Optimal synergistic formulation of essential oils: Antimicrobial and physical-mechanical properties of cinnamon-oregano oils-incorporated cassava starch films for fresh Vietnamese bread preservation

The synergistic effects of cinnamon and oregano essential oils (EOs) against Staphylococcus aureus , Bacillus cereus , and Aspergillus flavus were evaluated by using a disc volatilization assay. Minimum inhibitory concentration (MIC) was indicated at 5 μL L −1 air when the ratios of cinnamon and oregano EOs were 8:2 and 9:1 (v/v) for all tested bacteria, which also showed strongly synergistic activities (fractional inhibition concentration index (FIC) ≤ 0.48). However, there was only the combination ratio 6:4 showing a synergistic effect on the inhibition of A . flavus . Therefore, this combination was selected for incorporating with cassava starch films according to the central composite design. Desirability function approach indicated the optimal film formulation was 45.54 % of sorbitol and 0.65 % of EOs. The tensile strength and elongation at break of the optimal film were 8 MPa and 27 %, respectively while the AM film showed 100 % inhibition for all tested microorganisms. In the artificial contamination test, the antimicrobial film could express the inhibition at 85 % and 100 % on the growth of A . flavus in artificially and naturally contaminated Vietnamese bread, respectively. • FICs index at 6:4 showed synergistically inhibitory effects of all tested strains. • Physical-mechanical film properties were strongly affected by sorbitol content. • AM activity of films increased with increasing EOs concentration, and vice versa. • Optimal synergistic formulation of AM film could be defined using RSM. • This indicated the promising technology in preservation of fresh Vietnamese bread.