نشریه بهداشت مواد غذایی
سال سوم شماره 4 (پیاپی 12، زمستان1392)

Isolation, identification and grouping of Staphylococcal enterotoxins in milk is of great importance since these toxins are considered as a major potential source of human illness. In this study, 22 coagulase positive strains of Staphylococcus aureus isolated from white brine cheese produced in rural areas of Maragheh, were assessed for the existence of six genes encoding enterotoxin synthesis using multiplex PCR. For this, extracted DNA was subjected to multiplex PCR for the presence of enterotoxin a, b, g, h, i and j genes. Amongst seg was the most frequent (8 strains) gene; meanwhile seb gene was not detected in any of the isolates. According to the results, 9 strains (40.9%) harbored the genes encoding enterotoxin production. Four strains (18.18%) contained more than one enterotoxin gene. The results of this study indicated that most of Staphylococcus aureus isolates in traditional cheeses have the potency to produce enterotoxin.

Various laboratory methods have been developed to evaluate the effectiveness of anti mould effect of lactic acid bacteria. However، most of these investigations have been conducted in culture medium. Due to the occurrence of complex interaction between food components and antimicrobial substances produced by lactic acid bacteria، the result achieved from these studies may be different from those seen in food model. In various studies growth inhibition of molds on the surface of foods are considered as antifungal activity. Consequently، introduction and comparison of efficient methods for evaluation of anti mould effect of lactic acid bacteria would be helpful. In this study، antifungal activity of lactic acid bacteria inoculated in cheese was estimated using Microdilution method. Pieces of cheese samples were overlaid with molds and the antifungal effect of this bacteria was studied against Aspergillus flavus and Aspergillus parasiticus. All three methods showed the effectiveness of lactic bacteria on mold inhibition. Comparison of the results showed that there was significant positive correlation between antifungal overlay assay and direct growth of mold on cheese، since this two test showed antifungal effect in the same way including interaction between bacteria and mold and also producing antifungal compound.

Biogenic amines are organic, basic nitrogenous compounds of low molecular weight that are mainly generated by the enzymatic decarboxylation of amino acids by microorganisms. Dairy products are among the foods with the highest amine content. A wide variety of methods and procedures for determination of histamine and biogenic amines have been established. Amongst, HPLC method is considered as reference method. The aim of this study was to validate Reversed Phase HPLC method determination of histamine in yoghurt. The mobile phase consisted of acetonitrile/water (18:88 v/v) and the flow rate was set at 0.5 ml/min using isocratic HPLC. Detection was carried out at 254 nm using UV-detector. Calibration curve that was constructed using peak area of standards was linear and value of correlation coefficient (2) was estimated at 0.998. Good recoveries were observed for histamine under investigation at all spiking levels and average of recoveries was 84%. The RSD% value from repeatability test was found to be %4.4. Limit of detection and limit of quantitation were 0.14 and 0.42 μ/ml, respectively. The results of validation tests showed that the method is reliable and rapid for quantification of histamine in yoghurt.

Excessive accumulation of heavy metals in agricultural soils not only leads to environmental pollution, but also results in increased uptake of heavy metals by plants, which in turn affects the quality and safety of the foods. Cadmium and copper are considered as the major pollutants of greenhouse soils that stem from agricultural techniques and chemical materials. This is a study aimed to investigate the contamination of greenhouse tomatoes crop with copper and cadmium in Hamadan province. A total of 72 samples were obtained from 18 greenhouses (4 samples from each) located in 6 cities of the province. Following preparation procedure, the concentrations of the elements were measured using atomic emission. According to the results, the concentrations of cadmium and copper in tomato samples were estimated at the range of 0.08–5.25 and 0.01–9.25 mg/kg, respectively. Statistical analysis showed a correlation between cadmium and copper concentrations. Moreover, comparing the results with the approved level of these elements revealed that the concentration of cadmium and copper in some of the greenhouse tomatoes were above the acceptable level. That is to say, the concentration of cadmium in all of the samples was determined as health threatening level.

Reduction of oil uptake in battered and breaded products is one of the critical aspects to obtain a safe and good quality product. In this study, combined effects of light salting (8, 10 %) and microwaving (180 °C, 30, 60 and 90 sec) pre-treatments on physical parameters and oil uptake in rainbow trout nuggets were investigated. Results show that highest moisture content was observed in control (p 0.05), and treatment with 10 percent light salting and 30 second pre-drying in 180 °C led to the lowest oil uptake compare with control (p˂0.05). No significant differences, on the product yield, adhesion of coating, water holding capacity and sensory evaluation were obtained among the different treatments. In comparison with control, all treatments presents lower levels of color indexes and percentage of reduction oil uptake (p˂0.05). As a result, treating the substrate with 10% light salting and pre-drying in microwave for 30 sec (A10) highly recommended for reduction of oil uptake.

Coagulase-positive Staphylococcus aureus is introduced as the third major source of animal origin food borne disease. This bacterium can proliferate and produce toxin in protein and carbohydrate foods leading to food-poisoning. The aim of this study was isolation, identification and enumerating of S. aureus in meat as well as intestinal contents of native duck around Tabriz area. For this purpose, a total number of 35 native ducks randomly was purchased in the nearby villages of Tabriz. Fifty g of thigh meat together with 10 g of intestinal content of each carcass were sampled and analyzed according to the ISIRI protocols. The isolates were confirmed by PCR technique. Results showed that 17.14% of meat and fecal samples were found contaminated with S. aureus. Mean values of S. aureus load in meat and feces were estimated at 87 CFU/g and 64 CFU/g, respectively. It was assumed that contamination of duck meat with S. aureus can be occurred through non-hygienic practices during slaughter as well as contamination with intestinal contents and/or skin of the carcass.

Nitrate is the one of flavors compounds, color stabilizer and inhibits the growth of anaerobic microorganisms in meat products. Its high levels in food can cause methaemoglobinaemia and is recognized as carcinogenic. Therefore, accurate determination of nitrate is crucial to ensure consumer health. Regularly, nitrate is estimated by Colorimetric and HPLC methods. For nitrate measurement, the efficiency, accuracy, speed and amount of material are important from economical point of view. In this study, the cost of initial investment, staff, consumable material and non-consumable equipments used by the two methods were calculated and finally Net Present Value (NPV) was calculated for each of them. The rate of interest was considered from 4 until 30%. The results showed that the amount of initial investment, annual cost of staff and consumable materials for Colorimetric method were 274000000, 379080000 and 214289130 Rials, respectively. These costs for HPLC method were 342000000, 252720000 and 7633080 Rials, respectively. Finally, NPV in minimum and maximum rates of interest (4 and 30%) for Colorimetric method were equal to 8368344000 and 2242330000 Rials and HPLC method were estimated at 4035848000 and 1207544000 Rials. As a result, HPLC is more economical (NPV is two times lower of Colorimetric method) and this technique could be recommended for the routine measurement of nitrate in laboratories of regulatory agencies.