بررسی ویژگیهای ضد میکروبی و فیزیکوشیمیایی فیلم خوراکی بر پایه کازئینات سدیم حاوی عصاره گزنه.

Introduction: The spread of microbial diseases caused by food has led to extensive research in order to discover new ways to control microbial growth in food while maintaining their quality, freshness and safety. Coating food with biopolymers is one of the ways to improve the organoleptic properties of products. In order to increase the positive effects of this process, appropriate plant extracts and essential oils can be used. In addition to creating a good taste, these herbal compounds mainly have antimicrobial and antioxidant properties. The inclusion of this material in the formulation of coatings is mainly to improve their antimicrobial properties. The use of food coatings have advantages such as being biodegradable, having nutritional value, preventing or postponing microbial spoilage, preventing moisture absorption or dehydration, preventing the destruction of nutritious compounds due to unwanted reactions such as oxidation and The browning reactions prevent the juice from leaving the meat and also act as a carrier of additives such as antimicrobial compounds, antioxidants, flavorings and colors. One of the biodegradable compounds that can be used to prepare films is sodium caseinate. This substance is highly soluble and can spread very quickly in an aqueous mixture and become homogenized in the presence of oil or fat. Roman nettle (Urtica pilulifera) is a one-or two-year-old plant and is one of the native medicinal plants of West Azerbaijan region, which has extensive therapeutic, antioxidant and antimicrobial properties. This extracts have high inhibitory activity against the growth of gram-positive, gram-negative bacteria; Therefore, nettle extract can be used as one of the natural antioxidant and antimicrobial compounds in the packaging industry. In this research, the physical and mechanical properties of the sodium caseinate edible film containing this extract were investigated and its effectiveness in inhibiting the growth of food poisoning and contaminating agents was investigated. Materials and methods: Two bacterial strains of Escherichia coli H7:O157 and Staphylococcus aureus were selected to investigate the antimicrobial properties of the produced films. When preparing a liquid culture of bacteria, one full loop of each bacterial sample was removed and cultured under completely sterile conditions in 50 ml of Moller Hinton Broth liquid medium, then at 37 °C and 140-150 rpm for 24 h in a machine. The process of diluting cultures using sterile distilled water until the microbial population was 1x106CFU/ml. 10 g of sodium caseinate was dissolved in 150 g of distilled water containing determined amounts of glycerol at a temperature of 80 ± 5 °C and a stirring speed of 550 rpm then Nettle extract in three concentration levels 0, 1, 3 and 5 (%W/W) along with Tween 80 emulsifier to the amount of 30% of the weight of the essential oil was added to the control film solution and by a thermal stirrer at a speed of 550 rpm for 1 min. 5 were uniformly distributed in the solution at a temperature of 60±5°C. The prepared solutions were poured amount of 35 ml in the glass plates. Then drying the samples was 13.5 h at 40 °C. The dried films were slowly separated from the plates and stored in desiccators containing saturated magnesium nitrate solution with relative humidity of 50% and temperature of 25°C for experiments. Measuring the thickness of the films-solubility of the films in water - measuring the transparency - determining the WVP- determining the mechanical properties-studying the microstructure of the samples was done through SEM. Experiments were determined based on a completely randomized design using the factorial test. Comparison of average data was done at 5% probability level based on One Way ANOVA test using Mini Tab version 17 software. Results and discussion: The results related to the evaluation of the physical characteristics of the antimicrobial films showed that with the increase in the nettle extract concentration, the thickness of the film samples increased from 85 μ in the control sample to 91 μ in the sample containing 5% essential oil, but this increase was not significant (P>0.05). According to the electron microscope images, with the addition of antimicrobial extract, the production films were found to have a spongy texture. As the water molecules were trapped in these pores, the humidity and swelling of the films increased and as a result, their thickness increased. Adding extract to the samples reduced the transparency so that at 1 and 3% level, this change was not statistically significant (P>0.05); But at the 5% level, it decreased significantly (P<0.05). Adding the extract to the samples increased the solubility significantly (P<0.05) due to the increase of pores in the structure of the films, which is due to the destruction of the film layers and subsequently the ease of water entering the polymer matrix. The surface of the sodium caseinate films was uneven due to the swelling of the biopolymer chains; But this unevenness did not disturb the order and coherence of the film and the matrix still maintained its compact structure, the microscopic images also confirm this. The WVP in the control film was 3.36 ± 9.79 × 10- 11. Although the hydrophobic nature of the extract could affect the hydrophilic-hydrophobic characteristics of the films; But physical factors had a major effect on the WVP. As mentioned before, it seems that the spongy structure created in the films containing nettle extract was caused by the disruption of the regular structure of the polymer chains due to the presence of compounds in the extract. This phenomenon increased the permeability to water vapor significantly (P<0.05). The tensile strength of the control film based on sodium caseinate was 7.97 ± 0.60 MPa. The tensile strength values of films containing extract with a concentration of 5% were significantly (P<0.05) lower than the control film. The decrease in tensile strength of antimicrobial films was due to the destruction of the film network as a result of the addition of nettle extract can play the role of softener in films and as a result reduce the tensile strength of the film and improve the elongation at break of the film.The addition of extract led to the creation of transparent areas of inhibition around the films, and with the increase in the concentration of the extract, the inhibition area increased significantly (P<0.05). was more effective than Escherichia coli (gram negative). The images related to the SEM of different film samples indicate that the control film sample has a smooth, dense and uniform surface. The sample images of the film containing antimicrobial extract indicate the presence of many pores and holes on the surface. Conclusions: Considering the need to develop green packaging films in the food industry, in this research the physical, mechanical, morphological and antimicrobial properties of sodium caseinate films containing nettle extract were investigated. Adding nettle extract to edible films caused a decrease in transparency by creating a spongy structure, and due to the increase of pores in the films' structure, it increased the film's solubility and permeability to water vapor. The tensile strength of the films also decreased when the extract entered the film matrix and disrupted the network order. Films containing nettle extract in microbial tests showed larger inhibition areas compared to the control film, and the resistance of gram-positive bacteria (Staphylococcus aureus) to the antimicrobial film containing nettle extract compared to gram-negative bacteria (Escherichia coli) Lower. [ABSTRACT FROM AUTHOR]