Implication of food safety measures on microbiological quality of raw and pasteurized milk

The effects of implementing food safety measures including pre-requisite programs (PRPs) and/or Hazard Analysis Critical Control Points (HACCP) on the microbiological quality of raw and pasteurized milk during four years was investigated in one of the biggest diary plant in Serbia. On the dairy farm, the measures included training of farmers, investments in the infrastructure of gathering points for the collection of raw milk and transportation, improvement of hygiene and decrease of the number of small farmers. As a result of these measures, the contribution of raw milk with of lower total plate count (TPC) in total raw milk quantity decreased over time.As a result of HACCP system implementation in the dairy plant, TPC of pasteurized milk decreased from 3.32 ± 0.48 till 3.11 ± 0.30 log CFU/ml. Eight months after HACCP system was implemented, a significant decrease in TPC from 3.11 ± 0.30 till 2.18 ± 0.54 log CFU/ml in pasteurized milk which could be related to the additional investments covering pasteurisation unit and automated cleaning and disinfection system. The research confirmed constrains of a solely HACCP system without adequate PRPs.Food safety improvements through PRPs and HACCP both on farm level and in the dairy plant present a basis for the production of dairy products.     

Evaluation of the factors affecting the activity of sakacin C2 against E. coli in milk

Sakacin C2 is a novel, broad spectrum bacteriocin secreted by Lactobacillus sake C2 isolated from Chinese traditional fermented cabbage. Effects of milk fat, emulsifiers, preservatives and homogenization on the activity of sakacin C2 against Escherichia coli ATCC 25922 in milk were evaluated by determined the changes of viable cell counts of E. coli ATCC 25922 after inoculation (10⁵ CFU/ml) then storage at 4 °C. Milk fat in pasteurized and homogenized milk products (low fat milk and whole milk) decreased the activity of sakacin C2 against E. coli ATCC 25922. Addition of 5 μl/ml of Tween 80 decreased the effect of sakacin C2 against E. coli ATCC 25922, but 5 mg/ml of lecithin increased the effect against E. coli ATCC 25922 in pasteurized and homogenized whole milk. Nisin and ε-Polylysine significantly increased the effect of sakacin C2 against E. coli ATCC 25922 in pasteurized and homogenized whole milk. Homogenization interfered with the activity of sakacin C2 against E. coli ATCC 25922 in pasteurized skim milk and whole milk. This study might lay the groundwork for the application of sakacin C2 as bio-preservative in milk and dairy products.     

Effects of temperature on the viability,growth and gene profile of Yersinia pseudotuberculosis and Yersinia enterocolitica inoculated in milk

This study was aimed at deciphering the viability and growth of Yersinia pseudotuberculosis and Yersinia enterocolitica in milk at different temperatures, and at identifying the temperature-dependent changes in gene expression in Yersinia. Fresh Yersinia culture was suspended either in pasteurized or in autoclaved milk and subjected to different temperature ranges. Colony forming units (CFU) were determined from inoculated milk after one and two weeks of storage using direct plating technique. In both one and two weeks of storage, growth of Y. pseudotuberculosis and Y. enterocolitica increased significantly at 4 °C and 24 °C (P < 0.05). Furthermore, gene expression profile and DNA microarray analyses were conducted. After one-week storage, the growths of Y. pseudotuberculosis and Y. enterocolitica were optimal at 4 °C and 24 °C. Remarkably, at 37 °C there was no detectable level of CFU from both Yersinia spp inoculated in pasteurized milk, whereas they grew well at 37 °C in autoclaved milk. The NotI-profile of Y. pseudotuberculosis grown at 24 °C generated different banding patterns from other treatment groups when compared to FseI and XbaI-PFGE pulso-type. Microarray interrogation of 4038 genes of Y. pseudotuberculosis revealed that 38 genes were upregulated by ≥8 fold and 237 genes exhibited ≥2 fold downregulation (at 95% significant level) after temperature shift from 4 °C to 24 °C. The findings of this study highlight the survival potential of Y. pseudotuberculosis and Y. enterocolitica in milk under different temperatures and the associated gene expression patterns, which may be important in the processing and safety of milk and dairy products.     

Contamination of milk with Bacillus cereus by post-pasteurization surface exposure as evaluated by automated ribotyping

Over the last decade, increased transportation of refrigerated raw milk from farms to factories has raised concerns over Bacillus cereus contamination in the Brazilian dairy industry. Twelve isolates from pasteurized milk and 30 isolates from the post-pasteurization equipment surfaces of a dairy processing unit were characterized as B. cereus. Seven ribotypes were identified, demonstrating the genetic variability of this microorganism. Most of the isolates belonged to the same ribogroup (RIBO1222-73-S4), and they were found on four surfaces and also in the milk, indicating the role of the equipment surfaces as reservoirs for milk recontamination.     

Aflatoxin M1 in raw,pasteurized and powdered milk available in the Syrian market

The incidence of contamination of aflatoxin M1 (AFM1) in milk samples collected from the Syrian market was investigated by using the competitive enzyme linked immunosorbent assay (ELISA) technique. A total of 126 samples composed of raw cow milk (74 samples), raw sheep milk (23), raw goat milk (11), pasteurized cow milk (10) and powdered milk (8) showed that 80% of tested samples were contaminated with various levels of AFM1 ranging from >20 to 765 ng/l. Percentages of AFM1-contaminated samples exceeding the American, Syrian and European tolerance limits were 22%, 38% and 52%, respectively.The range of contamination was relatively higher in pasteurized milk than in raw cow and sheep milk. 80% of AFM1-contaminated pasteurized cow milk samples exceeded the European tolerance limit with a range of contamination between 89 and 765 ng/l. Percentages of contaminated raw cow, sheep and goat milk exceeding the European tolerance limit were 59%, 24% and 14%, respectively.Milk powder was almost free of AFM1 contamination with only one sample containing a concentration lower than the European tolerance limit (12 ng/l).Extrapolation of aflatoxin B1 (AFB1) from AFM1 levels of contamination in milk samples indicates that contamination in dairy cattle feeds may range from 0.5 to 47.8 μg/kg.     

Assessment of aflatoxin M1 levels in pasteurized and UHT milk consumed in Prishtina,Kosovo

To assess public health hazards associated with the occurrence of AFM1 residues in pasteurized milk and UHT milk a survey was carried out, in Prishtina, capital city of Kosovo. In the present study, a total of 178 samples, 84 pasteurized milk and 94 UHT milk were collected during 6 months (July to December 2013). They were obtained from retail outlets in Prishtina city (Kosovo). The occurrence and concentration range of AFM1 in the samples were investigated by competitive enzyme-linked immunosorbent assay (ELISA) method. There was a high incidence of AFM1 (81.0%) in both pasteurized and UHT milk samples. Eighty three percent (83.3%) of the pasteurized milk samples and seventy eight percent (78.7%) of the UHT milk samples contained AFM1. The positive incidence of AFM1 in the pasteurized milk and the UHT milk samples ranged from 5.16 to 110 ng/L and from 5.02 to 62 ng/L, respectively. AFM1 levels in 18 (21.4%) pasteurized milk samples and 4 (4.2%) UHT milk samples exceeded the maximum tolerable limit of the EC according to the European Union regulation limits of 50 ng/L. AFM1 levels in the samples show that there is a presence of high AFM1 level that constitutes a human health risk in Kosovo. The results of this study imply that more emphasis should be given to the routine AFM1 inspection of milk and dairy products in the Prishtina region.     

Growth potential of Listeria monocytogenes in soft,semi-soft and semi-hard artisanal cheeses after post-processing contamination in deli retail establishments

Opportunities for post-processing contamination of cheese may occur in deli retail establishments, either during the further cheese ripening (at maximum 14 °C), during storage and display in the refrigeration cabinet (at maximum 7 °C) or during slicing. A L. monocytogenes post-processing contamination was simulated by inoculation either on the cheese slicing surface or the cheese rind of three soft cheeses (one white-molded raw cow's milk cheese, one pasteurized cow's milk cheese with spicy herbs, one washed rind pasteurized cow and sheep's milk cheese) and two semi-hard cheeses (one smear-ripened raw cow's milk cheese and one natural-ripened raw cow's milk cheese). L. monocytogenes challenge testing was performed on 3 batches of each cheese to assess the growth potential of L. monocytogenes after 14 days storage at either 7 or 14 °C. Substantial growth of L. monocytogenes (>0.5 log CFU/g) was obtained in 79.2% of all individual challenge tests (n = 178) that were performed although huge variation in growth potential was noted among the different cheese types and storage conditions. The growth potential on soft cheeses stored at 7 °C ranged from 1.8 to 4.0 log units and from 3.6 to 5.5 log units upon storage at 14 °C, whilst on semi-hard cheese, this was in general lower, and ranged from 0.1 to 1.4 log units at 7 °C and from 0.0 to 3.0 log units at 14 °C. Overall, increased outgrowth of L. monocytogenes was noted when inoculation was performed on the cheese slicing surface compared to the cheese rind. Thus if occasional post-processing contamination takes place during storage or handling of the cheese, L. monocytogenes has the potential to grow to elevated numbers throughout a reasonably expected storage period of up to 14 days notwithstanding the presence of high numbers of indigenous lactic acid bacteria in these cheeses. Also for a defined cheese type both a considerable inter-batch and intra-batch variability was sometimes noted from the replicate testing, indicating no consistent behavior of L. monocytogenes in these fermented dairy products. As such it is recommended that appropriate hygienic measures are taken to prevent post-processing contamination. Noting the growth potential, absence of L. monocytogenes in 25 g of cheese using a multiple sample subunit approach (n = 5) at the time of production is important to ensure compliance to EU legislation 2073/2005.     

Barriers and benefits of the implementation of food safety management systems among the Turkish dairy industry: A case study

The aim of this research was to determine the barriers and advantages of the Hazards Analysis and Critical Control Points (HACCP) and food safety programs (FSPS) employed by the dairy industry in Ayd?n, Turkey. By conducting face-to-face interviews and using questionnaires, the structure of Ayd?n dairy plants’ food safety management systems was characterized. The questionnaires elicited information about the applications of food safety systems, dairy plant managers’ opinions about any inspection systems, and their expectations for government and local legal authorities in food safety systems. Twenty-eight operating dairy plants in Ayd?n with a production licence from the Ministry of Food, Agriculture and Livestock show activity in the sector for more than 10 years (53.5%) with joint-stock or limited company status (60.7%). These plants produce white cheese, fermented milk products and butter. Implementing a clear and efficient food safety management system can improve legal issues (85.7%) and increase client trust (64.3%). This is positively correlated with the ages of dairy plant managers in the dairy industry in Ayd?n (p < 0.05 and p < 0.01). All the same, not understanding the HACCP was specified as one of the main barriers to its utilization. Almost half of managers (46.5%) reported not really knowing what HACCP was, while 35.8% reported that it was too expensive to employ. On the other hand, the main difficulties with prerequisite program (PRP) applications in Ayd?n dairy plants was determined to be a result of insufficient physical conditions (35.7%) and cost (46.4%).A lack of knowledge relating to and the cost of HACCP and other food safety programs were the main barriers to implementation in the Ayd?n dairy industry. Providing periodical training and consultation services for FSMS applications in the dairy industry by the government and also providing financial support must be provided.     

Seasonal study of aflatoxin M1 contamination in milk of four dairy species in Yazd,Iran

This survey was conducted to determine the occurrence of aflatoxin M₁ (AFM₁) in samples of raw milk obtained from cow, sheep, goat, and camel herds in Yazd province during different seasons. Aflatoxin M₁ was analyzed using the competitive enzyme-linked immunosorbent assay technique for screening and high-performance liquid chromatography with fluorescence detection for confirmatory purposes. The detection rates of AFM₁ in cow, sheep, goat, and camel milk samples were 46.5%, 21.6%, 20.1%, and 4.03%, respectively. Levels of the toxin in 15.4% of cow milk, 11.5% of sheep milk, and 9.15% of goat milk samples exceeded the legal limit (0.050 μg/kg) recommended by the Institute of Standards and Industrial Research of Iran; while none of the camel milk samples exceeded the legal limit. The occurrence and levels of AFM₁ in cow milk samples from industrial dairy farms was significantly lower (P ≤ 0.05) than those from traditional ones. Seasonal variations influenced the occurrence and levels of AFM₁ in cow, sheep, and goat milk; however, no statistically significant seasonal effect was found for camel milk. This study indicates a high occurrence of AFM₁ in cow milk especially those obtained from traditional dairy farms. Therefore, more supervision is required on these farms; and traditional dairy farms should be gradually replaced by industrial ones.     

Aflatoxin M1 contamination in dairy products marketed in Iran during winter and summer

In the present study, 298 dairy product samples consisting of pasteurized milk (91 samples), yoghurt (68 samples), white cheese (72 samples), butter (31 samples) and ice cream (36 samples) collected from popular markets in four large Iranian cities were examined for aflatoxin M₁ (AFM₁) by thin layer chromatography (TLC) technique. The toxin was detected in 66 (72.5%) pasteurized milk samples (mean: 0.052 μg/l; range: 0.013–0.250 μg/l), 45 (66.1%) yoghurt samples (mean: 0.032 μg/kg; range: 0.015–0.119 μg/kg), 59 (81.9%) white cheese samples (mean: 0.297 μg/kg; range: 0.030–1.200 μg/kg), 8 (25.8%) butter samples (mean: 0.005 μg/kg; range: 0.013–0.026 μg/kg) and 25 (69.4%) ice cream samples (mean: 0.041 μg/kg; range: 0.015–0.132 μg/kg). The concentration of AFM₁ in 36.2%, 20.6%, 30.5%, 9.6% and 27.7% of pasteurized milk, yoghurt, white cheese, butter and ice cream samples, respectively, were higher than Iranian national standard limits. Levels of AFM₁ in samples of pasteurized milk, yoghurt, butter and ice cream collected in winter were significantly higher (P < 0.05) than those collected in summer. In the case of white cheese, level of AFM₁ was higher in winter than in summer, but the difference was not statistically significant (P > 0.05). The results indicated that the contamination of the dairy products in such a level could be a serious public health problem at the moment.     

Isolation, identification and monitoring of contaminant bacteria in Iranian Kefir type drink by 16S rDNA sequencing

Iranian Kefir type drink (IKTD) is a highly consumed, traditional Iranian, fermented milk product. To improve monitoring procedures for food safety 32 industrial Kefir type drinks from 4 brands and 8 different production dates as well as 32 samples from pasteurized milk of the same Kefir manufacturers and air of the production sites were analyzed for contaminations. 16S rDNA extraction from Kefir samples as well as 16S rDNA obtained from samples incubated on Columbia agar were analyzed using PCR/DGGE, cloning, sequencing and phylogenetic classification. Already DGGE analysis indicated contaminations including Bacillus strains. Subsequently analysis of cultured clones indicated contaminations with Bacillus sp. including Bacillus cereus, Bacillus thuringiensis and Paenibacillus sp. in 9 (28%) from all analyzed samples. Also 38% of pasteurized milk samples were contaminated with B. cereus. The average count of B. cereus was 74 ± 19 cfu/ml. B. cereus and B. thuringiensis were found as contaminant bacteria in the air of the all manufacturing sites. These results suggest that milk is one of the most important sources of contamination with Bacillus sp., especially B. cereus for Kefir products in Iran. But bacterial contamination in Kefir samples might also originate from the air of the production sites. 16S rDNA analysis accelerates monitoring strategies.     

How safe is European Internet cheese? A purchase and microbiological investigation

The suitability for consumers of a variety of raw milk cheeses purchased over the Internet was investigated in terms of packaging, labelling, physicochemical parameters and microbiological safety. 108 purchases from seven European countries were examined. The prevalences of Salmonella spp., Listeria monocytogenes, Escherichia coli and coagulase positive staphylococci (SA) were determined. All 108 samples were described on websites as raw milk cheeses and thereby qualified for this study. However, after delivery it was noted that 4.6% (5/108) of cheeses were labelled to be manufactured from heat-treated or pasteurized milk. Delivery duration ranged from 24 h to six days. Immediately upon receipt cheese temperatures were observed to range between 5 and 23 °C, whereas in 61.5% of all cases the temperature was higher than 15 °C. Cheese labelling was examined in respect of EC Guideline 2000/13 and Regulation No. 853/2004. Only 17.6% (19/108) of cheeses were properly labelled and fulfilled all European guideline requirements. In 50.9%, 38.8%, 46.3% and 39.8% of all cases (i) specific storage requirements, (ii) name and address of the manufacturer/packer or seller, (iii) net weight and (iv) shelf life (use by date), were missing. Even the labelling information “made from raw milk” was not apparent on 36% of all cheese items delivered. The major foodborne pathogen L. monocytogenes was detected in 1.9% of all samples, one of which had counts of 9.5 × 10³ CFU/g. None of the 108 investigated cheeses showed a pH ≤ 5.0 and a_w value ≤0.94 which are the limiting values for growth of L. monocytogenes. For two samples (0.9%) and 11 samples (10.2%) the pH and the a_w value was ≤4.4 or ≤0.92, respectively at least at one of three stipulated time points (receipt, mid-shelf-life and at expiry). Salmonella spp. could not be detected in any of the samples. E. coli and SA could be detected in a total of 29.6% (≥10 CFU/g; 32/108) and 8.3% (≥100 CFU/g; 9/108) of samples, respectively, indicating poor conditions of hygiene. Results reveal that labelling and hygiene concerns about the safety of Internet purchased cheeses in Europe are justified.     

Validation of a Real-time PCR assay for fast and sensitive quantification of Brucella spp. in water buffalo milk

Water buffalo milk and derived dairy products, including mozzarella cheese, represent a possible source of Brucella contamination for consumers. Brucella is a severe pathogen for human health even at low concentrations. It is therefore fundamental to develop an assay that is faster and more sensitive than the traditional bacterial culturing method for the detection of the pathogen in the food matrix. We designed a Real-time PCR assay able to detect as low as 1 CFU/ml of Brucella spp. in water (80% probability) and 3 CFU/ml of Brucella spp. in buffalo milk (50% probability) in less than 3 h without any enrichment step. The assay was validated by calculating specificity, sensitivity, detection limit, precision, PCR efficiency, DNA extraction efficiency and food matrix inhibition. When this method was employed to detect and quantify Brucella spp. in 109 buffalo milk samples, the assay demonstrated a higher sensitivity in comparison to bacteriological analysis (27 positive samples and 2 positive samples, respectively).     

Occurrence of macrocyclic lactones in milk and yogurt from Brazilian market

Avermectins and milbemycins belong to a family of compounds called macrocyclic lactones (ML) and are highly used as antiparasitic agents in the treatment of cattle for control of gastrointestinal nematodes, ticks and myiasis. In Brazil, there are five substances (ivermectin, abamectin, doramectin, eprinomectin and moxidectin) registered for bovines. The use of these compounds may bring benefits to the cows but indiscriminate use might result in the presence of residues in milk and dairy products. In this context, the objective of the study was to validate an analytical method for determination of five ML in dairy products and verify the occurrence of these compounds in milk and yogurt available in the Brazilian market. The method involved QuEChERS sample preparation, derivatization and determination by high performance liquid chromatography with fluorescence detection. The methodology was validated using organic samples of milk and yogurt for the following parameters: linearity, precision, accuracy, repeatability and limits of detection (LOD) and quantification (LOQ). The method showed good linearity. Average recovery, performed at three different levels varied from 83% to 112% (RSDs < 14%). The method provides LOD ranging from 0.4 to 3.2 μg L⁻¹ for milk and 0.6 to 0.9 μg kg⁻¹ for yogurt. The LOQ was established according to the lower spike level (0.2–10 μg L⁻¹ for milk and 2.5 μg kg⁻¹ for yogurt). Repeatability and within-laboratory reproducibility were in satisfactory for both matrixes. In order to monitor milks and yogurts marketed in Campinas, SP, Brazil, 13 brands of UHT milk (135 samples), 8 brands of pasteurized milk (103 samples) and 13 brands of yogurt (104 samples) were acquired. A total of 342 samples were analyzed in duplicate for the presence of ivermectin, abamectin, doramectin, eprinomectin and moxidectin. Moxidectin was detected in one sample of pasteurized milk. No residue of the analyzed compounds was found in UHT milk or yogurt. Results indicate that the consumption of milk and yogurt does not represent a health risk for Brazilian consumers.     

Quality of raw milk intended for direct consumption in Estonia

The main aim of the present study was to estimate the occurrence of zoonotic bacteria in raw milk intended for sale directly to consumers in Estonia. In-line milk filters, bulk milk samples and milk samples from selling points were collected from a total of 14 dairy farms and respective retail selling points. The somatic cell counts, total bacterial counts and the presence of Salmonella spp and Listeria monocytogenes were studied from bulk milk samples. Campylobacter spp., Salmonella spp., L. monoscytogenes and Shiga-toxin producing Escherichia coli (STEC) were studied in farms in-line milk filters. The total bacterial counts exceeded 100,000 cfu/ml in three (21.4%) bulk milk samples and in 10 samples (71.4%) collected at the retail level. STEC genes were detected in 64.3% of the in-line milk filter samples. More than one STEC serogroup-specific gene was detected in four dairy farms. L. monocytogenes was found in 36% of the in-line milk filters. Neither Salmonella spp. nor Campylobacter spp. were found in any samples.     

Incidence and genetic variability of Listeria species from three milk processing plants

The presence of Listeria in three milk processing environments as a potential source of milk contamination was assessed. Swab samples (n = 210) taken from milk processing plants were examined. Sample sites included the milk processing equipment, besides areas handling raw and pasteurized milk. The USDA Listeria-selective enrichment procedure was used to process the samples. Forty one (19.52%) Listeria isolates were recovered. The isolates were further subjected to biochemical and genotypic characterization. Out of 41 isolates, 16 (7.62%) were confirmed as Listeria monocytogenes, 2 (0.95%) as L. ivanovii, 19 (9.05%) as L. innocua. 1 (0.48%) as L. seeligeri and 3 (1.43%) as L. grayi. All the L. monocytogenes isolates were positive for the hlyA gene. PCR based serotyping revealed all L. monocytogenes to be of 1/2a, 1/2c, 3a and 3c serovar group. AscI and ApaI restriction analysis yielded four PFGE clusters for 16 L. monocytogenes isolates obtained from raw milk collector, milk silos, buttermilk mixer, cheese and other milk product processor. No predominant PFGE cluster was observed among these L. monocytogenes isolates. The main sources of L. monocytogenes were found to be raw milk collector and milk silos. In the present study L. monocytogenes was isolated from milk and milk products processing plants which could cross-contaminate the processed products and may possess a potential threat to public health.     

Immunoaffinity pre-concentration combined with on-column visual detection as a tool for rapid aflatoxin M1 screening in milk

A non-instrumental rapid test was developed for the screening of aflatoxin M1 (AfM1) in milk at the 40 ng/L level. The method combines on one immunoaffinity gel layer, AfM1 pre-concentration and direct competitive immunoassay detection with visual evaluation. Aflatoxin B1-horse radish peroxidase (AfB1-HRP) and Sepharose 4B-immobilized anti-aflatoxin B1 monoclonal antibody with a 79% cross-reaction for AfM1 were used. The assay was performed in a standard column for solid phase extraction using a milk sample volume of 10 mL. Raw milk, pasteurized milk, milk powder, kefir and yogurt were analyzed with the developed test. It was shown that pasteurized milk could be analyzed without any sample preparation. The other types of milk were analyzed after centrifugation. For the assay procedure an aliquot of milk was flowed through the immunoaffinity gel layer in the tube by pushing the plunger of a syringe. Further, AfB1-HRP was applied and bound to free antibody binding sites. After addition of the chromogenic substrate the results were visually evaluated. Blue colour developed in case of negative milk samples while no colour appeared for positive samples. This method showed a false negative rate of only 2% and a high throughput (20–35 min for six samples).     

Prevalence and sources of cheese contamination with pathogens at farm and processing levels

Cheeses, even though characterized as safe for consumption, have been implicated in foodborne outbreaks associated with severe symptoms and high fatality rate. The foodborne pathogens in raw milk originate from the farm environment and direct excretion from animals infected udder, whereas in dairy plants the pathogens may enter via contaminated raw milk, colonize the dairy plant environment and consequently contaminate dairy products. Important source of contamination during the handling and processing might be the workers as well. The objective of this study was to review literature on the prevalence of pathogens in various types of cheese, raw milk and dairy environment, identify sources of contamination and present concisely prevention measures for farm and dairy plant.     

Inactivation of thermoduric aerobic sporeformers in milk by ultrasonication

Thermoduric sporeformers can survive milk pasteurization and cause spoilages of dairy products. In the present study, ultrasonication was evaluated as a non-thermal processing technique to inactivate the thermally resistant vegetative cells of spore forming Bacillus spp. During the challenge studies, vegetative cells of Bacillus coagulans (ATCC^® 12245), Anoxybacillus flavithermus (DSM 2641), Bacillus sporothermodurans (DSM 10599), Bacillus licheniformis (ATCC^®6634), and Geobacillus stearothermophilus (ATCC^® 15952) were studied for their survivability to batch pasteurization (63 °C/30 min) in skim and whole milk samples. Experiments were conducted to study the effect of ultrasonication alone or in combination with pasteurization on inactivation of vegetative cells of some thermoduric Bacillus spp. Effect of ultrasonication on milk pH, color, and alkaline phosphatase activity was also investigated. Vegetative cells of B. coagulans and A. flavithermus survived pasteurization treatment in both skim and whole milk samples. Ultrasonication at 80% amplitude for 10 min however, inactivated the vegetative cells of B. coagulans and A. flavithermus in skim milk by 4.53, and 4.26 logs, respectively. A combined treatment of pasteurization (63 °C/30 min) followed by ultrasonication completely eliminated approximately log 6 cfu/mL of these cells in skim milk. As visualized under the scanning electron microscope, ultrasonication physically disintegrated vegetative cells of sporeformers. Ultrasonication treatment caused significant reduction (P < 0.05) in brightness and greenness of milk; whereas, blueness (b*) of milk was increased. However, pH and alkaline phosphatase activity (P > 0.05) of treated skim milk were not affected.     

Farm to consumption risk assessment for Staphylococcus aureus and staphylococcal enterotoxins in fluid milk in China

The objective of this study was to conduct a risk assessment to determine the food poisoning risk from the consumption of milk in China that might be contaminated by Staphylococcus aureus. Data related to prevalence and concentration of S. aureus in fluid raw milk in China were collected from the literature and used to calculate the initial contamination levels. Two main consumption routes were considered and the results of the Monte Carlo simulation model indicated that the storage temperature in the processing plant and heat processing of milk in the home were the primary factors affecting the S. aureus concentration at the processing plant and the home before consumption, respectively. Other important factors were distribution of log (D)-value's for S. aureus, storage temperature and time on farm, temperature of the thermal treatment of milk, and treatment time at the dairy processing plant. To minimize the risk of milk-borne staphylococcal intoxication in China, the key step appears to be the control of storage conditions during the period after heat treatment and before consumption. The risk assessment model developed in present study provides valuable information for Chinese government and dairy processors to improve milk safety. It also could provide valuable recommendations for Chinese consumer education on safe handling of milk products.