Cholesterol concentrations in goat milk, goat milk cheeses, ewe’s milk, ewes milk cheeses, dairy bioproducts, and concentrations of cholesterol, stigmasterol and sitosterol in butter, butter with added vegetable fats and margarines were evaluated by RP HPLC method. Parallel analyses by capillary GC were performed. Prior to the final chromatographic analyses the saponification step was used, followed by the extraction of the unsaponificable residue into <I>n</I>-hexane. Parameters of RP HPLC method were compared with parameters of GC determination. The detection limits (LOD) determinated on the bases of blank samples analysis were 5.2 mg/kg for cholesterol, 4.8 mg/kg for stigmasterol and 14.7 mg/kg for sitosterol. Recovery ranged between 80–92%, repeatibility expressed as RSD of 12 parallel samples measurements was 4.2–6.8%. Accuracy tested on the SRM 1845 Whole Egg Powder (NIST) was 95.7%.
The aim of this study was to evaluate the effects of temperature and storage time on the formation of biogenic amines (BAs) in the traditional Czech curd cheese (Olomoucké tvarůžky). Samples were stored for 7 weeks at 5 °C and 20 °C. BAs were studied as dansyl derivatives by the RP-HPLC method with fluorescence detection, histamine was determined using a photodiode array detector. Physical and chemical properties were analyzed as specified by the Czech National Standard, as were the sensory characteristics (colour, odour, texture and flavour). The major amines found were cadaverine (124-2 413 mg·kg -1 ) and tyramine (117-1 058 mg·kg -1), followed by putrescine (75-767 mg·kg -1) and histamine (74-411 mg·kg -1 ). Low concentrations of tryptamine, spermine and spermidine were present. Total concentrations of BAs significantly increased with storage time (P 0.01), depending significantly on temperature (P 0.01). Total BAs in cheese stored at 20 °C compared to 5 °C were more than three times higher, reaching 4 600 mg·kg −1 at the end of storage. The toxicologically critical value of 900 mg·kg −1 for the sum of histamine + tyramine + putrescine + cadaverine was reached 17 days later in the cheese stored at 5 °C compared to 20 °C. When stored at 5 °C, the samples retained adequate sensory characteristics for the entire safe storage time. The effects of storage conditions on BAs formation are relevant to reducing the risk associated with consumption of cheese high in BAs.
The main aim of this work was to determine the effect of high pasteurization of milk (85 °C/3 s) on the residues of tetracycline and oxytetracycline. The samples of raw cow's milk, purchased from a vending machine, were spiked with standard solutions of tetracycline and oxytetracycline. The content of the residues of tetracycline antibiotics was measured before and after heating. Precleaned samples were extracted by a mixed-mode solid phase extraction technique and analysed using high performance liquid chromatography/diode array detection. Whereas the residues of tetracycline decreased only by 5.74% and were not significantly different (P > 0.05), the residues of oxytetracycline decreased by 15.3% and this distinction was highly significant (P ≤ 0.01). Based on the results of our study, the tetracycline antibiotics were proved to have differences in the thermostability of particular substances at pasteurisation temperatures.
Navrátilová P., Borkovcová I., Dračková M., Janštová B., Vorlová L. (2009): Occurrence of tetracycline, chlortetracycline, and oxytetracycline residues in raw cow's milk. Czech J. Food, Sci., 27: 379-385.The objective of this study was the detection of tetracycline, chlortetracycline and oxytetracycline residues in raw cow's milk. When analysing bulk milk (n = 57) and tanker trailer'a (n = 113) samples, two methods were used simultaneously: a specific rapid test Milk Tetrasensor Kit and high performance liquid chromatography (HPLC) with ultraviolet detection and isocratic elution. For HPLC analysis, Breeze (Waters, USA), a liquid chromatographic system, was used. The samples underwent solid phase extraction before the HPLC analysis. The Nova Pack C8 column (3.9 × 150 mm, 4 μm, Waters) and mobile phase (0.8 ml/min) consisting of acetonitrile, methanol, and 0.05 mol/l of oxalic acid in a 13:13:74 ratio were used. None of the samples analysed with the use of the specific rapid test displayed the presence of tetracycline antibiotics. In all of the samples analysed by means of HPLC, low concentrations of tetracycline antibiotics residues were detected. None of the samples displayed the presence of chlortetracycline. All of the analysed samples displayed residues of tetracycline. Oxytetracycline residues were detected only in 50.6% of analysed samples.
Abstract:The aim of this study was the determination of lactoferrin in goat milk using HPLC method. Milk samples were collected at a goat farm in the South Moravia Region, the Czech Republic. It were established bulk tank samples of raw milk (n = 24) and pasteurised milk (n = 27) that were collected during lactation. Lactoferrin contents were analysed by reverse phase high-performance liquid chromatography (RP-HPLC) with diode-array detector PDA 2996. Detection was carried out at the wavelength 205 nm. The average concentration of lactoferrin in goat milk was 120 ± 18 µg/ml. The lactoferrin content was increasing within the lactation period in the ranges of 98 ± 170 µg/ml in April to 149 ± 19 µg/ml in November. The heat treatment (pasteurisation at 72°C for 20 s) resulted in no significant effect on the lactoferrin content. No statistically significant differences (P = 0.05) were found between the values of raw and pasteurised goat milk.
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