Comparing the effect of Nepeta glomerulosa essential-oil and its nanoemulsion on quality properties of mayonnaise

The current work aims to compare the effect of essential oil (pure and emulsified) Nepeta glomerulosa as natural preservatives for improving the shelf life of high-fat mayonnaise during 6 weeks of storage at 35 ºC. The nanoemulsion of Nepeta glomerulosa essential oil was prepared by the ultrasound cavitation method and physical properties were determined. Soy oil was substituted by 0.5 %w/w of the Nepeta essential oil or its nanoemulsion to compare the effect of natural and chemical (BHT and sodium-benzoate/potassium-sorbate) preservatives on the chemical (pH, acidity, peroxide-value, thiobarbituric acid-reactive-substances), microbial (acid-resistant bacteria, heterofermentative lactic acid bacteria, Escherichia coli, mold and yeast content, and salmonella) and sensory properties of mayonnaise. 1,8-Cineole (26.9%), α-Pinene (7.3%), and Limonene (6.8%) were the main compounds of this essential oil. The mean droplet diameter, PDI and viscosity of Nepeta nanoemulsions were 191.95 nm, 0.255, and 1.03 cP, respectively. The addition of the essential oil (pure or emulsified) significantly improved the oxidative stability of mayonnaise. There was no significant difference between the antioxidant activity of BHT and the essential oil. Over time, a decreasing and increasing trend was observed in pH and acidity, respectively, the slope of these trends was greater in the control sample. Nepeta essential oil and benzoate/sorbate significantly delayed microbial spoilage. The antimicrobial potential of the essential oil and its nanoemulsion were comparable with benzoate/sorbate activity (P > 0.05). At the end of storage, the overall-sensory scores of the sample containing the nanoemulsion were higher than the threshold-limit (>3) while in the 5th week, the control sample was introduced as unacceptable by evaluators. Nepeta nanoemulsion showed good potential to enhance the shelf-life of mayonnaise. Using essential oil in the form of nanoemulsion, not only reduced the consumption of essential oil but the bioactivity of the essential oil was protected for a longer time.