction cycles) and in the corresponding residues (acidic hydrolyzates to release condensed proanthocyanidins and hydrolyzable phenolics). Different aspects, such as type of solvent and possible interferences form non-antioxidant compounds, that may affect the results of the most common methods of antioxidant capacity (FRAP, ABTS, DPPH and ORAC) are discussed. The different ways of expressing antioxidant capacity results, including kinetic parameters, are described.
Scope
Dietary polyphenols have shown promising effects in mechanistic and preclinical studies on the regulation of cardiometabolic alterations. Nevertheless, clinical trials have provided ...contradictory results, with high inter‐individual variability. This study explores the role of gut microbiota and microRNAs (miRNAs) as factors contributing to the inter‐individual variability in polyphenol response.
Methods and Results
49 subjects with at least two factors of metabolic syndrome are divided between responders (n = 23) or non‐responders (n = 26), depending on the variation rate in fasting insulin after grape pomace supplementation (6 weeks). The populations of selected fecal bacteria are estimated from fecal deoxyribonucleic acid (DNA) by quantitative real‐time polymerase chain reaction (qPCR), while the microbial‐derived short‐chain fatty acids (SCFAs) are measured in fecal samples by gas chromatography. MicroRNAs are analyzed on a representative sample, followed by targeted miRNA analysis. Responder subjects show significantly lower (p < 0.05) Prevotella and Firmicutes levels, and increased (p < 0.05) miR‐222 levels.
Conclusion
After evaluating the selected substrates for Prevotella and target genes of miR‐222, these variations suggest that responders are those subjects exhibiting impaired glycaemic control. This study shows that fecal microbiota and miRNA expression may be related to inter‐individual variability in clinical trials with polyphenols.
Subjects at high metabolic risk with
higher levels of plasma insulin concentration are sensitive to grape pomace
(Responders) while showing reduced levels of Firmicutes and Prevotella, along with increased expression of miR‐222.
The variations in miR‐222 as well as in Prevotella could be indicators of responsiveness, suggesting that responders are those subjects showing impaired glycaemic control.
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.
Practical Application
In this study, the composition of several edible seaweeds from Chile, in terms of macromolecular antioxidants and dietary fiber, was evaluated. All the seaweeds showed relevant content of these constituents. Given the nutritional interest of these compounds, the consumption of these seaweeds might be promoted within the frame of a healthy diet and they can also be used as sources of macromolecular antioxidants and dietary fiber for the production of new ingredients.
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.
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