Identification and quantification of adducts between oxidized rosmarinic acid and thiol compounds by UHPLC-LTQ-Orbitrap and MALDI-TOF/TOF tandem mass spectrometry

Identification of Protein-Phenol Adducts in Meat Proteins: A Molecular Probe Technology Study

Plant polyphenols with a catechol structure can form covalent adducts with meat proteins, which affects the quality and processing of meat products. However, there is a lack of fast and effective methods of characterizing these adducts and understanding their mechanisms. This study aimed to investigate the covalent interaction between myofibrillar protein (MP) and caffeic acid (CA), a plant polyphenol with a catechol structure, using molecular probe technology. The CA-MP adducts were separated via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and detected via Western blot and LC-MS/MS analyses. The Western blot analysis revealed that various specific adducts were successfully enriched and identified as bands around 220 kDa, 45 kDa, and two distinct bands between 95 and 130 kDa. Combined with the LC-MS/MS analysis, a total of 51 peptides were identified to be CA-adducted, corresponding to 31 proteins. More than 80% of the adducted peptides carried one adducted site, and the rest carried two adducted sites. The adducted sites were located on cysteine (C/Cys), histidine (H/His), arginine (R/Arg), lysine (K/Lys), proline (P/Pro), and N-terminal (N-Term) residues. Results showed that the covalent interaction of CA and MP was highly selective for the R side chain of amino acids. Moreover, the adducts were more likely to form via C-N bonding than C-S bonding. This study provides new insights into the covalent interaction of plant polyphenols and meat proteins, which has important implications for the rational use of plant polyphenols in the meat processing industry.

Biotinylated caffeic acid covalent binding with myofibrillar proteins in alkaline conditions: Identification of protein-phenol adducts and alterations in protein properties

In this study, the effects of covalent interactions between myofibrillar proteins (MP) and caffeic acid (CA) were investigated. Protein-phenol adducts were identified by biotinylated caffeic acid (BioC) used as a substitution of CA. The total sulfhydryls and free amines content were decreased (p < 0.05). The α-helix structure of MP increased (p < 0.05) and MP gel properties enhanced slightly at low dosages of CA (10 and 50 μM), and both were impaired significantly (p < 0.05) at high dosages of CA (250 and 1250 μM). Two prominent adducts of myosin heavy chain (MHC)-BioC and Actin-BioC were identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), which gradually increased at low concentrations of BioC (10 and 50 μM), and raised significantly at the concentration of 1250 μM. According to the correlation analysis, MHC-BioC and Actin-BioC adducts showed a significant negative correlation with gel properties, such as G', hardness, and water holding capacity (WHC) (p < 0.01), which indicated that the covalent interactions between MP and CA significantly affected the quality of meat products.

The Effects of Tea Polyphenol on Chicken Protein Digestion and the Mechanism under Thermal Processing

Meat product is the main food and major source of daily protein intake. Polyphenols are always introduced into many meat products during processing. Some complex interactions may occur between polyphenol and meat protein during the processing, especially thermal processing, which may affect the digestion of protein. In this experiment, chicken protein and tea polyphenol were interacted in simulated systems to explore the effects of the interaction between meat protein and polyphenols on the digestion of meat protein. The mechanism of tea polyphenol inhibiting chicken protein digestion was studied by analyzing the changes of chicken protein in intrinsic fluorescence, surface plasmon resonance (SPR), reactive sulfhydryl group, and solubility in different solvents. The results showed that the chicken protein digestion had a negative correlation with tea polyphenol concentration and interaction temperature, and the meat protein has a higher affinity to EGCG than protease. The mechanism of tea polyphenol inhibiting chicken protein digestion was related to the changing spatial structure of chicken protein and the decreasing activity of proteases. In the simulation system, at low-concentration tea polyphenol, the inhibition of the tea polyphenol on the digestibility of chicken protein might be mainly caused by the changes in chicken protein structure, while at high concentration, the changes in protein structure and the inhibition of proteases activity played a role together. This experiment revealed the effect and the mechanism of polyphenols on the digestion performance of meat protein and provide more references for the further application of polyphenols in meat processing.

Concentration-dependent effect of eugenol on porcine myofibrillar protein gel formation

The effects of different concentrations of eugenol (EG = 0, 5, 10, 20, 50, and 100 mg/g protein) on the structural properties and gelling behavior of myofibrillar proteins (MPs) were investigated. The interaction of EG and MPs decreased free thiol and amine content, and reduced tryptophan fluorescence intensity and thermal stability, but enhanced surface hydrophobicity and aggregation of MPs. Compared with the control (EG free), the MPs' gels treated with 5 and 10 mg/g of EG had a higher storage modulus, compressive strength, and less cooking loss. A high microscopic density was observed in these EG-treated gels. However, EG at 100 mg/g was detrimental to the gelling properties of the MPs. The results indicate that an EG concentration of 20 mg/g is a turning point, i.e., below 20 mg/g, EG promoted MPs gelation, but above 20 mg/g, it impeded gelation by interfering with protein network formation. The EG modification of MPs could provide a novel ingredient strategy to improve the texture of comminuted meat products.

Insights into Feruloylated Oligosaccharide Impact on Gel Properties of Oxidized Myofibrillar Proteins Based on the Changes in Their Spatial Structure

Polyphenolic compounds can protect against myofibrillar protein (MP) oxidation in meat products. In this study, the inhibitory effect of feruloyl oligosaccharides (FOs) on MP oxidation was investigated, and the gel properties of MPs were further studied. The results showed that 50–100 μmol/g protein of FOs could effectively inhibit damage to amino acid side chains by reducing carbonyl contents by 60.5% and increasing sulfhydryl and free amine contents by 89.5% and 66%, which may protect the secondary and tertiary structures of MPs. Additionally, FOs at 50 μmol/g protein had better effects on the crosslinking of MPs, leading to effective improvements in the gel properties, which can be seen in the rheology properties, scanning electron microscope (SEM) photographs, and the distribution of water in the MP gel. On the contrary, 150–200 μmol/g protein of FOs showed peroxidative effects on oxidatively stressed MPs, which were detrimental to MPs and contributed to their denaturation in the electrophoresis analysis and irregular aggregation in the SEM analysis. The concentration-dependent effects of FOs depended on MP-FOs interactions, indicating that an appropriate concentration of FOs has the potential to protect MPs from oxidation and enhance the gelation ability of pork meat during processing.

Moderate Protein Oxidation Improves Bovine Myofibril Digestibility by Releasing Peptides in the S2 Region of Myosin: A Peptidomics Perspective

This study aimed to investigate the influence of protein oxidation on the digestive properties of beef myofibrillar protein (MP). MP was treated with a hydroxyl radical-generating system containing various concentrations of H₂O₂. The increased content in a free sulfhydryl group and surface hydrophobicity indicated that oxidation treatment with 1 mM H₂O₂ induced unfolding of MP. Reducing and nonreducing SDS-PAGE results suggested that 10 mM H₂O₂ oxidation treatment resulted in aggregation of MP; meanwhile, the disulfide bond was the major covalent bond involved in aggregation. Peptidomics showed that peptides in the digestion products of MP were mainly derived from myosin tail. Moderate oxidation (1 mM H₂O₂) facilitated the release of peptide in the rod portion (S2) of myosin, whereas excessive oxidation (10 mM H₂O₂) inhibited peptide release in the light meromyosin region. This work presents insightful information for the crucial impact of oxidation on meat protein digestibility from the peptidomics perspective.

Comparative study on the in vitro digestibility of chicken protein after different modifications

The effects of tea polyphenols (TPPs) and ultrasound treatment (UDT) on the digestibility of chicken myofibrillar protein (MPN) in anenhanced oxidation system were investigated. As observed, the original aggregates of MPN were much lower in the UDT-assisted group than in the control protein group, and the difference widened after the incorporation of TPPs. The covalent structures of the UDT-assisted oxidation groups were verified via mass spectrometry and amino acid (AAD) measurements. The peptide abundance increased after the UDT-assisted covalent reaction and most of these peptides were derived from the structural proteins of MPNs according to the results of nano-LC-ESI-MS/MS. Digestion kinetic analysis showed that the digestion level of the EGCG-treated group was better than that of the other treated groups, regardless of the UDT-assisted covalent reaction. Overall, the combination of EGCG oxidation and UDT may be an efficient way to promote the nutritional value of the final MPN products.

Muscle protein oxidation and functionality: a global view of a once neglected phenomenon

Muscle is a highly organized apparatus with a hierarchicmicrostructure that offers the protection of cellular components againstreactive oxygen species (ROS). However, fresh meat immediately postmortem andmeat undergoing processing become susceptible to oxidation due to physicaldisruption and the influx of molecular oxygen. Upon the activation byendogenous prooxidants, oxygen species are rapidly produced, and bothmyofibrillar and sarcoplasmic proteins become their primary targets. Direct ROSattack of amino acid sidechains and peptide backbone leads to proteinconformational changes, conversion to carbonyl and thiol derivatives, andsubsequent aggregation and polymerization. Interestingly, mild radical andnonradical oxidation enables orderly protein physicochemical changes, which explainswhy gels formed by ROS-modified myofibrillar protein has improved rheologicalproperties and binding potential in comminuted meat and meat emulsions. Theincorporation of phenolic and other multi-functional compounds promotes gelnetwork formation, fat emulsification, and water immobilization; however,extensive protein modification induced by high levels of ROS impairs proteinfunctionality. Now recognized to be a natural occurrence, once-neglectedprotein oxidation has drawn much interest and is being intensively studiedwithin the international community of meat science. This review describes thehistory and evolution of muscle protein oxidation, the mechanism andfunctionality impact hereof, and innovative oxidant/antioxidant strategies tocontrol and manipulate oxidation in the context of meat processing, storage,and quality. It is hoped that the review will stimulate in-depth discussion of scientificas well as industrial relevance and importance of protein oxidation and inspirerobust international collaboration in addressing this global challenge.&nbsp;

Identification of adducts between oxidized rosmarinic acid and glutathione compounds by electrochemistry, liquid chromatography and mass spectrometry

Natural polyphenols are omnipresent and are an integral part of the human diet as well as quinones. Glutathione (GSH) is present in a significant amount inside cells and consequently, GSH conjugates of polyphenols will be encountered in the body. In the current work, voltammetry and liquid chromatography-mass spectrometry were carried out to characterize the reaction mechanism of the electrochemical oxidation of polyphenolic rosmarinic acid (RA) with GSH nucleophiles in aqueous solution. Electrochemical investigation of RA revealed that two consecutive transfer steps (which depend on pH) of two electrons and protons occur during the reversible oxidation of RA. Moreover, it was found that the first oxidation step is associated with the 3,4-dihydroxyphenyl lactic acid moiety, whereas the second oxidation step corresponds to the oxidation of the caffeic acid one. By using ultrahigh-performance liquid chromatography-diode array detection-mass spectrometry (UPLC-DAD-MS) in the negative ion mode, the oxidation pathways of RA in the presence of GSH were analyzed, and a total of four RA-GSH conjugates were identified. The oxidative degradation pathway of RA can be better apprehended and forecasted by the acquired results in this study.

Analytical approaches to assess metabolic changes in psoriasis

Psoriasis is one of the most common human skin diseases, although its development is not limited to one tissue, but is associated with autoimmune reactions throughout the body. Overproduction of pro-inflammatory cytokines and growth factors systemically stimulates the proliferation of skin cells, which manifests as excessive exfoliation of the epidermis, and/or arthritis, as well as other comorbidities such as insulin resistance, metabolic syndrome, hypertension, and depression. Thus, there is a great need for a thorough analysis of the pathophysiology of psoriatic patients, including classical methods, such as spectrophotometry, chromatography, or Western blot, and also novel omics approaches such as lipidomics and proteomics. Moreover, the extensive pathophysiology forces increased research examining biological changes in both skin cells, and systemically. A wide range of techniques involved in lipidomic research based on a combination of mass spectrometry and different types of chromatography (RP-LC-QTOF-MS/MS, HILIC-QTOF-MS/MS or RP-LC-QTRAP-MS/MS), have allowed comprehensive assessment of lipid modification in psoriatic skin and provided new insight into the role of lipids and their mechanism of action in psoriasis. Moreover, proteomic analysis using gel-nanoLC-OrbiTrap-MS/MS, as well as MALDI-TOF/TOF techniques facilitates the description of panels of enzymes involved in lipidome modifications, and the response of the endocannabinoid system to metabolic changes. Psoriasis is known to alter the expression of proteins that are involved in the inflammatory and antioxidant response, as well as protein biosynthesis, degradation, as well as cell proliferation and apoptosis. Knowledge of changes in the lipidomic and proteomic profile will not only allow the understanding of psoriasis pathophysiology, but also facilitate proper and early diagnosis and effective pharmacotherapy.

High-throughput and high-sensitivity capillary electrophoresis–mass spectrometry method for sulfur-containing amino acids

Biological thiol amino acids have been suggested as biomarkers for pathological changes because they are reactive chemicals that participate in various physiological processes. In this study, multisegmented injection capillary electrophoresis–mass spectrometry with online sample preconcentration was used for analysis of thiol amino acids and intermediates of sulfur metabolism in human glioma cell line U-251 with high accuracy, throughput, and sensitivity. This was achieved using multiple, large-volume injections for online sample preconcentration. The 16 intermediates of sulfur metabolism had a good linear correlation coefficient range of 0.984–1 and the limit of detection range was 1.4–203.9 ng/mL. The recovery ranges of most amino acids were 88.1–114.5%, 89.0–104.3%, and 76.9–104.5% at 0.3, 0.75, and 1.5 μg/mL, respectively. The relative standard deviation ranges for the inter- and intra-day precision were 1.8–10.7% and 4.3–18.8%, respectively. Compared with the traditional injection method, the analytical time for compounds in sulfur metabolism was reduced to 4 min/sample, the method throughput was enhanced five times, and the sensitivity was increased 14.4–33.1 times. Customized injection sequences were applied in experimental optimization. The developed method simplified the experimental optimization to one injection and is suitable for the analysis of sulfur metabolites in biological samples and has high sensitivity, throughput, speed, and accuracy.

Multi-colored shades of betalains: recent advances in betacyanin chemistry

Covering: 2001 to 2021Betacyanins cover a class of remarkable natural red-violet plant pigments with prospective chemical and biological properties for wide-ranging applications in food, pharmaceuticals, and the cosmetic industry. Betacyanins, forming the betalain pigment group together with yellow betaxanthins, have gained much attention due to the increasing social awareness of the positive impact of natural products on human health. Betalains are commercially recognized as natural food colorants with preliminarily ascertained, but to be further investigated, health-promoting properties. In addition, they exhibit a remarkable structural diversity based on glycosylated and acylated varieties. The main research directions for natural plant pigments are focused on their structure elucidation, methods of their separation and analysis, biological activities, bioavailability, factors affecting their stability, industrial applications as a plant-based food, natural colorants, drugs, and cosmetics as well as methods for high-yield production and stabilization. This review covers period of the last two decades of betacyanin research. In the first part of the review, we present an updated classification of all known betacyanins and their derivatives identified by chemical means as well as by mass spectrometric and NMR techniques. In the second part, we review the current research reports focused on the chemical properties of the pigments (decarboxylation, oxidation, conjugation, and chlorination reactions as well as the acyl group migration phenomenon) and describe the semi-synthesis of natural and artificial fluorescent betalamic acid conjugates, showing various prospective research directions.

Myoprotein-phytophenol interaction: Implications for muscle food structure-forming properties

Phenolic compounds are commonly incorporated into muscle foods to inhibit lipid oxidation and modify product flavor. Those that are present in or extracted from plant sources (seeds, leaves, and stems) known as "phytophenols" are of particular importance in the current meat industry due to natural origins, diversity, and safety record. Apart from these primary roles as antioxidants and flavorings, phytophenols are now recognized to be chemically reactive with a variety of food constituents, including proteins. In processed muscle foods, where the structure-forming ability is critical to a product's texture-related quality attributes and palatability, the functional properties of proteins, especially gelation and emulsification, play an essential role. A vast amount of recent studies has been devoted to protein-phenol interactions to investigate the impact on meat product texture and flavor. Considerable efforts have been made to elucidate the specific roles of phytophenol interaction with "myoproteins" (i.e., muscle-derived proteins) probing the structure-forming process in cooked meat products. The present review provides an insight into the actions of phytophenols in modifying and interacting with muscle proteins with an emphasis on the reaction mechanisms, detection methods, protein functionality, and implications for structural characteristics and textural properties of muscle foods.

Bean phenolic compound changes during processing: Chemical interactions and identification

The common bean (Phaseolus vulgaris L.) represents one of the main crops for human consumption, due to its nutritional and functional qualities. Phenolic compounds have beneficial health effects, and beans are an essential source of these molecules, being found mainly in the seed coat and its color depends on the concentration and type of phenolic compounds present. The bean during storage and processing, such as cooking, germination, extrusion, and fermentation, undergoes physical, chemical, and structural changes that affect the bioavailability of its nutrients; these changes are related to the interactions between phenolic compounds and other components of the food matrix. This review provides information about the identification and quantification of phenolic compounds present in beans and the changes they undergo during processing. It also includes information on the interactions between the phenolic compounds and the components of the bean's cell wall and the analytical methods used to identify the interactions of phenolic compounds with macromolecules.

Animal and Plant Protein Oxidation: Chemical and Functional Property Significance

Protein oxidation, a phenomenon that was not well recognized previously but now better understood, is a complex chemical process occurring ubiquitously in food systems and can be induced by processing treatments as well. While early research concentrated on muscle protein oxidation, later investigations included plant, milk, and egg proteins. The process of protein oxidation involves both radicals and nonradicals, and amino acid side chain groups are usually the site of initial oxidant attack which generates protein carbonyls, disulfide, dityrosine, and protein radicals. The ensuing alteration of protein conformational structures and formation of protein polymers and aggregates can result in significant changes in solubility and functionality, such as gelation, emulsification, foaming, and water-holding. Oxidant dose-dependent effects have been widely reported, i.e., mild-to-moderate oxidation may enhance the functionality while strong oxidation leads to insolubilization and functionality losses. Therefore, controlling the extent of protein oxidation in both animal and plant protein foods through oxidative and antioxidative strategies has been of wide interest in model system as well in in situ studies. This review presents a historical perspective of food protein oxidation research and provides an inclusive discussion of the impact of chemical and enzymatic oxidation on functional properties of meat, legume, cereal, dairy, and egg proteins based on the literature reports published in recent decades.

Soy protein isolate -(-)-epigallocatechin gallate conjugate: Covalent binding sites identification and IgE binding ability evaluation

The conjugate prepared from (-)-epigallocatechin gallate (EGCG) and soy protein isolate (SPI) under alkaline and aerobic conditions was analyzed using a Nano-LC-Q-Orbitrap-MS/MS technique. The sulfhydryl and free amino groups of SPI were involved in covalent binding. Fifty-one peptides were conjugated with EGCG. Fifty-nine modified sites were identified, located on Cys, His, Arg, and Lys, respectively. It is the first time to confirm that each of the two phenolic rings of EGCG contained a reactive site that bound to an amino acid residue. The amino acid residue reactivity, amino acid sequence and composition affected the EGCG binding site in SPI. Lys and Arg residues are the most likely sites for modification, and modification appears to reduce IgE binding. This study is helpful to elucidate the pattern of covalent binding of polyphenols to proteins in food systems and provides a theoretical basis for the directional modification of soy proteins with polyphenols.

The gelation properties of myofibrillar proteins prepared with malondialdehyde and (-)-epigallocatechin-3-gallate

Impact of malondialdehyde (MDA) and (-)-Epigallocatechin-3-gallate (EGCG) on gelling properties of myofibrillar proteins (MPs) was investigated. Addition of 6 mM MDA enhanced molecular interactions of proteins, thus the strength and elastic modulus (G') of gel were improved. EGCG addition aggravated gel quality deterioration due to further modification of MPs induced by EGCG. Addition of 12 mM MDA jeopardized gel quality according to the increasing of strength and G', but the decreasing of water-holding capacity (WHC), and the collapse of microstructure. Nevertheless, EGCG reacted with MDA forming EGCG-MDA adducts, hence improved gel quality, which was supported by the decreasing of strength, but the increasing of WHC, and the repaired microstructure of gel at 12 mM MDA. Addition of 24 mM MDA severely jeopardized gel quality, which became even worse due to EGCG addition. This work is helpful to understand the impact of MDA and polyphenols on the gel-forming capacity of MPs.

Combination of light and oxygen accelerates formation of covalent protein-polyphenol bonding during chill storage of meat added 4-methyl catechol

Plant polyphenols applied as natural antioxidant ingredients, are known to bind to cysteine residues on meat proteins. The aim of this study was to examine the effect of light exposure on the formation of cysteine-phenol adduct in meat added 4-methylcatechol (4MC), a model polyphenol, during storage through quantitative LC-MS/MS-based analysis. Cysteine-4-methylcatechol adduct (Cys-4MC) formation in meat added 1500 ppm 4-MC increased significantly (by 50%) when stored under light in oxygen at 4 °C for 7 days as compared to storage in the dark. This was reflected by a significant decrease in thiol concentrations in the same sample. Gel electrophoresis showed loss in myosin heavy chain (MHC), and a resulting increase in cross-linked MHC (CL-MHC) and larger protein polymers in samples added 4MC. Protein blots stained with nitroblue tetrazolium (NBT) showed intensive protein-polyphenol binding in the meat samples added 4MC, but no major differences between storage conditions.

Identification of Novel Low-Weight Sulfhydryl Conjugates of Oxidized 5-O- and 6-O-Substituted Betanidin Pigments

The formation of conjugates of oxidized betacyanin pigments with selected low-weight sulfhydryl scavengers was studied. Short-lived quinonoids, quinone methides, and aminochromes derived from oxidized betacyanins are able to form adducts with different efficiencies. In this report, mass spectrometric and NMR identifications of CS-linked conjugates of cysteine, cysteamine, N-acetylcysteine, and dl-dithiolthreitol with quinonoid forms generated through oxidation of betanidin, betanin, and gomphrenin is presented. An adduct that formed between cysteine and quinonoid generated from betanin by its oxidation and decarboxylation (2-decarboxy-xanbetanin) was detected and reported for the first time. The most stable gomphrenin CS-conjugate, N-acetylcysteinylated gomphrenin, was isolated by semipreparative chromatography and its structure was established by NMR analysis. This enabled to confirm the conjugation position at carbon C-4 and to indicate the presence of a dopachromic intermediate during oxidation of gomphrenin. Conjugation of betacyanins with thiol-bearing moieties may generate new molecules with modified chemical and biological properties. Obtained results confirm that gomphrenin is capable of forming CS-conjugates with higher efficiency than betanin.

Quantitation of Protein Cysteine-Phenol Adducts in Minced Beef Containing 4-Methyl Catechol

Thiol groups of cysteine (Cys) residues in proteins react with quinones, oxidation products of polyphenols, to form protein-polyphenol adducts. The aim of the present work was to quantify the amount of adduct formed between Cys residues and 4-methylcatechol (4MC) in minced beef. A Cys-4MC adduct standard was electrochemically synthesized and characterized by liquid chromatography-mass spectrometry (LC-MS) as well as NMR spectroscopy. Cys-4MC adducts were quantified after acidic hydrolysis of myofibrillar protein isolates (MPIs) and LC-MS/MS analysis of meat containing either 500 or 1500 ppm 4MC and stored at 4 °C for 7 days under a nitrogen or oxygen atmosphere. The concentrations of Cys-4MC were found to be 2.2 ± 0.3 nmol/mg MPI and 8.1 ± 0.9 nmol/mg MPI in meat containing 500 and 1500 ppm 4MC, respectively, and stored for 7 days under oxygen. The formation of the Cys-4MC adduct resulted in protein thiol loss, and ca. 62% of the thiol loss was estimated to account for the formation of the Cys-4MC adduct for meat containing 1500 ppm 4MC. Furthermore, protein polymerization increased in samples containing 4MC as evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the polymerization was found to originate from protein-polyphenol interactions as evaluated by a blotting assay with staining by nitroblue tetrazolium.

Conjugation of Oxidized Betanidin and Gomphrenin Pigments from Basella alba L. Fruits with Glutathione

Formation of glutathionic conjugates with quinonoid forms generated through oxidation of betanidin and gomphrenin obtained from fruits of Basella alba L. was studied by high-performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (HPLC-DAD-ESI-MS/MS) and ion-trap time-of-flight high-resolution mass spectrometry (LCMS-IT-TOF). The conjugates were studied for the aim of trapping the formed quinonoids by glutathione which would indicate a presence of specific quinonoid structures in reaction products of the pigments with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radicals. The structure of betanidin conjugate, which was formed with high efficiency, was established by NMR analysis. In the case of gomphrenin conjugate, its structure was tentatively indicated as analogous to betanidin conjugate by MS ⁿ fragmentation paths. In contrast, no detectable glutathionic conjugate of betanin quinonoid (quinone methide) was present in similar betanin reaction mixtures. As a result of additional experiments performed during oxidation of gomphrenin by ABTS cation radicals in the absence of glutathione, except for decarboxylated and dehydrogenated gomphrenin derivatives, generation of betanidin and its derivatives was observed which indicated that the subsequent dopachromic intermediate rearrangement affected hydrolysis of the glucosidic bond. This is in contrast to betanin which is not deglucosylated in the same conditions during the oxidation. The obtained results shed some light on the oxidation pathways of various glycosylated betacyanins with gomphrenin being presumably the most potent antioxidant ascertained in this group of pigments.

Enzymatic synthesis of a thiolated chitosan-based wound dressing crosslinked with chicoric acid

This work describes the enzymatic synthesis of multifunctional hydrogels for chronic wound treatment using thiolated chitosan and the natural polyphenol chicoric acid. Gelation was achieved by laccase-catalyzed oxidation of chicoric acid, a natural compound used for the first time as a homobifunctional crosslinker, reacting subsequently with nucleophilic thiol and amino groups from the chitosan derivative. This approach allowed for twice as fast gelation at a three-fold reduced crosslinking reagent concentration, compared to reported enzymatic synthesis of hydrogels using gallic acid as a phenolic provider. Hydrogels with 600% swelling capacity, coupled with only 20% weight loss after 6 days under physiological conditions, were obtained. The clinically relevant Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa were reduced by up to 4.5 and 5.5 logs, respectively. A tunable, in the range of 20-95%, ex vivo inhibition of myeloperoxidase (MPO) activity in chronic wound exudate was achieved, together with control over the total matrix metalloproteinase (MMP) activities.

Hydroxytyrosol extracts, olive oil and walnuts as functional components in chicken sausages

BACKGROUND

Olive oil, hydroxytyrosol and walnut can be considered ideal Mediterranean ingredients for their high polyphenolic content and healthy properties. Three extracts of hydroxytyrosol obtained using different extraction processes (HXT 1, 2, 3) (50 ppm) were evaluated for use as antioxidants in eight different chicken sausage formulas enriched in polyunsaturated fatty acids (2.5 g 100 g^-1 walnut) or using extra virgin olive oil (20 g 100 g^-1 ) as fat replacer. Lipid and protein oxidation, colour, emulsion stability, and the microstructure of the resulting chicken sausages were investigated and a sensory analysis was carried out.

RESULTS

The sausages with HXT extracts were found to decrease lipid oxidation and to lead to the loss of thiol groups compared with control sausages. Emulsion stability (capacity to hold water and fat) was greater in the sausages containing olive oil and walnut than in control sausages. In contrast, the HXT extracts produced high emulsion instability (increasing cooking losses). Sensory analysis suggested that two of the HXT extracts studied (HXT₂ and HXT₃ ) were unacceptable, while the acceptability of the other was similar to that of the control products. Sausages incorporating HXT showed different structures than control samples or sausages with olive oil, related to the composition of the emulsion.

CONCLUSION

These results suggest the possibility of replacing animal fat by olive oil and walnut in order to produce healthy meat products. © 2017 Society of Chemical Industry.

Emulsifying Properties of Oxidatively Stressed Myofibrillar Protein Emulsion Gels Prepared with (-)-Epigallocatechin-3-gallate and NaCl

The dose-dependent effects of (-)-epigallocatechin-3-gallate (EGCG; 0, 100, or 1000 ppm) on the textural properties and stability of a myofibrillar protein (MP) emulsion gel were investigated. Addition of EGCG significantly inhibited formation of carbonyl but promoted the loss of both thiol and free amine groups. Addition of EGCG, particularly at 1000 ppm, initiated irreversible protein modifications, as evidenced by surface hydrophobicity changes, patterns in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and differential scanning calorimetry. These results indicated that MP was modified by additive reactions between the quinone of EGCG and thiols and free amines of proteins. These adducts increased cooking loss and destabilized the texture, especially with a large EGCG dose. Confocal laser scanning microscopy and scanning electron microscopy images clearly indicated the damage to the emulsifying properties and the collapse of the internal structure when the MP emulsion gel was treated with a large EGCG dose. A high concentration of NaCl (0.6 M) improved modification of MP and increased the rate of deterioration of the internal structure, especially with the large EGCG dose (1000 ppm), resulting in an MP emulsion gel with extremely unstable emulsifying properties.

Identification of Rosmarinic Acid-Adducted Sites in Meat Proteins in a Gel Model under Oxidative Stress by Triple TOF MS/MS

Triple TOF MS/MS was used to identify adducts between rosmarinic acid (RosA)-derived quinones and meat proteins in a gel model under oxidative stress. Seventy-five RosA-modified peptides responded to 67 proteins with adduction of RosA. RosA conjugated with different amino acids in proteins, and His, Arg, and Lys adducts with RosA were identified for the first time in meat. A total of 8 peptides containing Cys, 14 peptides containing His, 48 peptides containing Arg, 64 peptides containing Lys, and 5 peptides containing N-termini that which participated in adduction reaction with RosA were identified, respectively. Seventy-seven adduction sites were subdivided into all adducted proteins including 2 N-terminal adduction sites, 3 Cys adduction sites, 4 His adduction sites, 29 Arg adduction sites, and 39 Lys adduction sites. Site occupancy analyses showed that approximately 80.597% of the proteins carried a single RosA-modified site, 14.925% retained two sites, 1.492% contained three sites, and the rest 2.985% had four or more sites. Large-scale triple TOF MS/MS mapping of RosA-adducted sites reveals the adduction regulations of quinone and different amino acids as well as the adduction ratios, which clarify phenol-protein adductions and pave the way for industrial meat processing and preservation.

Simultaneous assessment of endogenous thiol compounds by LC-MS/MS

Biological thiol compounds are very important molecules that participate in various physiological events. Alteration in levels of endogenous thiols has been suggested as a biomarker of early stage of pathological changes. We reported a chemical derivatization- and LC-MS/MS-based approach to simultaneously determine thiol compounds including glutathione (GSH), cysteine (Cys), N-acetyl cysteine (NAC), homocysteine (Hcy), and cysteinylglycine (CysGly) in biological samples. Thiol-containing samples were derivatized with monobromobimane (mBrB) at room temperature, followed by LC-MS/MS analysis. Assessment of the analytes with baseline separation was completed within 10min, using a gradient elution on a C18 reversed-phase column. Excellent linearity was observed for all analytes over their concentration ranges of 1-400μM. The lowest limits of detection (S/N=3) in a range from 0.31fmol (for NAC) to 4.98fmol (for CysGly) were achieved. The results indicate that this approach was sensitive, selective, and well suited for high-throughput quantitative determination of the biological thiols.

Dual Role (Anti- and Pro-oxidant) of Gallic Acid in Mediating Myofibrillar Protein Gelation and Gel in Vitro Digestion

The dose-dependent effects of gallic acid (GA; at 0, 6, 30, and 150 μmol/g protein) on chemical changes and gelling properties of oxidatively stressed porcine myofibrillar protein (MP) and in vitro digestibility of the gels were investigated. The incorporation of GA suppressed lipid oxidation and protein carbonyl formation but promoted the loss of thiol and amine groups, destabilization of the tertiary structure, aggregation, and cross-linking. The gelling potential (storage modulus) of MP was increased by nearly 50% with 6 and 30 μmol/g of GA, corresponding to enhanced protein unfolding and aggregation and formation of disulfide-dominant covalent bonds. However, GA at 150 μmol/g induced macroscopic aggregations and insolubility of MP, resulting in poorly structured gels. Despite the oxidative changes, MP gels did not show reduced susceptibility to digestive enzymes in vitro.

Sodium Hydroxide Enhances Extractability and Analysis of Proanthocyanidins in Ensiled Sainfoin (Onobrychis viciifolia)

Little information exists on the effects of ensiling on condensed tannins or proanthocyanidins. The acetone-butanol-HCl assay is suitable for measuring proanthocyanidin contents in a wide range of samples, silages included, but provides limited information on proanthocyanidin composition, which is of interest for deciphering the relationships between tannins and their bioactivities in terms of animal nutrition or health. Degradation with benzyl mercaptan (thiolysis) provides information on proanthocyanidin composition, but proanthocyanidins in several sainfoin silages have proved resistant to thiolysis. We now report that a pretreatment step with sodium hydroxide prior to thiolysis was needed to enable their analysis. This alkaline treatment increased their extractability from ensiled sainfoin and facilitated especially the release of larger proanthocyanidins. Ensiling reduced assayable proanthocyanidins by 29%, but the composition of the remaining proanthocyanidins in silage resembled that of the fresh plants.