Effects of structural differences of biflavonoids from fruits of the Brazilian peppertree (<em>Schinus terebinthifolius</em> Raddi) on food-associated microorganisms

Abstract

Economic, health, or sensory aspects are affected by microbial contamination of food. The preservation of food is crucial for ensuring food safety and reducing economic losses. With increasing resistance, allergies, and intolerances to conventional preservatives, the interest of consumers in natural preservatives is growing. Plants, such as <em>Schinus terebinthifolius</em>, which belongs to the Anacardiaceae family, are known to contain a diverse range of phytochemicals with bioactive properties. <em>Schinus</em> fruits contain several phenolic compounds, including gallotannins and flavonoids. Flavonoids have a wide range of chemical structures that greatly affect their biological activity, e.g., as antioxidants, anti-inflammatory or antibacterial agents. <br /> The present thesis aimed to investigate the effects of structural differences of flavonoids, including tetrahydroamentoflavone, amentoflavone, agathisflavone, and their monomers apigenin and naringenin, on planktonic cells, biofilm formation, bacterial membrane properties, and components of pigment-forming food-associated microorganisms. <br /> Our investigations showed that the antibacterial efficacy of flavonoids is influenced by their degree of oxidation and dimerization. Tetrahydroamentoflavone, a biflavonoid with a reduced C-ring at positions I-2,3 and II-2,3, exhibited the highest antibacterial activity, particularly against Gram-positive microorganisms. A minimum bactericidal concentration of 0.063 mg/ml was observed against <em>Bacillus subtilis</em>. Tetrahydroamentoflavone also exhibited remarkable inhibitory effects of biofilm formation, reducing biofilms by up to 99% in <em>Listeria innocua</em> and <em>Staphylococcus carnosus</em>. <br /> Analysis of the effects of flavonoids on bacterial lipids and membrane properties showed a significant influence on carotenoids, fatty acids, menaquinones, and membrane fluidity and suggested a stress response of the microorganisms to the envelope or adaptive mechanisms. The addition of naringenin led to an increase in carotenoid content and a simultaneous decrease in membrane fluidity, causing changes in the fatty acid composition of the bacteria, such as an increase in longer-chain fatty acids. This led to the assumption of membrane stabilization and alteration of the penetration barrier. An adjustment of the permeability barrier can also be inferred from the addition of amentoflavone, as it reduces the total carotenoid content of <em>Micrococcus luteus</em> J3. <br /> Tetrahydroamentoflavone addition mainly reduced the staphyloxanthin content in <em>Staphylococcus xylosus</em> strains and showed similar trends to naringenin exposure. Considering the reduction of staphyloxanthin, the impact on biofilm formation, and the CCS value of 220.99 ± 0.27 Ų, which suggests steric hindrance, interactions with external cell components, particularly cell wall interactions, are conceivable and might be crucial for the higher antibacterial efficacy of the biflavonoid tetrahydroamentoflavone as a promising antibacterial agent.