Document Type : Full Research Paper
Authors
1 Ph.D. student, Department of Food science and Technology, Faculty of Agriculture, Ferdowsi University of Mashhad (FUM), Mashhad, Iran
2 Full professor, Department of Food science and Technology, Faculty of Agriculture, Ferdowsi University of Mashhad (FUM), Mashhad, Iran
3 Fellowship researcher, German Federal Institute for Risk Assessment (BfR), Department of Chemicals and Product Safety, Berlin, German
Abstract
Introduction: The main sources of Salmonella for humans are pork, beef, chicken, eggs, fruits, vegetables, and their derivatives such as mayonnaise, and peanut butter. Different species of Salmonella can adapt, grow or survive in different environmental conditions. Salmonella enterica is one of the main global agents caused by food in humans, and Salmonella typhimurium and Salmonella enteritidis serovars are the most prevalent. One strategy is to use active packaging to reduce the microbial load or prevent the growth of microorganisms on food. Antimicrobial active packaging has received much attention in recent years due to maintaining food quality and safety, and increasing shelf life. Among the antimicrobials used in the food industry, bacteriophages have a very good efficiency to control pathogenic bacteria. Pullulan has a good ability to form a film, its film has good characteristics such as transparency, odorlessness, tastelessness, solubility in water, and low permeability to oxygen and fat, but its problem is related to high price. The combination of polysaccharides with proteins has been done in order to improve the performance and reduce the costs of production films. Gelatin is a suitable option to combine with pullulan in terms of good mechanical properties, reduced permeability, and reasonable price. Different ratios of gelatin and pullulan were studied and suitable film selected, but it needed to modify, so nanofiber cellulose was added in order to improve the mechanical properties and water resistance, adding cellulose nano fiber can be a good and appropriate option. The aim of this research is to evaluate the effectiveness of gelatin-pullulan-cellulose nanofiber antibacterial composite film containing bacteriophage against Salmonella Typhimurium bacteria at two different temperatures over time.
Materials and Methods: 6 gr of each gelatin and pullulan were prepared separately and mixed with together at a ratio of 20 gelatin- 80 pullulan. Cellulose nanofiber was extracted from rice bran and were added at three different levels (1 %, 3 %, and 5 %). Commercial bacteriophage solution was added to each of the films separately and the films were prepared by molding method. Zone inhibitory of films containing different percentage of cellulose nanofibers on the agar media against Salmonella typhimurium (104 CFU/ml) were evaluated. As well as, antibacterial effect of selected film on the poultry meat inoculated to S. typhimurium (104 CFU/ml) and numbers of phages on the surface meat at different 4 and 12 temperatures during times were investigated.
Results and Discussion: The results indicated that 20 gelatin- 80 pullulan films containing different percentages of cellulose nanofibers showed approximately 2 mm of zone inhibitory compare to the control film, but zone inhibitory among films at different percents of cellulose nanofiber did not observe significant change. The antibacterial effect on poultry meat was dependent on temperature, films loaded with bacteriophages at higher temperature (12 ) was more effective compared to lower temperature (4 ). The populations of S. Typhimurium were decreased 1 log and 0.7 log than control samples at 4 after 7 and 9 days, while at 12 , after 1 and 9 days decreased 1 log and around 2.55 log rather control samples, respectively. In a study, beef inoculated with salmonella bacteria was treated by SALMONELEXTM bacteriophage and resulted in decrease 1.29 log reduction of pathogen bacteria compared to the control sample (Yeh et al., 2017). In another study, the antibacterial effect of double-layer poly lactic acid/xanthan film at 10 °C compared to 4 °C against pathogenic bacteria of Salmonella and Listeria was different and at higher temperatures, the number of pathogenic bacteria decreased more (Radford et al., 2017). The number of phages decreased during times at both temperatures, as well as, their numbers did not significantly change at both temperatures. Kamali et al. (2022) displayed that the release of phages from the film of 30 poly lactic acid/70 whey protein to the meat surface after one hour was 63.22 % and 63.18 % at temperatures of 4 °C and 10 °C, respectively, which presents they did not have a significant difference, after one day at both temperatures.
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