The antimicrobial potential of whey protein isolate (WPI) edible films containing 1–4% (v/v) Zataria multiflora Boiss. essential oil (EO) on food-borne pathogenic bacteria (Escherichia coli, Salmonella enteritidis, Staphylococcus aureus and Bacillus cereus) and probiotic bacteria (Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus plantarum and Lactobacillus casei subsp. casei) was evaluated. WPI films incorporated with 2% (v/v) of this EO inhibited the growth of all tested pathogenic bacteria and gram-negative bacteria were more sensitive than gram-positive bacteria. Incorporation of the EO at higher than 2% (v/v) showed significant antimicrobial effects (P < 0.05) for S. enteritidis and L. acidophilus. The growth of all probiotic lactic acid-producing bacteria also inhibited when 2% of the EO was added. Comparison of an image processing-based method with conventional method for measuring of inhibitory effects of edible films exhibited high correlations (R2 ≥ 0.876) between the two methods. These results revealed that Z. multiflora Boiss. EO is a good antimicrobial additive for some food applications when included into WPI edible films.

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