مجله میکروب شناسی مواد غذایی
سال هفتم شماره 1 (بهار 1399)

Essential oils are considered as alternative to synthetic preservatives in food products because of their antimicrobial properties. The aim of this study was to identify the main components of thyme (Zataria multiflora boiss) essential oil and to evaluate the antimicrobial activity of essential oil in vitro and mayonnaise. The essential oil was extracted by distillation and analyzed by gas chromatography. The antimicrobial activity of the essential oil was evaluated by determining the minimum inhibitory concentration and minimum bactericidal concentration. GC analysis of the essential oil resulted in the identification of forty compounds by a high number of monoterpenes such as thymol and carvacrol. The most susceptible pathogens were the fungi (lowest MIC) and the most resistant pathogen to Gram-negative bacteria. This study confirms that the essential oil of thyme possessed antimicrobial properties in vitro. In the second phase, efficiency of essential oil as natural preservative in high fat and low fat mayonnaise kept during storage at 4 oC for 6 months was studied. The results showed that of essential oil had influence against all of the tested microorganisms in mayonnaise and the pathogens did not grow in mayonnaise formulations, whereas in the control mayonnaise all of the pathogens and fungus grew. In conclusion the essential oil of thyme (Zataria multiflora boiss) would lead to control food pathogen and food spoilage organisms as natural food preservative and therefore, it would be used in biotechnological fields as natural preservative ingredients in food industry.

Mastitis is defined as an inflammation of the mammary gland usually resulting from a bacterial infection. The number of somatic cell is the one of the important indices of quality and healthy evaluations of milk. The objective of this research was to evaluate the effect of 3 levels of somatic cell counts in raw milk and lipase enzyme addition on free fatty acids and sensory properties of white brined cheese during 70 days of ripening period. Three levels of SCC and one level of lipase enzyme addition (2%) and 3 levels of storage time (5, 35 and 70 days) were selected. Initially, 3 groups of dairy cows were selected to obtain low (1000000 cells/mL) SCC in milks that were used to manufacture 6 vats of cheese: 3 vats with added 2% lipase enzyme and 3 vats with not added lipase enzyme. Experimental design was carried out by using Completely Randomized Design (CRD). Six treatments at 3 replications during 5, 35 and 70 days of ripening period were selected. Free fatty acids profile showed that oleic acid had the highest content of free fatty acids among others. The content of free fatty acids of all treatments often increased until 35 days of ripening period and then decreased at the end of ripening period. Sensory properties showed that flavor and texture scores of all treatments decreased during 70 days of ripening period. According to obtained results, (T1) as a control sample (was the best treatment among others. The raise of somatic cells can be decreased yield of cheese making and also sensory qualities of final products.

The contamination of foodstuffs with different bacteria such as Listeria spp, is important from the viewpoint of public health. Therefore, this study was conducted to check the presence and occurrence of Listeria species in cattle meats from abattoirs and butcher shops located in Chaharmahal and Bakhtiary province. Two hundred and fifty-five of meat samples were collected. The total prevalence of Listeria spp. was equal to 12.94%.  The highest (16.4%) and the lowest (8%) prevalence of Listeria spp. was found in samples from Farrokhshar abattoir and Shahrekord butcher shops, respectively. Among the six species of Listeria, Listeria innocua was the most prevalent (7.4%) species; while Listeria seeligeri and Listeria ivanovii were the least prevalent (0.4%) species. The highest percentage of prevalence (6.7%) of Listeria monocytogenes was detected in meat samples from the Hafshejan butcher shops. In the current study, none of the samples was contaminated by Listeria welshimeri. Of the ten isolates of Listeria monocytogenes, the most prevalent (40%) serotypes were 1/2a and 4b. In addition, the prevalence of serotype 1/2b was 20%. The results indicated that, due to the presence of Listeria contamination, improvement of sanitation principles in abattoirs and butcher shops is a guarantee of public health safety.

Today, chemical drugs are replaced by herbal medicines because of the harmful effects they place on the human body. Although the proportion of herbal medicines to chemical drugs in the world is negligible, the replacement process is followed more quickly. The aim of this study was to investigate the antibacterial effect of polar, semi-polar and non-polar fractions of Lnula helenium extract on some food-borne bacteria . In this study, Lnula helenium plant was collected from Arak natural areas and then extracts of methanolic, chloroform and hexane of Lnula helenium were obtained. The effect of different concentrations of this extract was investigated. All experiments were carried out using Agar well diffusion and determination of MIC and MBC on standard strains of Pseudomonas aeruginosa, Staphylococcus aureus, Listeria monocytogenes, Escherichia coli and Streptococcus mutans. Methanol extract of Lnula helenium(6.25 μg / ml) inhibits the growth of Gram-positive and Gram-negative bacteria. Chloroform extract with minimum concentrations (12.5 mg / ml, 50 and 100%) had lethal effect on Streptococcus mutans, Staphylococcus aureus and Listeria monocytogenes, respectively and hexane extract only affected gram-positive bacteria. The herbal extract can be used as an herbal medicine after completing clinical trials.

Pistacia Atlantica subsp.kurdica is one of the varieties of herbs with anti-microbial activitiy which can also play an important role in dough's flavor. The purpose of this study was to evaluate the microbial and sensory properties of samples containing essential oil of Pistacia atlantica and also physicochemical characteristics of the Dough samples containing microorganisms and essential oil of Pistacia atlantica in comparison with non-essential oil samples at two temperatures were determind. Dough samples were inoculated with essential oil and microorganisms (Staphlicoccus Aureus, Escherichia coli, Kluyveromyces matxianus, Penicillum natatum) (108 CFUmL-1) and also microbial According to the results Dough samples containing essential oil showed a higher reduction of microbial load. Also pH and acidity of the samples showed a significant difference with each other and with the essential oil-free sample (P<0.05). In terms of sensory evaluation there are significant difference in the stability properties of the samples with each other and with the control sample (P<0.05). Also duration of shelf-life of dough, temperature, type of microorganisms in the product and utilization of essential oil effect on number of microorganisms, pH and acidity. Dough samples containing essential oil showed antimicrobial properties against inoculated microorganisms. Therefore, pH reduction and acidity increase were significantly lower in samples containing essential oil and in terms of sensory evaluation; it was also accepted by consumers.

Foodborne diseases contaminated with mycotoxins are a concern for human health. The use of bioactive compounds to improve food safety and preservation has been considered to reduce the economic losses and risks of these factors. The aim of this study was to use purple coneflower (Echinacea purpurea) essential oil as a bio preservative to control the growth of Aspergillus flavus and to prevent the production of aflatoxin B1. For this purpose, minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values were calculated using a disk diffusion method and then the effect of different concentrations of the essential oil on aflatoxin B1 production was evaluated. The amount of aflatoxin B1 production in the YES (yeast extract sucrose) culture media was measured by HPLC. The results of this study showed that MIC and MFC were 10000 ppm and 15000 ppm, respectively. The results of the growth inhibition zone showed that increasing concentration of the essential oil significantly (p<0.05) increased the diameter of the inhibition zone. It was also founded that aflatoxin B1 production was significantly (p<0.05) dependent on purple coneflower concentration so that by increasing of the essential oil concentration the aflatoxin production significantly (p<0.05) decreased. Accordingly, the aflatoxin B1 production by A. flavus was prevented using concentration of 15000 ppm of purple coneflower essential oil. Overall, it can be concluded that purple coneflower essential oil can control the production of aflatoxin by A. flavus to an acceptable level

Biosurfactants and bioemulsifiers are active surface compounds that significantly reduce the surface tensions in very small amounts. Generally, microorganisms synthesize wide ranges of biosurfactants. These compounds are classified based on molecular weight, physicochemical properties and mode of action. Phosphatidylcholine (PC), one of the major components of commercial lecithin, is the most important membrane phospholipid in eukaryotes which can be synthesized by two pathways, the methylation and/or the CDP-choline pathways. Many prokaryotes lack PC, but in the membranes of some bacteria, significant amounts of this material are found. Due to the high importance of lecithin in the food and medicine industry, studies on the ingredients of lecithin such as phosphatidylcholine and phosphatidylserine are matter of interests. Recognition of the biosynthesis pathways of phosphatidylcholine compounds, especially in the bacteria for optimal production of these microbial metabolites is a matter of great importance. In this study, the structure, biochemical function and biosynthesis pathways of biosurfactants are investigated in bacteria, the production technology and their important applications are also described.

Propolis plays an antibacterial, anti-fungal, anti-parasitic, antioxidant, anti-inflammatory, anti-caries role due to its plant-derived compounds such as polyphenols and proteins such as 10-HDA. It has long been a therapeutic role for diseases, especially infections. In this study antimicrobial activity of alcoholic, aqueous and buffer extract of propolis, on oral bacteria including Streptococcus mutans, Streptococcus epidermidis, Staphylococcus aureus, and gastro-intestinal bacteria including Streptococcus salivarius and Escherichia coli measured using micro broth dilution test for assessing of minimum inhibitory concentration (MIC) and disk diffusion test for assessing of diameter of inhibition zone. The MIC did not differ significantly between the three alcoholic, aqueous and buffer extracts, i.e., the effect of the solvents on the solubility of the antibacterial compounds was approximately the same (P > 0.05). The most resistant gram-positive bacterium to alcoholic and buffer extract, Streptococcus mutans and the most resistant to all extracts, Escherichia coli, were reported. There was no significant difference between the bacterial resistance in the aqueous extract of propolis (P> 0.05). In the disk diffusion test, increasing the concentration of extracts had a significant effect on the bacterial killing rate and was identified as the most susceptible bacterium to the extracts Staphylococcus epidermidis and the most resistant bacterium Staphylococcus aureus. The bacteria were also more sensitive to buffer extract.