F. Tooryan , M. Reihani, M. Azizkhani,
Volume 7, Issue 2 (Spring 2018)
Abstract
Aims: Today, a part of studies on food science has investigated the effect of cooking methods on the oxidation of various types of meat and the use of natural herbal preservatives instead of synthetic preservatives. The aim of the present study was to evaluate the oxidative stability of pre-cooked rainbow trout (Oncorhynchus mykiss) fillet treated with Dill (Anethum graveolens L.) essential oil (EOs).
Materials and Methods: In the present experimental research, rainbow trout fillet with dill EOs and Butylated hydroxytoluene (BHT) were treated, each at 3 different concentrations, and cooked by 3 methods, including frying, oven baking, and steaming. The cooked samples were stored at -18◦C for 4 months and analyzed at the end of each month. The extracted oil was used to measure the value of free fatty acid (FFA), peroxide value (PV), and thiobarbituric acid (TBARS). The data were analyzed by SPSS 20, using two-way ANOVA, Tukey's post hoc, Kruskal-Wallis, and Mann-Whitney U tests.
Findings: The FFA formation showed increase in all samples, especially oven baked rainbow trout fillets (p<0.05). The highest value of PV was also obtained from the fried fillets treated by BHT. After cooking, TBARS values in treated samples with essential oil showed decrease in all samples cooked with EOs. FFA, PV, and TBARS increased in all samples, but the samples cooked with EOs had lower FFA, PV, and TBARS than the control samples.
Conclusion: In rainbow trout, the lipid oxidation increases with the thermal process, but the essential oil postpones the oxidation during the storage period as frozen. The samples cooked with Dill EOs have lower amount of FFA, PV, and TBARS compared with the control peers.
P. Shohreh , M. Azizkhani , F. Tooryan ,
Volume 8, Issue 1 (Winter 2019)
Abstract
Aims: Considering the high importance of food poisoning bacteria in terms of public health threats and economic damages, this research aimed at evaluating food poisoning bacteria in some commercially important fish species collected from markets in Mazandaran, Iran.
Materials and Methods: For this purpose, 200 frozen fish belonging to 4 species were purchased from the stores and transferred to the laboratory. Samples were tested for total counting of aerobic bacteria, Escherichia coli count, Staphylococcus aureus count, Vibrio parahaemolyticus and detection of Salmonella according to Iranian national standard methods.
Findings: In the studied samples, Salmonella, and Vibrio parahaemolyticus were not observed. Comparing the results with the Iranian national standards, the total number of aerobic bacteria and Staphylococcus aureus in all samples was in normal range. The number of E. coli in 14% of samples of Rain bow trout, 20% of Clupeonella Cultriventris, 20% of Hypophthalmichthys molitrix and 10% of Scomberomorus commerson samples was higher than the standard range, due to the importance of pathogenicity of different strains of E. coli in humans, microbial control of the packed fish is very important.
Conclusion: The results of microbial investigations of frozen raw fish collected from stores in different cities of Mazandaran province can be defined satisfactorily, since the majority of samples conform to reference standards.
Volume 16, Issue 90 (August 2019)
Abstract
PCR quantifies dead cells beside live cells and this makes the judgment of microbial quality of food samples complicated. The objective of this study was comparing the efficacy of ethidium monoazide-qPCR and propidium monoazide-qPCR in quantifying live pathogen cells (E.coli, Staphylococcus aureus, Enterococcus fecalis and Listeria monocyogenes) by real time PCR, in low-fat and high-fat milk, lactic cheese (low-fat) and processed cheese (high-fat). Different proportions of live and heat killed pathogen cells were inoculated into food samples. After separating bacterial pellets, EMA and PMA treatments qPCR was conducted. One-way ANOVA followed by Turkey’s Multiple Comparison tests were applied to analyze the data. In low-fat milk, EMA treatment resulted in 18, 20, 23 and 30% decrease in cell count of E.coli, S.aureus, E. fecalis and L. monocyogenes, respectively, compared to conventional culturing. Also, following treatment by PMA, 6, 3, 8 and 12% decrease in cell count was obtained for E.coli, S.aureus, E. fecalis and L. monocyogenes, respectively, compared to conventional culturing. In high-fat samples as processed cheese, a reduction of 20, 27, 30 and 25% in EMA treatment and 9, 6, 5 and 10% in PMA treatment was observed in cell count of E.coli, S.aureus, E. fecalis and L. monocyogenes , respectively. The inhibitory potential of EMA and PMA against signal emission was variable in different bacterial species and the fat content of the samples exerted no significant effect (p>0.05) on PMA and EMA functionality.
Volume 17, Issue 106 (December 2020)
Abstract
Escherichia coli O157:H7 is one of the most important and common foodborne pathogens in the world which is being resistant against some current synthetic antimicrobials. The aim of this study was to determine the minimum inhibitory concentration (MIC) and the minimum bacterial concentration (MBC) of Artemisia dracunculus (tarragon) essential oil and its nanoemulsion for enterohemorrhagic strain of Escherichia coli and then the effect of sub-MIC concentrations on growth rate and gene expression of virulence genes (stx1A and stx2A). Nanoemulsion of tarragon essential oil was prepared by the ultrasound method and the droplet size and zeta potential were determined. MIC and MBC of essential oil and nanoemulsion were determined using the broth microdilution method. The growth rate and expression of stx1A and stx2A genes in Escherichia coli were assessed after treatment with different concentrations of sub-MICs of essential oil and nanoemulsion. Estragol was identified as the main component in the essential oil. The average diameter of nanoemulsion particle was 50 nm and the zeta potential was -30mV. The MIC values of essential oil and nanoemulsion were 0.58±0.11 and 0.33±0.07mg/ml, respectively, and their MBC were 0.65 ± 0.20 and 0.38 ± 0.15 mg/ml, respectively. Nanoamulsion had a greater inhibitory effect against bacterial growth than free essential oil. At the end of the 72-hour period, nanoemulsion treatment at 75% MIC resulted in a reduction in stx1A and stx2A transcription of 3.75 and 4.10 folds, while at 75% MIC of essential oil stx1A and stx2A transcripts were reduced 1.91 and 2.02 folds compared with control, respectively. Higher activity of nanoemulsion of tarragon essential oil to reduce the growth and shigatoxin production of E. coli compared to pure EO, reveals its potential to be used as a natural food preservative and a solution to the global problem of emergence of antibiotic-resistant microbes.
