Preparation and antimicrobial activity of caprylic acid emulsion for food coating

Abstract

Antimicrobial food coating is the interesting method for food preservation, especially in fruits and vegetables. Previous studies have been reported that the caprylic acid had the antimicrobial activity against a variety of microorganisms. However, little research has been conducted on the use of caprylic acid in the form of food coatings. Therefore, this study aims to determine the optimum conditions for the caprylic acid emulsion preparation and to evaluate the antimicrobial activity of the emulsion, including the effect of food coatings with caprylic acid emulsion on physical properties and microbial growth inhibition. Emulsions containing 4% w/v caprylic acid (oil) and various concentration of surfactant mixture (polysorbate 80: monocaprylin at 1: 1 weight ratio) were prepared. The response surface methodology, Box-Behnken design, was used to optimize the factors for emulsion preparation which were surfactant concentration, sonication time and amplitude. The study showed that the optimized formula, which had small particle size, high values of zeta potential and low polydispersity index, could be prepared using 3.6% w/v surfactant mixture, sonication time of 120 sec and 30% sonication amplitude. The emulsion had the minimum bactericidal/fungicidal concentration at 0.25% w/v caprylic acid and was stable after storage at 30 ± 2 °C and 40 ± 2 °C, relative humidity (RH) 75 ± 5% for 28 days. Food coating formula contained caprylic acid (0.25% w/v) emulsion using 2% w/v alginate as a film-forming compound with 1.5% w/v glycerol and 2% w/v calcium chloride. Food sample (pitahaya pieces) coated with caprylic acid emulsion stored in the refrigerator for 12 days had statistically insignificant (p>0.05) change in color, weight loss and firmness compared with the uncoated food, whereas the growth of bacteria and fungi of coated samples was significantly reduced (p<0.0001). In conclusion, the caprylic acid emulsion could be used as antimicrobial food coating. Ongoing research should be conducted on sensory evaluation for further development in food preservation.