مجله میکروب شناسی مواد غذایی
سال نهم شماره 1 (بهار 1401)

In this study, chemical compounds of Salvia chorasanica essential oil were identified by GC-MS method. Then, nanoemulsion of essential oil was prepared by ultrasound method and the stability of its particle size during two weeks of storage was evaluated by DLS at room temperature. The antimicrobial activity of macroemulsion and nanoemulsion of S. chorasanica essential oil against six pathogenic bacteria and three food spoilage molds was investigated by microdilution method. The results showed that the essential oil had 20 different chemical compositions. The particle size of the nanoemulsion increased from 91.83 to 193.61 nm during two weeks. The nanoemulsion form of the essential oil had higher antimicrobial effect than its macroemulsion against all the studied microorganisms. Also, the antimicrobial activity of macroemulsion and nanoemulsion of essential oil on gram-positive bacteria was more than gram-negative. Among the pathogenic bacteria, the gram-positive bacterium Bacillus cereus indicated the highest sensitivity to the nanoemulsion of essential oil and had the lowest MIC, 3.125 µl/ml. In addition, MIC and MFC of essential oil nanoemulsion against all three molds were determined to be 6.25 µl/ml and 12.5 µl/ml, respectively. Thus, a lower effective concentration of essential oil in the form of nanoemulsion will be required to control food microorganisms and prevent the effects of the use of high concentrations of essential oil.

The present study was performed to evaluate the occurrence and pattern of antibiotic resistance of Enterococcus faecalis strains isolated from fish and shrimp samples caught from the Persian Gulf. A total of 240 seafood samples caught from the Persian Gulf, including 120 fish and 120 shrimp samples were collected from Bushehr province. The presence of Enterococcus faecalis was confirmed using microbial culture and biochemical tests. The pattern of antibiotic resistance of Enterococcus faecalis isolates was evaluated using Disc Diffusion Method. Fifty-four out of 240 (22.50%) samples were contaminated with Enterococcus faecalis. The contamination of Enterococcus faecalis in fish and shrimp samples were 30% and 15%, respectively. Enterococcus faecalis strains isolated from fish and shrimp samples had the highest resistance to gentamicin (100%), tetracycline (100%), erythromycin (100%), cefazolin (90.74%) and trimethoprim-sulfamethoxazole (88.88%) antibiotics. Resistance to chloramphenicol was not observed in any of the isolates. The results of the study showed that fish and shrimp can be considered as possible sources of antibiotic-resistant Enterococcus faecalis. Therefore, complete cooking of seafood before consumption, observance of hygiene in fishing and sale centers and prescribing antibiotics according to the results of the disk diffusion test can prevent gastrointestinal infections caused by antibiotic-resistant strains of Enterococcus faecalis.

The present study aimed to investigate the chemical composition of black pepper (Piper nigrum) aqueous-alcoholic extract and focus on its possible anti-biofilm activity against the two bacteria Bacillus subtilis and Pseudomonas aeruginosa in vitro and in simulated conditions of the food model. Chemical analysis was used to identify the chemical composition of black pepper extract by mass spectrometry gas chromatography (GC - MS). The anti-biofilm activity of black pepper was measured using an automatic ELISA reader at 570 nm wavelength. The GC - MS analysis results indicated that the major compounds in black pepper extract include -3-Carene (20.69%), Limonene (18%), Caryophyllene (17.90%) and -Pinene (10.52%). According to the results in this study, black pepper aqueous- alcoholic extract with a 50% concentration had the highest effect in preventing the biofilm formation of both bacteria In addition, there was no significant difference between black pepper extract (50%) and peracetic acid 0/5% in the antibiofilm activity. There was also no significant difference in the type of bacterial growth media (TSB culture and fish extract) on bacterial biofilm formation in the presence of black pepper extract.

Probiotic yogurt contains some potentially healthful effects on human body. In this study, supplementation of probiotic stirred yogurt by different percentages of green tea extract and measurement of survival rate of lactobacillus casei also some physicochemical(pH, acidity(dornic), dry matter%, fat%, synersis% , total phenol %, and sensory properties(flavor, color, texture and acceptability) were studied during storage in refrigerator. Four treatments were made with different percentages of green tea extract as follows: T1, T2, T3 and T4, which involved (0, 2, 4 and 6%) of green tea extract respectively. T1 as a control sample and also concentration of lactobacillus casei for all treatments was regulated about 108 cfu/ml. Three replications were determined for each sample and all experiments were done during (1,7 and 14) days of storage. The highest content of acidity was attributed to T4, the highest value for dry matter was attributed to T1. Fat % of all treatments was constant during storage and total phenol for T4 was the highest content. The measurement of survival rate of all treatments showed that T4 had highest value. Synersis% of T4 was highest value. Sensory evaluations were carried out according to hedonic,s test and all sensorial scores decreased by adding tea extract. Totally addition of green tea extract had negatively effects on synersis content according to microbial, physicochemical and sensory evaluations, the best treatments was T2 among other treatments and had more similarity to T1 as a control sample.

Enzymatic, chemical and microbial activities in chicken meat in the refrigerator lead to spoilage and reduced product quality. In this regard, the use of edible coatings with antimicrobial and antioxidant compounds is an effective way to keep the quality of meat. In this study, the effect of chia seed mucilage coating containing 0, 15 and 30% aqueous extracts of olive leaves on quality of chicken fillets in the refrigerator (4° C) during 12 days of storage was investigated. During storage at intervals of 0, 4, 8 and 12 days, microbial counts (Lactic acid bacteria, aerobic mesophilic, psychotropic and coliforms), volatile nitrogen bases, pH and sensory evaluation were determined. The results showed that during storage, the count of aerobic mesophilic bacteria, psychotropic bacteria, coliforms and lactic acid bacteria and the volatile nitrogen bases and pH in chicken fillet samples increased, which was less in samples coated with chia seed mucilage containing olive leaf extract than the other treatments (P <0.01). According to the results of sensory evaluation, on the 4th day of storage, no significant difference in overall acceptability was observed between the samples view of overall acceptability. But on the 8th day of storage, the control and sample coated by chia seed mucilage did not obtain the required overall acceptability score. According to the results obtained of this study, using the mucilage coating of chia seeds containing 30% of aqueous olive leaf extract, it is possible to increase the shelf life of chicken fillets at 4 °C for 8 days.

The aim of this study was to investigate the effect of ethanolic and aqueous extracts of shallot on the survival of yogurt starter bacteria (Lactobacillus bulgaricus and Streptococcus thermophilus). Aqueous and ethanolic extracts of shallots were extracted by soaking in distilled water and ethyl alcohol. Then MIC and MBC extracts were obtained for yogurt starter bacteria by microdilution method. Aqueous and ethanolic extracts were added to pasteurized milk at concentrations obtained in the MIC test along with 3% yogurt starter. The inoculated milk was incubated at 45 ° C until pH = 4.4 for 2 hours. After that, the yogurts were cooled to 4 ° C Then, on days 1, 3, 7, and 14, pH, acidity, and LAB count tests were performed on yogurt samples. The results showed that on days 1, 3, 7, and 14, the acidity and pH of the aqueous extract groups were significantly different to the ethanolic and control groups (p <0.05). Also, the lactic acid bacteria count test on days 1, 3, 7, and 14, the aqueous and ethanolic extract groups were significantly different from the control group (p <0.05). The results also showed that the inhibitory effect of aqueous extract of shallot was more on yogurt starter bacteria than ethanolic extract of shallot (p <0.05). In coclussion the revealed that the starter bacteria in yogurt in presence of Shallot extracts were alive and active until day 14 during refrigerator storage, which can transmit the probiotic effects of yogurt and shallots to the consumer.

Non-thermal processes such as ultraviolet radiation can be used for maintaining the beneficial and nutritious compounds of juices. This study was investigated the effect of pasteurization (LTLT) and UV-C radiation at doses of 8, 15 and 30 W on ascorbic acid, anthocyanins, total phenol and antioxidant capacity changes of cherry juice immediately after processing, and some chemical ( pH, acidity and color) and microbial properties for 120 days at room temperature (25 °C). Based on the results, irradiation at 10 minutes caused a significant increase in pH value. The titratable acidity level increased during the storage period and confirmed the pH results. Cherry juice treated with UV-C radiation had higher content of ascorbic acid, anthocyanin, total phenol and antioxidant activity compared to pasteurized samples. Increasing the dose and time irradiation had a positive effect on increasing the ascorbic acid, anthocyanins, total phenol and antioxidant activity. The brightness (L*) and redness (a*) indexes in irradiated samples were significantly higher than the pasteurized samples. Among the different treatments, irradiated samples at a dose of 30 W for 6 and 10 minutes were superior to other treatments in terms of qualitative and microbial properties. At the end of the storage period, the lowest count of mold and yeasts was obtained in the irradiated sample at a dose of 30 W for 10 minutes. Overall, it can be concluded that UV-C radiation is suggested as a suitable alternative to the pasteurization process (LTLT) of cherry juice.

Acinetobacter species are saprophytic and have emerged as an important nosocomial pathogen. In this study, 100 samples of traditional butter and cream, were evaluated for the presence of the A. baumannii. The A. baumannii isolates were genotyped based on virulence genes and phenotyped according to antibiotic resistance patterns. The results showed that from 50 samples of butter and cream, 2 samples (4%) and 1 sample (2%) were contaminated with A. baumannii. Antibiotic resistance examination showed that all isolates were resistant to the antibiotics of meropenem, amypenem, chloramphenicol, methylcillin, carbapenem and fusidic acid. The most abundant genes encoding antibiotic resistance in A. baumannii strains were tetA, tetB, dfrA1, aac (3) -IV, sul1, cnf2, csgA, jurA, citm, blasHV, aadA1 and Aac3IV. The results also showed that the most abundant virulent genes in A. baumannii strains that detected from traditional milk and dairy products were fimH, papC, Pai and kpsmTII, respectively. It is recommended to use a preventive method to reduce or eradicate A. baumannii from the human food chain and to prevent the spread of infection.