Reference and routine methods for the measurement of nitrogen fractions in milk and whey [Paracasein]
1994
Grappin, R. | Lefier, D. (INRA, Poligny (France). Station de Recherches en Technologie et Analyses Laitieres)
Because milk proteins form the cheese matrix, an accurate determination of nitrogen and nitrogen fractions in milk and whey is essential for the measurement of cheese yield. The analytical performances (precision, accuracy) of the nitrogen determination by Kjeldahl and of the measurement of milk true and crude protein content by mid infrared spectroscopy are given. Incorrect setting of the primary slope and of the intercorrection factors of the IR milk analysers, as well as variation of the proportion of NPN in milk, are the main sources of errors. Different procedures are possible for the measurement of casein or paracasein in milk with IR milk analysers. The relationship between casein and paracasein contents varies significantly between milks and seasonally.
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