Interactions between Salivary Proteins and Dietary Polyphenols: Potential Consequences on Gastrointestinal Digestive Events

Potential of polyphenols from Ligustrum robustum (Rxob.) Blume on enhancing the quality of starchy food during frying

The increasing concerns about health have led to a growing demand for high-quality fried foods. The potential uses of Ligustrum robustum (Rxob.) Blume, a traditional tea in China, as natural additives to enhance the quality of starchy food during frying was studied. Results indicated that L. robustum polyphenols extract (LREs) could improve the quality of fried starchy food, according to the tests of color, moisture content, oil content, texture property, and volatile flavor. The in vitro digestion results demonstrated that LRE reduced the final glucose content from 11.35 ± 0.17 to 10.80 ± 0.70 mmol/L and increased the phenolic content of fried starch foods from 1.23 ± 0.04 to 3.76 ± 0.14 mg/g. The appearance and polarizing microscopy results showed that LRE promoted large starch bulges on the surface of fried starchy foods. Meanwhile, X-ray diffraction results showed that LRE increased the intensity of characteristic diffraction peak of fried starch with a range of 21.8%-28%, and Fourier transform infrared results showed that LRE reduced the damage to short-range order structure of starch caused by the frying process. In addition, LRE increased the aggregation of starch granules according to the SEM observation and decreased the enthalpy of starch gelatinization based on the differential scanning calorimetry results. The present results suggest that LREs have the potential to be utilized as a natural additive for regulating the quality of fried starchy food in food industries. PRACTICAL APPLICATION: The enhancement of L. robustum polyphenols on the quality of starchy food during frying was found, and its mechanisms were also explored. This work indicated that L. robustum might be used as a novel economic natural additive for producing high-quality fried foods.

Interactions between Salivary Proteins and Apple Polyphenols and the Fate of Complexes during Gastric Digestion

Beneficial polyphenols in apples can reach the stomach as complexes formed with salivary proteins. The present study aimed at documenting the interactions between salivary proteins and cider apple polyphenols and the fate of complexes during gastric digestion. A polyphenolic extract was mixed with human saliva, and interactions were characterized by analyzing proteins and polyphenols in the insoluble and soluble fractions of the mixtures, before and after in vitro gastric digestion. Results confirmed that proline-rich proteins can efficiently precipitate polyphenols and suggested that two zinc-binding proteins can also form insoluble complexes with polyphenols. The classes of polyphenols involved in such complexes depended on the polyphenol-to-protein ratio. In vitro gastric digestion led to extensive proteolysis of salivary proteins, and we formulate the hypothesis that the resulting peptides can interact with and precipitate some procyanidins. Saliva may therefore partly modulate the bioaccessibility of at least procyanidins in the gastric compartment.

Development and validation of a LC-MS/MS method for the quantification of phenolic compounds in human saliva after intake of a procyanidin-rich pine bark extract

Plant-derived phenolic compounds are regularly ingested as food compounds or as food supplements. Concentrations of individual compounds and metabolites are typically measured in serum or urine samples. This, however, allows no conclusion on the distribution into organs and tissues. An easily accessible biofluid is saliva. At this point, it was not clear yet, whether polyphenols circulating in the blood would be secreted or diffuse into saliva. The purpose of the present study was to develop and validate a method using liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) for analysis of phenolic compounds in human saliva. Method validation for the quantification of taxifolin, ferulic acid, caffeic acid, gallic acid, para-coumaric acid, and protocatechuic acid and the gut microbial catechin metabolite δ-(3,4-dihydroxyphenyl)-γ-valerolactone (M1) in human saliva was performed according to current guidelines for bioanalytical method validation. The lower limit of quantification ranged from 0.82 ng/ml for M1 to 8.20 ng/ml for protocatechuic acid. The method was successfully applied to an authentic saliva sample of a volunteer after swallowing of procyanidin-rich pine bark extract capsules (dietary supplement Pycnogenol®). All polyphenols except ferulic acid were quantified at concentrations ranging from 1.20 ng/ml (M1) to 10.34 ng/ml (gallic acid). Notably, in contrast to serum samples, all phenolic compounds were present without sulfate or glucuronic acid conjugation in saliva, suggesting an enzymatic deconjugation, e.g., by a β-glucuronidase activity, during compound transfer from serum to saliva. Since M1 is only produced in the gut, its presence in saliva ruled out the possibility of sample contamination by phenolic compounds residing in the oral cavity after food intake. To the best of our knowledge, this is the first time that the gut microbiota-derived metabolite M1 has been detected in saliva. To further investigate the role of phenolic compounds in saliva, the described analytical method can be applied in clinical studies investigating the biodistribution of polyphenols and their metabolites.

Supercritical CO2 extraction of naringenin from Mexican oregano (Lippia graveolens): its antioxidant capacity under simulated gastrointestinal digestion

A supercritical CO2 method was optimized to recover naringenin-rich extract from Mexican oregano (Lippia graveolens), a flavanone with high antioxidant and anti-inflammatory activity. The effect of the extraction parameters like pressure, temperature, and co-solvent on naringenin concentration was evaluated. We used response surface methodology to optimize the naringenin extraction from oregano; the chemical composition by UPLC-MS of the optimized extract and the effect of simulated gastrointestinal digestion on its antioxidant capacity and total phenolic content were also evaluated. The optimum conditions were 58.4 °C and 12.46% co-solvent (ethanol), with a pressure of 166 bar, obtaining a naringenin content of 46.59 mg/g extract. Also, supercritical optimized extracts yielded high quantities of cirsimaritin, quercetin, phloridzin, apigenin, and luteolin. The results indicated that the naringenin-rich extract obtained at optimized conditions had higher total phenolic content, antioxidant capacity by TEAC and ORAC, and flavonoid content, compared with the methanolic extract, and the simulated gastrointestinal digestion reduced all these values.

Effects of Fermentation on Bioactivity and the Composition of Polyphenols Contained in Polyphenol-Rich Foods: A Review

Polyphenols, as common components with various functional activities in plants, have become a research hotspot. However, researchers have found that the bioavailability and bioactivity of plant polyphenols is generally low because they are usually in the form of tannins, anthocyanins and glycosides. Polyphenol-rich fermented foods (PFFs) are reported to have better bioavailability and bioactivity than polyphenol-rich foods, because polyphenols are used as substrates during food fermentation and are hydrolyzed into smaller phenolic compounds (such as quercetin, kaempferol, gallic acid, ellagic acid, etc.) with higher bioactivity and bioavailability by polyphenol-associated enzymes (PAEs, e.g., tannases, esterases, phenolic acid decarboxylases and glycosidases). Biotransformation pathways of different polyphenols by PAEs secreted by different microorganisms are different. Meanwhile, polyphenols could also promote the growth of beneficial bacteria during the fermentation process while inhibiting the growth of pathogenic bacteria. Therefore, during the fermentation of PFFs, there must be an interactive relationship between polyphenols and microorganisms. The present study is an integration and analysis of the interaction mechanism between PFFs and microorganisms and is systematically elaborated. The present study will provide some new insights to explore the bioavailability and bioactivity of polyphenol-rich foods and greater exploitation of the availability of functional components (such as polyphenols) in plant-derived foods.

The perception and influencing factors of astringency, and health-promoting effects associated with phytochemicals: A comprehensive review

Astringency as the complex sensory of drying or shrinking can be perceived from natural foods, including abundant phenolic compounds. Up to now, there have been two possible astringency perception mechanisms of phenolic compounds. The first possible mechanism involved chemosensors and mechanosensors and took salivary binding proteins as the premise. Although piecemeal reports about chemosensors, friction mechanosensor's perception mechanisms were absent. There might be another perception way because a part of astringent phenolic compounds also triggered astringency although they could not bind with salivary proteins, however, the specific mechanism was unclear. Structures caused the differences in astringency perception mechanisms and intensities. Except for structures, other influencing factors also changed astringency perception intensity and aimed to decrease it, which probably ignored the health-promoting effects of phenolic compounds. Therefore, we roundly summarized the chemosensor's perception processes of the first mechanism. Meanwhile, we speculated that friction mechanosensor's probably activated Piezo2 ion channel on cell membranes. Phenolic compounds directly binds with oral epithelial cells, activating Piezo2 ion channel probably the another astringency perception mechanism. Except for structure, the increase of pH values, ethanol concentrations, and viscosity not only lowered astringency perception but were beneficial to improve the bioaccessibility and bioavailability of astringent phenolic compounds, which contributed to stronger antioxidant, anti-inflammatory, antiaging and anticancer effects.

Reduction of phenolics in faba bean meal using recombinantly produced and purified Bacillus ligniniphilus catechol 2,3-dioxygenase

Pulse meal should be a valuable product in the animal feed industry based on its strong nutritional and protein profiles. However, it contains anti-nutritional compounds including phenolics (large and small molecular weight), which must be addressed to increase uptake by the industry. Microbial fermentation is currently used as a strategy to decrease larger molecular weight poly-phenolics, but results in the undesirable accumulation of small mono-phenolics. Here, we investigate cell-free biocatalytic reduction of phenolic content in faba bean (Vicia faba L.) meal. A representative phenolic ring-breaking catechol dioxygenase, Bacillus ligniniphilus L1 catechol 2,3-dioxygenase (BLC23O) was used in this proof-of concept based on its known stability and broad substrate specificity. Initially, large-scale fermentative recombinant production and purification of BLC23O was carried out, with functionality validated by in vitro kinetic analysis. When applied to faba bean meal, BLC23O yielded greatest reductions in phenolic content in a coarse air classified fraction (high carbohydrate), compared to either a fine fraction (high protein) or the original unfractionated meal. However, the upstream hydrolytic release of phenolics from higher molecular weight species (e.g. tannins, or complexes with proteins and carbohydrates) likely remains a rate limiting step, in the absence of other enzymes or microbial fermentation. Consistent with this, when applied to a selection of commercially available purified phenolic compounds, known to occur in faba bean, BLC23O was found to have high activity against monophenolic acids and little if any detectable activity against larger molecular weight compounds. Overall, this study highlights the potential viability of the biocatalytic processing of pulse meals, for optimization of their nutritional and economical value in the animal feed industry.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s40643-023-00633-8.

Grape Polyphenols in the Treatment of Human Skeletal Muscle Damage Due to Inflammation and Oxidative Stress during Obesity and Aging: Early Outcomes and Promises

Today, inactivity and high-calorie diets contribute to the development of obesity and premature aging. In addition, the population of elderly people is growing due to improvements in healthcare management. Obesity and aging are together key risk factors for non-communicable diseases associated with several co-morbidities and increased mortality, with a major impact on skeletal muscle defect and/or poor muscle mass quality. Skeletal muscles contribute to multiple body functions and play a vital role throughout the day, in all our activities. In our society, limiting skeletal muscle deterioration, frailty and dependence is not only a major public health challenge but also a major socio-economic issue. Specific diet supplementation with natural chemical compounds such as grape polyphenols had shown to play a relevant and direct role in regulating metabolic and molecular pathways involved in the prevention and treatment of obesity and aging and their related muscle comorbidities in cell culture and animal studies. However, clinical studies aiming to restore skeletal muscle mass and function with nutritional grape polyphenols supplementation are still very scarce. There is an urgent need for clinical studies to validate the very encouraging results observed in animal models.