مجله میکروب شناسی مواد غذایی
سال ششم شماره 1 (بهار 1398)

Fish is a highly perishable food and it seems necessary to use natural preservative with antimicrobial properties. This study aimed to evaluate the effect of chitosan coating with garlic extract and coriander essential on microbial and sensory quality of rainbow trout fillet during 12 days at refrigerator storage condition. For this purpose, 8 treatments were prepared with chitosan coating containing garlic extract and coriander essential oil both separately and in combination forms (in amounts of 0.1 and 0.5%) and 2 control samples including control 1 (without coating) and control 2 (chitosan coating without extract and essential oil). Then all samples were evaluated by microbiological tests including total microbial counts, total psychotropic counts, and coliforms, and sensory properties including texture, color, odor, and overall acceptance at days of 0, 3, 6, 9, and 12 during storage. The results showed that the treatment coated with chitosan containing 0.5% garlic extract and 0.5% coriander essential oil had the lowest total microbial counts, total psychotropic counts and coliforms during 12 days of storage, and the highest amounts of microbial counts were observed in control 1 and then control 2 samples (P<0.05). Also the treatment with the highest amounts of garlic extract and coriander essential oil had better sensory scores by the end of storage period compared to control samples. So, it is suggested that chitosan coating with garlic extract and coriander essential oil as an antimicrobial agent, can be used for extending shelf-life of fish fillet.

Acinetobacter baumannii (A. baumannii) strains with multiple drug resistance are mainly opportunistic pathogens in the development of hospital infections and as an emerging contaminant in livestock-based foods. The aim of this study was to determine the antibiotic resistance pattern and genotyping of this bacterium strains in raw meat of poultry and livestock. 22 strains isolated from raw meat were tested by multi-locus sequence typing and simple disk diffusion methods. The highest antimicrobial resistance was observed to tetracycline with 90.9% and the least antibiotic resistance was azithromycin and imipenem with 9.09%. Five strains were identified as non-typing isolates in 22 isolates of A. baumannii. Five genetic profiles (Sequence Types=ST) including ST15, ST10, ST12, ST25, ST25 were identified. Identifying the acceptable level of genetic variation among isolates using the MLST technique indicates that this method is considered as a useful method in the study and typing of Acinetobacter spp. strains and can be strains isolated from different origins in different groups. In this study, it was found that by sequencing of house-keeping genes, it is possible to typing of Acinetobacter spp. strains, and this amount of polymorphism indicates that this technique is a useful method for analyzing the genetic diversity of A. baumannii strains is a source of animal origin.

This study was carried out to investigate the possibility of using Ulva intestinalis macroalgae extract as a natural antibacterial agent in Beluga minced meat. For this purpose, the minimum of inhibitory concentration (MIC) of the hydroalcoholic extract of the algae was determined in vitro by micro-well dilution method against Listeria monocytogenes pathogen. Then, the concentrations of controls (without any additive), BHT (as a synthetic antioxidant), MIC, 2 fold of the MIC (2MIC) and 3 fold of the MIC (3MIC) concentrations, were mixed with minced meat and refrigerated. Microbial properties of the samples including psychrophilic bacteria count, mesophilic bacteria count, Pseudomonas count and Enterobacteriaceae count were measured at 0, 4, 8, and 12 days. According to the results, the MIC was 12.5 mg/mL. The result of this study showed that the samples with the algae extract had less microbial load in comparison with control and BHT groups (p <0.01). Also, 3MIC showed the most antibacterial effect among other algae extract treatments by the lowest amount of mesophilic bacteria (6.27 Log cfu/g), cold (09.08 Log cfu/g) Pseudomonas (6.6 Log cfu/g) and Enterobacteriaceae (6.21 Log cfu/g) population size at the end of storage period. The results indicated that grass kelp macroalgae is a suitable species for use as a natural preservative, and the minced fish with three fold of the MIC concentration had less bacterial spoilage during the storage period in a refrigerator.

Due to increased attention and nutritional importance of turkey meat between consumers, researchers are looking for new ways in order to improve its shelf-life. Furthermore, in recent decades, consumer demands for healthier foods (without common chemical preservatives) have been increased. The aim of this study was to evaluate simultaneous effect of chitosan coating and rosemary essence on indicator bacteria including Salmonellatyphimurium (S. typhimurium)and E.coliO157:H7 in turkey meat fillets during refrigerated storage. For this purpose turkey fillets inoculated with 106 CFU/g S. typhimurium and Escherichia coli O157:H7. Then, all of inoculated fillets divided into 3 groups; without coating (control), treated with 1% acetic acid and suspended in chitosan solution containing 1% rosemary essence. All samples were kept at refrigerated temperature for 15 days. Bacterial count of S. typhimurium and Escherichia coli O157:H7 was performed at 3 day intervals (0, 3, 6, 9, 12, 15 days). Chemical tests which related to chemical spoilage and quality control of turkey fillets including pH and thiobarbituric acid (TBA) were evaluated at 3 day intervals (0, 3, 6, 9, 12, 15 days). The results indicated that the chitosan-rosemary coating has the significant effect (P<0.05) on decrease of bacterial load of S. typhimurium and E.coli O157:H7. Also, suspended samples in chitosan containing rosemary essence have fewer pH and TBA during storage than other groups.

Staphylococcus aureus (S. aureus) is one of the three major causes of food poisoning in the world, causing the disease in hundreds of thousands of people every year. Today, due to the production and processing the varieties of different foodstuffs, it is necessary to employ faster and more sensitive methods for controlling food quality, to gain the requirements of the regulatory centers. New qualitative control methods can be used for impedance and also for using chromogenic culture media. Their advantage over the reference method is the lack of high-volume laboratory operations and their relatively high rate of achievement. Therefore, evaluation of applying impedance, chromogenic and reference environments in the food quality control was considered. In the present work, 100 samples were evaluated for S. aureus infection by reference, impedance and chromogenic methods. Based on the results, 32, 21 and 57 samples were contaminated by S. aureus, respectively. The statistical analysis by SPSS16 software, using Cochran test showed that there is a significant difference between the three methods in detecting S. aureus (P<0.001). Statistical analysis showed that there is not a significant difference between reference and impedance methods, Although there is significant difference between the chromogenic technique and reference method (P>0.05), which means the reference and impedance methods have the same function and impedance can be used as an alternative technique for the reference method. Also the chromogenic technique could not be used instead of the impedance method.

Lysine is an essential amino acid that is not synthesized in the human body, but due to the body's need and its application in different parts of the health area, it is important to optimize and economize the production process. The most commonly used lysine production method is microbial fermentation and the nutrient composition of the fermentation media is effective on the microorganism growth and the production of microbial metabolite. Accordingly, the aim of this study was to investigate the effect of native and inexpensive nutritional substrates, as the main supplier of energy for microorganism, on the growth and productivity of strains. For this purpose, different amounts (g/lit) of whey (100, 135, 170), rice flour (100, 135,170) and oat bran (100, 170, 220) were separately added to culture of Corynebacterium glutamicum, and at 68 and 116 fermentation time, growth indices such as pH of the environment, production biomass, specific growth rate of microorganism, strain morphology and amount of produced amino acid were measured and compared with control (100 g/lit glucose). The results showed that the highest amount of lysine produced was obtained in media containing 135 g/lit whey, 170 g/lit rice flour and 220 g/lit oat bran. These results indicate that these compounds are suitable for use in biological processes and can be used as the main nutrient source.

Kashk-e-Zard from Sistan and Baloochestan province and Tarkhineh from Hamedan and Kermanshah provinces are two cereal-dairy fermented products that are prepared by wheat based and a dairy product such as yogurt, fermented milk or doogh via fermentation process. Cereals as a functional food have a high protein digestibility and are also a fermentable substrate for the growth of probiotic microorganisms. In this study, Enterococcus and Pseudococcus genotypes were isolated from40 Kashk-e-Zard and Tarkhineh samples by microbial and biochemical methods, and then the bacterial genome was confirmed by the PCR method as part of the 16s rRNA encoding gene. The PCR fragments were sequenced and compared to the sequences in the gene bank and enterococcus and pediococcus strains were identified. Considering the processing of Kashk-e-Zard and Tarkhineh by using probiotic bacteria; therefore, isolation and identification of these strains and preserving of these genetic reserves, can be useful for the expanding its use and export to other countries.

Today food safety is a public health issue. One of the methods of healthy food production is the use of natural materials. The use of essential oils and plant extracts as antibacterial and antifungal additives is one of these methods. Antimicrobial compositions obtained from plants were removed by different mechanisms of antibiotics, in which the effective influences of walnut and its components are significant. The aim of this study was to evaluate the antimicrobial effect of walnut leaf extract on Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), determine the optimal amount of extract and sensitivity to each of the bacteria against the extract and determine the most sensitive method of the study. In this study, the leaves was extracted from the walnut and then the antimicrobial properties of the extract and its optimal concentrations were measured using disc and well methods on S. aureus and E. coli. Based on the results, the extract of walnut leaves in the concentrations of 12.5% up to the above has antimicrobial effect. By increasing the amount of extract, the growth rate of the bacteria significantly decreases (p<0.01). The highest non-growth halo in both methods was obtained from the control sample containing chloramphenicol disk on the E. coli (24 mm) and after it, the sample that contain 50% extract on S. aureus had 13.33 non-growth halo in the well method, and in the disc method, the 50% extract of S. aureus had the highest non-growth halo (11 mm). In fact, S. aureus was more susceptible to walnut leaves extract than E. coli in both methods. However, between the two methods, the sensitivity of the wells samples was more than the discontinuation method. The overall result shows that the sample containing 50% walnut leaf extract on S. aureus has the most antimicrobial activity among other samples after the control sample (chloramphenicol disc on E. coli).