مجله میکروب شناسی مواد غذایی
سال هفتم شماره 3 (پاییز 1399)

Irradiation is one of the most effective technologies for reducing the microbial load of food. This method can help improve the health of food products and increase their shelf life. This study aimed to evaluate the effects of gamma irradiation and freezing storage as a combined method to improve the shelf life of a chicken. Chicken samples were divided into four treatments: untreated (control) and irradiated (0.75, three, and five kg) and stored in freezing conditions for 0, 3, 6, and 9 months. The samples were stored at -18°C, and then microbial and chemical analyzes and their sensory quality were performed every three months. Microbial analysis showed that irradiation and freezing maintenance decreased mesophilic, coliform, Salmonella, and E. coli (P <0.05). Results showed that there was no significant difference in sensory quality and chemical analysis parameters such as volatile total nitrogen (P> 0.05) in treated and control groups but increased significantly (p> 0.05). P) Peroxide index was observed. The results of this study indicate that the combined use of irradiation and freezing reduces the bacterial burden and increases the shelf-life of chicken meat. However, there is no change in sensory quality and biochemical analyzes.

Microbial contamination of confectionery products can cause types of gastrointestinal infections in consumers. The aim of this research was the assessment of microbial quality in dry confectionaries which marketed in Birjand city. For this purpose, at different times, a total of 100 samples of dry confectioneries were collected randomly under sterile conditions, based on the number of confectionery stores in different regions of the city and tested according to the reference and national standard methods. The statistical analysis of the data showed that the rate of contamination with Enterobacteriaceae and coliforms was more significant than standard limits in 8% and 13% of the samples, respectively, and none of them were infected with Escherichia coli. Also, 35% of the samples contained mold& yeast, but in 15% of them, the rate of contamination was higher than the standard limits. The results of this survey showed that a total of 19% of the samples were unusable due to excessive microbial contamination, so more precautionary measures should be taken in the processes of production, storage, and delivery of this product.

Staphylococcus aureus (S. aureus) is one of the significant factors in the development of hospital infections. In the meantime, hospital personnel and foodstuffs are essential factors that can transfer germs to others. Our aim in this study is to determine the frequency of coagulase gene polymorphism in S. aureus isolated from food and human samples. This descriptive cross-sectional study was performed on suspicious samples infected to S. aureus in the microbiology lab of the Faculty of Veterinary Medicine in Islamic Azad University of Tabriz, during the first 6 months of the year 2016. After initial enrichment, the samples were grown in solid media Blood Agar, and Mannitol Salt agar was cultured. To confirm the presence of coagulase gene, Coa G2 and Coa G3 primers were used: Coagulase gene genotyping was performed by the RFLP method. For this purpose, the PCR product was digested in the presence of the enzyme ALUI. The PCR product was digested by agarose gel after digestion. A total of 63 samples, including 11 samples of samples and 52 food samples of 10 hamburgers and 7 samples of chicken and 11 samples of milk 8, cheese samples and 12 samples of ice cream and 1 sample of fish and 3 specimens of the quail were studied. Among them, 35 No genotypes were detected, and 28 samples of S. aureus were found. The results showed that no significant relation was observed between sample types and genotyping of isolated S. aureus strain. that needs further investigation.

One of the essential criteria for determining the quality of products containing probiotics is the presence of a certain number of viable cells per gram of product. To transmit enough viable cells to the gastrointestinal tract, the population of probiotic microorganisms should be preserved during storage. In the present study, culturable cells of some commercial products were isolated and enumerated by the plate count and flow cytometric methods. The isolates were then identified by biochemical and molecular methods. The viability of yeast cells was then assessed at different temperatures during 30 days by the methods above. The results showed that Protexin restore® contained the same types and number of bacteria that were claimed by the manufacturer. In contrast, protexin balance® and Dailyeast® contained a lower number of bacterial cells and yeast cells, respectively. It is noteworthy that only 33% of yeast cells were culturable on YPG agar, while flow cytometric analysis showed that 87% of cells were viable and exhibited cell membrane integrity. Also, yeast cells in Dailyeast® product were stable at 4-35°C. In conclusion, using different culture media and physicochemical conditions for the enumeration of viable and culturable cells may lead to different results. Thus, a combination of different methods should be used to get good results.

In recent years, producing new antifungal drugs has been considered due to the resistance of fungal toxins and their pathogenicity. In this research, the effect of inhibitory growth of Acinetobacter isolated from frozen foods against pathogenic fungi of Aspergillus niger (A.niger) and A. flavus has been investigated. A total of 15 frozen food samples were collected from Jiroft city stores and tested for isolation and identification of potential Acinetobacter. A total of 28 bacterial isolates were obtained from frozen food that, from these, two isolates were identified Acinetobacter by biochemical methods. These bacteria were isolated from frozen hamburger and vegetables. The pathogenic fungi of Aspergillus niger and A. flavus were prepared from the center of the Iranian fungus and bacterial collection center. Then, the antagonistic effects of two isolates of Acinetobacter on these fungi were investigated. The results showed no inhibition of A. niger growth by two isolates of Acinetobacter isolated from frozen hamburger and vegetables, but isolates of frozen vegetables showed an inhibitory effect on A. flavus, and its inhibition zone was 11 mm. Finally, the inhibitory bacteria were selected for molecular identification. Based on the results of sequencing blast and phylogenetic tree drawing, the isolate studied was Acinetobacter baumannii.

Nitrite and nitrate are preservatives that have been used in meat products (sausages) and include carcinogenic effects. Natural antimicrobials with plant origin are incorporated into foods in the forms of essential oils or extracts. They can control spoilage bacteria in foodstuffs (e.g., meat products). This work was aimed to evaluate the effect of partial nitrite replacement with Urticadioicaessential oil (UDE) on microbial properties of cooked sausage. Nitrite content (120 ppm) was reduced and replaced with 20, 40, and 60, 80, 100, and 120 ppm of UDE. The effect of UDE on antimicrobial properties of the essential oil was evaluated by MICs determination against Escherichia coli and Clostridium perfringens by the microdilution method. Results indicated that samples with 20 ppm of nitrite and 100 ppm UDEwerenot significantly samples with control at the end of storage period. The high level of nitrite and nitrate in meat products is worrying. Consequently, Reduction and Replacement of these food additives is essential.in this study, all samples with different essential oil levels were acceptable after 60 days of storage. Replacement of 83 % of nitrite with UDE is a reasonable approach in order to put down the harmful effects of nitrite in sausage and to enhance the functionality of the product.

One of the most critical challenges facing dairy products is decreasing or eliminating of Aflatoxins, especially Aflatoxin M1. On the other hand, the production of probiotic dairy products is another aim of the dairy industry. Therefore, in this study, using pulse electric field technology in the range of 10 to 30 microseconds, ozonation in the range of 0 to 10 mg/min and ultraviolet radiation in the range of 0 to 5 J/cm2 in acidophilus milk attempted to obtain a probiotic-free aflatoxin product. To investigate the impact of the applied the mentioned processes, a central response method (RSM) was used in the full quadratic model so that these processes were considered as operational variables. For this purpose, the central composite design with three independent variables, including pulsed electric field, ozonation and UV irradiation to complete quadratic form has been used. The results showed a significant effect of independent variables and their synergistic effect at 0.05 levels on the reduction of aflatoxin in acidophilus milk. The best-operating conditions based on the lowest amount of aflatoxin in acidophilus milk consisted of 13.15-microsecond pulses in the electric field, 9.99 mg/min of ozone, and 4.99 J/cm2 of UV waves. In optimum conditions, pH 6.22, Acidity 19.76 (Dornic), dry matter 10.69%, total color change 8.13, and overall acceptance score 4.77 were obtained. Finally, in optimum condition, 84.61% and 86.76% of aflatoxin M1 and total aflatoxins were reduced, and the final product contained 5.2×106 cfu/g Lactobacillus acidophilus, respectively.

Goat's milk is a proper alternative to cow's milk because of its higher digestibility and lower allergic characteristics, as well as its higher functional nutrient. On the other hand, its health benefits can be increased by the incorporation of probiotics into goat's milk. This research aimed to investigate the survivability of Lactobacillus acidophilus and Bifidobacterium lactis (B. lactis) individually and in combination on the physicochemical and sensory properties of yogurt made of goat's milk during 21days storage. In this research, 4 treatments were prepared, including control (with no probiotic bacteria), La treatment containing Lactobacillus acidophilus, Bb treatment containing B. lactis, and LaBb treatment containing a combination of Lactobacillus acidophilus and B. lactis. The results showed that the count of Lactobacillus acidophilus, B. lactis, and their combination reached from 8.54 log cfu/g on the first day to 9.43, 10.06 and 10.75 log cfu/g at the end of the storage period, respectively. At the end of the storage period, the control sample had significantly the highest pH and syneresis and the lowest acidity, water holding capacity, viscosity, and overall acceptability among treatments. However, no significant difference between samples containing probiotic in acidity, pH, viscosity, syneresis, water holding capacity, and overall acceptability was observed. According to the results obtained of this study, yogurt made of goat's milk, in addition to being a suitable carrier for probiotics, its sensory properties improve as a result of the incorporation of these probiotics.