Regional Differences in Nitrogen Fractions in California Herd Milks

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Abstract
Concentrations of protein calculated from total Kjeldahl N and total Kjeldahl N corrected for the nonprotein N were determined in samples of herd milk collected from dairy farm tanks in California''s San Joaquin Valley (45 samples) and from the area north of San Francisco Bay (55 samples) [USA]. Means for the San Joaquin Valley and North Bay Area were for protein determined from N corrected for nonprotein N 3.15 and 3.61%, for total N 522 and 598 mg/100 g milk, and for nonprotein N 28.6 and 32.6 mg/100 g. Nonprotein N was 5.5% of the total N in the North Bay Area and 5.5% of total N in the San Joaquin Valley. Regional differences were statistically significant. Protein content of milk and dairy products should be determined from Kjeldahl total N concentration corrected for the nonprotein N and instrumental procedures, such as IR and dye-binding, should be calibrated to actual protein content excluding nonprotein N.