(464a) Self-Emulsification of Alkaline-Dissolved Clove Bud Oil By Whey Protein, Gum Arabic, Lecithin, and Their Combinations
Essential oils (EOs) are well-known for their antioxidant and antimicrobial activities and have been widely used as functional ingredients in food, pharmaceutical and cosmetic products. However, poor water solubility and high volatility during processing are two major obstacles for utilizing EOs as preservatives in food matrices or as sanitizing agents. In the present study, a novel self-emulsifying process was studied to prepare clove bud oil (CBO) emulsion without any specialized equipment or organic solvents. In this method, the major CBO component (eugenol) was deprotonated at alkaline conditions, which was accelerated by heating. Heating 10% v/v CBO in 3 M NaOH at 110 °C for 10 min was observed to be optimal conditions to obtain a transparent CBO solution. The alkaline-dissolved CBO was mixed at an overall CBO concentration of 1% v/v in aqueous neutral solutions containing 1% w/v naturally-occurring emulsifiers - whey protein concentrate (WPC), gum arabic, lecithin, and their combinations. Emulsions were obtained after neutralization to pH 7, during which eugenol became re-protonated and encapsulated in situ by emulsifiers. CBO extracted from emulsions had identical UV-visible absorption spectrum as native CBO, and the peak in reversed-phase HPLC had a same elution time and peak area as the native eugenol. These results verified the maintained structure of eugenol after self-emulsification. The freshly prepared emulsions had hydrodynamic diameters in the range of 160–540 nm, but their dimension and stability were dependent on the emulsifiers. The sample self-emulsified with WPC only had the smallest particles, followed by the combination of all three emulsifiers and the WPC-lecithin mixture, while that with gum arabic alone had the largest particles. The emulsifier blend generally resulted in better stability of the emulsion particle size than individual compounds. Emulsions were evaluated for their antimicrobial activities against Escherichia coli O157:H7 ATCC 43895, Listeria monocytogenes Scott A and Salmonella Enteritidis. Emulsions generally exhibited better activity than same amounts of ethanol-dissolved CBO, showing lower minimum inhibitory and bactericidal concentrations and stronger inhibition of bacterial growth in tryptic soy broth. Our findings indicated that this novel self-emulsifying process may find promising applications in preparing EO emulsions using low cost food ingredients for use as antimicrobial food preservatives.