Persistence of α-cypermethrin residues in milk of lactating donkeys (Equus asinus) using UHPLC-MS/MS

The aim of this study was to measure the persistence of residues of the pyrethroid insecticide α-cypermethrin (ACYP) in the milk of lactating donkeys following pour-on treatment. Milk was collected from animals (n = 7) before the treatment and at 12, 24, 36, 48, 60, 72 and 84 h post-treatment. The last sampling was taken 7 days post-treatment (168 h). Milk samples were analysed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The analytical method was validated following requirements of Commission Decision 2002/657/EC. All samples showed levels of ACYP below the maximum residue limit (MRL) of 20 μg kg^?1 established for bovine milk (Commission Regulation (EU) No. 37/2010). The results demonstrate that there is minimal partitioning of ACYP into milk in lactating donkeys from pour-on treatment.     

Role of β-lactoglobulin in the fouling of stainless steel surfaces by heated milk

Fouling occurred in sudden expansion (SE) test pieces in holding tubes downstream of a direct steam injection (DSI) heater. The fouling deposit contained high levels of protein, mainly β-lactoglobulin, and fat. Fouling during a run was monitored using heat flux sensors to determine the local fouling rate. The overall fouling rate was determined after a run from the weight of deposit and the overall time that fouling occurred during a run. Local and overall fouling rates were correlated. Fouling was high in SEs close to the DSI heater and diminished in SEs placed further downstream. The fouling rate was correlated with the level of native β-lactoglobulin remaining at the position of the SE. It is proposed that the fouling was due to a reactive intermediate of β-lactoglobulin that interacted with deposits on the SE surface. The considerable variation in fouling rates between runs suggests other environmental factors are also important.     

Assessment and validation of methods for the determination of γ-glutamyltransferase activity in sheep milk

The determination of enzymatic activity in sheep milk is still today a practically unexplored field of research. This study proposes and fully validates two analytical procedures (i.e. by means of UV–vis spectrophotometry and RP-HPLC methods) for the determination of γ-glutamyltransferase activity in sheep milk. Both methods are characterised by low detection and quantification limits, excellent linearity over a wide enzymatic activity interval, very good repeatability and reproducibility, and are bias-free. The RP-HPLC method provides better sensitivity and automation capability levels than that of UV–vis, and its use is hence suggested for screening purposes. These methods have been preliminarily tested with a number of real samples of whole sheep milk, obtaining an average γ-glutamyltransferase activity value of 2.93 ± 0.50 U ml⁻¹ and a range from 2.72 ± 0.10 U ml⁻¹ to 3.46 ± 0.11 U ml⁻¹.     

Effect of Sicilian pasture feeding management on content of α-tocopherol and β-carotene in cow milk

This study was performed to evaluate α-tocopherol and β-carotene contents of pasture milk under ordinary Sicilian farming conditions. Fourteen dairy farms were allocated into 2 balanced groups on the basis of cultivated (CULT) or spontaneous (SPO) pasture type feeding. Bulk milk per farm was collected 4 times from February through April at 3-wk intervals. Pasture botanical and diet composition, diet nutritional quality, milk yield and composition were estimated each time. Pasture intake levels were calculated based on feed analyses, hay and concentrate amounts fed, and milk yield and chemical composition. According to pasture intake, the farms were split into low pasture intake (LPI; <29.5% of dry matter) and high pasture intake (HPI; >29.5% of dry matter) groups. Milk samples per farm were analyzed for α-tocopherol and β-carotene contents by HPLC. The SPO group had higher levels of α-tocopherol and β-carotene in milk (0.7 and 0.3 mg/L, respectively) and milk fat (19.0 and 7.5 mg/kg fat, respectively) compared with the CULT group in milk (0.5 and 0.2 mg/L, respectively) and milk fat (14.6 and 4.9 mg/kg, respectively). High pasture intake compared with LPI increased α-tocopherol in milk fat (18.0 and 16.0 mg/kg of fat, respectively). However, only in the SPO (not in CULT), HPI compared with LPI increased milk α-tocopherol (0.8 vs. 0.6 mg/L, respectively), milk β-carotene (0.3 vs. 0.2 mg/L, respectively), and milk fat β-carotene (8.4 vs. 6.6 mg/kg, respectively). Results may be related to the different botanical composition of the respective pasture types and pasture intake. Spontaneous pasture compared with CULT contained a higher mass proportion of Asteraceae, Fabaceae, Cruciferae, Euphorbiaceae, and Malvaceae plants. Milk and milk fat α-tocopherol levels were higher on test-days (TD)-1, TD-2, and TD-4 compared with TD-3. For HPI farms, milk fat β-carotene content was higher on the first 2 TD compared with the last 2 TD. These differences could be related to plant biological stage. On Sicilian dairy farms, the highest milk α-tocopherol and β-carotene contents may be obtained feeding high levels of SPO pasture in the spring.     

Simultaneous HPLC–DAD quantification of vitamins A and E content in raw,pasteurized, and UHT cow’s milk and their changes during storage

An improved extraction and HPLC method for the simultaneous extraction and quantitation of retinol, α-tocopherol, α-tocotrienol, and β-carotene was developed to analyze commercial whole/semi-skim/skim samples of raw/pasteurized/UHT milk in transparent plastic/glass bottles and Tetra Brik? containers. The sample preparation method required prior saponification at 40 °C for 15 min followed by n-hexane extraction. An isocratic acetonitrile/methanol (65:35 v/v) mobile phase, C₁₈ analytical column, and UV detector were chosen for HPLC quantification. The liposoluble vitamin content in raw, pasteurized conventional/organic, and UHT milk ranged 0.055–5.540 (retinol), 0.135–1.410 (α-tocopherol), and 0.040–0.850 mg/L (β-carotene). No significant differences (p > 0.05) were observed on losses of retinol, α-tocopherol, and β-carotene content in UHT whole milk after 5 days at 4 °C in the dark. After 14 days at 4 °C in the dark, the contents of retinol, α-tocopherol, and β-carotene remained higher in milk with higher fat content and were higher in unopened containers. In UHT whole milk, samples containing 0.02 % NaN₃, retinol (33 %), and α-tocopherol (11 %) but not β-carotene (2 %) decreased significantly (p < 0.05).     

Nutritional utilization in Malagueña dairy goats differing in genotypes for the content of alphaS1-casein in milk

A study was carried out with 20 goats of the Malagueña breed, half with a high (HG) and half with a low (LG) genetic capability for α_S1-casein (AS1-CN) synthesis, to determine whether the 2 different genotypes (that cause differences in goat milk composition) are related to differences in nutritional feed utilization. Among the 10 HG goats, 7 had BB and 3 had AB genotypes for AS1-CN, whereas there were 7 EF and 3 FF genotypes in the 10 LG goats. The goats were fed diets differing in crude protein content (13.6 vs. 17.7% dry matter for diets 1 and 2, respectively). For each genotype group, a balance trial was conducted with each of the 2 diets in a 2-period balanced changeover designed with half the animals consuming diet 1 and the other half diet 2, determining individual feed intake and the utilization of N and energy in the diets. Greater voluntary feed intake on a metabolic body weight basis among the HG goats was identified as the first possible cause of their milk production. The HG goats also had a greater level of feed utilization, on a metabolic body weight basis, for N and energy intake. Greater ratios of N balance/ digestible N, milk protein N/digestible N, milk energy/ digestible energy, and milk energy/ME were found for HG goats compared with LG. These effects appear to be dependent on the level of protein in the diet, indicating interactive effects. The greater N and energy utilization of HG versus LG goats may explain the differences in milk composition between the 2 genotype groups.     

Extended-spectrum β-lactamase,shigatoxin and haemolysis capacity of O157 and non-O157 E. coli serotypes from producer-distributor bulk milk

We investigated for virulence genes (stx1, stx2 and hlyA), serotypes and extended-spectrum β-lactamases (ESBLs) producing capacity in O157 and non-O157 Escherichia coli isolated from producer-distributor bulk milk (PDBM). Fifteen different E. coli O-serogroups were observed from the isolates (n = 121). The prevalence of stx1 and stx2 genes among the E. coli isolates was 8.3% and 11.6%, respectively, while 5.8% harboured both stx1 and stx2. Four E. coli isolates (3.3%) had ESBLs producing capacity, resisted multiple cephalosporins and aztreonam, and carried stx genes. Cluster analysis using GTG₅ finger printing revealed a diversity of E. coli seropathotypes in PDBM that are known to be associated with human diarrhoeal diseases. These results highlight a potential risk posed on human health by the consumption of PDBM contaminated with pathogenic E. coli. A further quantitative risk assessment of the impact of pathogenic E. coli contamination in PDBM on human health is therefore recommended.     

Electrochemical nucleic acid-based sensors for detection of Escherichia coli and Shiga toxin-producing E. coli—Review of the recent developments

Escherichia coli are a group of bacteria that are a natural part of the intestinal flora of warm-blooded animals, including humans. Most E. coli are nonpathogenic and essential for the normal function of a healthy intestine. However, certain types, such as Shiga toxin-producing E. coli (STEC), which is a foodborne pathogen, can cause a life-threatening illness. The development of point-of-care devices for the rapid detection of E. coli is of significant interest with regard to ensuring food safety. The most suitable way to distinguish between generic E. coli and STEC is by using nucleic acid-based detection, focusing on the virulence factors. Electrochemical sensors based on nucleic acid recognition have attracted much attention in recent years for use in pathogenic bacteria detection. This review has summarized nucleic acid-based sensors for the detection of generic E. coli and STEC since 2015. First, the sequences of the genes used as recognition probes are discussed and compared to the most recent research regarding the specific detection of general E. coli and STEC. Subsequently, the collected literature regarding nucleic acid-based sensors is described and discussed. The traditional sensors were divided into four categories such as gold, indium tin oxide, carbon-based electrodes, and those using magnetic particles. Finally, we summarized the future trends in nucleic acid-based sensor development for E. coli and STEC including some examples of fully integrated devices.     

β-Galactosidase activity of commercial lactase samples in raw and pasteurized milk at refrigerated temperatures

Many consumers are unable to enjoy the benefits of milk due to lactose intolerance. Lactose-free milk is available but at about 2 times the cost of regular milk or greater, it may be difficult for consumers to afford. The high cost of lactose-free milk is due in part to the added cost of the lactose hydrolysis process. Hydrolysis at refrigerated temperatures, possibly in the bulk tank or package, could increase the flexibility of the process and potentially reduce the cost. A rapid β-galactosidase assay was used to determine the relative activity of commercially available lactase samples at different temperatures. Four enzymes exhibited low-temperature activity and were added to refrigerated raw and pasteurized milk at various concentrations and allowed to react for various lengths of time. The degree of lactose hydrolysis by each of the enzymes as a function of time and enzyme concentration was determined by HPLC. The 2 most active enzymes, as determined by the β-galactosidase assay, hydrolyzed over 98% of the lactose in 24 h at 2°C using the supplier's recommended dosage. The other 2 enzymes hydrolyzed over 95% of the lactose in 24 h at twice the supplier's recommended dosage at 2°C. Results were consistent in all milk types tested. The results show that it is feasible to hydrolyze lactose during refrigerated storage of milk using currently available enzymes.     

Effects of postpartum oral calcium supplementation on milk yield,milk composition,and reproduction in multiparous Jersey and Jersey × Holstein crossbreed cows

The objective of the present study was to evaluate the effects of postpartum oral calcium supplementation on milk yield, energy-corrected milk yield, milk fat concentration, milk protein concentration, and somatic cell count linear score across the first 3 monthly tests postpartum, peak milk yield, risk of pregnancy at first service, and hazard of pregnancy by 150 d in milk on 1,129 multiparous Jersey and Jersey × Holstein crossbreed cows from 2 commercial dairies. After calving, cows were systematically assigned to control (no oral calcium supplementation; n = 567) or oral calcium supplementation at 0 and 1 d in milk (oral Ca; 50 to 60 g of calcium as boluses; n = 562). Monthly test milk yield, composition, and somatic cell count information was obtained from the Dairy Herd Improvement Association. Herd records were used for reproductive data. Statistical analysis was conducted using generalized multiple linear, Poisson, and Cox's hazard regressions. Treatment effects were evaluated considering cow-level information available at parturition (parity, breed, previous lactation milk yield, previous lactation length, dry period length, gestation length, body condition, and locomotion score at calving, calving ease, and calf sex). In addition, for a subset of cows serum calcium concentration before treatment administration was evaluated (n = 756). Overall, oral calcium supplementation did not affect the evaluated productive and reproductive variables. However, effects conditional to previous lactation length and calving locomotion score were observed. Milk yield and energy-corrected milk yield across the first 3 monthly tests were 1.8 kg/d higher for supplemented cows with a previous lactation length within the fourth quartile, compared with control cows on the same quartile. Energy-corrected milk yield tended to be 1.1 kg/d lower for supplemented cows with a previous lactation length within the first quartile, compared with control counterparts. Peak milk yield tended to be 1.6 kg higher for supplemented cows with a calving locomotion score ≥2, compared with control cows with the same locomotion score. Treatment effects were not conditional to serum calcium concentration before treatment administration. Our results suggest that postpartum oral calcium supplementation effects are conditional to cow-level factors such as previous lactation length and calving locomotion score in multiparous Jersey and Jersey × Holstein crossbreed cows.     

Microbial inactivation of E. coli cells by a combined PEF–HPCD treatment in a continuous flow system

A laboratory scale continuous flow unit was set up and used to study the effect of pulsed electric fields (PEF) pre-treatments on microbial inactivation by high pressure carbon dioxide (HPCD) processing with the aim of investigating the synergistic effect of the combined treatment. McIlvaine buffer solution inoculated with Escherichia coli cells ATCC26 was pre-treated with PEF (25 °C) at different field strength (E = 6–12 kV/cm) and energy input (W_T = 10–40 J/mL) and then processed with HPCD (25 °C) at pressures of 8.0, 14.0 and 20.0 MPa and holding times of 4, 7 and 11 min.Results showed that treating the microbial suspension only with PEF, the inactivation level slightly increased with increasing the field strength and energy input with no significant effect of the pressure applied. The maximum inactivation level obtained was 2.25 Log-cycles at 12 kV/cm and 40 J/mL. When the bacterial cells were treated only with HPCD, the inactivation level was almost independent on the pressure of CO₂, and gradually increased with increasing the holding time up to a maximum value of 2.41 Log-cycles. The combination of PEF and HPCD treatment resulted in a marked increase of the microbial inactivation with increasing the field strength, energy input, holding time and operative pressure. A clear synergistic effect was evident when holding time was longer than 4 min, regardless the intensity of the PEF treatment applied.Industrial relevanceConsumers demand for fresh and natural products forces food manufacturers to investigate milder preservation processes and stimulate the current trend to use hurdle technologies. Pulsed electric field (PEF) and high pressure carbon dioxide (HPCD) are emerging non-thermal technologies which have antimicrobial capabilities when applied alone or in combination with other physicochemical hurdles. The present work demonstrated, for the first time, the feasibility of combined PEF-HCPD process based on the coupling of a PEF pretreatment stage to HPCD treatment in a continuous flow unit. The results support the view that the combined process is able to induce substantial microbial inactivation at mild treatment conditions and at room temperature suggesting the idea that this process could be applied to foods with thermosensitive components.     

Prediction of blood β-hydroxybutyrate content and occurrence of hyperketonemia in early-lactation,pasture-grazed dairy cows using milk infrared spectra

The objective of this study was to evaluate the ability of milk infrared spectra to predict blood β-hydroxybutyrate (BHB) concentration for use as a management tool for cow metabolic health on pasture-grazed dairy farms and for large-scale phenotyping for genetic evaluation purposes. The study involved 542 cows (Holstein-Friesian and Holstein-Friesian × Jersey crossbreds), from 2 farms located in the Waikato and Taranaki regions of New Zealand that operated under a seasonal-calving, pasture-based dairy system. Milk infrared spectra were collected once a week during the first 5 wk of lactation. A blood “prick” sample was taken from the ventral labial vein of each cow 3 times a week for the first 5 wk of lactation. The content of BHB in blood was measured immediately using a handheld device. After outlier elimination, 1,910 spectra records and corresponding BHB measures were used for prediction model development. Partial least square regression and partial least squares discriminant analysis were used to develop prediction models for quantitative determination of blood BHB content and for identifying cows with hyperketonemia (HYK). Both quantitative and discriminant predictions were developed using the phenotypes and infrared spectra from two-thirds of the cows (randomly assigned to the calibration set) and tested using the remaining one-third (validation set). A moderate accuracy was obtained for prediction of blood BHB. The coefficient of determination (R²) of the prediction model in calibration was 0.56, with a root mean squared error of prediction of 0.28 mmol/L and a ratio of performance to deviation, calculated as the ratio of the standard deviation of the partial least squares model calibration set to the standard error of prediction, of 1.50. In the validation set, the R² was 0.50, with root mean squared error of prediction values of 0.32 mmol/L, which resulted in a ratio of performance to deviation of 1.39. When the reference test for HYK was defined as blood concentration of BHB ≥1.2 mmol/L, discriminant models indicated that milk infrared spectra correctly classified 76% of the HYK-positive cows and 82% of the HYK-negative cows. The quantitative models were not able to provide accurate estimates, but they could differentiate between high and low BHB concentrations. Furthermore, the discriminant models allowed the classification of cows with reasonable accuracy. This study indicates that the prediction of blood BHB content or occurrence of HYK from milk spectra is possible with moderate accuracy in pasture-grazed cows and could be used during routine milk testing. Applicability of infrared spectroscopy is not likely suited for obtaining accurate BHB measurements at an individual cow level, but discriminant models might be used in the future as herd-level management tools for classification of cows that are at risk of HYK, whereas quantitative models might provide large-scale phenotypes to be used as an indicator trait for breeding cows with improved metabolic health.     

Validation of a rapid lateral flow method for the detection of cows’ milk in water buffalo,sheep or goat milk

For many years, the adulteration of milk from sheep, goats or water buffalos with cows’ milk has been a widespread practice due to the higher cost of milk from those other species. Because of this, great concern has been shown by many Protected Designation of Origin councils that have to assure the quality and genuineness of the cheese produced by their associates. Therefore, the whole production chain needs analytical tools that allow the control of potential adulteration. Rapid methods to be used in the field are scarce and have not been validated according to international guidelines. The aim of this work has been to validate a rapid test based on lateral flow immunochromatography to detect cows’ milk in milk from other species, including buffalo’s milk, according to AOAC guidelines. No false-positive result was found after analysing 146 known negative samples from individual animals. The lowest level of adulteration with a Probability of Detection (POD) of 1.00 (confidence interval between 0.94 and 1.00) was found at 0.5% of cows’ milk. This level is below the current EU allowed level of cows’ milk, set at 1%. Variations in the time of assay, volume of the analysis buffer and different batches of the test were evaluated to detect any effect on the false-positive rate or on the limit of detection of the test. The effects of compositional factors (such as high level of fat, protein and somatic cell counts) were also evaluated. The new rapid test to detect cows’ milk in milk from other species is shown to be an adequate tool to control milk quality in routine analysis. This kind of test is very easy to use and it can be performed by untrained staff during milk collection at the farm or upon arrival at dairies.     

Effect of κ-casein B relative content in bulk milk κ-casein on Montasio, Asiago, and Caciotta cheese yield using milk of similar protein composition

The aim of this study was to investigate the effect exerted by the relative content of κ-casein (κ-CN) B in bulk milk κ-CN on coagulation properties and cheese yield of 3 Italian cheese varieties (Montasio, Asiago, and Caciotta). Twenty-four cheese-making experiments were carried out in 2 industrial and 1 small-scale dairy plant. Detailed protein composition of bulk milk of 380 herds providing milk to these dairies was analyzed by reversed-phase HPLC. To obtain 2 experimental milks differing in the relative content of κ-CN B in κ-CN, herds were selected on the basis of bulk milk protein composition and relative content of κ-CN genetic variants. Milk was collected and processed separately for the 2 groups of selected herds. A difference of 20% in the relative content of κ-CN B in κ-CN was obtained for the 2 experimental milks for Montasio and a difference of 15% for Asiago and Caciotta. The 2 experimental milks were of similar protein and CN content, casein number, pH, CN composition, and β-CN genetic composition. For each cheese-making trial, amounts of milk, ranging from 2,000 to 6,000 kg, were manufactured. Each vat contained milk collected at least from 4 dairy herds. Cheese yield after brining and at the end of the aging was recorded. Milk with a greater proportion of κ-CN B in κ-CN (HIGHB) exhibited similar coagulation properties and greater cheese yield compared with milk with a lower proportion of κ-CN B in κ-CN (LOWB). The increased cheese yield observed for HIGHB when manufacturing Montasio cheese was ascribed to a greater fat content compared with LOWB. The probability of HIGHB giving a cheese yield 5% greater than that of LOWB ranged from 51 to 67% for Montasio cheese, but was less than 21% for Asiago and Caciotta cheeses. Variation in relative content of κ-CN B in κ-CN content did not relevantly affect industrial cheese yield when milks of similar CN composition were processed. An indirect effect due to the increased κ-CN content of κ-CN B milk is thought to explain the favorable effects of κ-CN B on cheese yield reported in the literature.     

Size of native and heated casein micelles,content of protein and minerals in milk from Norwegian Red Cattle—effect of milk protein polymorphism and different feeding regimes

Milk samples of 59 cows of the Norwegian Red Cattle breed receiving three different supplementary concentrates, were analysed for genotypes of caseins and whey proteins, the content of different milk salts (Ca²⁺, Ca, Mg and citrate), the content of total protein, casein and whey protein and the mean micellar size of native and heated casein micelles. The genotype of α_s1-casein had a statistically significant effect on the content of protein and casein, and the content of whey protein and the casein number were significantly influenced by different feeding regimes, and the content of citrate. The mean size of native and heated casein micelles was significantly influenced by the feeding regimes, genotype of α_s1-casein (native mean size only) and κ-casein, pH and the content of casein, whey protein and casein number. The heat-induced changes in mean micellar size were significantly affected by the calcium ion activity which accounted for approximately 40% of the total variation.     

Determination and validation of D-values for Listeria monocytogenes and Shiga toxin–producing Escherichia coli in cheese milk

Certain cheeses can be legally produced in the United States using raw milk, but they must be aged for at least 60 d to reduce pathogen risks. However, some varieties, even when aged for 60 d, have been shown to support growth of Listeria monocytogenes or survival of Shiga toxin–producing Escherichia coli (STEC). Thermization, as a subpasteurization heat treatment, has been proposed as a control to reduce the risk of pathogens in raw cheese milk while retaining some quality attributes in the cheese. However, the temperature and time combinations needed to enhance safety have not been well characterized. The objective of this research was to determine and validate decimal reduction values (D-values) for L. monocytogenes and STEC at thermization temperatures 65.6, 62.8, and 60.0°C; a D-value at 57.2°C was also determined for L. monocytogenes only. Nonhomogenized, pasteurized whole-milk samples (1 mL) were inoculated with 8-log cfu/mL L. monocytogenes or STEC (5- or 7-strain mixtures, respectively), vacuum-sealed in moisture-impermeable pouches, and heated via water bath submersion. Duplicate samples were removed at appropriate intervals and immediately cooled in an ice bath. Surviving bacteria were enumerated on modified Oxford or sorbitol MacConkey overlaid with tryptic soy agar to aid in the recovery of heat-injured cells. Duplicate trials were conducted, and survival data were used to calculate thermal inactivation rates. D_65.6°C-, D_62.8°C-, and D_60.0°C-values of 17.1 and 7.2, 33.8 and 16.9, and 146.6 and 60.0 s were found for L. monocytogenes and STEC, respectively, and a D_57.2°C-value of 909.1 s was determined for L. monocytogenes. Triplicate validation trials were conducted for each test temperature using 100 mL of milk inoculated with 3 to 4 log cfu/mL of each pathogen cocktail, A 3-log reduction of each pathogen was achieved faster in larger volumes than what was predicted by D-values (D-values were fail-safe). Data were additionally compared with published results from 21 scientific studies investigating L. monocytogenes and STEC in whole milk heated to thermization temperatures (55.0–71.7°C). These data can be used to give producers of artisanal raw-milk cheese flexibility in designing thermal processes to reduce L. monocytogenes and STEC populations to levels that are not infectious to consumers.     

Total antioxidant activity and trace elements in human milk: the first 4 months of breast-feeding

The content of many nutrients in breast milk are dependent on the nutritional status of the lactating woman. This is particularly true for fat and water-soluble vitamins, some of which have antioxidant properties. The aim of the study entertained herein was to evaluate the changes in total antioxidant status of human milk during the first 4 months of lactation, and to correlate such changes with the contents in specific antioxidant oligoelements (Cu, Zn, Mn and Se). Milk samples were collected from (31) lactating women recruited at the Service of Obstetrics of the Hospital de São João in Porto, after 1, 4, 8, 12 and 16 weeks after birth. The total antioxidant status (TAS) of human milk was measured by the Randox^® commercial kit and trace metals by ICP-MS (inductively coupled plasma-mass spectrometry). The results found for TAS and oligoelements under study show a decrease in the concentration of these parameters from 7 days to 4 months of breast-feeding and significant correlations (p < 0.05) were found between TAS and Cu, Zn and Se (not Mn). The decreases of Cu, Zn and Se were also correlated, but not proportional between them, suggesting diverse excretion mechanisms for all. Between primipara and multipara women, a significant difference was found only for Cu and Zn concentrations at 7 days of lactation, but not for the other metals or TAS. With respect to the mother’s age, no correlation was found, either for trace metal concentrations or TAS.     

Validation of the βeta-s.t.a.r. 1 + 1 for rapid screening of residues of β-lactam antibiotics in milk

The 2-min protocol (1 + 1) for the βeta-s.t.a.r. (manufactured by Neogen Corporation, Lansing, MI, USA) was validated at the Technology and Food Science Unit of the Institute for Agricultural and Fisheries Research according to Commission Decision 2002/657/EC. The test was very selective for the group of β-lactam compounds: the only interference found was by clavulanic acid at 2500 µg kg^?1 and above. The modified protocol (βeta-s.t.a.r. 1 + 1) detected all β-lactams with a maximum residue limit (MRL) in milk, but not all these compounds were detected at their respective MRL. The detection of cefalexin (detection capability = 6000 µg kg^?1; MRL = 100 µg kg^?1) and penethamate (detection capability = 80 µg kg^?1; MRL = 4 µg kg^?1) was especially poor, and also ceftiofur was only detected from 500 µg kg^?1 (MRL = 100 µg kg^?1). The repeatability of the reader and of the test was very good. The test was very robust: test results were not significantly influenced by small changes in the test protocol, by the milk composition or by the type of milk. The test was also suitable to test the milk of animal species other than cow. Favourable results were obtained in testing monitoring samples, in two national ring trials, and in an international proficiency test. The βeta-s.t.a.r. 1 + 1 is a very fast, simple, and reliable test that could be used at the farm level to prevent tanker milk contamination by β-lactams.     

Recovery of heat-stressed E. coli O157:H7 from ground beef and survival of E. coli O157:H7 in refrigerated and frozen ground beef and in fermented sausage kept at 7°C and 22°C

A study was undertaken to obtain information on survival of Escherichia coli O157:H7 in ground beef subjected to heat treatment, refrigeration and freezing and on survival of E. coli O157:H7 in fermented sausage kept at 7°C and 22°C. For the challenge test, a mixture of E. coli O157:H7 strains (EH 321, EH 385, EH 302) was used and enumeration was performed on an isolation medium suitable for recovery of stressed organisms: modified Levine's eosin methylene blue agar (mEMB). Heat resistance of E. coli O157:H7 decreased after pre-incubation at a reduced temperature.Escherichia coli O157:H7 was more susceptible to heat inactivation after storage at 7°C and die-off was even more enhanced if cultures were frozen prior to heat inactivation. The enhanced reduction of the pathogen at 56°C after prior storage under refrigeration was confirmed in a test with inoculated ground beef.Escherichia coli O157:H7 was able to survive in ground beef at 7°C for 11 days and at −18°C for 35 days showing maximal one log reduction during the storage period. Thus, ground beef contaminated with E. coli O157:H7 will remain a hazard even if the ground beef is held at low or freezing temperatures. At both 7°C and 22°C, a gradual reduction of E. coli O157:H7 was noticed in fermented sausage over the 35 days storage period resulting in a 2 log decrease of the high inoculum (10⁶cfu 25 g⁻¹). For the low inoculum (10³cfu 25 g⁻¹) a 2·5 log reduction was obtained in 7 and 28 days storage at respectively 22 and 7°C. Application of good hygienic practices and implementation of HACCP in the beef industry are important tools in the control of E. coli O157:H7.