نشریه بهداشت مواد غذایی
پیاپی 3 (پاییز 1390)

The effect of nisin A and sodium benzoate on Listeria monocytogenes, as well as some microbial (mesophilic, psychrotrophic and lactic acid bacteria) and chemical (peroxide and TVN) in silver carp (Hypophtalmichtys molitrix) fillet during storage period (0, 3, 6, 9 and 12 days) at 4°C were evaluated. For this, Listeria monocytogenes (4 logCFU/g) was inoculated to the fillets and were dipped into 2% sodium benzoate solution for 15 min and left to stand for 10 min at 4°C. Subsequently nisin A was added to the fillet (0/15 g/kg) and samples were kept at 4°C while packaged in vacuum condition. The results showed that, application of nisin A and sodium benzoate decrease the number of Listeria monocytogenes from 4/12 to 3/66. However, in control groups the number of bacterium was increased from 4/43 to 5/14.Moreover, the number of mesophilic bacteria in treatment and control groups was increased from 4/39 to 6/79 and 4/48 to 7/93, respectively. The number of psychrotrophic bacteria in treatment and control groups was increased from 4/16 to 6/72 and 4/34 to 7/92, respectively. The similar result was achieved for lactic acid bacteria in which the number of these bacteria was increased from 2/74 to4/08 and 2/9 to 4/78, respectively. Moreover, different peroxide value and TVN for treatment and control groups was achieved. In conclusion, application of nisin A and sodium benzoate showed different inhibitory effects on Listeria monocytogenes in culture media and silver carp.

The diseases due of the consumption septic and unsafe nutrition are one of the major problems in developed and developing countries yet. Ice cream is a dairy product which favors the growth of microorganisms. Production of non-pasteurized hand made ice cream as traditional ice cream is very popular in Iran. In attention to more consumption of ice cream in warm seasons, especially in tropical areas, this study was conducted from the aspect of indicator microorganisms in ice cream. In this research, totally 120 samples were collected during summer of 2009 from different part of Ahvaz. According to reference methods and in order to examine Coliform and E.coli and Staphylococcus aureus contamination of samples, selective media and finally biochemical test were carried out. The results showed that 94 (78.33%) and 13 (10.83%) samples were contaminated to coliform and E.coli respectively, while 38 (31.67%) out of 120 samples were contaminated to coagulase positive Staphylococcus aureus. The result of this study showed that in attention the standard limits, the most of the examined ice creams were not allowed for consumption. Therefore, the more seriously monitoring to prevent bacterial contaminations should be considered by responsible authorities.

In the present study, the anti-listeria activity of onion (Allium cepa L.) essential oil (EO), nisin as well as their combination at various pH values (4.8, 5.8 and 6.8) and different NaCl concentrations (0, 0.5, 2.5 and 4.5%) was investigated against Listeria monocytogenes by microtiter plates at 30°C. Minimum inhibitory concentrations (MICs) were assessed for the nisin, onion EO as well as their combination. Subsequently, fractional inhibitory concentration (FIC) was evaluated under different pH and NaCl concentrations. Both nisin and EQ showed significant antimicrobial effects against L.monocytogenes. Moreover, the nisin and onion EO exhibited MICs of 12.5 IU mL-1 and 125 μg mL-1, respectively. FICs of the nisin and onion EO alone and in combined form, along with various combinations of pH and NaCl concentration, showed clearly anti-listeria effect as synergistic, additional or indifference. Regardless of NaCl concentrations, the anti-listeria activity of both agents was strongly influenced by pH. Moreover, regardless of pH value, the growth of the bacterium was also affected by increasing of NaCl concentrations. It was concluded that, pH value of 4.8 and NaCl concentration of 4.5% had significant anti-listeria effect. In addition, it was found that, the effect of NaCl concentrations for each of the combination forms of treatments at various pH was different.Therefore, there are necessity to design and apply a comprehensive predictive model.

The aim of this survey was to determine the occurrence of liver abscesses and identification of associated bacterial etiology in cattle carcasses of Tabriz industrial abattoir. A total of 355 cattle carcasses were inspected for the presence of liver abscesses. In the case of liver abscess presence, some characteristics of the carcasses were recorded; such as cattle’s age, gender, pregnancy and also abscesses’ characteristics (i.e., number, size and location of abscesses on liver). Abscesses as whole, were sampled and kept cold until microbiological examinations. Microbial analysis was performed on samples and cultures were incubated at aerobic, anaerobic and microaerophilic atmospheres. From 355 cattle carcasses, liver abscess was found in 28 (7.8%). Among positive results, 22 (78.57%) of livers had only 1, while 6 (21.42%) had 2 or more abscesses. Fusobacterium necrophorum was isolated from 15 53.57%) and Arcanobacterium pyogenes from 10 (35.71%) of abscesses. According to the results ofthis study, Fusobacterium necrophorum was found as the most frequent bacterial causative agent of cattle liver abscess in Tabriz industrial abattoir, while Arcanobacterium pyogenes was considered as the second most frequent agent.

Heavy metal contaminants in fish are of particular interest because of their potential risk to human. This study was undertaken to determine the levels of arsenic in two fish type including tiger tooth croaker and Indian halibut in Esfahan. A total of 42 fish samples including 28 tiger tooth croaker (Otolithes ruber) and 14 Indian halibut (Psettodes erumei) were collected from retails of Esfahan from May 2010 to January 2011. For detection of arsenic contamination, the edible muscles of fish samples were analyzed by hydride generation atomic absorption spectrophotometer. The arsenic contamination in fish samples were found to be in the range of 11 to 98 μg/kg. Concentration of arsenic in tiger tooth croaker and Indian halibut was 11-56 and 32-98 μg/kg, respectively. Arsenic concentrations were below the limit was acceptable to the World Health Organization. According to the results, the concentration of arsenic did not exceed the maximum acceptable intake limit.

The aim of this study was to determine the effect of microwaving and frying processes on microbial properties of hamburger. Samples were achieved throughout summer of 2010. Experiments were carried out on 30 samples of different hamburger brands achieved from various meat processing establishments around Tabriz. After preparation of the samples, microbial properties were examined while raw as well as after frying (5min in 100ºC) and microwaving (2 min in 10 watt). Microbial properties such as total bacterial count together with yeast and mold count were preformed. Results were statically analyzed withANOVA test. Although, results showed a significant reduction in microbial count of fried and microwaved hamburger compared to raw hamburger (P<0.001), the difference of total bacterial count in fried and micro-waved hamburgers were not satistically significant (0.374=P). However, satistically significant (P<0.05) decrement of yeasts and molds count in micro-waved samples were observed comparing with fried samples. According to the results, for cooking of hamburger, microwaving is preferred to frying method. However, the cost of microwaving should be considered.

In this study, the inhibitory effects of bacteriocins of lactobacilli which were isolated from Iranian traditional dairy products was determined against known gram positive, gram negative and yeast by well diffusion technique. Among 8 isolates with higher capability of bacteriocin production, 2 isolates were selected for further investigations. The bacteriocins were purified by iso-propanol and ammonium sulfate precipitation following by dialysis and chromatography technique. The molecular weight of bacteriocins was determined as 45 to 66/2 KDa. by SDS-page electrophoresis. According to the results, the produced bacteriocins had more inhibition effect on Micrococcus luteus PTCC1169, Staphylococcus epidermidis PTCC1435 as well as Bacillus cereus PTCC1247 and with lesser degree of extent on Listeria monocytogenes PTCC 1301. Results also revealed that, Micrococcus luteus was the most sensitive bacterium among indicator bacteria, while Candid albicans PTCC 5027 identified as the most resistance organism. This research showed that, bacteriocins produced by lactobacilli isolated from traditional dairy products have high potency to be used against microbial pathogens and could be applied as biopreservative in food products.

Coliforms are considered as hygienic indicator organisms in foodstuffs and Escherichia is one of its genera. Escherichia coli is the most important species of the genus Escherichia and generally is considered as part of natural bacterial flora of human and most animals intestine. Pathogenic Escherichia coli is causative agent of diarrhea in developing countries and areas with poor hygienic condition. The purpose of this study was to investigate the contaminated status of traditional white cheese in Tabriz retails in terms of coliforms, faecal coliforms, Escherichia coli, and pathogenic Escherichia coli. Ninety samples of white cheese were randomly collected from retails of different part of Tabriz. The samples were transferred to the laboratory under refrigerated conditions. Coliforms were counted by means of VRBA with pour plate method at 37±1°C. For Faecal Coliforms Briliant Green Bile broth at 44±0.5 °C were used. For confirming Escherichia coli among coliform bacteria, IMViC tests were applied. Pathogenic Escherichia coli was distinguish by polyvalent antiserums. The results of the study indicated that, the mean of coliforms were estimated at (27.07±1.51) ×105 cfu/ml. The number of coliforms in 88(98%) samples was more than the limit allowed by the national standard for Iranian industrial white ripened cheese. Moreover, Sixty-three (70%) of the samples were contaminated to faecal coliforms. Although, 11 (12%) of the samples were contaminated to Escherichia coli, any sample was contaminated to pathogenic Escherichia coli. It can be concluded that, hygienic status of traditional white cheese offered in Tabriz markets was not satisfactory in terms of contamination to coliforms and Escherichia coli is. However, no samples was found positive as pathogenic Escherichia coli.