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Determination of lysinoalanine in pasteurized and sterilized milks consumed in the city of Tehran, 2011
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N Khorshidian   , A Taslimi * , M Mashayekh , E Azadniya |
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Abstract: (9053 Views) |
| Background and objective: Milk pasteurization and sterilization processes prolong its shelf-life and also promote the safety of dairy products. On the other hand, these processes can also have adverse effects on the nutritional quality and safety of milk and dairy products. Formation of cross-linkages between amino acids in the protein molecules may produce undesirable compounds, e.g., lysinoalanine (LAL), resulting in reduced availability of some of the essential amino acids, as well as nephrotoxicity effects. The aim of this project was to determine the LAL content of pasteurized and sterilized milks consumed in the City of Tehran.
Materials and Methods: Determination of protein in milk samples was done by the Kjeldahl method. Hydrolysis of milk proteins was done using 6N hydrochloric acid and placing the samples in the oven at 110 0C for 22 hours. The hydrolyzed protein samples were then dissolved in distilled water and the pH was adjusted to 9 by addition of 12N sodium hydroxide. For derivitization of the liberated LAL, dansylation was done by adding dansyl chloride (10mg/ml isopropyl alcohol) at 40°C for 60 minutes. LAL then measured in the samples by high performance-liquid chromatography.
Results: The LAL content of raw milk samples obtained from a milk processing plant and dairy shops was zero and 5 mg/kg, respectively, while it was 35-86mg/kg in the pasteurized, and 110-233mg/kg in the sterilzed, samples. In addition, the data showed that the LAL content of sterile milk samples would increase gradually at days 1, 7, 15, 30 and 60 during storage at 25°C.
Conclusion: The findings of this study show that lysinoalanine is prsesent in both pasteurized and sterilized milks, it being higher in the latter. In addition, the lysinoalanine contents of pasteurized and sterilized milks consumed in Tehran are higher than those in other countries. Considering that both children and adults consume milk daily in Tehran, controlling lysinoalanine content in pasteurized and sterilized milks marketed (by contolling time amd temperature) is of utmost importance.
Keywords: Milk, Pasteurization, Sterilization, Lysinoalanine, HPLC |
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| Keywords: Milk, Pasteurization, Sterilization, Lysinoalanine, HPLC |
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Full-Text [PDF 250 kb]
(2731 Downloads)
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Article type: Research |
Subject:
Food Science
Received: 2013/08/6 | Accepted: 2014/05/4 | Published: 2014/05/4
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