Binding of dietary polyphenols to cellulose: structural and nutritional aspects

Studies on the binding characteristics of three polysaccharides with different molecular weight and flavonoids from corn silk (Maydis stigma)

Polysaccharides and flavonoids co-existed in corn silk (Maydis stigma) could interact inevitably during processing and digestion. In this study, the binding interaction between three polysaccharides with different molecular weight and flavonoids from corn silk was characterized using molecular dynamic and thermodynamic simulation. And the corn silk polysaccharides-flavonoids complex (CSP - CSF complex) was characterized using fourier transform infrared (FT-IR) spectra, circular dichroism (CD), scanning electron microscope (SEM) and differential scanning calorimetry (DSC). The three polysaccharides from corn silk showed the molecular weight distributions of 43.3 kDa, 61.3 kDa and 106.6 kDa, respectively, and they had the same monosaccharide types with different ratios. The adsorption of flavonoids to polysaccharides might be mostly driven by van der Waals forces and hydrogen bonding, and it could be described through various isothermal models and thermodynamic equations such as Langmuir, Freundlich equations and Clausius-Clapeyron equation. This type of interactions could improve the biological activities of polysaccharides such as α-amylase and α-glucosidase inhibition.

Gastrointestinal interactions, absorption, splanchnic metabolism and pharmacokinetics of orally ingested phenolic compounds

The positive health effects of phenolic compounds (PCs) have been extensively reported in the literature. An understanding of their bioaccessibility and bioavailability is essential for the elucidation of their health benefits. Before reaching circulation and exerting bioactions in target tissues, numerous interactions take place before and during digestion with either the plant or host's macromolecules that directly impact the organism and modulate their own bioaccessibility and bioavailability. The present work is focused on the gastrointestinal (GI) interactions that are relevant to the absorption and metabolism of PCs and how these interactions impact their pharmacokinetic profiles. Non-digestible cell wall components (fiber) interact intimately with PCs and delay their absorption in the small intestine, instead carrying them to the large intestine. PCs not bound to fiber interact with digestible nutrients in the bolus where they interfere with the digestion and absorption of proteins, carbohydrates, lipids, cholesterol, bile salts and micronutrients through the inhibition of digestive enzymes and enterocyte transporters and the disruption of micelle formation. PCs internalized by enterocytes may reach circulation (through transcellular or paracellular transport), be effluxed back into the lumen (P-glycoprotein, P-gp) or be metabolized by phase I and phase II enzymes. Some PCs can inhibit P-gp or phase I/II enzymes, which can potentially lead to drug-nutrient interactions. The absorption and pharmacokinetic parameters are modified by all of the interactions within the digestive tract and by the presence of other PCs. Undesirable interactions have promoted the development of nanotechnological approaches to promote the bioaccessibility, bioavailability, and bioefficacy of PCs.

Bioaccessibility of hydroxycinnamic acids and antioxidant capacity from sorghum bran thermally processed during simulated in vitro gastrointestinal digestion

Sorghum is a source of hydroxycinnamic acids (HCA), which have shown antioxidant, anti-inflammatory and anti-proliferative capacities. However, a high proportion of them have low bioaccessibility due the complex structural disposition of the plant's cell wall. The effects of boiling and extrusion processes on sorghum bran and their effects on the antioxidant capacity and bioaccessibility of HCA during simulated in vitro gastrointestinal digestion were investigated. The bioaccessibility of phenolic compounds was significantly higher in extruded sorghum bran (38.4%) than that obtained by boiling (29.5%). This is consistent with the increase of the antioxidant capacity after in vitro digestion. In contrast, a low bioaccessibility of pure monomeric HCA was observed when they were exposed to in vitro gastrointestinal digestion. There were significant bioaccessibility reductions of 36.8, 19.5, 13.5, 62.1% for caffeic, ρ-coumaric, ferulic and sinapic acids, respectively, when unproccessed sorghum bran was added. Although the bioaccessibility of monomeric HCA was low, the total phenolic compounds and antioxidant capacity increased during the digestion simulation due to the thermal processes of extrusion and boiling. Extrusion and boiling could be utilized to produce food based on sorghum bran with biological potential.

Gut Fermentation of Dietary Fibres: Physico-Chemistry of Plant Cell Walls and Implications for Health

The majority of dietary fibre (DF) originates from plant cell walls. Chemically, DF mostly comprise carbohydrate polymers, which resist hydrolysis by digestive enzymes in the mammalian small intestine, but can be fermented by large intestinal bacteria. One of the main benefits of DF relate to its fermentability, which affects microbial diversity and function within the gastro-intestinal tract (GIT), as well as the by-products of the fermentation process. Much work examining DF tends to focus on various purified ingredients, which have been extracted from plants. Increasingly, the validity of this is being questioned in terms of human nutrition, as there is evidence to suggest that it is the actual complexity of DF which affects the complexity of the GIT microbiota. Here, we review the literature comparing results of fermentation of purified DF substrates, with whole plant foods. There are strong indications that the more complex and varied the diet (and its ingredients), the more complex and varied the GIT microbiota is likely to be. Therefore, it is proposed that as the DF fermentability resulting from this complex microbial population has such profound effects on human health in relation to diet, it would be appropriate to include DF fermentability in its characterization-a functional approach of immediate relevance to nutrition.

The influences of added polysaccharides on the properties of bacterial crystalline nanocellulose

Acid hydrolyzed bacterial crystalline nanocellulose (BCNC) with different nanofiber morphologies, geometrical dimensions, crystalline structure and mechanical properties were obtained by adding different polysaccharides into the growing culture medium. Arabinogalactan had little effect on the characteristics of BCNC due to its negligible binding affinity to bacterial cellulose (BC). Bacterial exopolysaccharides were capable of modulating the bundling of cellulose microfibrils during BC formation, resulting in BCNC with bundled nanocrystals, high crystallinity, a less sulfated surface, and improved thermal stability and tensile properties. Xylan/BCNC and xyloglucan/BCNC exhibited the most significant improvements, including an increased length and aspect ratio, a significantly less sulfated surface and superior thermal stability and tensile properties. It is hypothesized that the improvement in CNC characteristics results from a change in amorphous cellulose formation in the native BC. This study also suggests that improved feedstocks for producing CNCs may be obtained by modulating hemicellulose production in plants.

Cell wall biomechanics: a tractable challenge in manipulating plant cell walls 'fit for purpose'!

The complexity and recalcitrance of plant cell walls has contributed to the success of plants colonising land. Conversely, these attributes have also impeded progress in understanding the roles of walls in controlling and directing developmental processes during plant growth and also in unlocking their potential for biotechnological innovation. Recent technological advances have enabled the probing of how primary wall structures and molecular interactions of polysaccharides define their biomechanical (and hence functional) properties. The outputs have led to a new paradigm that places greater emphasis on understanding how the wall, as a biomechanical construct and cell surface sensor, modulates both plant growth and material properties. Armed with this knowledge, we are gaining the capacity to design walls 'fit for (biotechnological) purpose'!

Food processing strategies to enhance phenolic compounds bioaccessibility and bioavailability in plant-based foods

Phenolic compounds are important constituents of plant-based foods, as their presence is related to protective effects on health. To exert their biological activity, phenolic compounds must be released from the matrix during digestion in an absorbable form (bioaccessible) and finally absorbed and transferred to the bloodstream (bioavailable). Chemical structure and matrix interactions are some food-related factors that hamper phenolic compounds bioaccessibility and bioavailability, and that can be counteracted by food processing. It has been shown that food processing can induce chemical or physical modifications in food that enhance phenolic compounds bioaccessibility and bioavailability. These changes include: (i) chemical modifications into more bioaccessible and bioavailable forms; (ii) cleavage of covalent or hydrogen bonds or hydrophobic forces that attach phenolic compounds to matrix macromolecules; (iii) damaging microstructural barriers such as cell walls that impede the release from the matrix; and (iv) create microstructures that protect phenolic compounds until they are absorbed. Indeed, food processing can produce degradation of phenolic compounds, however, it is possible to counteract it by modulating the operating conditions in favor of increased bioaccessibility and bioavailability. This review compiles the current knowledge on the effects of processing on phenolic compounds bioaccessibility or bioavailability, while suggesting new guidelines in the search of optimal processing conditions as a step forward towards the design of healthier foods.

Interactions between cell wall polysaccharides and polyphenols

In plant-based food systems such as fruits, vegetables, and cereals, cell wall polysaccharides and polyphenols co-exist and commonly interact during processing and digestion. The noncovalent interactions between cell wall polysaccharides and polyphenols may greatly influence the physicochemical and nutritional properties of foods. The affinity of cell wall polysaccharides with polyphenols depends on both endogenous and exogenous factors. The endogenous factors include the structures, compositions, and concentrations of both polysaccharides and polyphenols, and the exogenous factors are the environmental conditions such as pH, temperature, ionic strength, and the presence of other components (e.g., protein). Diverse methods used to directly characterize the interactions include NMR spectroscopy, size-exclusion chromatography, confocal microscopy, isothermal titration calorimetry, molecular dynamics simulation, and so on. The un-bound polyphenols are quantified by liquid chromatography or spectrophotometry after dialysis or centrifugation. The adsorption of polyphenols by polysaccharides is mostly driven by hydrophobic interactions and hydrogen bonding, and can be described by various isothermal models such as Langmuir and Freundlich equations. Quality attributes of various food and beverage products (e.g., wine) can be significantly affected by polysaccharide-polyphenol interactions. Nutritionally, the interactions play an important role in the digestive tract of humans for the metabolism of both polyphenols and polysaccharides.

Cyanidin-3-O-glucoside: Physical-Chemistry, Foodomics and Health Effects

Anthocyanins (ACNs) are plant secondary metabolites from the flavonoid family. Red to blue fruits are major dietary sources of ACNs (up to 1 g/100 g FW), being cyanidin-3-O-glucoside (Cy3G) one of the most widely distributed. Cy3G confers a red hue to fruits, but its content in raspberries and strawberries is low. It has a good radical scavenging capacity (RSC) against superoxide but not hydroxyl radicals, and its oxidative potential is pH-dependent (58 mV/pH unit). After intake, Cy3G can be metabolized (phases I, II) by oral epithelial cells, absorbed by the gastric epithelium (1%-10%) and it is gut-transformed (phase II &amp; microbial metabolism), reaching the bloodstream (<1%) and urine (about 0.02%) in low amounts. In humans and Caco-2 cells, Cy3G's major metabolites are protocatechuic acid and phloroglucinaldehyde which are also subjected to entero-hepatic recycling, although caffeic acid and peonidin-3-glucoside seem to be strictly produced in the large bowel and renal tissues. Solid evidence supports Cy3G's bioactivity as DNA-RSC, gastro protective, anti-inflammatory, anti-thrombotic chemo-preventive and as an epigenetic factor, exerting protection against Helicobacter pylori infection, age-related diseases, type 2 diabetes, cardiovascular disease, metabolic syndrome and oral cancer. Most relevant mechanisms include RSC, epigenetic action, competitive protein-binding and enzyme inhibition. These and other novel aspects on Cy3G's physical-chemistry, foodomics, and health effects are discussed.

Re-evaluation of the mechanisms of dietary fibre and implications for macronutrient bioaccessibility, digestion and postprandial metabolism

The positive effects of dietary fibre on health are now widely recognised; however, our understanding of the mechanisms involved in producing such benefits remains unclear. There are even uncertainties about how dietary fibre in plant foods should be defined and analysed. This review attempts to clarify the confusion regarding the mechanisms of action of dietary fibre and deals with current knowledge on the wide variety of dietary fibre materials, comprising mainly of NSP that are not digested by enzymes of the gastrointestinal (GI) tract. These non-digestible materials range from intact cell walls of plant tissues to individual polysaccharide solutions often used in mechanistic studies. We discuss how the structure and properties of fibre are affected during food processing and how this can impact on nutrient digestibility. Dietary fibre can have multiple effects on GI function, including GI transit time and increased digesta viscosity, thereby affecting flow and mixing behaviour. Moreover, cell wall encapsulation influences macronutrient digestibility through limited access to digestive enzymes and/or substrate and product release. Moreover, encapsulation of starch can limit the extent of gelatinisation during hydrothermal processing of plant foods. Emphasis is placed on the effects of diverse forms of fibre on rates and extents of starch and lipid digestion, and how it is important that a better understanding of such interactions with respect to the physiology and biochemistry of digestion is needed. In conclusion, we point to areas of further investigation that are expected to contribute to realisation of the full potential of dietary fibre on health and well-being of humans.