الفهرس 
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Abstract
Edible coating is considered as eco-friendly technology for food preservation, improving quality as well as prolonging shelf-life. It can help to meet several challenges involved in the storage and marketing of foods that are safe, nutritious, of high quality, stable and economic. Also, edible coatings developed from biodegradable materials such as starch and Zinc oxide nanoparticles (ZnO NPs) are efficient antimicrobials that could be used as a food additive to reduce the bacterial load on the food surface.
Therefore, the current study aimed to examine the effect of starch-based biodegradable antimicrobial coating incorporated with Lavandula officinalis essential oil, nano-emulsion, ethanolic extract, chemical and green synthesized ZnO NPs with different concentrations on the survival of E.coli and S.aureus in tilapia fillets during chilling storage at 4±1⁰C using agar disk diffusion method .
According to the preliminary experiments, starch-based biodegradable coatings incorporated with different antimicrobials had antimicrobial effect but only B-ZnO NPs and Ch-ZnO NPs were selected for the challenge study, while the other antimicrobials weren’t used due to their weak antimicrobial activity and poor mechanical and physical quality of the coating.
Tilapia fillet samples were inoculated with 8.8 log10 CFU/ml of S.aureus and E.coli cocktails to obtain concentration of 6.6 log10 CFU/cm2, coated with starch-based biodegradable coating incorporated with different antimicrobials then stored at 4±1⁰C for 10 days. Samples were examined at zero day (4hr), 2, 4, 6, 8, and 10 days, the total colony count was detected.
The remaining S.aureus counts of biosynthesized and chemically synthesized ZnO biodegradable coating at different concentrations (2% and 5%) were 5.25, 5.01 and 5.28, 5.09 log10 CFU/cm2 after 4 h of storage and at the end of the storage period the final counts were 3.83, 3.71 and 3.87, 3.82 log10 CFU/cm2, respectively.
On the other hand, the remaining E.coli counts of biosynthesized and chemically synthesized ZnO biodegradable coating at different concentrations (2% and 5%) were 5.39, 5.33 and 5.40, 5.36 log10 CFU/cm2 after 4 h of storage and at the end of the storage period the final counts were 3.90, 3.78 and 3.95, 3.86 log10 CFU/cm2, respectively.
Both control coated and uncoated tilapia fillets samples showed continuous increase in S.aureus counts, which progressed from 6.21 to 7.65 log10 CFU/cm2 and 6.11 to 7.66 log10 CFU/cm2 respectively at the end of the storage period, While the control coated and uncoated tilapia fillet samples showed continuous increase in E.coli counts, which progressed from 6.38 to 7.65 log10 CFU/cm2 and 6.41 to 7.69 log10 CFU/cm2 respectively at the end of the storage period.
Additionally, the sensory evaluation of Tilapia samples showed that the control coated and non-coated samples maintained good sensory characters until the fourth day of storage. On day 6, the control coated and non-coated samples were evaluated this is due to appearance of sings of spoilage. But other treated samples still have good sensory characters till day 8 of chilled storage, this indicates 4 days extension of shelf-life of samples coated with the antimicrobial biodegradable coating compared to the control samples.
Our study showed that starch based biodegradable coating incorporated with bio-synthesized and chemically synthesized methods had antimicrobial activity against different Gram-positive and Gram-negative bacteria mainly S.aureus and E.coli. Also, the current study demonstrated that the incorporation of L.officinalis into ZnO Biodegradable coating may be a promising method in reducing the microbial growth on food surface.