Designing and making stabilized emulsion of Carum copticum essential oil with gum arabic and modified starch by spontaneous emulsification method and investigating its physicochemical and antimicrobial properties.

Abstract

Abstract: Introduction: Plant essential oil extracts, such as those from thyme, serve as secondary metabolites in plants and find applications in various industries, including food, health, cosmetics, and agriculture, due to their unique properties such as oily nature and aromatic characteristics. The increasing demand for natural additives in food products has led to a growing interest in the use of essential oil emulsions. However, challenges such as low solubility in water, potent effects on flavor and aroma, and high consumption hinder their widespread use. To address these challenges, emulsion systems and nanoemulsions have been proposed as potential solutions. Emulsion production methods can be categorized into low-energy and high-energy methods. High-energy methods utilize mechanical equipment like microfluidizers and high-pressure homogenizers, while low-energy methods rely on controlling interfacial phenomena and phase inversion. Self-emulsification, as a cost-effective and efficient alternative, aims to produce micro and nano droplets with minimal energy consumption based on the spontaneous formation of fine oil droplets in a surfactant-oil-water system under specific environmental conditions. However, the effectiveness of this method is hindered by issues such as high surfactant concentration (SOR). Overcoming these challenges through the use of natural stabilizers and adjusting the carrier oil to target oil ratio presents effective solutions for reducing surfactant concentrations. Materials and Methods: Thyme essential oil emulsions were prepared using various ratios of OSA-S modified starch in the aqueous phase through a self-emulsification process. It is noteworthy that all conditions for emulsion stabilization were adjusted similarly for both OSA-S modified starch and arabic gum; however, the emulsions formed were unstable in all cases with arabic gum, leading to its exclusion from further investigation. The oil phase comprised different ratios of Tween 80 surfactant (80T), thyme essential oil, and corn oil or MCT as oil phase inhibitors. Consequently, emulsions with varying SORs and in two oil-to-water ratios (10:90 and 80:20) were prepared. The stability of the emulsions during storage was assessed by measuring particle size and zeta potential at different environmental temperatures, including room temperature and refrigeration. Furthermore, the emulsion stability against thermal cycles, freeze-thaw cycles, and freeze-thaw recovery was investigated. The antioxidant properties, turbidity, and the relationship between turbidity and emulsion characteristics were examined through regression analysis. The antimicrobial features against Staphylococcus aureus and Proteus mirabilis were evaluated using MIC and MBC tests, time-kill assays, and electron microscopy. Finally, the antimicrobial effect of the emulsions at a 0.5% SOR in yogurt against spoilage yeasts was investigated. Results: The main constituents of thyme essential oil were thymol (38%), γ-terpinene (33.2%), and p-cymene (21.2%). Stability assessments revealed that thyme essential oil emulsions (CCEO) formulated at an SOR of 0.5 and using MCT as an inhibitory agent achieved the lowest starch requirement and exhibited larger particle size and reduced stability compared to emulsions prepared with corn oil as an inhibitory agent at a similar SOR. The particle size of emulsions was significantly influenced by SOR and the oil-to-water ratio. Storage at different temperatures affected the stability of CCEO nanoemulsions, with the least stability observed in emulsions prepared with the lowest SOR and the highest starch percentage with corn oil as the inhibitory agent. Results indicated particle growth over time, with more pronounced effects at refrigeration temperatures. Stress conditions, including heat-cool and freeze-thaw cycles, led to an increase in particle size and PDI; however, the emulsions remained visually stable. Turbidity of nanoemulsions was affected by starch percentage, SOR, and the oil-to-water ratio. Regression models were developed to estimate the impact of these factors on turbidity. Antioxidant and antibacterial activities against CCEO nanoemulsions formulated with MCT (nano MCT) and corn oil (nano corn) were found to be higher compared to free essential oil (EO). The addition of 4% nano corn and nano MCT to yogurt resulted in the highest sensory scores during storage. Furthermore, yogurt containing nano corn and nano MCT inhibited spoilage yeasts, including Rhodotorula mucilaginosa and Kluyveromyces lactis, during refrigerated storage. Conclusion: The amphiphilic nature of modified starch not only reduces the surface tension of T80 surfactant but also stabilizes CCEO emulsions through the self-emulsification process. Based on the findings of this study, in an emulsion system comprising CCEO, T80, and corn oil or MCT in the oil phase and modified starch in the aqueous phase, particle size, PDI, and nanoemulsion stability are significantly influenced by SOR, inhibitory agent type (RI), and the percentage of modified starch. This method enables the food and beverage industry to utilize the antimicrobial, antioxidant, and flavor-enhancing properties of essential oils with minimal energy consumption and cost-effective systems. The results of this study could be beneficial for addressing the industrial challenge of spoilage in yogurt caused by yeasts, contributing to the reduction of artificial preservatives and enhancing food safety. Keywords: Carum copticum essential oil, spontaneous emulsification, modified starch, antimicrobial activity