Antioxidant and Antimicrobial Properties of Hydro-Ethanolic Extract of Rosemary (Rosmarinus officinalis L.) and its Application in Pasteurized Milk

Milk is a dairy product which is susceptible to contamination by pathogenic and spoilage microorganisms. One way to control the growth of pathogenic bacteria is to use preservatives and antimicrobial compounds. Due to the general concerns about the side effects of chemical preservatives, there is a tendency to consume products that use natural preservatives. Natural products provide unlimited opportunities for novel and suitable additives. The main objective of this study was to evaluate the antioxidant and antimicrobial activities of hydro-ethanolic extract of rosemary (Rosmarinus officinalis L.) against some gram positive (Staphylococcus aureus and Listeria innocua) and gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and the next stage was to investigate the impact of hydro-ethanolic extract of this plant at 0.25, 0.5 and 0.75% (w/w) concentrations on the shelf life of pasteurized milk.

The present experimental study was conducted in 2022 at Nahavand Higher Education Complex. The total phenolic content of the extract was measured by Folin-ciocalteau method. Antioxidant activity of different concentration of extract were assessed by diphenyl picrylhydrazyl radical-scavenging activity and compared with synthetic antioxidant butylated hydroxyl anisole (BHA). Antibacterial effects of resemary on pathogenic bacteria was determined by well diffusion agar, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) methods. Experimental data were analyzed using ANOVA by the SPSS version 20 software and mean comparison were done using Duncan's multiple range test.

The phenolic content of hydro-ethanolic extract weas 96.47±0.35 mg galic acid/g extract. Hydro-ethanolic extract of rosemary had the greatest effect on Staphylococcus aureus. The MIC of rosemary ethanolic extract ranged from 12.5 to 50 mg/ml, depending on the type of bacteria (gram positive or gram negative). Also, the treatments of pasteurized milk with 0.5%, acceptable sensory properties had a significantly lower total microbial count and longer shelf life compared to the control sample.

Therefore, considering that the hydro-ethanolic extract of rosemary had a significant effect on preventing the growth of pathogenic and spoilage microorganisms, as a result, this extract can be used as a natural antibiotic in milk.