Natural Polyphenols as Direct Trapping Agents of Lipid Peroxidation-Derived Acrolein and 4-Hydroxy-trans-2-nonenal

Recent Advances in the Inhibition of Membrane Lipid Peroxidation by Food-Borne Plant Polyphenols via the Nrf2/GPx4 Pathway

Lipid peroxidation (LP) leads to changes in the fluidity and permeability of cell membranes, affecting normal cellular function and potentially triggering apoptosis or necrosis. This process is closely correlated with the onset of many diseases. Evidence suggests that the phenolic hydroxyl groups in food-borne plant polyphenols (FPPs) make them effective antioxidants capable of preventing diseases triggered by cell membrane LP. Proper dietary intake of FPPs can attenuate cellular oxidative stress, especially damage to cell membrane phospholipids, by activating the Nrf2/GPx4 pathway. Nuclear factor E2-related factor 2 (Nrf2) is an oxidative stress antagonist. The signaling pathway regulated by Nrf2 is a defense transduction pathway of the organism against external stimuli such as reactive oxygen species and exogenous chemicals. Glutathione peroxidase 4 (GPx4), under the regulation of Nrf2, is the only enzyme that reduces cell membrane lipid peroxides with specificity, thus playing a pivotal role in regulating cellular ferroptosis and counteracting oxidative stress. This study explored the Nrf2/GPx4 pathway mechanism, antioxidant activity of FPPs, and mechanism of LP. It also highlighted the bioprotective properties of FPPs against LP and its associated mechanisms, including (i) activation of the Nrf2/GPx4 pathway, with GPx4 potentially serving as a central target protein, (ii) regulation of antioxidant enzyme activities, leading to a reduction in the production of ROS and other peroxides, and (iii) antioxidant effects on LP and downstream phospholipid structure. In conclusion, FPPs play a crucial role as natural antioxidants in preventing LP. However, further in-depth analysis of FPPs coregulation of multiple signaling pathways is required, and the combined effects of these mechanisms need further evaluation in experimental models. Human trials could provide valuable insights into new directions for research and application.

Improvement of Theaflavins on Glucose and Lipid Metabolism in Diabetes Mellitus

In diabetes mellitus, disordered glucose and lipid metabolisms precipitate diverse complications, including nonalcoholic fatty liver disease, contributing to a rising global mortality rate. Theaflavins (TFs) can improve disorders of glycolipid metabolism in diabetic patients and reduce various types of damage, including glucotoxicity, lipotoxicity, and other associated secondary adverse effects. TFs exert effects to lower blood glucose and lipids levels, partly by regulating digestive enzyme activities, activation of OATP-MCT pathway and increasing secretion of incretins such as GIP. By the Ca2+-CaMKK ꞵ-AMPK and PI3K-AKT pathway, TFs promote glucose utilization and inhibit endogenous glucose production. Along with the regulation of energy metabolism by AMPK-SIRT1 pathway, TFs enhance fatty acids oxidation and reduce de novo lipogenesis. As such, the administration of TFs holds significant promise for both the prevention and amelioration of diabetes mellitus.

Protective effects of EGCG on acrolein-induced Caenorhabditis elegans and its mechanism of life extension

In this study, it was found that epigallocatechin-3-gallate (EGCG) could extend the lifespan of Caenorhabditis elegans (C. elegans) induced by 100 μM acrolein (ACR) at all test concentrations (300, 400, 500, 600, and 700 μM). Notably, 500 μM EGCG exhibited the most significant mean lifespan extension, increasing it by approximately 32.5%. Furthermore, 500 μM EGCG effectively reduced elevated levels of reactive oxygen species (ROS) and lipofuscin production caused by acrolein. It also bolstered the activity of antioxidant enzymes and mitigated malondialdehyde (MDA) levels compared to the ACR-only group. These effects appeared independent of dietary restrictions. Additionally, qPCR results revealed different changes in the transcription levels of 11 genes associated with antioxidative and anti-aging functions following EGCG treatment. At the expression level, GST-4::GFP, SOD-3::GFP and HSP-16.2::GFP exhibited an initial increase with ACR treatment followed by a decrease with EGCG treatment, while the expression pattern of these three GFPs remained consistent with the enzyme activity and transcription regulation level. EGCG treatment also reduced the nuclear localization of SKN-1 and DAF-16 in the MAPK and IIS pathways that were enhanced by ACR. Moreover, the longevity-promoting effects of EGCG were diminished or absent in 13 longevity gene-deletion mutants. In conclusion, EGCG demonstrates protective effects on ACR-induced C. elegans, with the IIS and MAPK pathways playing a critical role in enhancing resilience to ACR.

Overview of alkyl quercetin lipophenol synthesis and its protective effect against carbonyl stress involved in neurodegeneration

Oxidative stress and carbonyl stress resulting from the toxicity of small aldehydes are part of the detrimental mechanisms leading to neuronal cell loss involved in the progression of neurodegenerative diseases such as Alzheimer's disease. Polyunsaturated alkylated lipophenols represent a new class of hybrid molecules that combine the health benefits of anti-inflammatory omega-3 fatty acids with the anti-carbonyl and oxidative stress (anti-COS) properties of (poly)phenols in a single pharmacological entity. To investigate the therapeutic potential of quercetin-3-docosahexaenoic acid-7-isopropyl lipophenol in neurodegenerative diseases, three synthetic pathways using chemical or chemo-enzymatic strategies were developed to access milligram or gram scale quantities of this alkyl lipophenol. The protective effect of quercetin-3-DHA-7-iPr against cytotoxic concentrations of acrolein (a carbonyl stressor) was assessed in human SHSY-5Y neuroblastoma cells to underscore its ability to alleviate harmful mechanisms associated with carbonyl stress in the context of neurodegenerative diseases.

The evaluation of catechins reducing heterocyclic aromatic amine formation: Structure-activity relationship and mechanism speculation

The favorable inhibitory effect of tea polyphenols on heterocyclic aromatic amines (HAAs) has been confirmed in many past studies. The objective of this study was to investigate the structure-activity relationship of catechins that act as inhibitors of HAA formation in chemical models. Two kinds of quantitative structure-activity relationship models for catechin-inhibiting-HAA were established. We chose two kinds of HAAs including 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and five catechins including epigallocatechin gallate (EGCG), epicatechin gallate (ECG), epigallocatechin (EGC), epicatechin (EC), and catechin (C). The inhibitory effect of five catechins were in the following order: EGCG > ECG > EGC > C > EC. Thereinto, EGCG and ECG showed dramatically better inhibition on the formation of PhIP and MeIQx, especially EGCG. Further, the mechanisms of catechin-inhibiting-HAA were speculated by correlation analysis. The free radical-scavenging ability was predicted to be the most relevant to the inhibitory effect of ECG, EGC, EC and C on HAAs. Differently, the phenylacetaldehyde-trapping ability might be the more important mechanism of EGCG inhibiting PhIP in chemical model system. This study may bring a broader idea for controlling the formation of HAAs according to the structure of catechins.

Reactive Carbonyl Species Scavenger: Epigallocatechin-3-Gallate

Epigallocatechin-3-gallate (EGCG), a prominent polyphenol found abundantly in tea, has garnered significant attention for its potential in preventing and ameliorating a wide range of diseases. Its remarkable antioxidant properties and ability to capture reactive carbonyl species make it a key player among tea's polyphenolic components. This paper delves into the synthesis and origins of both EGCG and reactive carbonyl species (RCS), emphasizing the toxicity of RCS in various food sources and their formation during food processing. Understanding EGCG's capability to capture and metabolize RCS is crucial for harnessing its health benefits. Thus, this paper explores the underlying mechanisms of EGCG for RCS inhibition and its role in capturing these compounds to generate EGCG-RCS adducts. And the absorption and metabolism of EGCG-RCS adducts is also discussed.

Elimination of Acrolein by Disodium 5'-Guanylate or Disodium 5'-Inosinate at High Temperature and Its Application in Roasted Pork Patty

Acrolein (ACR) is a highly active, simple unsaturated aldehyde found in various high-temperature processed foods. Its long-term accumulation in the human body increases the risk of chronic diseases. Animal and plant foodstuffs are rich in disodium 5'-guanylate (GMP) and disodium 5'-inosinate (IMP), which are authorized flavor enhancers. Herein, we used liquid chromatography with tandem mass spectrometry to explore the reaction-active kinetics and pathway of the interaction between GMP/IMP and ACR and validated it in roasted pork patties. Our results suggested that GMP and IMP could efficiently eliminate ACR by forming ACR adducts (GMP-ACR, IMP-ACR). In addition, IMP exhibited a higher reaction rate, whereas GMP had a good trapping capacity at a later stage. As carriers of GMP and IMP, dried mushrooms and shrimp exhibited an effective ACR-trapping ability in the ACR model and roasted pork patty individually and in combination. Adding 10% of dried mushroom or shrimp alone or 5% of dried mushroom and shrimp in combination eliminated up to 53.9%, 55.8%, and 55.2% ACR in a roasted pork patty, respectively. This study proposed a novel strategy to eliminate the generation of ACR in roasted pork patties by adding foodstuffs rich in GMP and IMP.

Influence of in vitro gastrointestinal digestion and colonic fermentation on carbonyl scavenging capacity of fiber-bound polyphenols from quinoa

Whole grain insoluble dietary fiber (IDF) is a good source of bound-form polyphenols. In the present study, insoluble dietary fiber rich in bound polyphenols (BP-IDF) from quinoa, rye and wheat was prepared. The carbonyl scavenging capacities of these three BP-IDFs and the effects of in vitro gastrointestinal (GI) digestion and colonic fermentation on their scavenging activities were studied. The results indicated that the fiber-bound polyphenols from quinoa showed the highest carbonyl scavenging capacity compared to those from rye and wheat. After colonic fermentation, more than 73% of the bound polyphenols were still retained in the fermented residues of the quinoa BP-IDF. The fiber-bound polyphenols in the GI-digested residues of quinoa retained considerable carbonyl scavenging activities. During the fermentation process, the residual fiber-bound polyphenols in the fermented residues still scavenged 35.8% to 45.2% of methylglyoxal, 19.3% to 25.4% of glyoxal, 50.7% to 60.5% of acrolein and 5.2% to 9.7% of malondialdehyde, showing a critical role in the scavenging of carbonyl compounds compared to the released and metabolized polyphenols. These findings confirm the capacity of fiber-bound polyphenols from three whole grains to scavenge carbonyls during in vitro digestion and fermentation processes, suggesting that they could be used as functional ingredients to maintain continuous defenses against carbonyls along the digestive tract.

Effect of fiber-bound polyphenols from highland barley on lipid oxidation products of cooked pork during in vitro gastrointestinal digestion

BACKGROUND

The gastrointestinal (GI) tract is a major site of lipid oxidation, and the lipid oxidation products are related to an increased risk of various chronic diseases. In this study, the inhibition capacity of bound-polyphenol rich insoluble dietary fiber (BP-IDF) from highland barley (HB) to lipid oxidation was evaluated during simulated GI digestion.

RESULTS

We found that the level of lipid hydroperoxides (LOOH) and aldehydes were significantly inhibited when highland barley bound-polyphenol rich insoluble dietary fiber (HBBP-IDF) co-digestion with cooked pork. The lipid oxidation products were more effectively scavenged during simulated gastric digestion, with inhibition of 77.4% for LOOH, 52.3% for malondialdehyde, 46.5% for 4-hydroxy-2-hexenal and 48.7% for 4-hydroxy-2-nonenel, respectively. The fiber-bound polyphenols are the principal scavengers of lipid oxidation products.

CONCLUSION

These findings suggest that HBBP-IDF could be used as a functional ingredient able to scavenge lipid oxidation products across the GI tract. © 2023 Society of Chemical Industry.

Detoxification of the Lipid Peroxidation Aldehyde, 4-Hydroxynonenal, by Apple Phloretin In Vitro and in Mice

4-Hydroxy-2-nonenal (4-HNE) is a secondary cytotoxic product generated from lipid peroxidation of polyunsaturated fatty acids (PUFAs). The accumulation of 4-HNE can covalently modify biomolecules, such as DNA and proteins, leading to various pathological conditions. Apple phloretin has been shown to be able to trap 4-HNE in vitro, but the trapping mechanisms of 4-HNE by phloretin are not fully understood. Moreover, whether the in vitro trapping efficacy of phloretin toward 4-HNE could be transferred into in vivo environments has never been investigated. In the present study, we observed the formation of 4-HNE conjugates of phloretin increased as phloretin decreased during the in vitro incubation. We then purified and characterized three mono-4-HNE-conjugates of phloretin using NMR and LC-MS/MS techniques. We thereafter demonstrated that apple phloretin could scavenge in vivo 4-HNE via the formation of at least three mono-4-HNE-conjugates of phloretin in a dose-dependent manner in mice after oral administration of three doses of phloretin (25, 100, and 400 mg/kg). The findings from this study pave the way to understanding how dihydrochalcones could act as effective scavengers of 4-HNE by working as sacrificial nucleophiles in vivo, thereby preventing or reducing the risk of 4-HNE-associated chronic diseases.

Organoiridium Complexes Enhance Cellular Defense Against Reactive Aldehydes Species

Although reactive aldehyde species (RASP) are associated with the pathogenesis of many major diseases, there are currently no clinically approved treatments for RASP overload. Conventional aldehyde detox agents are stoichiometric reactants that get consumed upon reacting with their biological targets, which limits their therapeutic efficiency. To achieve longer-lasting detoxification effects, small-molecule intracellular metal catalysts (SIMCats) were used to protect cells by converting RASP into non-toxic alcohols. It was shown that SIMCats were significantly more effective in lowering cell death from the treatment with 4-hydroxynon-2-enal than aldehyde scavengers over a 72 h period. Studies revealed that SIMCats reduced the aldehyde accumulation in cells exposed to the known RASP inducer arsenic trioxide. This work demonstrates that SIMCats offer unique benefits over stochiometric agents, potentially providing new ways to combat diseases with greater selectivity and efficiency than existing approaches.

Inhibitory mechanisms of polyphenols on heme protein-mediated lipid oxidation in muscle food: New insights and advances

Lipid oxidation is a major cause of quality deterioration that decreases the shelf-life of muscle-based foods (red meat, poultry, and fish), in which heme proteins, particularly hemoglobin and myoglobin, are the primary pro-oxidants. Due to increasing consumer concerns over synthetic chemicals, extensive research has been carried out on natural antioxidants, especially plant polyphenols. The conventional opinion suggests that polyphenols inhibit lipid oxidation of muscle foods primarily owing to their strong hydrogen-donating and transition metal-chelating activities. Recent developments in analytical techniques (e.g., protein crystallography, nuclear magnetic resonance spectroscopy, fluorescence anisotropy, and molecular docking simulation) allow deeper understanding of the molecular interaction of polyphenols with heme proteins, phospholipid membrane, reactive oxygen species, and reactive carbonyl species; hence, novel hypotheses regarding their antioxidant mechanisms have been formulated. In this review, we summarize five direct and three indirect pathways by which polyphenols inhibit heme protein-mediated lipid oxidation in muscle foods. We also discuss the relation between chemical structures and functions of polyphenols as antioxidants.

Rutin alleviated acrolein-induced cytotoxicity in Caco-2 and GES-1 cells by forming a cyclic hemiacetal product

Acrolein (ACR), an α, β-unsaturated aldehyde, is a toxic compound formed during food processing, and the use of phenolics derived from dietary materials to scavenge ACR is a hot spot. In this study, rutin, a polyphenol widely present in various dietary materials, was used to investigate its capacity to scavenge ACR. It was shown that more than 98% of ACR was eliminated under the conditions of reaction time of 2 h, temperature of 80 °C, and molar ratio of rutin/ACR of 2/1. Further structural characterization of the formed adduct revealed that the adduct of rutin to ACR to form a cyclic hemiacetal compound (RAC) was the main scavenging mechanism. Besides, the stability of RAC during simulated in vitro digestion was evaluated, which showed that more than 83.61% of RAC was remained. Furthermore, the cytotoxicity of RAC against Caco-2 and GES-1 cells was significantly reduced compared with ACR, where the IC50 values of ACR were both below 20 μM while that of RAC were both above 140 μM. And the improvement of the loss of mitochondrial membrane potential (MMP) by RAC might be one of the detoxification pathways. The present study indicated that rutin was one of the potential ACR scavengers among natural polyphenols.

Origin and Fate of Acrolein in Foods

Acrolein is a highly toxic agent that may promote the occurrence and development of various diseases. Acrolein is pervasive in all kinds of foods, and dietary intake is one of the main routes of human exposure to acrolein. Considering that acrolein is substantially eliminated after its formation during food processing and re-exposed in the human body after ingestion and metabolism, the origin and fate of acrolein must be traced in food. Focusing on molecular mechanisms, this review introduces the formation of acrolein in food and summarises both in vitro and in vivo fates of acrolein based on its interactions with small molecules and biomacromolecules. Future investigation of acrolein from different perspectives is also discussed.

Effect of acrolein, a lipid oxidation product, on the formation of the heterocyclic aromatic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in model systems and roasted tilapia fish patties

•

Acrolein was able to contribute to PhIP formation.

•

Acrolein facilitated Strecker degradation of phenylalanine.

•

Acrolein increased the formation of some key intermediates of PhIP.

•

Acrolein reacted with phenylalanine, creatinine, and PhIP to form adducts.

•

The oxidation of tilapia fish increased the PhIP formation in the roasted fish patties.

The effect of acrolein on the formation of the 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was investigated in a chemical model. Acrolein was found to increase PhIP formation at each tested addition level. 0–0.2 mmol of acrolein increased PhIP formation dose-dependently, while high levels of acrolein (>0.2 mmol) did not further increase PhIP formation. Mechanistic study showed that acrolein addition decreased the residue of phenylalanine and creatinine, but increased the content of some key intermediates. Further analysis indicated that acrolein can react with phenylalanine, creatinine, and PhIP to form adducts. These results suggested that acrolein was able to contribute to PhIP formation as a consequence of its comprehensive ability to facilitate Strecker degradation of phenylalanine and react with phenylalanine, creatinine, and PhIP. In addition, oxidation of the tilapia fish increased the PhIP formation in the roasted fish patties, further supporting the potential contribution role of lipid oxidation products to the formation of PhIP.

Dual effects of cardamonin/alpinetin and their acrolein adducts on scavenging acrolein and the anti-bacterial activity from Alpinia katsumadai Hayata as a spice in roasted meat

Acrolein (ACR) is frequently produced by the thermal degradation of carbohydrates and amino acids and lipid peroxidation in the thermal processing of food. Long-term exposure to ACR can cause various chronic diseases. Here, we screened two high-temperature-resistant ACR inhibitors, cardamonin (CAR) and alpinetin (ALP), which can interconvert without any loss at 100 °C, and were obtained from Alpinia katsumadai Hayata (AKH). They demonstrated the best activity among the six spices investigated and could scavenge ACR generated in roasted pork by forming adducts. After three ACR adducts were prepared, namely CAR-ACR-1, CAR-ACR-2 and ALP-ACR, quantitative analysis showed that the amount of CAR-ACR-1 generated in lean roasted pork with 2% AKH addition reached the minimal inhibitory concentration against Escherichia coli and Staphylococcus aureus, which was 20 times lower than that of CAR, and the higher the generation of ACR, the stronger its antibacterial activity. These results provided well-defined evidence to promote the application of AKH to ACR inhibitors in food processing.

Effect of Acrolein, a Lipid Oxidation Product, on the Formation of the Heterocyclic Aromatic Amine 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in Model Systems and Roast Salmon Patties

The effect of acrolein, a lipid oxidation product, on the formation of the heterocyclic aromatic amine 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was investigated in a chemical model containing glycine, creatinine, and glucose. Acrolein addition at 0.02-0.2 mmol increased MeIQx formation, while high levels of acrolein (>0.2 mmol) did not further increase MeIQx formation. Moreover, acrolein addition decreased the residue of glycine and creatinine but increased the residue of glucose; it also increased the formation of volatile intermediates in the MeIQx-producing chemical model. Further analysis indicated that acrolein can react with glycine, creatinine, and MeIQx to eliminate them. These results revealed that acrolein was able to contribute to MeIQx formation as a consequence of the comprehensive ability of acrolein to facilitate Strecker degradation of glycine, increase the formation of volatile intermediates, and react with glycine, creatinine, and MeIQx. In addition, the oxidation of minced salmon increased the content of MeIQx in the roasted salmon patties, further supporting the potential contribution role of lipid oxidation products in the formation of MeIQx.

Metabolic Investigation on the Interaction Mechanism between Dietary Dihydrochalcone Intake and Lipid Peroxidation Product Acrolein Reduction

SCOPE

Acrolein (ACR), a lipid peroxidation product, pathologically participates in various chronic diseases. In vitro evidence suggestes that dietary dihydrochalcones (DHCs) potentiate safe and alternative therapeutics to synthetic pharmaceuticals for ACR scavenging. Here, to investigate whether ingested DHCs could trap ACR and thereof result in reductions in endogenous ACR in mice is aimed.

METHODS AND RESULTS

Three doses of phloretin (25, 100, and 400 mg kg-1 ), a major dietary DHC, are orally administrated to mice and 24 h urine and fecal samples are collected, respectively. High-resolution MS-based targeted metabolomics reveal for the first time that phloretin and its oxidized metabolite are able to trap endogenous ACR via formation of ACR conjugates. Quantification further demonstrate that a) more than 13% of ingested phloretin can dose-dependently trap 0.77-9.92 nmol of ACR within 24 h; b) phloretin ingestion leads to marked reductions in both free ACR and ACR metabolites in mouse urine compared to control; and c) trapping reactions by phloretin can account for up to 20.1% of the total decreases in endogenous ACR, depending on the administration doses.

CONCLUSION

Findings from this study indicate that regular consumption of DHCs-rich diets holds great promise to alleviate the development of ACR-associated chronic diseases.

Interconversion and Acrolein-Trapping Capacity of Cardamonin/Alpinetin and Their Metabolites In Vitro and In Vivo

People are at high risk of exposure to endogenous and exogenous acrolein (ACR). ACR can cause a multitude of illnesses, including cardiovascular disease, Alzheimer's disease, and diabetes. In this study, we investigated the reaction pathway of cardamonin (CAR) or alpinetin (ALP) with ACR and the interconversion of CAR and ALP in vitro at 37 °C in phosphate-buffered saline using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Subsequently, ACR adducts of CAR, ALP, and their metabolites, for example, CAR-ACR-1, ALP-ACR, mono-ACR-pinocembrin chalcone (PIN-ACR), and mono- and di-ACR-naringenin (NAR-ACR and NAR-2ACR), were detected in urine samples, but only CAR-ACR-1 and ALP-ACR were detected in fecal samples from the CAR- and ALP-treated mouse groups using ultraperformance liquid chromatography-MS/MS, respectively. Quantitative analyses showed that CAR, ALP, and their metabolites markedly scavenged ACR in a dose-dependent manner in vivo. Furthermore, we also found that the metabolites of CAR or ALP remained and promoted the ACR-trapping ability.

Inhibitory Effect on Acrolein by Cyanidin-3-O-glucoside and Its Acrolein Adducts from the Pigment of Mynica Red

Acrolein (ACR), the simplest α,β-unsaturated aldehyde, possesses high reactivity and toxicity both in vitro and in vivo and results in various chronic diseases. This has attracted increasing interest from researchers to screen various bioactive compounds to control it. In this article, we attempted to discover a new attribute of cyanidin-3-O-glucoside (C3G), including its ACR-scavenging capacity, reaction pathway, and possible application. Our findings revealed that C3G could capture ACR to form mono- and diadducts at room temperature by using liquid chromatography-mass spectrometry, and we further synthesized and elucidated the structures of C3G-ACR and C3G-2ACR using HRMS and 2D NMR. The structural data validated that there were two active sites of C3G for trapping ACR: at C-6 in the A-ring and C-5' in the B-ring. In addition, we found that C3G-ACR exhibited a more remarkable clearing ability than C3G within a short time. More than 65.9% of ACR was eliminated by C3G-ACR within 5 min via further formation of C3G-2ACR, but there was no obvious effect of C3G on ACR. When the incubation time was extended to 120 min, C3G could remove up to 83.2% of ACR. Subsequently, we also observed that mynica red (>5% C3G), as a pigmented food additive, could efficiently eliminate ACR generated in the Chinese liquor model and real red bayberry wine products to form C3G-ACR and C3G-2ACR. Both adducts increased significantly, by 10 times to a 100 times, after adding mynica red to red bayberry wine products for 24 h; they also increased rapidly with prolonged incubation time in the liquor-mynica red model system. Therefore, our findings suggest that C3G or mynica red may be developed as a promising novel ACR inhibitor in fruit wine and assembled alcoholic drinks or as a health food.

Inhibitory effects of hyperoside and quercitrin from Zanthoxylum bungeanum Maxim. leaf on 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine formation by trapping phenylacetaldehyde

2-amino-1-methyl-6-phenylimidazole[4,5-b]pyridine (PhIP) is one of the most abundant Heterocyclic amines (HAs) in meat products. Zanthoxylum bungeanum Maxim. leaf (ZML) extract has been shown to be rich in polyphenols, which are gaining increasing interest as efficient tools for inhibiting the formation of HAs. In the present work, the effects of ZML extract, major polyphenols, chlorogenic acid, hyperoside and quercitrin on the formation of PhIP in both roast beef patties and chemical model systems were investigated. UPLC-MS showed that ZML extract and those three polyphenols effectively inhibited PhIP formation. Additionally, GC-MS analysis showed that those three polyphenols significantly reduced the content of phenylacetaldehyde in the model systems, a key intermediate involved in PhIP formation. The subsequent UPLC-MS and TOF-MS/MS analysis found that hyperoside and quercitrin reacted with phenyacetaldehyde to form those four adducts, 8-C-(E-Phenylethenyl)hyperoside, 6-C-(E-Phenylethenyl)hyperoside, 8-C-(E-Phenylethenyl)quercitrin and 6-C-(E-Phenylethenyl)quercitrin, respectively. The results revealed that hyperoside and quercitrin could trap phenylacetaldehyde to form adducts, thereby, retarding the reaction of phenylacetaldehyde and creatinine, blocking the generation of PhIP.

Effects of resveratrol on lipid and protein co-oxidation in fish oil-enriched whey protein isolate emulsions

In this study, the impact of resveratrol (RES) on co-oxidation of lipid and protein in a fish oil-fortified whey protein isolate (WPI) emulsion was investigated. Oil-in-water (O/W) emulsions containing 1% fish oil, 6 mg/mL of WPI and RES (0.08 ~ 2 mM) were oxidatively stressed using a Fenton system at 25 °C for 24 h. The incorporation of RES significantly suppressed lipid oxidation (TBARS) and protein carbonylation. Oxidation-induced decrease on protein sulfhydryl content and surface hydrophobicity were partially attenuated by RES, but protein tryptophan fluorescence was further decreased with the increased concentration of RES. Visualization of protein patterns and MDA-bound protein suggested that RES is capable of inhibiting protein modification induced by secondary products of lipid oxidation. Significant decrease in protein digestibility under oxidizing condition was also mitigated by RES. Our study contributes to the exploration of complicated interactions between oxidized lipids and proteins when phenolic compounds are present.

Puerarin inhibited 3-chloropropane-1,2-diol fatty acid esters formation by reacting with glycidol and glycidyl esters

The inhibitory effects of seven polyphenols on 3-chloropropane-1,2-diol fatty acid esters (3-MCPDE) formation were investigated in palm oil models. Results showed that there was not a positive significant correlation between the free-radical scavenging activities of the tested compounds and their 3-MCPDE-formation inhibitory activities; puerarin, with weak antioxidant activity, showed the highest inhibitory capacity. Moreover, puerarin reduced the content of glycidol and glycidyl esters (GEs), two key intermediates of 3-MCPDE formation in the oil models; and a puerarin-adduct was discovered in the oil fortified with glycidol or GEs, with its structure elucidated by LC-MS/MS and comparison with newly synthesized ones. Based on its chemical structure, we proposed that puerarin, at least in part, reacted with glycidol and GEs to inhibit 3-MCPDE formation. In addition, the formed compound, puerarin-7-O-propanediol was identified in the potato chips frying system, further confirming reacting with glycidol/GEs as a key mechanism of puerarin to inhibit 3-MCPDE formation.

Catechins in green tea powder (matcha) are heat-stable scavengers of acrolein, a lipid peroxide-derived reactive carbonyl species

Lipid peroxidation-derived reactive carbonyl species (RCS) such as acrolein and 4-hydroxynonenal pose health risks. We characterized the RCS-scavenging reactions of tea catechins in an aqueous solution and in baked cake. Acrolein's reaction with each of the major tea catechins (epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate) resulted in the formation of mono-, di-, and tri-acrolein conjugates of each catechin as revealed by our LC-linear ion trap MS analysis. The formation of the acrolein-conjugates of the four catechins was confirmed in the reaction of acrolein with green tea powder (matcha) extract. The addition of matcha tea powder to cake dough significantly suppressed the accumulation of RCS during cake baking. The mono-acrolein conjugates of the four major catechins were detected in the baked cake. The RCS-scavenging capability of tea catechins offers a new functionality of matcha tea powder, and its heat stability demonstrates the usefulness of matcha as a food additive.

Black Tea Theaflavin Detoxifies Metabolic Toxins in the Intestinal Tract of Mice

SCOPE

This study is to determine the in vivo efficacy of black tea theaflavin (TF) to detoxify two metabolic toxins, ammonia and methylglyoxal (MGO), in mice METHODS AND RESULTS: Under in vitro conditions, TF is able to react with ammonia, MGO, and hydrogen peroxide to produce its aminated, MGO conjugated, and oxidized products, respectively. In TF-treated mice, the aminated TF, the MGO conjugates of TF and aminated TF, and the oxidized TF are searched using LC-MS/MS. The results provide the first in vivo evidence that the unabsorbed TF is able to trap ammonia to form the aminated TF; furthermore, both TF and the aminated TF have the capacity to trap MGO to generate the corresponding mono-MGO conjugates. Moreover, TF is oxidized to dehydrotheaflavin, which underwent further amination in the gut. By exposing TF to germ-free (GF) mice and conventionalized mice (GF mice colonized with specific-pathogen-free microbiota), the gut microbiota is demonstrated to facilitate the amination and MGO conjugation of TF.

CONCLUSION

TF has the capacity to remove the endogenous metabolic toxins through oxidation, amination, and MGO conjugation in the intestinal tract, which can potentially explain why TF still generates in vivo efficacy while showing a poor systematic bioavailability.

Antioxidative Properties and Chemical Changes of Quercetin in Fish Oil: Quercetin Reacts with Free Fatty Acids to Form Its Ester Derivatives

In this research, we studied the antioxidative properties and chemical changes of quercetin in fish oil during accelerated storage at 60 °C for 5 days. Gas chromatography (GC) analysis showed that quercetin inhibited aldehyde formation and unsaturated fatty acid oxidation in fish oil significantly; however, the inhibitory effects decreased gradually with prolonged heating time. Moreover, quercetin was consumed with increasing heating time. Some new phenolic derivatives were discovered in the fish oil with quercetin, with their structures fully elucidated by LC-MS/MS and comparison with newly synthesized ones (characterized by MS and NMR spectroscopy). Based on their chemical structures, we proposed that quercetin reacted with EPA and DHA to form the corresponding quercetin fatty acid esters in fish oil. In addition, the newly formed quercetin-3-O-eicosapentaenoate and quercetin-3-O-docosahexaenoate showed weaker DPPH and ABTS radical cation scavenging activity but much improved lipophilicity, higher cell membrane affinity, and hence enhanced cellular antioxidant activity compared with the parent quercetin. Overall, quercetin could be used as a safe dietary polyphenol to inhibit lipid oxidation. The newly formed quercetin-polyunsaturated fatty acid esters may render improved bioactivity to humans, which needs further investigation.

4-hydroxy-2-alkenals in foods: a review on risk assessment, analytical methods, formation, occurrence, mitigation and future challenges

Undoubtedly, significant advances were performed concerning 4-hydroxy-2-alkenals research on foods, and their formation by double oxidation of polyunsaturated fatty acids. But further studies are still needed, especially on their occurrence in foods enriched with n-3 and n-6 fatty acids, as well as in foods for infants and processed foods. Major factors concerning the formation of 4-hydroxy-2-alkenals were discussed, namely the influence of fatty acids composition, time/temperature, processing conditions, salt, among others. Regarding mitigation, the most effective strategies are adding phenolic extracts to foods matrices, as well as other antioxidants, such as vitamin E. Exposure assessment studies revealed 4-hydroxy-2-alkenals values that could not be considered a risk for human health. However, these toxic compounds remain unaltered after digestion and can easily reach the systemic circulation. Therefore, it is crucial to develop in vivo research, with the inclusion of the colon phase, as well as, cell membranes of the intestinal epithelium. In conclusion, according to our review it is possible to eliminate or effectively decrease 4-hydroxy-2-alkenals in foods using simple and economic practices.

New lipophenols prevent carbonyl and oxidative stresses involved in macular degeneration

Dry age-related macular degeneration and Stargardt disease undergo a known toxic mechanism caused by carbonyl and oxidative stresses (COS). This is responsible for accumulation in the retinal pigment epithelium (RPE) of A2E, a main toxic pyridinium bis-retinoid lipofuscin component. Previous studies have shown that carbonyl stress in retinal cells could be reduced by an alkyl-phloroglucinol-DHA conjugate (lipophenol). Here, we performed a rational design of different families of lipophenols to conserve anti-carbonyl stress activities and improve antioxidant properties. Five synthetic pathways leading to alkyl-(poly)phenol derivatives, with phloroglucinol, resveratrol, catechin and quercetin as the main backbone, linked to poly-unsaturated fatty acid, are presented. These lipophenols were evaluated in ARPE-19 cell line for their anti-COS properties and a structure-activity relationship study is proposed. Protection of ARPE-19 cells against A2E toxicity was assessed for the four best candidates. Finally, interesting anti-COS properties of the most promising quercetin lipophenol were confirmed in primary RPE cells.

Lipid Peroxide-Derived Reactive Carbonyl Species as Mediators of Oxidative Stress and Signaling

Oxidation of membrane lipids by reactive oxygen species (ROS) or O₂/lipoxygenase leads to the formation of various bioactive compounds collectively called oxylipins. Reactive carbonyl species (RCS) are a group of oxylipins that have the α,β-unsaturated carbonyl structure, including acrolein and 4-hydroxy-(E)-2-nonenal. RCS provides a missing link between ROS stimuli and cellular responses in plants via their electrophilic modification of proteins. The physiological significance of RCS in plants has been established based on the observations that the RCS-scavenging enzymes that are overexpressed in plants or the RCS-scavenging chemicals added to plants suppress the plants' responses to ROS, i.e., photoinhibition, aluminum-induced root damage, programmed cell death (PCD), senescence, abscisic acid-induced stomata closure, and auxin-induced lateral root formation. The functions of RCS are thus a key to ROS- and redox-signaling in plants. The chemical species involved in distinct RCS signaling/damaging phenomena were recently revealed, based on comprehensive carbonyl determinations. This review presents an overview of the current status of research regarding RCS signaling functions in plants and discusses present challenges for gaining a more complete understanding of the signaling mechanisms.

Mechanistic studies of inhibition on acrolein by myricetin

Acrolein (ACR) is an unsaturated aldehyde with high activity and toxicity and is produced in vivo and in food. This study investigated the impact of B-ring structure on the trapping of ACR by flavonols and the trapping mechanism and efficacy of ACR by myricetin. Galangin, kaempferol, quercetin, and myricetin, which possess the same A- and C-ring but different numbers of -OH groups on the B-ring, were selected for this study. Our results suggested that increasing the number of -OH groups on the B-ring can enhance the ACR trapping efficacy of flavonol and myrectin was identified as the most active flavonol. The adducts of myricetin with ACR under different ratios and incubation times were analyzed using LC-MS/MS. We also purified and identified the major mono- and di-ACR-myricetin adducts. Furthermore, myricetin could dose-dependently inhibit the formation of ACR in cookies through the formation of mono- and di-ACR adducts.

Isopropyl-phloroglucinol-DHA protects outer retinal cells against lethal dose of all-trans-retinal

All‐trans‐retinal (atRAL) is a highly reactive carbonyl specie, known for its reactivity on cellular phosphatidylethanolamine in photoreceptor. It is generated by photoisomerization of 11‐cis‐retinal chromophore linked to opsin by the Schiff's base reaction. In ABCA4‐associated autosomal recessive Stargardt macular dystrophy, atRAL results in carbonyl and oxidative stress, which leads to bisretinoid A2E, accumulation in the retinal pigment epithelium (RPE). This A2E‐accumulation presents as lipofuscin fluorescent pigment, and its photooxidation causes subsequent damage. Here we describe protection against a lethal dose of atRAL in both photoreceptors and RPE in primary cultures by a lipidic polyphenol derivative, an isopropyl‐phloroglucinol linked to DHA, referred to as IP‐DHA. Next, we addressed the cellular and molecular defence mechanisms in commonly used human ARPE‐19 cells. We determined that both polyunsaturated fatty acid and isopropyl substituents bond to phloroglucinol are essential to confer the highest protection. IP‐DHA responds rapidly against the toxicity of atRAL and its protective effect persists. This healthy effect of IP‐DHA applies to the mitochondrial respiration. IP‐DHA also rescues RPE cells subjected to the toxic effects of A2E after blue light exposure. Together, our findings suggest that the beneficial role of IP‐DHA in retinal cells involves both anti‐carbonyl and anti‐oxidative capacities.

Translating In Vitro Acrolein-Trapping Capacities of Tea Polyphenol and Soy Genistein to In Vivo Situation is Mediated by the Bioavailability and Biotransformation of Individual Polyphenols

SCOPE

Acrolein (ACR) is a highly toxic unsaturated aldehyde. Humans are both endogenously and exogenously exposed to ACR. Long-term exposure to ACR leads to various chronic diseases. Dietary polyphenols have been reported to be able to attenuate ACR-induced toxicity in vitro via formation of ACR-polyphenol conjugates. However, whether in vitro ACR-trapping abilities of polyphenols can be maintained under in vivo environments is still unknown.

METHODS AND RESULTS

Two most commonly consumed dietary polyphenols, (-)-epigallocatechin-3-gallate (EGCG) from tea and genistein from soy, are evaluated for their anti-Acrolein behaviors both in vitro and in mice. Tea EGCG exerts a much higher capacity to capture ACR than soy genistein in vitro. But translation of in vitro anti-ACR activity into in vivo is mainly mediated by bioavailability and biotransformation of individual polyphenols. It is found that 1) both absorbed EGCG and genistein can trap endogenous ACR by forming mono-ACR adducts and eventually be excreted into mouse urine; 2) both absorbed EGCG and genistein can produce active metabolites, methyl-EGCG (MeEGCG) and orobol, to scavenge endogenous ACR; 3) both MeEGCG and non-absorbed EGCG show ability to trap ACR in the gut; 4) considerable amounts of microbial metabolites of genistein display enhanced anti-ACR capacity both in the body and in the gut, compared to genistein; and 5) biotransformation of genistein is able to boost its in vivo anti-ACR capacity, compared to EGCG.

CONCLUSION

The findings demonstrate that in vivo anti-ACR ability of dietary polyphenols cannot be reflected solely based on their in vitro ability. The bioavailability and biotransformation of individual polyphenols, and especially the gut microbiome, contribute to in vivo anti-ACR ability of dietary polyphenols.

Reactive Carbonyl Species: A Missing Link in ROS Signaling

As reactive oxygen species (ROS) play critical roles in plants to determine cell fate in various physiological situations, there is keen interest in the biochemical processes of ROS signal transmission. Reactive carbonyl species (RCS), the ,-unsaturated aldehydes and ketones produced from lipid peroxides, due to their chemical property to covalently modify protein, can mediate ROS signals to proteins. Comprehensive carbonyl analysis in plants has revealed that more than a dozen different RCS, e.g., acrolein, 4-hydroxy-(E)-2-nonenal and malondialdehyde, are produced from various membranes, and some of them increase and modify proteins in response to oxidative stimuli. At early stages of response, specific subsets of proteins are selectively modified with RCS. The involvement of RCS in ROS signaling can be judged on three criteria: (1) A stimulus to increase the ROS level in plants leads to the enhancement of RCS levels. (2) Suppression of the increase of RCS by scavenging enzymes or chemicals diminishes the ROS-induced response. (3) Addition of RCS to plants evokes responses similar to those induced by ROS. On these criteria, the RCS action as damaging/signaling agents has been demonstrated for root injury, programmed cell death, senescence of siliques, stomata response to abscisic acid, and root response to auxin. RCS thus act as damage/signal mediators downstream of ROS in a variety of physiological situations. A current picture and perspectives of RCS research are presented in this article.

Characterization of Carbonyl-Phenol Adducts Produced by Food Phenolic Trapping of 4-Hydroxy-2-hexenal and 4-Hydroxy-2-nonenal

4-Hydroxy-2-alkenals disappear in the presence of food phenolics (i.e., cathechin or quercetin), and the corresponding carbonyl-phenol adducts are produced. In an attempt to identify structure(s) of formed adducts, the reactions between model phenolics (resorcinol, 2-methylresorcinol, orcinol, and 2,5-dimethylresorcinol) and hydroxyalkenals (4-hydroxy-2-hexenal and 4-hydroxy-2-nonenal) were studied and the produced adducts were isolated by column chromatography and unambiguously characterized by one- and two-dimensional nuclear magnetic resonance and mass spectrometry as dihydrobenzofuranols (1), chromane-2,7-diols (2), and 2 H-chromen-7-ols (3). These compounds were mainly produced at slightly basic pH values and moderate temperatures. Their activation energies ( E_a) of formation were ∼25 kJ mol^-1 for adducts 1, ∼32 kJ mol^-1 for adducts 2, and ∼38 kJ mol^-1 for adducts 3. A reaction pathway that explains their formation is proposed. All of these results confirm that, analogously to other lipid-derived carbonyl compounds, phenolics can trap 4-hydroxy-2-alkenals in an efficient way. Obtained results provide the basis for the potential detection of carbonyl-phenol adducts derived from hydroxyalkenals in food products.

Microbiota facilitates the formation of the aminated metabolite of green tea polyphenol (-)-epigallocatechin-3-gallate which trap deleterious reactive endogenous metabolites

The in vivo mechanism of tea polyphenol-mediated prevention of many chronic diseases is still largely unknown. Studies have shown that accumulation of toxic reactive cellular metabolites, such as ammonia and reactive carbonyl species (RCS), is one of the causing factors to the development of many chronic diseases. In this study, we investigated the in vivo interaction between (-)-epigallocatechin-3-gallate (EGCG), the most abundant polyphenol in tea leaves, and ammonia and RCS. We found that EGCG could be oxidized to EGCG quinone in mice, and then rapidly react with ammonia to generate the aminated EGCG metabolite, 4'-NH₂-EGCG. Both EGCG and its aminated metabolite could further scavenge RCS, such as methylglyoxal (MGO), malondialdehyde (MDA), and trans-4-hydroxy-2-nonenal (4-HNE), to produce the RCS conjugates of EGCG and the aminated EGCG. Both the aminated and the RCS conjugated metabolites of EGCG were detected in human after drinking four cups of green tea per day. By comparing the levels of the aminated and the RCS conjugated metabolites in EGCG exposed germ-free (GF) mice and specific-pathogen-free (SPF) mice, we demonstrated that gut microbiota facilitate the formation of the aminated metabolite of EGCG, the RCS conjugates of EGCG, and the RCS conjugates of the aminated EGCG. By comparing the trapping capacities of EGCG and its aminated metabolite under aerobic and anaerobic conditions, we found that oxygen is not essential for the trapping of reactive species by EGCG and 4'-NH₂-EGCG suggesting that EGCG and its aminated metabolite could scavenge RCS in the GI track and in the circulation system. Altogether, this study provides in vivo evidences that EGCG has the capacity to scavenge toxic reactive metabolic wastes. This finding opens a new window to understand the underlying mechanisms by which drinking tea could prevent the development of chronic diseases.

New Lipophenol Antioxidants Reduce Oxidative Damage in Retina Pigment Epithelial Cells

Age-related macular degeneration (AMD) is a multifactorial pathology and its progression is exacerbated by oxidative stress. Oxidation and photo-oxidation reactions modify lipids in retinal cells, contribute to tissue injury, and lead to the formation of toxic adducts. In particular, autofluorescent pigments such as N-retinylidene-N-retinylethanolamine (A2E) accumulate as lipofuscin in retinal pigment epithelial cells, contribute to the production of additional reactive oxygen species (ROS), and lead to cell degeneration. In an effort to develop efficient antioxidants to reduce damage caused by lipid oxidation, various natural polyphenols were structurally modified to increase their lipophilicity (lipophenols). In this study, resveratrol, phloroglucinol, quercetin and catechin were selected and conjugated to various polyunsaturated fatty acids (PUFAs) using classical chemical strategies or enzymatic reactions. After screening for cytotoxicity, the capacity of the synthesized lipophenols to reduce ROS production was evaluated in ARPE-19 cells subjected to H₂O₂ treatment using a dichlorofluorescein diacetate probe. The positions of the PUFA on the polyphenol core appear to influence the antioxidant effect. In addition, two lipophenolic quercetin derivatives were evaluated to highlight their potency in protecting ARPE-19 cells against A2E photo-oxidation toxicity. Quercetin conjugated to linoleic or α-linolenic acid were promising lipophilic antioxidants, as they protected ARPE-19 cells from A2E-induced cell death more effectively than the parent polyphenol, quercetin.

Carbonyl compounds in different stages of vinification and exposure risk assessment through Merlot wine consumption

The objective of this research was to estimate for the first time the transformations that the free form of some target carbonyl compounds may undergo during winemaking and assess the exposure risk to these compounds through the consumption of the Merlot commercial wines under study. Acrolein and furfural were found in grapes and the respective wines, although levels were observed to decline throughout the winemaking process. Formaldehyde was found in all stages of wine production in levels lower than the limit of quantification of the method and ethyl carbamate was not found in samples. Acetaldehyde seems to be a precursor of acetoin and 2,3-butanediol, since the levels of this aldehyde decreased along winemaking and the formation of the ester and alcohol was verified. Furfural levels decreased, while the occurrence of furan-containing compounds increased during winemaking. The formation of acetaldehyde during alcoholic fermentation and the potential environmental contamination of grapes with acrolein and furfural are considered as the critical points related to the presence of toxic carbonyl compounds in the wine. Acrolein was found in the samples under study in sufficient quantities to present risk to human health, while other potentially toxic carbonyl compounds did not result in risk. This study indicated for the first time the presence of acrolein in grapes suggesting that environmental pollution can play an important role in the levels of this aldehyde detected in wines. Reduction of the emission of this aldehyde to the environment may be achieved by replacing wood burning by another heat source in fireplaces or wood stones, and abandoning the practice of burning garbage and vegetation.

Phloretin cytoprotection and toxicity

Phloretin (Phl) is a dihydrochalcone flavonoid with significant cytoprotective properties; e.g., free radical trapping, electrophile scavenging. Based on this, it has been suggested that Phl might be useful in the treatment of pathogenic processes and prevention of drug toxicities. Therefore, we determined the ability of Phl to provide route- and dose-dependent hepatoprotection in a mouse model of acetaminophen (APAP) overdose. Intraperitoneal (i.p.) administration of Phl produced a bimodal effect; i.e., the highest dose (2.40 mmol/kg) did not prevent APAP-induced lethality, whereas lower doses (0.2-0.4 mmol/kg) afforded modest hepatoprotection. When given alone, the highest i.p. Phl dose was lethal within 24 h, whereas the lower doses were not toxic. Oral Phl (0.40-2.40 mmol/kg) did not prevent APAP-induced hepatotoxicity. The highest oral dose given alone (2.4 mmol/kg) produced 64% lethality, whereas lower doses were not lethal. This toxicity profile was reflected in a study using APAP-exposed isolated mouse hepatocytes, which showed that the Phl pharmacophores, 1,3,5-trihydroxyacetophenone (PG) and 2',4',6'-trihydroxyacetophenone (THA) where protective. Corroborative cell free studies showed that polyphenol protectants prevented glutathione loss mediated by the APAP metabolite, N-acetyl-p-benzoquinone imine (NAPQI). Thus, in spite of possessing cytoprotective attributes, Phl was generally toxic in our APAP models. These and earlier findings suggest that Phl is not a candidate for drug design. In contrast, we have found that the enol-forming pharmacophores, THA and PG, are potential platforms for pharmacotherapeutic development.

Isotopic labelling for the characterisation of HNE-sequestering agents in plant-based extracts and its application for the identification of anthocyanidins in black rice with giant embryo

Reactive carbonyl species (RCS) are cytotoxic molecules that originate from lipid peroxidation and sugar oxidation. Natural derivatives can be an attractive source of potential RCS scavenger. However, the lack of analytical methods to screen and identify bioactive compounds contained in complex matrices has hindered their identification. The sequestering actions of various rice extracts on RCS have been determined using ubiquitin and 4-hydroxy-2-nonenal (HNE) as a protein and RCS model, respectively. Black rice with giant embryo extract was found to be the most effective among various rice varieties. The identification of bioactive compounds was then carried out by an isotopic signature profile method using the characteristic isotopic ion cluster generated by the mixture of HNE: ²H₅-HNE mixed at a 1:1 stoichiometric ratio. An in-house database was used to obtain the structures of the possible bioactive components. The identified compounds were further confirmed as HNE sequestering agents through HPLC-UV analysis.

Carbonyl-Phenol Adducts: An Alternative Sink for Reactive and Potentially Toxic Lipid Oxidation Products

Different from the well-characterized function of phenolics as antioxidants, their function as lipid-derived carbonyl scavengers is mostly unknown. However, phenolics react with lipid-derived carbonyls as a function of the nucleophilicity of their reactive groups and the electronic effects and steric hindrances present in the reactive carbonyls. Furthermore, the reaction produces a wide variety of carbonyl-phenol adducts, some of which are stable and have been isolated and characterized but others polymerize spontaneously. This perspective updates present knowledge about the lipid-derived carbonyl trapping ability of phenolics, its competition with carbonyl-amine reactions produced in foods, and the presence of carbonyl-phenol adducts in food products.

Model Studies on the Effect of Aldehyde Structure on Their Selective Trapping by Phenolic Compounds

The reaction among flavor-relevant saturated aldehydes (propanal, 2-methylpropanal, butanal, 2-methylbutanal, 3-methylbutanal, pentanal, hexanal, and glyoxal) and phenolic compounds (resorcinol, 2-methylresorcinol, 2,5-dimethylresorcinol, and orcinol) was studied both to identify and to characterize the formed carbonyl-phenol adducts and to understand the differences in the carbonyl-trapping abilities of phenolic compounds. The obtained results showed that carbonyl-trapping by phenolics is selective and that the formation of carbonyl-phenol adducts depends on the structures of both the phenol and aldehyde involved. In relation to the phenolic derivative, the presence of groups that increase the nucleophilicity of phenolic carbons will increase the carbonyl-trapping ability of these compounds. On the other hand, the presence of groups that increase the steric hindrance of these positions without affecting nucleophilicity will inhibit the reaction. Analogously, the presence of branching at position 2 of the aldehyde will also inhibit the reaction by steric hindrance. All of these results suggest that the addition of phenolics to foods may change food flavor not only because of their sensory properties but also because they can modify the ratio among food odorants by selective reaction of phenolics with determined carbonyl compounds.