Ferulic Acid and Eugenol Have Different Abilities to Maintain Their Inhibitory Activity Against Listeria monocytogenes in Emulsified Systems

Natural phenolic compounds are found in large quantities in plants and plant extracts and byproducts from agro-industries. They could be used to ensure food quality and safety due to their antimicrobial properties demonstrated in systems such as culture media. The aim of this study was to evaluate the ability of two natural phenolic compounds, ferulic acid and eugenol, to maintain their inhibitory activity against the growth of Listeria monocytogenes in an oil-in-water emulsion, simulating a complex food system. The minimum inhibitory concentration (MIC) of each phenolic compound was first determined in culture medium, consisting of TS broth and an added emulsifier. Whey proteins and Tween 80 increased the MIC of the antimicrobial activity of eugenol. The MIC of ferulic acid was less affected by the addition of Tween 80. The inhibitory activities of both phenolic compounds were then compared at the same concentration in emulsions and their corresponding aqueous phases by following the growth of L. monocytogenes by plate counting. In emulsified systems, eugenol lost the high inhibitory activity observed in the aqueous phase, whereas ferulic acid retained it. The partition coefficient (logPoct/wat) appears to be a key factor. Eugenol (logPoct/wat = 2.61) dispersed in the aqueous phase intercalates into the bacterial membrane and has high antimicrobial activity. In contrast, it likely preferentially partitions into the lipid droplets when dispersed in an emulsion, consequently losing its antimicrobial activity. As ferulic acid is more hydrophilic, a higher proportion probably remains in the aqueous phase of the emulsion, retaining its antimicrobial activity

Click-Chemistry Based Fluorometric Assay for Apolipoprotein N-acyltransferase from Enzyme Characterization to High-Throughput Screening

International audienceLipoproteins from proteobacteria are posttranslationally modified by fatty acids derived from membrane phospholipids by the action of three integral membrane enzymes, resulting in triacylated proteins. The first step in the lipoprotein modification pathway involves the transfer of a diacylglyceryl group from phosphatidylglycerol onto the prolipoprotein, resulting in diacylglyceryl prolipoprotein. In the second step, the signal peptide of prolipoprotein is cleaved, forming an apolipoprotein, which in turn is modified by a third fatty acid derived from a phospholipid. This last step is catalyzed by apolipoprotein N-acyltransferase (Lnt). The lipoprotein modification pathway is essential in most γ-proteobacteria, making it a potential target for the development of novel antibacterial agents. Described here is a sensitive assay for Lnt that is compatible with high-throughput screening of small inhibitory molecules. The enzyme and substrates are membrane-embedded molecules; therefore, the development of an in vitro test is not straightforward. This includes the purification of the active enzyme in the presence of detergent, the availability of alkyne-phospholipids and diacylglyceryl peptide substrates, and the reaction conditions in mixed micelles. Furthermore, in order to use the activity test in a high-throughput screening (HTS) setup, direct readout of the reaction product is preferred over coupled enzymatic reactions. In this fluorometric enzyme assay, the alkyne-triacylated peptide product is rendered fluorescent through a click-chemistry reaction and detected in a multiwell plate format. This method is applicable to other acyltransferases that use fatty acid-containing substrates, including phospholipids and acyl-CoA

Inhibitory activity of phenolic acids against Listeria monocytogenes: deciphering the mechanisms of action using three different models.

Phenolic compounds are well known for their antimicrobial activity. They may provide an interesting solution to ensure food safety by preventing the growth of foodborne pathogens while addressing the wishes of consumers for the use of natural preservatives in food and favoring the reuse of agro-industry byproducts. However, their mechanism of action is still not very well understood. Here, we aimed to decipher the complex mechanism of action of eight phenolic acids by decomposing their effects, such as the general effect of the decrease of ex-tracellular pH ( γ (pH)) and specific inhibitory effects of the undissociated ( γ (A u )) and dissociated ( γ (A d )) forms. We thus developed three different models and applied them to a dataset of Listeria monocytogenes growth rates experimentally obtained in the presence of various concentrations of phenolic acids at several pHs. The model that best fits the dataset was selected for each phenolic acid to explore the potential mechanisms. The results show that the antimicrobial activity is mainly due to the effect of the undissociated forms, except for chlorogenic and gallic acids, for which the antimicrobial activity is mainly due to a decrease in extracellular pH. In addition, the dissociated forms of p -coumaric and ferulic acids show signi ficant inhibitory activity

Inhibitory activity of phenolic acids against Listeria monocytogenes: deciphering mechanisms of action using three different models

Inhibitory activity of phenolic acids against Listeria monocytogenes: deciphering mechanisms of action using three different models. 5. International ISEKI_Food Conference

Ferulic acid and eugenol have different abilities to maintain their inhibitory activity against Listeria monocytogenes in emulsified systems

Natural phenolic compounds are found in large quantities in plants and plant extracts and byproducts from agro-industries. They could be used to ensure food quality and safety due to their antimicrobial properties demonstrated in systems such as culture media. The aim of this study was to evaluate the ability of two natural phenolic compounds, ferulic acid and eugenol, to maintain their inhibitory activity against the growth of Listeria monocytogenes in an oil-in-water emulsion, simulating a complex food system. The minimum inhibitory concentration (MIC) of each phenolic compound was first determined in culture medium, consisting of TS broth and an added emulsifier. Whey proteins and Tween 80 increased the MIC of the antimicrobial activity of eugenol. The MIC of ferulic acid was less affected by the addition of Tween 80. The inhibitory activities of both phenolic compounds were then compared at the same concentration in emulsions and their corresponding aqueous phases by following the growth of L. monocytogenes by plate counting. In emulsified systems, eugenol lost the high inhibitory activity observed in the aqueous phase, whereas ferulic acid retained it. The partition coefficient (logP(oct/wat)) appears to be a key factor. Eugenol (logP(oct/wat) = 2.61) dispersed in the aqueous phase intercalates into the bacterial membrane and has high antimicrobial activity. In contrast, it likely preferentially partitions into the lipid droplets when dispersed in an emulsion, consequently losing its antimicrobial activity. As ferulic acid is more hydrophilic, a higher proportion probably remains in the aqueous phase of the emulsion, retaining its antimicrobial activity

Phenolic compounds can be valued for their dual antioxidant and antimicrobial potential : structure-activity relationships

Phenolic compounds can be valued for their dual antioxidant and antimicrobial potential : structure-activity relationships. 28. International Conference on Polyphenol

How Different Are Industrial, Artisanal and Homemade Soft Breads?

Soft bread has a significant relevance in modern diets, and its nutritional impact on human health can be substantial. Within this product category, there is an extensive range of ingredients, formulations, and processing methods, which all contribute to the vast diversity found in the final products. This work compared the impact of three different processing methods (industrial, artisanal, and homemade preparation) on the technological (formulation and processing, as they are interconnected in real-life conditions), nutritional, and physicochemical properties of soft bread. In total, 24 types of soft bread were analyzed: 10 industrial, 6 artisanal, and 8 homemade. Although production diagrams were similar among the three methods, industrial recipes contained on average more ingredients and more additives. Industrial bread was lower in saturated fat compared to the other two groups, but contained more sugar than homemade bread. The physical properties of all loaves were comparable, with the exception of higher crumb elasticity in industrial bread compared to homemade. An analysis of volatile molecules revealed more lipid oxidation markers in industrial bread, more fermentation markers in artisanal bread, and fewer markers of Maillard reactions in homemade bread. Chemical reactions during processing seem to be the principal criterion making possible to discriminate the different processing methods. These results offer a quantitative assessment of the differences within a single product category, reflecting the real-world choices for consumers

Lipid oxidation in oil-in-water rmulsions rich in omega-3: Effect of aqueous phase viscosity, Emulsifiers, and antioxidants

International audiencePhenolic compounds offer a solution to limit oxidation and bacterial growth in food products. This study aims to better understand the impact of compositional and structural parameters of o/w emulsions on oxidative stability in several realistic models, composed of fish oil, an aqueous phase supplemented or not with guar gum, and whey proteins or Tween 80 as emulsifiers. Some systems include phenolic antioxidants, alone or in mixture (alpha-tocopherol, eugenol, ferulic acid). The presence of guar gum slightly delays oxidation by limiting oxygen transfer from the headspace to the emulsion and within the different compartments of the emulsion. Moreover, oxidation is lower in emulsions formulated with whey proteins, due to their potent interference with oxidation reactions. Ferulic acid shows no antioxidant activity. Eugenol and alpha-tocopherol are efficient in emulsions formulated with whey proteins due to their localization in the reactional system and therefore their proximity to oxidation sites. Practical Applications: These results can find practical applications in protecting essential omega-3 fatty acids with natural phenolic antioxidants in food emulsions. They would also contribute to limit the use of additives in food by promoting synergistic actions of phenolic compounds with complementary antioxidant mechanisms. At least, they could offer a sustainable valorization of by-products from agro-industry by producing ingredients rich in phenolic compounds, not only having antioxidant properties but also antibacterial effects. The nature and partition of emulsifier (whey proteins, Tween 80), thickener (guar gum), and antioxidant (ferulic acid, alpha-tocopherol and/or eugenol) play a major role in the oxidation kinetics of omega-3 polyunsaturated fatty acids in o/w emulsions

Phenolic compounds from agroindustrial by-products could be valued as antimicrobials: influence of their chemical structure on their efficiency to inhibit Listeria monocytogenes growth

Phenolic compounds from agroindustrial by-products could be valued as antimicrobials: influence of their chemical structure on their efficiency to inhibit Listeria monocytogenes growth. 4th ISEKI-food conference

Phenolic compounds can delay the oxidation of polyunsaturated fatty acids and the growth of Listeria monocytogenes: structure‐activity relationships

Early viewBACKGROUND Phenolic compounds present a potential solution to ensure food quality and safety. Indeed, they can limit oxidation reactions and bacterial growth in food products. Although their antioxidant mechanisms of action are well known, their antibacterial ones are less well understood, especially in light of their chemical structures. The aim of this study was first to quantify both aspects of a series of natural phenolic compounds and then link these activities to their chemical structure. RESULTS We evaluated antioxidant activity by measuring the capacity of phenolic compounds to delay free linoleic acid oxidation caused by the action of a hydrophilic azo‐radical initiator (AAPH). We evaluated antibacterial activity by measuring the growth inhibition of Listeria monocytogenes and determining the non‐inhibitory and minimum inhibitory concentrations for each compound. Compounds with ortho‐diphenolic structures were the best antioxidants, whereas those belonging to the simple phenol category were the best antibacterial compounds. CONCLUSION The physico‐chemical properties of the compounds influenced both activities but not in the same way. The chemical environment of the phenolic group and the presence of delocalization structures are the most important parameters for antioxidant activity, whereas the partition coefficient, logP, is one of the most important factors involved in antibacterial activity