Exploring Stevia Leaf Residue Extracts: Antibacterial and Antioxidant Potential as Natural Food Preservatives

Abstract

Chemical preservatives commonly used in food preservation often pose health risks and contribute to bacterial resistance, prompting the search for safer alternatives from natural sources. Stevia rebaudiana Bertoni leaves are well-known for their role as natural sweeteners and sugar substitutes in both culinary and medicinal applications. Additionally, their extracts exhibit diverse biological activities, such as anti-diabetic, antibacterial and antioxidant properties, and have previously been confirmed for use in food preservation. Nevertheless, limited research has explored the potential of leaf residues, which are plentiful wastes from steviol glycoside extraction. These residues might still retain valuable bioactive compounds suitable for food preservation, emphasizing the need for additional investigation. Therefore, in this study, stevia leaf residues were subjected to ethanol (RE), a 50 % ethanol/water mixture (REW), and hot water (RW) extraction, and the antibacterial and antioxidant properties of 3 distinct extracts were examined. Evaluation of antibacterial activity against Staphylococcus aureus revealed significant inhibition zones for all extracts, with the REW extract exhibiting the highest efficacy, reaching up to 25.58 ± 2.54 mm. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 0.0125 mg per spot and 0.2 mg per spot, respectively, were recorded for the most effective extract (REW), indicating a bacteriostatic effect. Quantification of total phenolic content (TPC) and total flavonoid content (TFC) revealed a strong correlation between phenolic compounds and the tested biological activities, antibacterial and DPPH radical scavenging. Furthermore, HPLC Orbitrap MS analysis identified 6 compounds in the extract: 1 phenolic acid, 4 flavonoids and 1 fatty amide. These identified compounds may be responsible for the observed biological activities of the stevia leaf residue extract. The results confirm the retained potential of stevia leaf residue extracts as sources of natural preservatives in the food industry, offering both antimicrobial and antioxidant benefits.