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The inclusion of natural antioxidants and nanoparticles into edible coatings can improve their structure, functionality and applicability in foods. This study aims to determine the antibacterial effect of new nano-composite based on bean pod shell gum (BPSG), silver nanoparticle (SNP) and herbal essential oil (EO).

For this purpose, BPSG (4 per cent w/v), SNP (0.5-1 per cent w/v) and Helichrysum arenarium EO (1-2 per cent v/v) were mixed. After preparation the edible film, the antibacterial activity was tested on five food-borne pathogenic bacteria in two categories including two-gram positives and three-gram negatives bacteria. The EO composition was determined by GC–mass spectrometry and the antibacterial activity was tested using disk diffusion test.

Results showed that gram-positive bacteria were more susceptible than gram-negative bacteria. Increasing Helichrysum arenarium EO and SNP content increased antimicrobial activity of the edible film based on BPSG, so that the treatment containing 2 per cent v/v Helichrysum arenarium EO and 1 per cent w/v SNP led to the highest inhibition zone (8.1-13.1 mm) compared to treatment containing 1 per cent v/v Helichrysum arenarium EO and 0.5 per cent w/v SNP with inhibition zone range of 5.4-9.9 mm and the difference was statistically significant (p = 0.41). Also, the chemical composition analysis of the EO identified a total of 38 compounds in which a-pinene (32 per cent), 1,8-cineole (16 per cent), α-humulene (15 per cent) and ß-caryophyllene (8 per cent) were the main fractions. Other separated components accounted less than 29 per cent of the oil.

In general, SNP and Helichrysum arenarium EO improved the functional properties including the antimicrobial activity of the edible film based on BPSG, which increases the potential to be used as active packaging for fresh products.