the effect of chitosan edible coating containing (zataria) thyme essntial oils on physicochemical and sensorial properties in common carp at refrigerator temperture

Chitosan is a water-soluble polysaccharide that has the properties of recyclability, antimicrobial, antifungal, antioxidant, gas barrier, and film and coating formation.1 zataria thyme essential oil has antimicrobial properties that affect many pathogens and food spoilage organisms.2 the aim of the present study was to investigate the possibility of using an edible chitosan coating containing zataria thyme essential oil on carp to increase the storage time at refrigerated temperature. the samples were stored at 4°c for fifteen days and subjected to physical (weight loss), chemical (moisture, ash, fat, peroxide, ph), and sensory analysis at three-day intervals. all tests were performed in triplicate in a full factorial design. meandifference comparison analysis was performed using tukey s test (p<0.05). sensory evaluation showed that zataria thyme essential oil had a pleasant effect on all sensory characteristics of carp such as (aroma, color, texture, overall acceptability). the lowest weight loss was related to the treatments of 1% chitosan and 1.5% zataria thyme essential oil. also, the lowest ash content was related to the concentration of 1% chitosan containing 1.5% zataria thyme essential oil. during the study, samples coated with edible chitosan coating containing zataria thyme essential oil showed a lower ph compared to the control sample. treatments with chitosan coating containing zataria thyme essential oil had a better condition than the control sample in terms of peroxide level on day 15. the lowest fat loss was related to chitosan coating containing 1.5% zataria thyme essential oil. carp coated with zataria thyme essential oil has better physicochemical properties than uncoated carp. this coating can be very effective in increasing the shelf life of carp stored in the refrigerator. the required amount of zataria thyme and cinnamon were purchased from a medicinal plant store in the spring and their scientific names were confirmed by a reputable medicinal plant laboratory. their essential oils were prepared by hydrodistillation using a clevenger apparatus, and the essential oils of cinnamon and thyme were extracted by water distillation. since essential oils are sensitive to light, oxygen, and temperature, and their compounds change and evolve under such conditions, the extracted essential oils were immediately transferred to a dark glass bottle in a seal and stored in the refrigerator until use. in this study, freshly caught farmed freshwater crayfish samples were tested. their average weight was 29±5 grams. 300 samples were taken from freshwater crayfish by random sampling method. the crayfish samples were kept at 0-4°c (ice powder) and placed in an insulated container. after necessary examinations, healthy and uniform samples were selected, washed, skinned, and decapitated, and were divided into 35 groups including 34 treatment groups and 1 control group. each freshwater crayfish was completely coated based on the type of treatment (a: chitosan coating with a concentration of 0% + 3% gelatin (pure coating); b: chitosan coating with concentrations of 0, 0.5, 1, 1.5, and 2% + 3% gelatin + thyme essential oil with concentrations of 0.5 and 1%; c: chitosan coating with concentrations of 0, 0.5, 1, 1.5, and 2% + 3% gelatin + cinnamon essential oil with concentrations of 0.5 and 1%; d: chitosan coating with concentrations of 0, 0.5, 1, 1.5, and 2% + 3%gelatin + thyme essential oil with concentrations of 0.5 and 1%; d: chitosan coating with concentrations of 0, 0.5, 1, 1.5, and 2% + 3% gelatin + thyme essential oil with concentrations of 0.5 and 1%, + cinnamon essential oil with concentrations of 0.5 and 1%) and then stored in polyethylene containers at refrigerator temperature. after 7 days of storage, 1 treatment was repeated every day and each treatment was repeated 3 times. in each repetition, 8 coated freshwater crab samples were tested. to form a coating on the surface of the freshwater crab samples, the samples were refrigerated for 2 hours and then packaged in polypropylene containers and stored at 4°c andevaluated on the seventh day.1considering the risks of chemical preservatives for consumers and also considering the high consumption of aquatic products including carp, it seems necessary to replace them with natural preservatives in coating formulations. the components of zataria thyme essential oil are one of these natural compounds, and in this study, its antimicrobial effect on carp was investigated. natural coatings combined with plant essential oils have antimicrobial properties and can reduce oxidation reactions, improve microbial characteristics, maintain product quality, and increase product shelf life, and provide a basis for the practical use of these compounds compared to synthetic compounds. 4 chitosan-based coatings combined with essential oils were better than coatings without essential oils in maintaining the quality characteristics of carp at refrigerator temperature, and 1% chitosan and 1% and 0.5% zataria thyme essential oils combined coatings had the best optimal concentration in inhibiting microbial growth, chemical spoilage, controlling microbial spoilage, and improving physical properties.