Protein-phenolic interactions and reactions: Discrepancies, challenges, and opportunities.

Although noncovalent interactions and covalent reactions between phenolic compounds and proteins have been investigated across diverse scientific disciplines, a comprehensive understanding and identification of their products remain elusive. This review will initially outline the chemical framework and, subsequently, delve into unresolved or debated chemical and functional food-related implications, as well as forthcoming challenges in this topic. The primary objective is to elucidate the multiple aspects of protein-phenolic interactions and reactions, along with the underlying overwhelming dynamics and possibilities of follow-up reactions and potential crosslinking between proteins and phenolic compounds. The resulting products are challenging to identify and characterize analytically, as interactions and reactions occur concurrently, mutually influencing each other. Moreover, they are being modulated by various conditions such as the reaction parameters and, obviously, the chemical structure. Additionally, this review delineates the resulting discrepancies and challenges of properties and attributes such as color, taste, foaming, emulsion and gel formation, as well as effects on protein digestibility and allergenicity. Ultimately, this review is an opinion paper of a group of experts, dealing with these challenges for quite a while and aiming at equipping researchers with a critical and systematic approach to address current research gaps concerning protein-phenolic interactions and reactions.

Fibrillization of lentil proteins is impacted by the protein extraction conditions and co-extracted phenolics.

Legume proteins can be induced to form amyloid-like fibrils upon heating at low pH, with the exact conditions greatly impacting the fibril characteristics. The protein extraction method may also impact the resulting fibrils, although this effect has not been carefully examined. Here, the fibrillization of lentil protein prepared using various extraction methods and the corresponding fibril morphology were characterized. It was found that an acidic, rather than alkaline, protein extraction method was better suited for producing homogeneous, long, and straight fibrils from lentil proteins. During alkaline extraction, co-extracted phenolic compounds bound proteins through covalent and non-covalent interactions, contributing to the formation of heterogeneous, curly, and tangled fibrils. Recombination of isolated phenolics and proteins (from acidic extracts) at alkaline pH resulted in a distinct morphology, implicating a role for polyphenol oxidase also in modifying proteins during alkaline extraction. These results help disentangle the complex factors affecting legume protein fibrillization.

Dietary protein-phenolic interactions: characterization, biochemical-physiological consequences, and potential food applications.

Dietary proteins and phenolic compounds are commonly co-existing components that readily interact with each other to yield complexes in a wide range of food systems. The formed complexes play a critical role in the physiochemical characteristics of both reacting molecules, thereby impacting nutritional and quality profiles of related products. In this review, we provided the most updated knowledge on dietary protein-phenolic interactions related with food science and human nutrition, including their mechanisms of complexation, analytical technologies, and alterations in the functionality and nutraceutical properties of both reacting partners. Their potential applications in the industries regarding stability during food processing and storage, impacts on product quality, and fabrication of novel delivery systems for liable bioactives were also discussed. The interactions between dietary proteins and phenolics, either via non-covalent or covalent processes, are ubiquitous in food systems and are closely associated with chemical structures of both compounds and the surrounding conditions, mainly temperature, pH, and the presence of phenolic oxidases. Albeit in different ways, such intermolecular associations induced changes in protein conformational structures, which subsequently impacted their techno-functional properties, digestibility, and allergenic potentials; in turn, the bioaccessibility/bioavailability and health-protecting features of interacted phenolics were modified to various extents, as noticed by in vitro and in vivo evidence. Largely depending on the interaction molecules and preparation steps, those influences can be either favorable or unfavorable in different systems and therefore can be tailored to develop food products and nutraceuticals with maximized functionality and quality attributes.

Complexation of whey protein with caffeic acid or (-)-epigallocatechin-3-gallate as a strategy to induce oral tolerance to whey allergenic proteins.

Proteins and phenolic compounds can interact and form soluble and insoluble complexes. In this study, the complexation of whey protein isolate (WPI) with caffeic acid (CA) or (-)­epigallocatechin­3­gallate (EGCG) is investigated as a strategy to attenuate oral sensitization in C3H/HeJ mice against WPI. Treatment with WPI-CA reduced the levels of IgE, IgG1, IgG2a and mMCP-1 in serum of mice measured by ELISA. This might be related to CD4+LAP+Foxp3+ T and IL-17A+CD4+ T (Th17) cell activation, evidenced by flow cytometry of splenocytes. Treatment with WPI-EGCG, in turn, decreased the levels of IgG2a and mMCP-1 in serum of mice, possibly by the modulation of Th1/Th2 response and the increase of CD4+ Foxp3+ LAP- T and IL-17A+CD4+ T (Th17) cell populations. In conclusion, WPI-CA and WPI-EGCG attenuated oral sensitization in C3H/HeJ mice through different mechanisms. We consider that the complexation of whey proteins with CA and EGCG could be a promising strategy to induce oral tolerance.

Interactions of green coffee bean phenolics with wheat bread matrix in a model of simulated in vitro digestion.

Interactions of phenolics from green coffee bean flour (GCS) with the matrix of wheat bread have been studied employing direct (electrophoretic and chromatographic techniques) and indirect tests (nutrient digestibility). According to the chromatograms of digests, the antiradical activity of enriched bread was exhibited by free phenolics. An increase the area of chromatograms and some additional peaks observed for enriched bread may confirm some interactions of proteins with phenolics. The electrophoretic profile of these extracts showed that the band corresponding to a protein with molecular mass of 38 kDA had much higher intensity in enriched bread. Electrophoretic analysis of pellets remaining after digestion revealed GCS dose-dependent differences in bands corresponding to proteins with molecular masses of 52 kDa and 23 kDa. The relative digestibility of both starch and proteins was slightly decreased by addition of GCS; however, these changes did not exceed 10%, which justifies the use of this functional material.

Phenolic-Protein Interactions: Effects on Food Properties and Health Benefits.

Phenolic-protein interactions (PPI), which naturally occur in most food systems, are being intentionally designed to enhance functional performance of phenolic compounds (PC). PPI have been primarily associated with changes related to sensorial, nutritional, and nutraceutical features of foods. Furthermore, these interactions affect properties such as astringency, protein digestibility, absorption, and bioavailability of antioxidants. Therefore, new product development should pay attention to these interactions and not only on the concentration of PC. PPI protect PC from degradation due to enzymatic attack or pH changes in the lumen of the intestinal tract. Due to PPI, PC are delivered to the colon where they are metabolized by the microbiota and generate an antioxidant environment. Interactions with proteins also may enhance the antiproliferative activity of PC in some specific tumor cell lines. In this review, the effects of PPI that affect both food properties and health benefits are discussed.

Changes of antioxidant potential of pasta fortified with parsley (Petroselinum Crispum mill.) leaves in the light of protein-phenolics interactions.

BACKGROUND: Pasta is considered as an effective carrier of prohealth ingredients in food fortification. The aim of this study was to examine the changes of antioxidant potential of wheat pasta affected by fortification with powdered parsley leaves. A special attention was paid to effectiveness of fortification in the light of proteinphenolic interactions. METHODS: To improve antioxidant activity of pasta, part of wheat flour was replaced with powdered parsley leaves from 1% to 4% (w/w). The total phenolics content was determined with Folin-Ciocalteau reagent. Antioxidant capacity was evaluated using in vitro assays - abilities to scavenge free radicals (ABTS) and to reduce iron (III) (FRAP). Predicted phenolic contents and antioxidant activity were calculated. To determine the protein-phenolics interactions SE-HPLC and SDS-PAGE techniques were used. RESULTS: Fortification of pasta had a positive effect on its phenolic contents and antioxidant properties. The highest phenolics level and antioxidant activity of pasta were obtained by supplementation with 4% of parsley leaves. However, in most cases experimental values were significantly lower than those predicted. The protein profiles obtained after SDS-PAGE differed significantly among control and enriched pasta. Furthermore, the addition of parsley leaves to pasta resulted in increase of peaks areas obtained by SE-HPLC. Results indicate the occurrence of the protein-phenolics interactions in fortified pasta. CONCLUSIONS: Overall, the effectiveness of fortification and consequently biological effect is limited by many factors including interactions between phenolics and pasta proteins. In the light of this results the study of potential interaction of bioactive supplements with food matrix should be taken into account during designing new functional food products.

Protein-binding and antioxidant potential of phenolics of mangosteen fruit (Garcinia mangostana).

Phenolics were extracted from mangosteen fruit parts with 70% (v/v) aqueous acetone. The yield of crude extracts of phenolics (CP) ranged from 5.8% to 7.9%. The total phenolics (TPH) content ranged from 9.3mg to over 250mg of gallic acid equivalents per g of extract in the edible aril and skin, respectively. The formation of phenolic-protein complexes was assayed by both the dye-labelled bovine serum albumin (BSA) and the fluorescence quenching methods. Phenolics from peel and rind displayed a strong protein-precipitating potential. On the other hand, phenolics from edible aril exhibited greater affinity for BSA, as determined by the fluorescence quenching assay. The static quenching was the dominant mode of quenching of BSA fluorescence by mangosteen fruit phenolics. Mangosteen phenolics occupied two binding sites on BSA molecules located most likely in or near both tryptophan residues in the BSA molecule acting as an intrinsic fluorescence probe.