Interactions between Beer Compounds and Human Salivary Proteins: Insights toward Astringency and Bitterness Perception.

Beer is one of the most consumed beverages worldwide with unique organoleptic properties. Bitterness and astringency are well-known key features and, when perceived with high intensity, could lead to beer rejection. Most studies on beer astringency and bitterness use sensory assays and fail to study the molecular events that occur inside the oral cavity responsible for those perceptions. This work focused on deepening this knowledge based on the interaction of salivary proteins (SP) and beer phenolic compounds (PCs) and their effect toward these two sensory attributes. The astringency and bitterness of four different beers were assessed by a sensory panel and were coupled to the study of the SP changes and PC profile characterization of beers. The human SP content was measured before (basal) and after each beer intake using HPLC analysis. The beers' PC content and profile were determined using Folin-Ciocalteu and LC-MS spectrometry, respectively. The results revealed a positive correlation between PCs and astringency and bitterness and a negative correlation between SP changes and these taste modalities. Overall, the results revealed that beers with higher PC content (AAL and IPA) are more astringent and bitter than beers with a lower PC content (HL and SBO). The correlation results suggested that an increase in whole SP content, under stimulation, should decrease astringency and bitterness perception. No correlation was found between the changes in specific families of SP and astringency and bitterness perception.

Functionalization of 7-Hydroxy-pyranoflavylium: Synthesis of New Dyes with Extended Chromatic Stability.

This work reports the functionalization of pyranoflavyliums pigment using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride coupling chemistry. Four cinnamic acids were used to establish an ester bond with the hydroxyl group of the pyranoflavylium, namely 4-dimethylamino-, 4-amino-, 4-bromo-, and trans-cinnamic acids. The experimental condition, namely the molar ratios, solvent, and reaction time, were adjusted to obtain higher reaction yields in a reduced period. Excellent reaction yields of 68%, 85%, 94%, and 99% were achieved for 4-amino, trans-, 4-bromo, and 4-dimethylamino pyranoflavylium cinnamates, respectively. The structure of the functionalized pigments was fully clarified using one-dimensional (1H) and two-dimensional (COSY, HSQC, and HMBC) NMR experiments and HRSM analysis. Regardless of the type of functionalization, the UV-Visible spectrum showed a bathochromic shift (red region) on the maximum absorption wavelength and the absence of acid-base reactions throughout a broad pH range in comparison to the pyranoflavylium precursor. This work offers a valuable environmentally friendly, quick, and straightforward alternative to flavylium compounds' challenging and labor-intensive functionalization, resulting in novel dyes with higher stability and dissimilar chromatic features.

Anthocyanin Color Stabilization by Host-Guest Complexation with p-Sulfonatocalix[n]arenes.

Flavylium-based compounds in their acidic and cationic form bring color to aqueous solutions, while under slightly acidic or neutral conditions they commonly bring discoloration. Selective host-guest complexation between water-soluble p-sulfonatocalix[n]arenes (SCn) macrocycles and the flavylium cationic species can increase the stability of the colored form, expanding its domain over the pH scale. The association constants between SCn and the cationic (acid) and neutral basic forms of flavylium-based compounds were determined through UV-Vis host-guest titrations at different pH values. The affinity of the hosts for synthetic chromophore was found to be higher than for a natural anthocyanin (Oenin). The higher affinity of SC4 for the synthetic flavylium was confirmed by 1H NMR showing a preferential interaction of the flavylium phenyl ring with the host cavity. In contrast with its synthetic counterpart, the flavylium substitution pattern in the anthocyanin seems to limit the inclusion of the guest in the host's binding pocket. In this case, the higher affinity was observed for the octamer (SC8) likely due to its larger cavity and higher number of negatively charged sulfonate groups.

An Insight into Kiwiberry Leaf Valorization: Phenolic Composition, Bioactivity and Health Benefits.

During kiwiberry production, different by-products are generated, including leaves that are removed to increase the fruit's solar exposure. The aim of this work was to extract bioactive compounds from kiwiberry leaf by employing microwave-assisted extraction (MAE). Compatible food solvents (water and ethanol) were employed. The alcoholic extract contained the highest phenolic and flavonoid contents (629.48 mg of gallic acid equivalents (GAE) per gram of plant material on dry weight (dw) (GAE/g dw) and 136.81 mg of catechin equivalents per gram of plant material on dw (CAE/g dw), respectively). Oppositely, the hydroalcoholic extract achieved the highest antioxidant activity and scavenging activity against reactive oxygen and nitrogen species (IC50 = 29.10 µg/mL for O2•-, IC50 = 1.87 µg/mL for HOCl and IC50 = 1.18 µg/mL for •NO). The phenolic profile showed the presence of caffeoylquinic acids, proanthocyanidin, and quercetin in all samples. However, caffeoylquinic acids and quercetin were detected in higher amounts in the alcoholic extract, while proanthocyanidins were prevalent in the hydroalcoholic extract. No adverse effects were observed on Caco-2 viability, while the highest concentration (1000 µg/mL) of hydroalcoholic and alcoholic extracts conducted to a decrease of HT29-MTX viability. These results highlight the MAE potentialities to extract bioactive compounds from kiwiberry leaf.

Solid Lipid Nanoparticles as Carriers of Natural Phenolic Compounds.

Phenolic compounds are one of the most widespread classes of compounds in nature, with several beneficial biological effects being associated with their anti-oxidant and anti-carcinogenic activities. Their application in the prevention or treatment of numerous chronic diseases have been studied, but a major drawback is still the low bioavailability of these compounds, as well as their instability towards pH, temperature, and light in some cases. Nanotechnology has emerged as an alternative to overcome these limitations, and the use of lipidic encapsulation systems is a promising technique to achieve an efficient drug delivery, protecting molecules from external factors and improving their bioavailability. In this review, solid lipid nanoparticles and nanostructured lipid carriers are highlighted as an important tool for the improvement of the bioavailability and stability of natural phenolic compounds, including their preparation methods and functionalization approaches and the discussion of several applications for putative use in cosmetic and pharmacologic products.

Correction: Effect of in vitro digestion on the functional properties of Psidium cattleianum Sabine (araçá), Butia odorata (Barb. Rodr.) Noblick (butiá) and Eugenia uniflora L. (pitanga) fruit extracts.

Correction for 'Effect of in vitro digestion on the functional properties of Psidium cattleianum Sabine (araçá), Butia odorata (Barb. Rodr.) Noblick (butiá) and Eugenia uniflora L. (pitanga) fruit extracts' by Juliana Vinholes, et al., Food Funct., 2018, 9, 6380-6390.

Development and optimization of a HS-SPME-GC-MS methodology to quantify volatile carbonyl compounds in Port wines.

A method based on headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-triple quadrupole/mass spectrometry detection (GC-TQ/MS) with a prior derivatization step with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was developed to quantify carbonyl compounds in different categories of Port wines. Optimal extraction conditions were obtained incubating 2 ml of wine with 2.3 g/l of PFBHA for 10 min and extracted during 20 min at 32 °C. The method was validated for 38 carbonyl compounds (alkanals, alkenals, Strecker aldehydes, dialdehydes, ketones and furan aldehydes) with regard to linearity, repeatability, inter and intra-day precision and accuracy, showing that the method is suitable for the determination of carbonyl compounds in wines. Tawny wines with 'indication of age' (10-40 years old) presented the highest levels of some carbonyl compounds, such as propanal, pentanal, hexanal, Strecker aldehydes, diacetyl, methyl glyoxal, 3-pentanone and 2-furfural, whereas Ruby wines were characterized by the highest amounts of some unidentified compounds.

Contribution of Human Oral Cells to Astringency by Binding Salivary Protein/Tannin Complexes.

The most widely accepted mechanism to explain astringency is the interaction and precipitation of salivary proteins by food tannins, in particular proline-rich proteins. However, other mechanisms have been arising to explain astringency, such as binding of tannins to oral cells. In this work, an experimental method was adapted to study the possible contribution of both salivary proteins and oral cells to astringency induced by grape seed procyanidin fractions. Overall, in the absence of salivary proteins, the extent of procyanidin complexation with oral cells increased with increasing procyanidin degree of polymerization (mDP). Procyanidin fractions rich in monomers were the ones with the lowest ability to bind to oral cells. In the presence of salivary proteins and for procyanidins with mDP 2 the highest concentrations (1.5 and 2.0 mM) resulted in an increased binding of procyanidins to oral cells. This was even more evident for fractions III and IV at 1.0 mM and upper concentrations. Regarding the salivary proteins affected, it was possible to observe a decrease of P-B peptide and aPRP proteins for fractions II and III. This decrease is greater as the procyanidins' mDP increases. In fact, for fraction IV an almost total depletion of all salivary proteins was observed. This decrease is due to the formation of insoluble salivary protein/procyanidin complexes. Altogether, these data suggest that some procyanidins are able to bind to oral cells and that the salivary proteins interact with procyanidins forming salivary protein/procyanidin complexes that are also able to link to oral cells. The procyanidins that remain unbound to oral cells are able to bind to salivary proteins forming a large network of salivary protein/procyanidin complexes. Overall, the results presented herein provide one more step to understand food oral astringency onset.

Intestinal oxidative state can alter nutrient and drug bioavailability.

Organic cations (OCs) are substances of endogenous (e.g. dopamine, choline) or exogenous (e.g. drugs like cimetidine) origin that are positively charged at physiological pH. Since many of these compounds can not pass the cell membrane freely, their transport in our out of cells must be mediated by specific transport systems. Transport by organic cation transporters (OCTs) can be regulated rapidly by altering their trafficking and/or affinities in response to a stimuli. However, for example, a specific disease could lead to modifications in the expression of OCTs. Chronic exposure to oxidative stress has been suggested to alter regulation and functional activity of proteins through several pathways. According to results from a previous work, oxidation-reduction pathways were thought to be involved in intestinal organic cation uptake modulation. The present work was performed in order to evaluate the influence of oxidative stressors, especially glutathione, on the intestinal organic cation absorption. For this purpose, the effect of compounds with different redox potential (glutathione, an endogenous antioxidant, and procyanidins, diet antioxidants) was assessed on MPP+ (1-methyl-4-phenylpyridinium iodide) uptake in an enterocyte cell line (Caco-2). Caco-2 cells were subcultured with two different media conditions (physiological: 5 mM glucose, referred as control cells; and high-glucose: 25 mM glucose, referred as HG cells). In HG cells, the uptake was significantly lower than in control cells. Redox changing interventions affected MPP+ uptake, both in control and in high-glucose Caco-2 cells. Cellular glutathione levels could have an important impact on membrane transporters activity. The results indicate that modifications in the cellular oxidative state modulate MPP+ uptake by Caco-2 cells. Such modifications may reflect in changes of nutrient and drug bioavailability.

Interaction of different polyphenols with bovine serum albumin (BSA) and human salivary alpha-amylase (HSA) by fluorescence quenching.

Phenolic compounds are responsible for major organoleptic characteristics of plant-derived food and beverages; these substances have received much attention, given that the major function of these compounds is their antioxidant ability. In the context of this study, our major aim was study the binding of several phenolic compounds such as (+)-catechin, (-)-epicatechin, (-)-epicatechin gallate, malvidin-3-glucoside, tannic acid, procyanidin B4, procyanidin B2 gallate, and procyanidin oligomers to different proteins (bovine serum albumin and human alpha-amylase) by fluorescence quenching of protein intrinsic fluorescence. From the spectra obtained, the Stern-Volmer, the apparent static, and the bimolecular quenching constants were calculated. The structure of polyphenols revealed to significantly affect the binding/quenching process; in general, the binding affinity increased with the molecular weight of polyphenol compounds and in the presence of galloyl groups. For catechin monomer and procyanidin dimer B4, the K(SV) was 14,100 and 13,800 M(-1), respectively, and for galloyl derivatives, the K(SV) was 19,500 and 21,900 M(-1), respectively. Tannic acid was shown to be the major quenching molecule for both proteins. However, comparing different proteins, the same polyphenol showed different quenching effects, which are suggested to be related to the three-dimensional structure of the proteins studied. For (+)-catechin and BSA, the K(SV) was 8700 M(-1), and with alpha-amylase, it was 14,100 M(-1); for tannic acid, the K(SV) was 10,0548 and 11,0674 M(-1), respectively. From the results obtained, besides the main binding analysis performed, we conclude that this technique is more sensitive than thought because we can detect several interactions that have not been proven by other methods, namely, nephelometry. Overall, fluorescence quenching has proven to be a very sensitive technique with many potentialities to analyze the interaction between polyphenols and proteins.

Preliminary study of oaklins, a new class of brick-red catechinpyrylium pigments resulting from the reaction between catechin and wood aldehydes.

Several structurally related pigments were found to result from the reaction between catechin and coniferaldehyde/sinapaldehyde extracted from oak wood. Their structures were tentatively identified by mass spectrometry, and their formation was studied in different pH and temperature conditions for several days. They were all found to have a characteristic catechinpyrylium core, thereby constituting a new class of compounds named as oaklins. One of the main oaklins was also detected in a commercial table red wine aged in oak barrels.