Biopolymer-based powders with encapsulated thyme oil: Characterization and comparison with free oil regarding thermal stability and antimicrobial activity

The prevention of food contamination by pathogenic microorganisms is a very important factor for food safety and security during storage time. The essential oils have the potential to be used as antimicrobial agents, but their full potential is limited due to the sensitivity and volatility of bioactive compounds. This study aimed to characterize Thymus vulgaris essential oil, free and nano-encapsulated in alginate-whey protein concentrate carriers using the freeze-drying technique. GC/MS analysis was done to identify the oil composition. The investigation of the antimicrobial effect of free and encapsulated oil was performed on Escherichia coli, Staphylococcus aureus, and Candida albicans, by microdilution method. The free thyme oil exhibited antimicrobial activity against all tested microorganisms in the range of 0.71–1.43 mg/ml. Interestingly, encapsulated oil was more effective at lower concentrations (0.625–1.25 mg/ml), as a consequence of a nano-size carrier (0.25 ± 0.5 μm) together with other properties (encapsulation efficiency of 86.04%). TGA pointed out a significant effect of encapsulation, in comparison to free oil, on the stability of thyme oil at temperatures from 25 to 500 °C. The results indicated a high potential of thyme oil powder carriers as natural antimicrobial additives in food products.