Lipid oxidation and antimicrobial activity of polyphenols
Microbial contamination and oxidation degradation result in unacceptable safety and quality of many foods. Phenolic compounds in essential oils extracted from plant sources may exhibit both radical scavenging and antimicrobial activities. Interest in the use natural phenolic compounds as part of food product formulation has therefore seen a significant increase in order to preserve both food quality and ensure food safety. Despite the high interest in their use, little is known about whether a direct relationship between antimicrobial activity and antioxidant activity of phenolic components exists, i.e. do these components have common characteristic physicochemical properties that allow them to exhibit the two functionalities. Moreover, if there are specific physicochemical properties required for optimal activity in terms of antioxidant and antimicrobial properties, these could be modulated through the design of a suitable delivery system. The objectives of this research were therefore twofold: (1) to determine the relationship between physicochemical properties of phytophenols on lipid oxidation and antimicrobial activity and (2) to develop a delivery polyphenols in complex food system approach to optimize their dual functionalities. To this purpose, model simple phenolic compounds (eugenol and carvacrol) and model complex polyphenolic compounds (polyphenols from cranberries) were characterized in terms of their antimicrobial and antioxidant activities. Results showed both eugenol and carvacrol had remarkably ability to maintain their antioxidant and antimicrobial activities after exposing to oxidative stresses. When complex polyphenolics in cranberries were investigated, CSE powder, a spray dried formulation from cranberry skins, had a higher total phenolic content than 90MX powder, a spray dried formulation from cranberry juice. Also CSE powder simultaneous showed surprisingly high antioxidant and antimicrobial activities. Even more active extracts from CSE powder could be extracted from the powders using solvent extraction. Methanol CSE crude extract had the highest antioxidant and antimicrobial activities compared to water and acetone crude extracts and the CSE powder raw materials compared on the basis of the same concentration of total phenolics. These results were attributed to the affinity of the polyphenolics to the specific solvent resulting in extracts with different polyphenol profiles.
The methanol cranberry crude extract (which was the most active extract) was used to formulate an oil-in-water emulsion-based delivery system. Results showed that interfacial composition had a significant effect on stability of emulsions containing the added polyphenols, affecting both antioxidant and also antimicrobial activities. Generally, nonionic surfactants, such as Tween 20, were more capable of formulating stable oil-in-water emulsions that were both oxidatively stable and had antimicrobial activities with cranberry polyphenols. In contrast, emulsions formulated with cationic surfactants were not suitable to produce stable emulsions due to the formation of electrostatically driven complexes with higher interfacial tensions and reduced surface charges. Results of this study thus have offer a new promising method to improve food quality by incorporating simple and complex phenolics in foods that inhibit both lipid oxidation and prevent growth of microorganism.