مجله میکروب شناسی مواد غذایی
سال نهم شماره 4 (زمستان 1401)

This study has investigated the effect of UV-C radiation at doses of 8, 15 and 30 W compare to pasteurization (LTLT) on turbidity and total phenol content changes of red grape juice immediately after processing, and some chemical (pH, acidity, ascorbic acid, anthocyanins, antioxidant capacity, and color), and microbial (mold and yeast) properties during the period of 0, 30, 60, 90 and 120 days of storage at room temperature. Eleven treatments were given, including UV-C treatments at 2, 6, and 10 minutes, as well as dosages of 8, 15, and 30 watts, with a control and a pasteurized grape juice sample. The results showed that overtime in during storage, the Brix values decreased, and also the irradiated samples at a dose of 30 W for 2 and 6 min showed the lowest Brix values. When compared to shorter irradiation intervals, irradiating grape juice for 10 minutes reduced acidity and increased pH. Irradiated grape juice had higher ascorbic acid, anthocyanin, total phenol, and antioxidant activity compared to pasteurized samples. Irradiated samples showed higher antioxidant activity at the end of the storage period compared to other treatments. UV-C radiation compare to pasteurization was able to prevent the turbidity and color changes in red grape juice. In terms of quality and microbiological features, 30 watt treatments for 6 and 10 minutes were favored above other treatments. Overall, UV-C radiation as a suitable alternative to the usual pasteurization led to better preservation of the qualitative and microbial properties of red grape juice.

Listeria monocytogenes is a foodborne pathogen that causes listeriosis in humans and animals. Microbial contamination of food usually leads to widespread food poisoning in the form of widespread epidemics in the region, which is very significant in terms of public health and is one of the most important issues in developing countries. The aim of this study was to determine the contamination of Listeria monocytogenes in dairy products using culture method and final confirmation by PCR method. In this study, 150 different dairy samples offered in the market were purchased randomly. The samples were transferred to the laboratory under hygienic conditions and examined. In addition to culture medium experiments, positive samples were evaluated for final confirmation and identification of the pathogen by molecular PCR.14 (9.33%) positive samples including 6 samples of white cheese (4%), 4 samples of cream cheese (2.6%), and 3 samples of curd (2%) were positive for contamination. Antimicrobial susceptibility to 16 antibiotics was highly sensitive to clindamycin (47.37%). It is noteworthy that it was resistant to several drugs.The presence of Listeria monocytogenes in dairy products (cheese, cream cheese, and whey) was proven. Based on the results, people who consume contaminated dairy products are at potential risk of listeriosis. As a result, food safety authorities must establish an effective standard for examining the presence of Listeria in food.

This study aimed to study the effect of tarragon and savory essential oils on the shelf life of minced beef. Appropriate concentrations of tarragon and savory essential oils were determined by sensory and microbial tests and mixed with minced beef. The treatment and control samples weighing about 100g were packaged in polyethylene containers and stretched films. Microbial, physicochemical and sensory assessments were performed on the samples every day for five days. The results showed that the trend of increasing aerobic mesophilic bacteria in control samples was significantly different (P <0.05) from the second day until the end of the five-day storage period. Similar results were observed for psychrotrophs and coliforms. From the day thee, the pH difference in the control and treatment groups was significant (P <0.05). Peroxide value, total volatile nitrogen content as well as sensory properties of tarragon and savory treatments had almost similar results. Nonetheless, from the third to the fifth day there was a significant difference (P <0.05) between the control and treatment groups. It seems that the use of tarragon and savory essential oils can retain the population of spoilage bacteria below the allowable level, for up to four and five days, respectively. It was concluded that tarragon and savory essential oils can be used as natural antimicrobial/antioxidants to improve the sensory properties of minced meat.

Probiotic bacteria are microbial food supplements that are present in appropriate amounts in the digestive system and are beneficial to human health. Emong the probiotic bacteria, lactobacillus most common type of bacteria that are in dairy products and production lactic acid during the fermentation. The aim of this study was to isolate and identify of lactobacillus from bacteria flora of traditional Maragheh cheese and determine the technological properties their lipolitic and proteolitic activity. For this purpose lactic bacteria isolated by common methods of cultivation and identification according to PCR and biochemical properties and then done supplementary tests for full recognition present isolates such warm coloration, oxidase, catalase test, and ability of acid production and pH changes by lactobacillus evaluated during different times and optimum temperature for growth. The results showed that in all samples, the acidity increased significantly (P <0.05) and the pH decreased over time. Acidity increased significantly (P <0.05) in all samples and in temperature 30, 37, 42, 45c and during 0, 4,8,24,48 h and observed in 48 to 72 h in several samples low decrease and also pH was regular decrease in all samples and high temperature to 48 h and in 48 to 72 h in most samples and temperatures were fixed amount. Therefore, Maragheh traditional cheese is a valuable source of Lactobacillus bacteria, which allows consumers to find a new way to enjoy health.

With the growing awareness of the importance of natural extracts with antimicrobial and antioxidant properties, today the food industry is looking for the use these compounds instead of synthetic preservatives. To date, no research has been done to find an optimal mixture of Origanum majorana, Long pepper, and Areca extracts against the gene expression of A and B enterotoxins of S. aureus. Therefore, in this study, we are seeking to provide a mixture of these extracts with the highest anti-enterotoxigenic activity using real-time PCR and mixture statistical methods. If successful, we introduce these extracts as an antagonist against the growth of pathogenic bacteria and the gene expression of enterotoxin of S. aureus. In the first stage, the antimicrobial activity of Origanum majorana, Long pepper, and Areca extracts was studied, which Origanum majorana had the highest antimicrobial activity among them. On the other hand, among the tested bacteria, gram-positive bacteria were more sensitive than gram-negative bacteria. The tested extracts had a synergistic effect on each other against the gene expression of A and B enterotoxins of S. aureus. The mixture of extracts including 47% Origanum majorana extract, 27% Long pepper extract, and 26% Areca extract showed the highest activity against the gene expression.

Salmonella Typhimurium (S. Typhimurium) is one of the most important worldwide public health concerns capable of forming biofilms on food contact surfaces. The aim of this study was to evaluate the antibacterial and anti-biofilm activity of Satureja sahendica hydroalcoholic extract (SSHE) and Trisodium Phosphate (TSP) against S. Typhimurium (n= 20) isolated from poultry. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined using the microdilution broth method. To evaluate the anti-biofilm effects, the isolates were treated with inhibitory and sub-inhibitory concentrations of both substances and after 24 hours, the biofilm formation was evaluated. According to the results, the MICs of SSHE and TSP against S. Typhimurium isolates were ranged from 1.25-10 and 5-80 mg ml-1, respectively. Also, MBCs value of SSHE and TSP were varied against isolates and were ranging from 40-160> and 80-160> mg ml-1, respectively. The results of statistical analysis showed that both of SSHE and TSP significantly reduced biofilm formation in S. Typhimurium compared to the control group (p <0.05). Also, the statistical results showed that SSEH reduces the rate of biofilm formation more than TSP (p <0.05). According to these results, SSHE can be a suitable alternative to chemicals such as TSP in the food industry to reduce bacterial contamination. However, its application requires further studies to determine its safety and toxicity.

Pseudomonas aeruginosa strains are considered as the main causes of food spoilage and occasionally foodborne diseases. The present study was performed to evaluate the pattern of antibiotic resistance and frequency of virulence factors in Pseudomonas aeruginosa strains isolated from meat. A total of 120 samples of raw and frozen meat were collected. Samples were evaluated for the presence of Pseudomonas aeruginosa using conventional microbial culture. The pattern of antibiotic resistance of Pseudomonas aeruginosa isolates was evaluated using the disk diffusion method. Genomic DNA was extracted from Pseudomonas aeruginosa isolates and the frequency of virulence factors was assessed using the polymerase chain reaction. Eleven out of 120 meat samples (9.16%) were contaminated with Pseudomonas aeruginosa. The prevalence of Pseudomonas aeruginosa in raw and curled meat samples was 5.00 and 13.33%, respectively. There was a statistically significant difference in the prevalence of Pseudomonas aeruginosa between raw and frozen meat samples (P <0.05). Pseudomonas aeruginosa isolates had the highest rate of antibiotic resistance against ampicillin (100%), penicillin (90.90%) and tetracycline (81.81%). The prevalence of resistance to imipenem (9.09%) and trimethoprim (18.18%) antibiotics was lower than other cases. ExoU (54.54%) and exoT (18.18%) genes were the most frequent virulence factors detected. The simultaneous presence of virulence factors and antibiotic resistance in Pseudomonas aeruginosa strains isolated from raw and frozen meat increases the need for further studies to confirm the role of this bacterium as an important food-spoilage bacterium.

Listeria is one of the most important bacteria that contaminates milk and milk products. The main species that causes listeriosis in humans and animals and is transmitted through contaminated food is Listeria monocytogenes. For this purpose, in order to identify Listeria monocytogenes in raw milk and traditional butter, in the spring of 1400, 40 samples of raw milk (20) and traditional butter (20) were collected from traditional dairy stores in Amol city. The samples were immediately transferred to a food microbiology laboratory in cold condition. The samples were first cultured in peptone water enrichment medium and then the enriched samples were transferred to Palkam Listeria selective agar medium with selective Listeria monocytogenes supplementation. Then antimicrobial susceptibility of Listeria monocytogenes isolates was determined by disk diffusion method using the antibiotics ampicillin, gentamicin, erythromycin, chloramphenicol, tetracycline, and ciprofloxacin. From the total samples, the prevalence of Listeria species in raw milk and butter was 35% and 10%, respectively. The results of antibiotic susceptibility and resistance test of raw milk samples showed that they were resistant to ampicillin 85.7% and tetracycline 71.4% and among butter samples only erythromycin was 100% resistant and ampicillin 100% semi-resistant. The mean of the obtained results in the antibiogram test were analyzed with 95% confidence and one-way analysis of variance. The results of the present study indicate the potential risk of infection due to consumption of raw milk and traditional butter to Listeria monocytogenes and raw milk had higher risk than butter.