Nano-encapsulation of a combination of clove oil and thymol and their application in fresh-cut apples and raw minced beef

Abstract

This study aimed to improve the antimicrobial activity of natural antimicrobials by combination and nanoencapsulation technology and to confirm the effect of combination and nanoencapsulation on their antimicrobial activity in fresh-cut apples and raw minced beef. The combinations of clove oil and thymol (CoTh), and clove oil and α-tocopherol (CoTo) were selected as primary synergistic antimicrobial combinations against 2 g-positive bacteria (Staphylococcus aureus and Listeria monocytogenes) and 2 g-negative bacteria (Escherichia coli and Salmonella typhimurium) using minimum inhibitory concentrations and fractional inhibitory concentration indices. CoTh-loaded and CoTo-loaded nanoparticles (NPs) were obtained by ionic gelation of chitosan (CS) with poly γ-glutamic acid (γ-PGA). CoTh was selected as the final combination based on the synergistic antimicrobial activity identified against all bacteria tested in this study using a time-kill assay. The CoTh-loaded CS/γ-PGA NPs more effectively inhibited the growth of gram-positive and gram-negative bacteria than free CoTh for an elongated period in the time-kill assay and fresh-cut apple and minced beef samples. Therefore, CS/γ-PGA nanoencapsulation could be a promising technique for improving and maintaining the inhibitory effects of CoTh against pathogenic bacteria, even in the presence of other ingredients, such as sugar, fat, and protein, in food.