مجله میکروب شناسی مواد غذایی
سال دهم شماره 1 (بهار 1402)

The purpose of this research is extracting propolis using the methods of soaking in 20% and 70% ethanol and the effect of ultrasound in 20% ethanol, and evaluating its physicochemical, antioxidant and antimicrobial properties as a natural preservative used in the food industry. The physicochemical properties, the amount of phenolic and flavonoid compounds, the antioxidant and antimicrobial properties of the extracts were measured. The results showed that most of the number of phenolic compounds (94.19 mg/g), flavonoid (89.46 mg/g) and antioxidant property by DPPH method (92.63%) in ultrasonic extracts. And the lowest number of phenolic compounds (87.85 mg/g), flavonoid (82.20 mg/g) and antioxidant property (85.87%) are in the method of soaking in 20% ethanol. Also, the results of the investigation of the antimicrobial property by the diffusion ability method from the well showed that the most sensitive bacterium was Staphylococcus aureus (20 mm) in front of the ultrasonic extract. Regarding the ability of Pseudomonas aeruginosa bacteria, there was no significant difference between the extracts (p<0.05) and none of the extracts had antibacterial power against Pseudomonas aeruginosa bacteria. The highest ability of Candida albicans (36 mm) was with ultrasonic extract, and in the investigation of the growth of Aspergillus niger after spraying for 8 days, the lowest growth rate was obtained with ultrasonic extract (9 mm) and then 70% ethanol extract (10 mm). Based on this, the amount of phenolic, flavonoid, antioxidant and antimicrobial compounds was 70% more than the 20% ethanol extract, and in the ultrasound, method based on Hurdel technology, a large number of active compounds were found in the 20% ethanol solvent in a short period of time.

Despite the high importance of Helicobacter pylori, the main source of the bacterium and the habits of its transmission to human populations have not been determined yet. The present study was performed to evaluate the prevalence and genotyping of Helicobacter pylori strains isolated from raw milk samples. A total of 180 raw bovine, ovine and caprine milk samples were randomly collected from Fars province. The presence of Helicobacter pylori in raw milk samples were was studied using the microbial culture. Genomic DNA was extracted from Helicobacter pylori isolates and the frequency of VacA, CagA, IceA and OipA genotypes was evaluated using polymerase chain reaction. In total, 53 out of 180 (29.44%) raw milk samples were contaminated with Helicobacter pylori. The prevalence of contamination in raw milk samples of bovine, ovine and caprine was 20, 38.33 and 30%, respectively. VacA s1a (69.71%), m1a (67.92%), s2 (62.26%) and m2 (58.49%) and cagA (50.94%) were the most abundant detected genotypes. The rarest detected genotypes were VacA s1c (7.54%), s1b (16.98%), m1b (18.86%) and iceA2 (7.54%), respectively. S1am1a (39.62%), s2m1a (32.07%), s1am2 (28.30%) and s2m2 (26.41%) were the most commonly detected combined genotypes. Raw milk, especially raw sheep milk, was considered as a carrier for transmission of virulent strains of Helicobacter pylori. The similarity in the genotyping pattern of the isolates probably indicates the similarity in the source of infection of the samples with Helicobacter pylori.

Carbohydrates and lipids are known as the most important sources of calorie intake in food products, much attention has been paid to low-calorie and non-caloric alternatives. In this research, stevia and inulin was used as sugar and fat replacer in chocolate dairy dessert formulation, respectively. Inorder to optimize the formula and low-calorie chocolate dairy dessert production, three factors of inulin concentration (0to 8 g/100 g), stevia concentration (0 to 0.06 g/100 g), and storage day (1 to 14 day) were evaluated using response surface methodology (RSM) with Face-Centered Central Composite. Then, the chemical characteristics including pH, acidity, fat and protein content, and microbial properties were analyzed in the chocolate dairy dessert after 1, 4, 7, 10 and 14 days’ storage. Folch method applied for fatty acids extraction and Gas Chromatography used for determination of fatty acids. The results showed that the pH value decreased with increase in inulin content. An increase in unsaturated fatty acids was observed in low calorie chocolate dairy dessert. The Highest percentage of fatty acids in chocolate dairy dessets were palmitic acid followed by oleic acid. The evaluation of Sucrose, Lactose and Glucose content with HPLC Technique showed that sucrose was the dominate sugar in the control sample but lactose had more content in low calorie desserts. Both total bacterial count and mold and yeast count, were lower than the standard range. According to the model obtained, the formulation with 5.628 g/100 g inulin, 0.032 g/100 g stevia and 5.83 g/100 g of sucrose was selected.

Staphylococcus aureus is an opportunistic pathogen in humans and animals, which can cause contaminating dairy products. In this research, 250 traditional dairy products, including butter, yogurt, cheese, curd, and cream, were prepared from different parts of Shahrekord city and transported to the microbiology laboratory of Shahrekord Azad University in sterile containers with ice. The isolation of Staphylococcus aureus bacteria was done according to standard protocols and molecular methods. Genetic evaluation of biofilm was done by PCR method to detect the most common biofilm coding genes (icaA, icaB, icaC, icaD, bap, fnbA, fnbB, clfB, clfA). From the total of 250 examined samples, 50 samples (20%) were positive for Staphylococcus aureus. Contamination was reported in 26% of curd, 24% of butter, 22% of cheese, 16% of cream, and 12% of yogurt. The frequency of the mentioned genes was reported as 74%, 68%, 64%, 76%, 30%, 96%, 90%, 32% and 28% respectively. In the microtiter plate method, biofilm reaction was observed in 30 isolates (60%), strong biofilm was observed in 20 isolates (66.66%), and weak biofilm was observed in 10 isolates (33.33%). No biofilm reaction was observed in 5 isolates (16.66%). Based on Fisher's exact test, a statistically significant relationship was reported between the studied genes and strong and moderate biofilm reaction.

Probiotic and antifungal properties of the yeasts isolated from fermented pseudo cereals have been rarely studied, yet. In the present study, after isolation of predominant yeasts isolated from fermented black rice, the yeast with the highest survival in simulated gastrointestinal conditions was selected for further studies. Then, the selected isolate was identified by PCR, and subsequently, its probiotic properties including antibacterial effects, antibiotic and antimycotic susceptibilities, aggregation, hydrophobicity and hemolytic potentials were also studied. Antifungal activity of the selected yeast was investigated against some of the foodborne fungi. Sequencing of the PCR products led to the identification of Rhodotorula mucilaginosa as the selected yeast isolate. The isolate maintained 84.39% of its survival in continues acid and bile treatment. Also, the inhibitory effect of the yeast isolate on Salmonella enterica was significantly (p<0.05) higher than the other foodborne bacteria. Yeast isolate had proper aggregation and hydrophobicity capabilities, and it was resistant to the antibiotics tested. Furthermore, the most inhibition of the yeast growth was observed in the presence of ketoconazole, while the selected yeast was resistant to propionate, sorbate, itroconazole and fluconazole. The studied yeast isolate had no hemolytic activity. The antifungal effect of the yeast isolate against Aspergillus flavus was also verified. In accordance with these results, the selected yeast isolate has a proper potential to use as a probiotic or protective culture in production of fermented foods.

The existence of different species of Enterococcus, which have a significant effect on the technological characteristics of cheese, particularly its flavor, has been established in milk and dairy products. This study aimed to explore some of the most significant technological features of Iranian Motal cheese-derived Enterococcus isolates with probiotic characteristics. For this, first the growth rates of Enterococcus isolates at 25, 30, 37, and 43 °C were measured, and their ability for acidification was then assessed by measuring pH and acidity by incubation at the optimal temperature for zero, 4, 8, 24, 48 and 72 hours. Subsequently, enzymatic aspects related to technological features including proteolytic and amylolytic activity as well as diacetyl production were evaluated. The results showed that the growth rates of 3TB and 7KB strains belonging to E. durans and E. faecium were greater at 30 °C and that other isolates had the maximum growth rates at 43 °C. Beginning with the fourth hour of incubation, the examined enterococci significantly decreased pH and increased acidity so that, all of the isolates were able to coagulate milk within 72 hours of incubation at the proper growth temperature, with the exception of the 3TB and 7KB strains. It was also observed that isolates 5C, 1D and 3B had all three desired technological characteristics. Overall, examined isolates, particularly the 5C, 1D, and 3B strains, can be employed as an adjunct culture for the manufacture of fermented dairy products such as various cheese types due to their appropriate technological properties.

Cold plasma is a novel non-thermal food processing technology that uses reactive medium and energetic photons and particles, to inactivate contaminating microbes on various foods. The aim of this study was to investigate the effect of atmospheric pressure cold plasma on Pseudomonas aeruginosa in vitro and rose water. In this experimental study, P. aeruginosa was exposed to 15 kHz plasma for 10, 30, 50 and 70 seconds. The effect of plasma on rose water inoculated with the bacterium at a concentration of 105 CFU / mL during storage for 7 days at room temperature was also investigated. The results showed that the highest non-growth halo diameter in P. aeruginosa was 31 mm in 70 seconds treatment. In addition, the plasma had an inhibitory effect on growth of P. aeruginosa in rose water during storage. Therefore, the use of plasma as a non-thermal and microbial reducing method in the rose industry is recommended.

Sesame oil meal is a protein-rich by-product obtained from sesame seed oil extraction, which is seen as one of the cultivation wastes with high nutritional value and cheap price and is abundantly accessible in the agriculture industry. This product can also be used as a cheap substrate for the growth of Beneficial microorganisms including probiotics. This research examines the growth of Lactobacillus Plantarum As a probiotic in the sesame meal culture media under different incubation conditions to achieve the best microbial count of probiotic bacterium of Lactobacillus Plantarum. Sesame meal paste with an initial pH of 6.5 was used as the culture medium, with incubation conditions including aerobic conditions under three temperature rates of 30, 37 and 44°C for 48 hours. The findings revealed that the bacterium could grow in the sesame meal medium, increasing the microbial population to 108cfu/g at the end of fermentation under 30 and 37°C. Also, Lactobacillus Plantarum significantly reduced the pH of all fermented samples under all temperatures (p<0/05), with the pH decreasing by most around 4.85 at 37°C. The findings also suggested that the combination of fatty acids of the sesame meal culture medium changed due to Lactobacillus Plantarum growth. Fatty acids (C15:0), (C15:1), (C16:0), (C16:1), (C18:1t), (C18:1c), (C21:0) and (C24:1) increased significantly (p<0.05), whereas fatty acids (C14:1), (C17:0), (C18:1c), (C18:2c), (C20:0), (C18:3n3), (C20:1), (C22: 0) and (C24: 0) decreased significantly (p<0/05). In the meantime, fermentation helped produce (C17:1) and (C22:1) and consume linoleic acid. In sum, sesame meal can serve as a nutrient and cost-saving medium to grow Lactobacillus Plantarum.