Contamination Of Raw Milk Research Articles

Development of a HPLC Fluorescence Method for Determining Efficacy of Milk Pasteurization

Alkaline phosphatase (ALP) is an active enzyme present in the raw milk. Due to its unique heat-sensitive properties, it is employed as an indicator to evaluate efficiency of the pasteurization treatment. In the present study, a method comprising of HPLC with fluorescence detector was developed for the quantification of ALP enzyme activity in the pasteurized milk. The method is based on the detection and quantification of 4-methylumbelliferone (4MU) liberated by the action of phosphatase enzyme (in the milk) on the substrate 4-methylumbelliferyl phosphate (4MUP). Extraction and purification of 4MU was done by clarification, centrifugation, and solid phase extraction processes. The target compound separation was achieved with the help of reversed-phase C18 column using gradient elution consisting of a binary mobile phase: HPLC grade water and methanol. The fluorescence detection was accomplished with the excitation and emission wavelengths being 365 and 460 nm, respectively. The method validation experiments clearly showed high specificity, good linearity (r2 > 0.9901), low limits of detection (0.349 mg/L) and quantification (LOQ, 0.432 mg/L), accuracy (> 100%), and precision (%RSD < 4.7652). Comparative evaluation against Lovibond comparator method revealed that the HPLC method has an advantage of detecting very low levels of ALP activity and raw milk contamination. This is the first report of detecting such low levels of ALP in the milk by HPLC-fluorescence detector technique. This new chromatographic method can be considered as a substitute to the existing standard methods that employ fluorometric technique for detecting ALP activity in the pasteurized milk. Our method could certainly enhance the quality assurance standards currently employed in the dairy industry.

Review on Milk Yield, Composition, Quality and Microbial Contamination Dairy Cattle Milk in Ethiopia

Ethiopian milk production depends on mainly indigenous livestock genetic resources dominated by small holder farmers. The estimated numbers of indigenous milking cows in Ethiopia is about nine million and are in the hands of smallholder farmers and pastoralists under traditional contributions of the sector to the country’s gross domestic product and exports. Milk and milk products play an important role in human nutrition throughout the world. Milk is also highly perishable and can easily be adulterated whilst the quality of the milk is highly dependent on farm management. Sources of microbial contamination of milk like milking environment, cows udder, milker, milking equipments and water the most dominant factor for the quality of milk. To prevent or retard growth of bacteria in milk and to maintain its quality for domestic consumption or transportation to the processing plant cooling, boiling and pasteurization are important to control measures of microbial contamination in raw milk. Clot on boiling test is performed by boiling a small amount of milk in a spoon, test tube or any other suitable container. Chemical composition, particularly milk fat content is used as quality test. The solid constituents of milk make an important food item from both nutritional as well as processing point of view. Keywords:- contamination, composition handling, milk quality DOI: 10.7176/JBAH/10-19-02 Publication date: October 31 st 2020

Effect of milk bactofugation on the counts and diversity of thermoduric bacteria

The objective of this work was to determine the effect of milk bactofugation on the counts and microbial diversity of mesophilic (MT), psychrotrophic (PT), and thermophilic (TT) thermoduric bacteria and its potential as a technological method to remove spoilage microorganisms resistant to pasteurization. Different batches of raw milk from 69 dairy farms divided into sets in 3 bulk tanks (A, B, C) were evaluated at different times during the technological process. As the raw milk was preheated (∼55°C) immediately before bactofugation (10,000 × g), the effect of bactofugation was estimated by comparing the counts in raw, preheated, and bactofuged milk. This centrifugation was sufficient to reduce the isolation of 88% of the MT in preheated milk. For PT, it was possible to verify a reduction of 72.5% in batch C. The TT were not recovered at higher detection limits (<5 cfu/mL). For diversity, 310 isolates were identified using a molecular approach; 15 species of contaminating thermoduric bacteria were identified from raw and preheated milk, and only 6 species were recovered in bactofuged milk. Only MT were recovered from the bactofuged milk, mainly the species Lysinibacillus fusiformis (61.7%) and Bacillus licheniformis (12.3%). Both species are known to be endospore-forming psychrotrophs and have proteolytic or lipolytic activity. The bactofugation of raw milk reduced the number of isolates of B. licheniformis, Bacillus toyonensis, Micrococcus aloeverae, and Aestuariimicrobium kwangyangense by 33, 43, 86, and 92%, respectively, and reduced the isolates of Macrococcus caseolyticus, Lysinibacillus varians, Carnobacterium divergens, Microbacterium hominis, Kocuria indica, Micrococcus yunnanensis, Gordonia paraffinivorans, Bacillus invictae, and Kocuria kristinae to undetectable levels. The results of this study indicate that bactofugation can be applied by the dairy industry to reduce pasteurization-resistant microorganisms in combination with prophylactic measures to prevent the contamination of raw milk by spores and vegetative forms of bacteria.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus from dairy farms in North-eastern Italy

Transmission of Staphylococcus aureus along the dairy production chain is an emerging public health problem with human, veterinary, and food safety issues. The prevalence of multidrug-resistant, particularly methicillin-resistant S. aureus (MRSA), has steadily increased in several European countries. In this study, the prevalence of S. aureus in raw cow milk and farm workers was investigated, and the trajectories of MRSA transmission at the primary stage of the dairy chain were assessed. To this purpose, a longitudinal survey was conducted in 618 dairy farms in two contiguous regions with high livestock density in North-eastern Italy. S. aureus contamination of bulk tank milk (BTM) was observed in more than 80% of farms, while MRSA prevalence was 3.6% and 15.9% in BTM and farm workers, respectively. The majority of MRSA isolates from both BTM and farm workers were assigned to ST398, and showed a worrisome multidrug-resistant phenotype. Enterotoxin and Panton-Valentine leukocidin genes were detected in 11.5% and 4.9% of MRSA isolates from both sources. Nearly all MRSA isolates from workers belonged to the same epidemiological type as BTM isolates from the corresponding farm, denoting a bidirectional MRSA transmission pattern. A focus on the ST398 spa type t899 MRSA lineage in the Italian livestock system highlighted the presence of two major clusters whose dissemination was likely facilitated by the selective pressure imposed by antimicrobial use in animal farming. Our findings emphasize the need for continuous monitoring of MRSA along the dairy production chain, not only to avoid transmission between animals and exposed workers, but also to contain the risk of raw milk and dairy product contamination by multidrug resistant and toxigenic strain.

Determination of Aflatoxin M1 in Raw Milk from Different Provinces of Ecuador.

Aflatoxin M1 (AFM1) is a mycotoxin from Aspergillus flavus and A. parasiticus, classified as carcinogenic and hepatotoxic. The objective of the present investigation was to determine its presence in raw milk from north-central Ecuador, constituted by the provinces of Pichincha, Manabí, and Santo Domingo de los Tsáchilas. These areas represent approximately 30% of Ecuadorian milk production. By the end of the investigation, a total of 209 raw milk samples were collected, obtained both during the dry (June and August) and rainy seasons (April and November) of 2019. AFM1 concentrations were measured with lateral flow immunochromatographic assays, and 100% of the samples were positive for this mycotoxin, presenting a mean value of 0.0774 μg/kg with a range of 0.023 to 0.751 μg/kg. These AFM1 levels exceeded the European Union regulatory limit of 0.05 μg/kg in 59.3% (124/209) of samples, while only 1.9% (4/209) exceeded the Ecuadorian legal limit of 0.5 μg/kg. By using non-parametric tests, significant differences were determined (p ≤ 0.05) between the provinces for months of study, climatic season (being higher in the dry season), and climatic region (greater in the coast region). On the other hand, there were no significant differences (p ≥ 0.05) between the types of producers or between production systems. Therefore, AFM1 contamination in raw milk does not present a serious public health problem in Ecuador, but a monitoring and surveillance program for this mycotoxin in milk should be developed to prevent consumer health problems.

Impact of salting and ripening temperatures on late blowing defect in Valtellina Casera PDO cheese

Clostridial contamination of raw milk can cause the late blowing defect (LBD) in semi-hard and hard cheeses. In this study we have evaluated the influence of salting and ripening temperatures on LBD appearance in Valtellina Casera PDO cheese. Four cheese lots were brined at two different temperatures (8 and 13 °C) and successively ripened at 8 or 13 °C for 90 days. To evaluate the spore content a modified most probable number (MPN) method was used. The brining temperature of 8 °C seemed to prevent clostridial germination. During the ripening we detected LBD symptoms in all the cheeses aged at 13 °C, while no defects were observed in those placed at 8 °C. Clostridium tyrobutyricum resulted to be the main cause of LBD and its development was temperature-dependent. Volatilome analysis highlighted rancid volatile compounds in cheeses ripened at 13 °C. A combination of salting and ripening temperatures resulted to be an effective strategy to prevent and control the LBD in cheeses. A brine temperature of 13 °C followed by an aging at 8 °C inhibited the germination of C. tyrobutyricum spores during brining and subsequent germination during ripening.

EVALUATION OF THE MICROBIAL LOAD AND IDENTIFICATION OF POSSIBLE SOURCES OF CONTAMINATION OF RAW COW’S MILK IN JOANNA, BLACK BUSH POLDER, REGION 6, GUYANA

Milk is one of the main sources of nutrients to animals, but due to its high water activity, it serves as an ideal medium for the growth of microorganisms. The purpose of this research was to evaluate the microbial load in raw cow’s milk and to identify the possible sources of raw milk contamination in Joanna. Fifteen (15) raw milk samples were collected randomly according to the simple random sampling method and farmers were interviewed. Raw milk samples were analysed for Escherichia coli and aerobic bacteria. From the 15 samples of raw milk, contamination with E. coli (93.33%) and aerobic bacteria (100%) was observed. Also, several factors, milk handling practices, unhygienic practices, extensive farming systems, and lack of general zoonoses exposure practices and awareness, predisposed raw milk to microbial contamination. This research concluded that the quality of milk was unsatisfactory since it was heavily contaminated with bacteria. It is recommended that there should be an increase in the agriculture extension education and awareness programme to help improve milk quality.

Human health risk assessment of heavy metals in raw milk of buffalo feeding at wastewater-irrigated agricultural farms in Pakistan.

Wastewater irrigation to grow fodder for animals and cattle farming is common practice in Pakistan. Hence, this study was conducted in Multan, Pakistan, to assess heavy metal pollution, human health risk and the total target health quotient (TTHQ) of heavy metals in raw milk of buffalo feeding at different agricultural farms and to identify sources of toxicity in milk. Samples of raw milk (n = 60) were analyzed for Cd, Cr, Cu, Mn, Ni, and Pb by ICP-OES, Perkin Elmer, USA. The TTHQ values of heavy metals ranged from 6.92 to 42.44 in raw milk of buffalo, highest at wastewater-irrigated agricultural farms and lowest at tube well water site, indicating high carcinogenic health risk to exposed population. The multivariate statistical analysis revealed that contaminated fodder like Maize and Brassica plants grown with wastewater and contaminated soil are common sources contributing the heavy metal contamination in raw milk. It invites attention of government to remediate the situation to avoid the potential risks to public health from resulting food chain contamination.

Sources of psychrotrophic contamination and proteolysis indices in raw milk

Storage of raw milk under refrigeration makes it possible to reduce operating costs for production and prevents losses of this raw material by the acidifying activity of mesophilic bacteria. Meantime, storage for prolonged periods may result in decreased quality of dairy products, due to the growth and enzymatic activity of psychrotrophic bacteria. Thus, in this study, we evaluated the presence of psychrotrophic microorganisms, Pseudomonas spp. and Pseudomonasaeruginosa tracing sources of microbiological contamination in the milking process as well as the level of proteolysis of the milk in the expansion tank. The highest contamination (P &lt;0.05) occurred with the psychrotrophic count, with maximum values of 5.11 log CFU•mL-1a value that has hydrolytic potential for K-casein. Some dairy farms were found to have a maximum caseinomacropeptide value of 142.93 mg•L-1, representing loss of quality for the industry and a raw material that is not suitable for human consumption. The points of greatest contamination were udder surface, insufflator, milking bucket and colling system. According to principal component analysis, the values obtained for the microbiological counts were not determinants of the release of caseinomacropeptide.

Persistent contamination of raw milk by Campylobacter jejuni ST-883.

Campylobacter jejuni has caused several campylobacteriosis outbreaks via raw milk consumption. This study reports follow-up of a milk-borne campylobacteriosis outbreak that revealed persistent C. jejuni contamination of bulk tank milk for seven months or longer. Only the outbreak-causing strain, representing sequence type (ST) 883, was isolated from milk, although other C. jejuni STs were also isolated from the farm. We hypothesized that the outbreak strain harbors features that aid its environmental transmission or survival in milk. To identify such phenotypic features, the outbreak strain was characterized for survival in refrigerated raw milk and in aerobic broth culture by plate counting and for biofilm formation on microplates by crystal violet staining and quantification. Furthermore, whole-genome sequences were studied for such genotypic features. For comparison, we characterized isolates representing other STs from the same farm and an ST-883 isolate that persisted on another dairy farm, but was not isolated from bulk tank milk. With high inocula (105 CFU/ml), ST-883 strains survived in refrigerated raw milk longer (4–6 days) than the other strains (≤3 days), but the outbreak strain showed no outperformance among ST-883 strains. This suggests that ST-883 strains may share features that aid their survival in milk, but other mechanisms are required for persistence in milk. No correlation was observed between survival in refrigerated milk and aerotolerance. The outbreak strain formed a biofilm, offering a potential explanation for persistence in milk. Whether biofilm formation was affected by pTet-like genomic element and phase-variable genes encoding capsular methyltransferase and cytochrome C551 peroxidase warrants further study. This study suggests a phenotypic target candidate for interventions and genetic markers for the phenotype, which should be investigated further with the final aim of developing control strategies against C. jejuni infections.

Анализ методов оценки общей бактериальной обсемененности молока-сырья при входном контроле на предприятиях молочной отрасли

Материалы для специалистов молочной промышленности. Технологии переработки молока Оборудование для отрасли. Состояние и тенденции развития рынка молочных продуктов. Новости и события молочной промышленности.

Prevalence and characterization of Staphylococcus aureus isolates from subclinical bovine mastitis in southern Xinjiang, China

Staphylococcus aureus is one of the major pathogens causing mastitis in dairy herds. The colonization of dairy cows and subsequent contamination of raw milk by S. aureus, especially strains exhibiting multidrug resistance and biofilm-forming and toxin-producing abilities, remains an important issue for both dairy farmers and public health. In this study, we investigated the prevalence, antimicrobial susceptibility, biofilm formation, and genetic diversity of S. aureus from subclinical bovine mastitis in dairy farms located in southern Xinjiang, China. Sixty-five isolates from 84 subclinical mastitic milk samples were identified as S. aureus. The resistance rates to penicillin, erythromycin, clindamycin, tetracycline, gentamicin, linezolid, rifampicin, quinupudin-dafupudin, ciprofloxacin, norfloxacin, and chloramphenicol were 58.5, 44.6, 40.0, 18.5, 12.3, 10.8, 9.2, 6.2, 4.6, 4.6, and 1.5%, respectively. All isolates were susceptible to cefoxitin, sulfamethoxazole-trimethoprim, and vancomycin. Isolates from farm A showed a significantly higher resistance rate to tetracycline (16.9%) than those from farm B (1.5%). The most frequently detected virulence factors were hla (96.9%, 63/65) and hlb (100.0%, 65/65). The percentage rates of the staphylococcal enterotoxin genes sea, sec, sed, seg, seh, sei, and sej in S. aureus isolates were 4.6, 33.8, 27.7, 3.1, 41.5, 41.5, and 7.7%, respectively. The percentage rate of the sec gene in isolates from farm B (30.8%) was significantly higher than that of farm A (3.1%). The percentage rates of the tsst and pvl genes in S. aureus isolates were 26.2 and 40.0%. The percentage rate of the pvl gene in isolates from farm B (32.3%) was significantly higher than that of farm A (7.7%). The adhesion molecules fnbA, fnbB, clfA, clfB, and cna were detected in 21 (32.3%), 23 (35.4%), 65 (100.0%), 65 (100.0%), and 65 (100.0%) isolates, respectively. The percentage rates of the icaA, sarA, tcaR, ccp, luxS, and sigB genes in S. aureus isolates were 69.2, 100.0, 86.2, 95.4, 84.6, and 100.0%, respectively. The fnbB and icaA genes were more frequently detected in isolates from farm A (29.2 and 40.0%, respectively) than those from farm B (6.2 and 29.2%, respectively). The luxS gene was more often found in isolates from farm B (50.8%) than those from farm A (33.8%). Using the microplate method, 61.5, 26.2, and 10.8% of the isolates showed weak, moderate, and strong biofilm-forming abilities, respectively. Different clonal complex (CC) and spa-types were identified, including CC81, CC398, CC88, CC5405, and CC5406. Importantly, in this study we report for the first time 41 new sequence types (ST) among 44 distinct ST. These results indicated high genetic diversity of S. aureus involved in subclinical bovine mastitis in southern Xinjiang, China. The results also showed that S. aureus from subclinical bovine mastitis cases in southern Xinjiang, China, were mainly resistant to β-lactams, erythromycin, and clindamycin. Also, biofilm- and adhesion-related genes, which are increasingly known as important virulence factors in the pathogenesis of S. aureus infections, were detected at a high rate. This study could help identify predominant clones and provide surveillance measures to decrease or eliminate S. aureus contamination in raw milk of dairy cows with subclinical mastitis.

Risk-based assessment and criteria specification of the microbial safety of wastewater reuse in food processing: Managing Listeria monocytogenes contamination in pasteurized fluid milk

Intense pressure on water resources has led to efforts to reuse reclaimed processing wastewater for cleaning purposes in food processing plants. The milk industry produces considerable amounts of wastewater, which can be used for cleaning of equipment after appropriate treatment. However, due to naturally occurring microbiological contamination in raw milk, the wastewater is often contaminated, and therefore the reuse of reclaimed wastewater is perceived as risky. This study aims to quantify the risks of Listeria monocytogenes infection and associated disease burden when wastewater reclaimed from milk processing operations is used in cleaning-in-place (CIP) systems for pasteurized fluid milk production following a quantitative microbial risk assessment (QMRA) approach. Furthermore, this study aims to inform risk-based tolerable limits for levels of contamination in CIP water based on a public health target of 10−6 DALY per person annually. The suggested model investigates the passage of L. monocytogenes throughout the fluid milk chain, from receipt of raw milk at the plant to the point of consumption and covering storage in receiving and storage tanks, pasteurization, and storage at retail and at home. Risk and disease burden estimates are simulated for general (younger than 65 years), elderly (65 years and older) and pregnant population subgroups. Additional scenarios covering the effect of using clean water, using water with different levels of contamination and using reclaimed wastewater modeled as recovered from cheese whey after membrane filtration (reclaimed water scenario) are considered to estimate a risk-based limit of contamination and simulate a real-life example. The tolerable limit of contamination in CIP water was estimated as −2 log10 CFU/mL to ensure the protection of the most vulnerable subgroup, pregnant women, while higher limits were estimated for the elderly and general subgroups. Under the reclaimed water scenario, the annual number of listeriosis cases was estimated as 3.36, 5.67, and 0.15 for the general, elderly and pregnant population subgroups, respectively, while in the clean water scenario, the estimates were 3.33, 5.56 and 0.15, respectively. In both scenarios, the DALY estimates were lower than the tolerable limit. The results indicate that reclaimed water can be an alternative to potable water for CIP applications.

Evaluation of Aflatoxin M1 contamination and physicochemical adulteration in raw milk from southeast Brazil

Evaluation of Aflatoxin M1 contamination and physicochemical adulteration in raw milk from southeast Brazil

Occurrence of aflatoxin M1 in raw, pasteurized, UHT cows’ milk, and dairy products in Lebanon

In this study, a total amount of 868 samples of raw cows' milk, pasteurized and UHT cows’ milk, and dairy products were analyzed for their AFM1 content. Milk and dairy consumption in Lebanon was evaluated through a food frequency questionnaire, and accordingly the exposure to AFM1 and its association with liver cancer risk in Lebanese population were evaluated. Results showed contamination in raw milk, pasteurized and UHT milk, and dairy products at a range of 0.011–0.440 μg/l, 0.013–0.219 μg/L, and 0.015–7.350 μg/L respectively; with 28%, 54.5%, and 45.5% respectively of samples with AFM1 above maximum tolerable limit (MTL) set by the European Commission. AFM1 consumption was shown to be associated with 0.0041 additional cancer cases per 100,000 persons per year. Based on these results, milk and dairy consumption in Lebanon can be considered hazardous and may present a significant risk on the health of the Lebanese population especially children.

Microbial and Chemical Adulterants Assessment of Raw Cow Milk Collected from Dairy Farms of Hlabisa Villages, KwaZulu-Natal Province, South Africa

Background: Milk is one of the most nutritious foods providing a variety of proteins, fats, minerals, and vitamins needed to maintain, grow, and develop the body. The aim of this study was to assess microbial and chemical adulterants of raw cow milk collected from dairy farms of Hlabisa villages, KwaZulu-Natal Province, South Africa. Methods: A total of 68 raw cow milk samples were obtained from teats sampling points, milking buckets, and communal pooling buckets. The bacteriological analysis was conducted for the detection of various bacteria in milk samples. Biochemical tests were also done to detect some chemical adulterants in milk samples. Results: Total bacterial count of teats, milking buckets, and communal milk pooling buckets were 6.91, 6.06, and 6.06 log Colony Forming Unit (CFU)/ml, respectively. The most found chemical adulterant was urea detected in 23 out of 68 (33.8%) samples, followed by hydrogen peroxide showed in 22 out of 68 (32.3%) samples. However, none of the samples were contaminated with formalin, starch, and neutralizer. Conclusion: The present study revealed high microbial contamination of raw cow milk produced by rural small-scale dairy farmers of Hlabisa villages, KwaZulu-Natal Province, South Africa, indicating the lack of standard operating sanitation. It was also stated that raw milk samples contained various types of chemical adulterants that may lead to severe health problems. Good hygiene practices must be adopted by small-scale dairy farmers at every stage of their milk handling and processing.

Coliforms Contamination in Raw Milk and Some Dairy Products with Special Reference to Comparative Identification of Enterobacter spp.

The current study was undertaken to examine 200 sample of raw milk and some dairy products (Kariesh cheese, plain yoghurt, milk powder and infant formula) for contamination with Coliform group especially Enterobacter spp. Coliforms were detected in; 42/50 (84%) raw milk samples from farmers' houses, 25/30 (83.33%) kariesh cheese samples and 23/30 (76.67%) plain yoghurt samples, however, they could not be detected in any of raw milk samples from dairy shops, milk powder and infant formula samples. The mean values of coliforms in the examined samples were 2.80x106 ±0.73x105, 2.30×106 ±0.75×104 and 1.08×106 ± 1.50×104 cfu /ml or gm in raw milk from farmers' houses, kariesh cheese and plain yoghurt samples, respectively. The biochemically identified coliforms were E. aerogenes, E. agglomerans, E. cloacae, C. diversus, C. freundii, E.coli, K. oxytoca and K. pneumonia with respective percentages of; 1.19, 1.19, 2.38, 25, 15.48, 26.19, 13.09 and 15.48, in raw milk from farmers' houses, 6, 0, 2, 28, 10, 22, 0, and 32 in kariesh cheese, 0, 0, 2.12, 23.91, 0, 36.96, 26.09, 10.87 in plain yoghurt. Comparative identification of isolated Enterobacter spp.by standard biochemical methods and Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry revealed that the total conformity of identification of Enterobacter strains between standard biochemical technique and MALDI-TOF MS technique was 66.6%, where, it ranged from 50% to 100 for E. aerogenes and E. cloaca, respectively. However, the only identified E. agglomerans isolatesfrom raw milk could not be confirmed by MALDI-TOF MS technique. It has been shown through these results that the presence of coliform and Enterobacter bacteria is an evidence of the lack of health requirements and thermal treatments of raw milk and some of its products (kariesh cheese and yoghurt).

Research of heat treatment influence of milk on quality and safety of hard cheeses

The object of research is raw milk used for the production of hard cheeses by milk processing enterprises of Ukraine. The quality of raw milk is especially important, a key factor determining the effectiveness of the milk processing industry. Without milk, which meets certain requirements, it is impossible to organize the production of high-quality products. Special requirements are placed on the quality of raw milk intended for the cheese production. One of the most problematic places is improving the quality and cheese suitability of raw milk and improving the technological process for the production of natural hard cheesesDuring the study, laboratory (biochemical and microbiological) research methods are used to determine the quality indicators of raw milk and finished products, as well as their microbial contamination. And for processing the results of the study, methods of mathematical statistics are used.The work shows that bacterial contamination of raw milk, which exceeds the normative limit values, poses a threat to both the technological process of cheese making and the quality of the finished product. Methods are proposed for preventing a decrease in the yield of cheese and deterioration in its quality due to prolonged storage of milk at low temperatures. It is proved that the best results are obtained with ultra-high-temperature processing of milk with an exposure of 2–4 s. And also, that high-temperature and, especially, ultra-high-temperature (UHT treatment) is a very effective way to destroy bacterial microflora and improve the quality of raw milk by such an indicator as a «pollution tank». This allows to increase the cheese ability of raw milk. High temperatures of heat treatment of milk lead to changes in the salt and protein composition of milk. These changes should have both negative consequences – a deterioration in the rennet coagulation of milk and the synergistic properties of the clot, and a positive result consisting in an increase in the transfer of milk solids, primarily whey proteins, to clot and cheese.

Aflatoxin M1 Contamination in Raw Cow Milk of Dairy Farms in Behbahan area, Khuzestan province, Iran

Introduction: Mycotoxins are among the environmental chemical agents with toxic effects on animals and humans. Aflatoxins (AF) are a major group of mycotoxins produced following the growth of some species of Aspergillus flavus and Aspergillus parasiticus, particularly in agricultural products. Aflatoxin M1 (AFM1) is secreted to milk and remains there since the process of pasteurization and sterilization has little effect on this metabolite. The aim of this study was to investigate the natural occurrence of AFM1 in raw milk in Behbahan area, which is an area of high-density livestock production in southwest of Iran. The other aim was to compare these obtained levels with the accepted level recommended by the European community (50 ng/L). Methods: In the present study, 90 samples of raw milk were collected from five dairy farms in Behbahan region, Khuzestan province, Iran. The AFM1 was analyzed using the Enzyme Linked Immune Sorbent Assay (ELISA) method by ELISA kits from Euro Clone, Italy. Data were analyzed by ANOVA and the results were reported as mean ± SE. The significant level was set at p ≤ 0.05. Results: The concentration of aflatoxin M1 in (15)16.54% of raw milk was higher than maximum tolerance limit accepted by European Union /Codex Alimentarius Commission (50 ng/l). The results of this study showed that all 90 investigated raw milk samples were contaminated with AFM1 (100%). Conclusion: A significant difference was observed between concentration means of AFM1 in various studied farms at P &lt; 0.05. Consequently, high occurrence of AFM1 in raw milk samples was considered as a possible hazard for human health. However, further longitudinal studies are required on milk samples and other dairy products in Behbahan as well as other regions of Iran to estimate the representative intake of AFM1 in Iran.

Antibiotic resistance and virulence genes in nisin-resistant Enterococcus faecalis isolated from raw buffalo milk modulate the innate functions of rat macrophages.

To elucidate the antibiotic resistance and virulence genes of nisin-resistant Enterococcus faecalis isolated from raw buffalo milk and to study the effect of nisin-sensitive and -resistant E. faecalis on the innate immunity of rats. Slanetz-Bartley agar plates containing nisin were used to isolate nisin-resistant E. faecalis. The virulence factors were ascertained using quantitative real-time polymerase chain reaction. Cell viability, phagocytosis, intracellular survival and enzyme assays were performed to investigate the interaction of E. faecalis with rat macrophages. Nisin-resistant E. faecalis was less prone to phagocytosis and survived longer inside the macrophages, due to reduced production of reactive oxygen species and nitric oxide. The viability and activation of macrophages was also reduced in the presence of resistant E. faecalis, as observed by enhanced lactate dehydrogenase production and reduced β-galactosidase. Nisin-resistant E. faecalis and its virulence factors were reported in raw buffalo milk. This study shows that nisin-resistant variants exhibited cross resistance to antibiotics and suppressed the innate immune responses of rats by directly affecting macrophage activity. This study elucidated the contamination of raw buffalo milk by nisin-resistant E. faecalis, which may pose food safety risk.