A survey of microbial levels for incoming raw beef,environmental sources,and ground beef in a red meat processing plant

A microbial survey was performed for a midwestern red meat processing plant that produces retail cuts and ground beef. Samples were obtained from incoming ingredients, beef during processing, finished product, food contact and environmental surfaces, and the air. Aerobic plate count (APC), coliform count (CC), andEscherichia colicount (ECC) were determined for each sample. Product samples (25 g) were taken from beef carcasses, boxed beef, and ground beef. Swab samples (10 cm²) were obtained from food surfaces, food contact surfaces, floors, and walls. All samples were plated on aerobic plate count Petrifilm (for APC) andE. coliPetrifilm (for CC and ECC). Average log₁₀APC for product samples ranged from 3 cfu g⁻¹for retail cuts to nearly 7 cfu g⁻¹for boxed beef and the brisket and flank areas of beef carcasses. Average log₈APC for ground beef samples was 4.6 cfu g⁻¹. Average log₁₀CC for product samples ranged from 1.4–2.3 cfu g⁻¹. Highest CC was usually obtained from the brisket area of the beef carcass. Average log₁₀ECC ranged from <1–2 cfu g⁻¹and ECC was usually highest in finished ground beef. Average surface counts for log₁₀APC ranged from <1 cfu cm⁻²on sanitized processing equipment to 5 cfu cm⁻²on processing floors. Coliforms andE. coliwere rarely recovered from food contact surfaces or from food surfaces. Airborne log₁₀APC was generally low (0.6 cfu m⁻³), except for the carcass receiving area where counts were 2.4 cfu m⁻³. The most important factor contributing to source and level of microbial contamination for ground beef and retail cuts was from incoming raw materials obtained from different suppliers of beef. Microbial testing for beef products and the environment is an important tool for identifying and monitoring potential hazards as part of HACCP and GMP program development.     

生乳、巴氏乳与酸败乳的电化学识别研究

阐述了一种以三电极体系为基础,研究溶液体系特性的高性能传感器阵列的设计原理和方法。它涵括了循环伏安法扫描、差分脉冲伏安法扫描、常规脉冲伏安法扫描、多电位阶跃扫描等多种功能等,能够对溶液体系施加多种方式的激发信号,得到多种相应特性,从而实现对溶液的全面分析。对新鲜生乳、熟乳（巴氏乳）、酸败乳溶液进行循环伏安法、脉冲伏安法、多电位阶跃等扫描方法检测,并进行主成分分析表征。研究结果表明,传感器阵列对生乳、熟乳（巴氏乳）、酸败乳有明显的辨别能力,不同的工作电极通过不同的检测方法对乳样有不同的区分力。     

The survival of foot-and-mouth disease virus in raw and pasteurized milk and milk products

The Foot-and-Mouth Disease virus (FMDV) is not a public health threat, but it is highly contagious to cloven-footed animals. The virus is shed into milk up to 33 h before there are apparent signs of the disease in dairy cows, and, in extreme cases, signs of disease may not appear for up to 14 d. During this time, raw milk can serve as a vector for spread of the disease both at the farm and during transport to the processing plant by milk tanker. Raw milk and milk products fed to animals have the potential to cause infection, but the potential for pasteurized milk products to cause infection is largely unknown. Current minimum pasteurization standards may not be adequate to eliminate FMDV in milk completely. The purpose of this paper is to assess the literature on the thermal resistance of FMDV in milk and milk products, to identify the risks associated with ingestion of pasteurized products by animals, and to lay a strategy to prevent the spread of FMDV from contaminated milk.     

Proteolysis in goat cheese made from raw,pasteurized or pressure-treated milk

Primary and secondary proteolysis of goat cheese made from raw (RA), pasteurized (PA; 72 °C, 15 s) and pressure-treated milk (PR; 500 MPa, 15 min, 20 °C) were examined by capillary electrophoresis, nitrogen fractionation and HPLC peptide profiles. PA milk cheese showed a more important hydrolysis (P<0.05) of α_s1-casein than RA milk cheese at the first stages of ripening (15 days), while PR milk cheese had a level between those seen in PA and RA milk cheeses. Degradation of β-casein was more important (P<0.05) in PA and PR than in RA milk cheeses at 15 days of ripening. However, from thereon β-casein in PR and RA milk cheeses was hydrolyzed at essentially similar rates, but at lower rates (P<0.05) than in PA milk cheeses. Pressure treatment could induce proteolysis of β-casein in a way, which is different from that produced by heat treatment. There was an increase in 4.6-soluble nitrogen (WSN) and in trichloroacetic acid (TCASN) throughout ripening in cheeses, but higher contents (P<0.05) in PA and PR milk cheeses at the end of ripening were observed. PR milk cheeses contained considerably higher content (P<0.05) of free amino acids than RA or PA milk cheeses. In general, heat and pressure treatments had no significant effect on the levels of hydrophobic and hydrophilic peptides.     

Influence of refrigeration and carbon dioxide addition to raw milk on microbial levels, free monosaccharides and myo-inositol content of raw and pasteurized milk

The influence of CO₂ treatment on free monosaccharides and myo-inositol in raw and pasteurized milk during cold storage was studied. Pasteurization did not cause significant changes in the monosaccharide fraction. No variations in the level of galactose and myo-inositol in untreated and CO₂-treated samples were observed during cold storage. The content of glucose decreased considerably during cold storage due to bacterial growth in pasteurized milk. During cold storage of pasteurized milk no changes in N-acetylgalactosamine were observed, whereas N-acetylglucosamine decreased considerably after 15 days. No differences between untreated and CO₂-treated milks were found. A substantial decrease in N-acetylglucosamine and a gradual increase in N-acetylgalactosamine were observed in raw milk during cold storage. The former was attributed to consumption of this hexosamine by microorganisms and the latter was probably due to microbial glycosidic enzymes. The addition of CO₂ to raw milk proved to be a useful treatment for milk preservation without modifying the free monosaccharide fraction. Received: 4 October 1999     

Incidence, source and some properties of psychrotrophic Bacillus spp found in raw and pasteurized milk

Spores of psychrotrophic Bacillus spp were isolated from 58% of farm bulk tank milks and about 69% of pasteurized milks. Counts of Bacillus spp in about 10% of raw milk samples reached 1 × 10⁵ cfu/ml and above within seven days at 6°C. Psychrotrophic spore counts in pasteurized milks ranged from <0.5 to 170 spores/litre with an average of about 17/1. There was little correlation between the total bacterial count of the raw milk and presence of psychrotrophic Bacillus spores. There was some evidence that the bulk tank itself may be a source of contamination. The spores in pasteurized milk probably were not the result of postpasteurization contamination. The optimum germination temperature for psychrotrophic Bacillus spores was lower than that for spores of mesophilic strains. About 50% of the psychrotrophic Bacillus strains isolated from milk were capable of growth at 2°C.     

北京市售巴氏杀菌乳的消费调查及实验验证研究

目的了解北京地区消费者巴氏杀菌乳的消费习惯,评估储存温度和时间对巴氏杀菌乳中微生物数量的影响,为消费者正确储存巴氏杀菌乳提供依据。方法北京10个行政区各选择1个大型超市进行问卷调查,调查内容包括巴氏杀菌乳的饮用频率、储存温度和时间等。依据调查结果模拟消费者储存条件,结合微生物生长规律,采用正交试验方法探究温度和时间对巴氏杀菌乳中菌落总数及金黄色葡萄球菌(Staphylococcus aureus)数量的影响。结果调查问卷结果表明,18岁以下、18～54岁和55岁以上的消费者中,每天饮用巴氏杀菌乳的比例最高分别为15.4%、49.0%和75.9%;所调查消费者中,将巴氏杀菌乳储存在2～6℃、室温、-20℃的比例分别为75.0%、14.6%、5.5%;模拟实验结果表明储存温度对巴氏杀菌乳中微生物影响更大, 37℃储存48h后,菌落总数和S.aureus数量达到1.26×10~5CFU/mL和1.20×10~4 CFU/mL。结论北京市饮用巴氏杀菌乳的消费者主要集中在中老年人群;部分消费者(24.2%)不明确巴氏杀菌乳的正确储存温度;不当的储存温度导致巴氏杀菌乳中的菌落总数和金黄色葡萄球菌的数量增加。     

The effect of extended low-temperature storage of raw milk on the quality of pasteurized and UHT milk

The effect of storage of raw milk at 2 and 6°C on the quality of pasteurized and UHT milks produced from them has been investigated. There was no difference in shelf-lives of pasteurized milks produced from raw milks which had no obvious physical defects, odours and taints after storage at 2 and 6°C. This was true for pasteurized milks in the presence and absence of post-heat-treatment contamination. However, pasteurized milks of good quality could be produced from more than 80% of raw milk samples which had been stored for up to 5 days at 2°C, but this was only possible with raw milks which had been stored at 6°C for 2 days.Failure rates of experimentally-produced UHT milks were much higher in products manufactured from raw milks stored at 6°C for 4 days than those produced from raw milks stored at 2°C for 4 days. The main cause of failure was due to thermostable bacterial protease associated with high levels of bacterial growth in the raw milks. Other causes of failure included spore-forming bacteria, which may have survived UHT processing, and other organisms probably introduced as contaminants on filling.     

Microbiological quality of retail cheeses made from raw, thermized or pasteurized milk in the UK

Two studies of retail fresh, ripened and semi-hard cheeses made from raw, thermized or pasteurized milk were undertaken in the UK during 2004 and 2005 to determine the microbiological quality of these products. Using microbiological criteria in European Commission Recommendations 2004/24/EC and 2005/175/EC, 2% of both raw, thermized (37/1819 samples) and pasteurized (51/2618 samples) milk cheeses were of unsatisfactory quality. Raw or thermized milk cheeses were of unsatisfactory quality due to levels of Staphylococcus aureus at 10(4)cfu g(-1), Escherichia coli at 10(5)cfu g(-1), and/or Listeria monocytogenes at 10(2)cfu g(-1), whereas pasteurized milk cheeses were of unsatisfactory quality due to S. aureus at 10(3)cfu g(-1) and/or E. coli at 10(3)cfu g(-1). Salmonella was not detected in any samples. Cheeses were of unsatisfactory quality more frequently when sampled from premises rated as having little or no confidence in management and control systems, and stored/displayed at above 8 degrees C. Raw or thermized milk cheeses were also more likely to be of unsatisfactory quality when they were unripened types, and pasteurized milk cheeses when they were: semi-hard types; from specialist cheese shops or delicatessens; cut to order. These results emphasize the need for applying and maintaining good hygiene practices throughout the food chain to prevent contamination and/or bacterial growth. Labelling of cheeses with clear information on whether the cheese was prepared from raw milk also requires improvement.     

Enterococcus and Lactobacillus contamination of raw milk in a farm dairy environment

Enterococci and lactobacilli are ubiquitously found in the intestinal microflora of humans and animals. The aim of the present study was to determine the importance of bovine faeces as a source of these organisms in raw milk. One hundred and fifty six putative enterococci and 362 lactobacilli were isolated from bovine faeces (n=26), cows' teats, raw milk, the milking machine and the milking environment on one farm. The clonal relationships of each group were investigated using Pulsed-Field Gel Electrophoresis and representatives of the different clusters were identified by repetitive DNA element (rep)-PCR fingerprinting, protein profiling, phenylalanyl-tRNA synthase (pheS) sequence analysis or 16S rDNA gene sequencing. Lactobacilli were present at approximately 3 orders of magnitude greater than enterococci in the bovine faeces. The majority of the bovine faecal enterococcal isolates were identified as Aerococcus viridans. Seven teat isolates belonged to a potential novel Aerococcus sp. and one bovine faecal isolate to a potential second novel Aerococcus sp. The lactobacilli present in the bovine faeces were predominantly Lactobacillus mucosae and Lactobacillus brevis, with small numbers of Lactobacillus plantarum. Only one Enterococcus (a strain of E. casseliflavus) out of 76 and one Lactobacillus (a strain of L. parabuchneri/kefir) out of 247 of the bovine faecal isolates was found in the milk. The major source of these bacteria in the milk was the milking equipment.     

Microbiological changes throughout ripening of goat cheese made from raw,pasteurized and high-pressure-treated milk

The bacteriological quality during ripening of raw (RA), pasteurized (PA; 72°C, 15 s) and pressure-treated (PR; 500 MPa, 20°C, 15 min) goat milk assessed by enumeration of total bacteria, psychrotrophic bacteria, Enterobacteriaceae, lactobacilli, enterococci, Micrococcaceae and lactococci was evaluated. The high pressure treatment applied was as efficient as pasteurization in reducing the bacterial population of milk. Experimental cheeses were made from RA, PA and PR milks to study the microbial population during ripening. Lactobacilli and lactococci were the predominant microbiota present during ripening in all the cheeses. There were no differences in numbers of starter bacteria during ripening. However, lactobacilli counts for RA milk cheese were significantly higher than for PA and PR cheeses in all the ripening stages studied. Micrococcaceae and enterococci remained at a secondary level, and no differences were observed between cheeses at the end of ripening. On the other hand, the number of Enterobacteriaceae decreased during ripening, but faster in PR milk cheese than in PA and RA milk cheeses. The results of this study suggest that goat cheese made from PR milk had similar microbiological characteristics to PA milk cheeses.     

一起由巴氏杀菌乳污染引起的济南市多家幼儿园食源性疾病暴发事件的流行病学分析

目的 对一起涉及济南市多家幼儿园食源性疾病暴发事件的发生原因和可疑危险因素进行分析,为加强学校食源性疾病防控提供依据.方法 采用现场流行病学的方法,对病例进行调查,运用描述性流行病学方法、队列研究方法对暴发事件数据和各因素进行分析.结果 事件涉及济南市4个区11家幼儿园195名儿童,罹患率17.06％,年龄范围为3～6...     

High-pressure homogenization of raw and pasteurized milk modifies the yield, composition, and texture of queso fresco cheese

High-pressure homogenization (HPH) of milk was studied as an alternative processing operation in the manufacturing of queso fresco cheese. Raw and pasteurized (65°C for 30 min) milks were subjected to HPH at 0, 100, 200, and 300 MPa and then used to manufacture queso fresco. The cheeses were evaluated for yield, moisture content, titratable acidity, nitrogen content, whey protein content, yield force, yield strain, and tactile texture by instrumental or trained panel analyses. The combination of HPH and thermal processing of milk resulted in cheeses with increased yield and moisture content. The net amount of protein transferred to the cheese per kilogram of milk remained constant for all treatments except raw milk processed at 300 MPa. The highest cheese yield, moisture content, and crumbliness were obtained for thermally processed milk subjected to HPH at 300 MPa. The principal component analysis of all measured variables showed that the variables yield, moisture content, and crumbliness were strongly correlated to each other and negatively correlated to the variables yield strain, protein content (wet basis), and sensory cohesiveness. It is suggested that the combination of thermal processing and HPH promotes thermally induced denaturation of whey protein, together with homogenization-induced dissociation of casein micelles. The combined effect results in queso fresco containing a thin casein-whey matrix that is able to better retain sweet whey. These results indicate that HPH has a strong potential for the manufacture of queso fresco with excellent yield and textural properties.     

Results from raw milk microbiological tests do not predict the shelf-life performance of commercially pasteurized fluid milk

Analytical tools that accurately predict the performance of raw milk following its manufacture into commercial food products are of economic interest to the dairy industry. To evaluate the ability of currently applied raw milk microbiological tests to predict the quality of commercially pasteurized fluid milk products, samples of raw milk and 2% fat pasteurized milk were obtained from 4 New York State fluid milk processors for a 1-yr period. Raw milk samples were examined using a variety of tests commonly applied to raw milk, including somatic cell count, standard plate count, psychrotrophic bacteria count, ropy milk test, coliform count, preliminary incubation count, laboratory pasteurization count, and spore pasteurization count. Differential and selective media were used to identify groups of bacteria present in raw milk. Pasteurized milk samples were held at 6°C for 21 d and evaluated for standard plate count, coliform count, and sensory quality throughout shelf-life. Bacterial isolates from select raw and pasteurized milk tests were identified using 16S ribosomal DNA sequencing. Linear regression analysis of raw milk test results versus results reflecting pasteurized milk quality consistently showed low R² values (<0.45); the majority of R² values were <0.25, indicating small relationship between the results from the raw milk tests and results from tests used to evaluate pasteurized milk quality. Our findings suggest the need for new raw milk tests that measure the specific biological barriers that limit shelf-life and quality of fluid milk products.     

Effect of alkalinization and ultra-high-pressure homogenization on casein micelles in raw and pasteurized skim milk

Mechanical and physicochemical treatments of milk induce structural modifications of the casein (CN) micelles, affecting their techno-functional properties in dairy processing. Here, we studied the effect of alkalinization and ultra-high-pressure homogenization (UHPH) on CN micelles in raw skim milk (rSM) and pasteurized skim milk (pSM). The pH of both skim milks (approximately 6.7) was adjusted to 8.5 and 10.5 before UHPH at 100, 200, and 300 MPa. The structural changes of the CN micelles during the treatments were assessed using laser diffraction, transmission electron microscopy, and turbidity measurements. Finally, ultracentrifugation (70,000 × g for 1 h at 20°C) was carried out to evaluate the protein's distribution between the supernatant (serum phase) and the pellet (colloidal phase) by gel electrophoresis and protein concentration measurement. Alkalinization of both skim milks induced a significant reduction in turbidity, whereas an increase of the average particle size was observed, the effect being more severe in pSM than rSM. At alkaline pH, more proteins were recovered in the serum phase, which suggested that the CN underwent major rearrangements into nonsedimentable CN forms of various sizes, as confirmed by transmission electron microscopy. The amount of CN found in the serum phase at pH 8.5 also increased with the UHPH pressure. Although UHPH did not influence the average CN micelle size at pH 6.7 and 8.5, a pressure-dependent decrease was observed at pH 10.5 for both skim milks. The structural changes of the CN micelles observed in this study throughout the combination of alkalinization and UHPH could be of interest for developing new dairy ingredients with improved functionality.     

应用PCR-DGGE对巴氏消毒乳中腐败细菌的污染溯源研究

运用PCR-DGGE技术分析了巴氏杀菌乳从原料乳到杀菌、灌装这两个加工关键控制点的微生物动态变化和差异性,容易发生污染的环节是挤乳环节、杀菌后的加工管道和包装环节。原料乳中易携带的细菌是乳酸链球菌（Lactococcus lactis subsp.）和乳酸杆菌（Lactobacillus sp.）;挤乳环节中易受无乳链球菌（Streptococcus agalactiae）污染;杀菌后的加工管道易受热杀环丝菌（Brochothrix thermosphacta）、钻黄肠球菌（Enterococcus casseliflavus）、瑞士乳杆菌（Lactobacillus helveticus）和2株非培养的假单胞菌属（Uncultured Pseudomonas sp.）污染;肉杆菌属（Carnobacterium sp.）和产乳酸菌素的肉杆菌（Carnobacterium maltaromaticum）则在挤乳环节、杀菌后的加工管道或包装环节都可能被污染。      

Occurrence of aflatoxin M1 in raw, pasteurized and UHT milk commercialized in Esfahan and Shahr-e Kord, Iran

Between September 2006 and September 2007, 236 samples of raw (n = 140), pasteurized (n = 48) and UHT (n = 48) milk were collected from supermarkets and from bulk milk tanks of eight dairy plants in the cities of Esfahan and Shahr-e Kord, Iran. All samples were analyzed for aflatoxin M₁ (AFM₁) contamination by ELISA and 213 (90.3%) were positive with mean concentrations 65 ng.l⁻¹. These concentrations are lower than the standards of Codex Alimentarius and FDA (500 ng.l⁻¹), but 119 samples (55.9%) had higher concentrations than the maximum tolerance accepted by some European countries (50 ng.l⁻¹). Mean concentrations of AFM₁ in raw, pasteurized and UHT milk were 68, 56, and 65 ng.l⁻¹, respectively. Mean concentrations of AFM₁ in autumn and winter samples were significantly higher (P < 0.05) than those of spring and summer but differences between AFM₁ concentrations of spring and summer samples were not significantly different. Concentrations of AFM₁ in milk from Shahr-e Kord were significantly lower (P ≤ 0.05) than those from Esfahan.     

Effect of ultrasonication on microbiological,chemical and sensory properties of raw,thermized and pasteurized milk

The combined effect of ultrasonication and heat treatment on microbiological, chemical and sensory properties of raw, thermized and pasteurized milk was studied. Microbiological parameters monitored included total viable counts and psychrotrophs, chemical parameters included thiobarbituric acid and volatiles determination and sensory evaluation included the monitoring of odour and taste as a function of storage time. Results showed a 1–2.1 log cfu mL^?1 reduction in total viable counts and psychrotrophs for raw, thermized and pasteurized milk up to 6 days of storage. For raw and pasteurized milk ultrasonication resulted in a taste score equal to or lower than that of untreated milk. However, thermized milk, ultrasonicated for 2 min gave a higher taste score than its untreated counter part on day 4 of storage. With regard to lipid oxidation, malondialdehyde ranged between 1.20 and 1.95 mg kg^?1. Finally, volatile compounds identified in all samples were mainly products of lipid oxidation that increased in concentration with sonication and storage time.     

Microbiological and biochemical characteristics of Canestrato Pugliese cheese made from raw milk, pasteurized milk or by heating the curd in hot whey

Canestrato Pugliese cheeses were produced from raw ewes' milk (R and R(II) cheeses), pasteurized ewes' milk (P cheese) and by heating the curd in hot whey according to a traditional protocol (T cheese). R(II) differed from R cheese mainly by having been produced from raw milk with a higher number of somatic cells, 950.000 vs. 750.000 ml(-1), respectively. Compared to P and T cheeses, R and R(II) cheeses had a higher concentration (one or two orders of magnitude) of cheese-related bacteria such as adventitious mesophilic lactobacilli, enterococci and staphylococci. At the end of ripening, all cheeses contained less than 1.0 log cfu g(-1) of total and fecal coliforms, and Escherichia coli and Staphylococcus aureus were not detected. As shown by phenotypic identification and RAPD-PCR, R cheese contained the largest number of mesophilic lactobacilli species and the greatest diversity of strains within the Lactobacillus plantarum species. Primary proteolysis did not differ appreciably among the cheeses. On the contrary, both urea-PAGE and the RP-HPLC analyses of the water-soluble N fractions showed the more complex profiles in cheeses produced by raw milks. R and R(II) cheeses had the highest values of water-soluble N/total N (ca. 30%) and the highest concentration of total free amino acids (ca. 40 mg g(-1) which approached or exceeded those reported for Italian cheeses with very high level of proteolysis during ripening. The main differences between R-R(II) and P-T cheeses were the concentrations of aspartic acid, proline, alanine, isoleucine, histidine and lysine. The water-soluble extracts of R and R(II) cheeses contained levels of amino-, imino- and di-peptidase activities, which were about twice those found in P and T cheeses. Cheeses differed slightly in the concentration of total free fatty acids that ranged between 1673 and 1651 mg kg(-1) in R and R(II) cheeses, and 1397 and 1334 mg kg(-1) in P and T cheeses. Butyric, caproic, capric, palmitic, oleic and linoleic acids were found at the highest concentrations.