Estimation of Protein in Anhydrous Milk Fat
- PDF / 206,946 Bytes
- 6 Pages / 595.276 x 790.866 pts Page_size
- 0 Downloads / 233 Views
Estimation of Protein in Anhydrous Milk Fat Paul W. Johns & Daniel J. Schmitz
Received: 7 April 2012 / Accepted: 24 May 2012 / Published online: 5 June 2012 # Springer Science+Business Media, LLC 2012
Abstract A method for the estimation of protein in anhydrous milk fat is described. The protein concentration is estimated by quantifying the arginine and aspartic acid (ASX) released upon acid hydrolysis of the anhydrous milk fat. Arginine and aspartic acid are derivatized with the fluorescent tag 9-fluorenylmethoxycarbonyl (FMOC), the derivatives are quantified by reversed phase HPLC, and the protein concentration in the anhydrous milk fat is estimated as 8.77×(Arg+ASX). Method suitability was defined by experimental assessments of FMOC-arginine and FMOC-aspartic acid linearity (R2 averages>0.999), protein estimate precision [day-to-day RSD values (n 08 days) ranged from 7.3 to 14 % for protein concentrations of 9.42 to 40.0 mg/kg of anhydrous milk fat], protein estimate accuracy [spike recovery average095.6 % (9.3 %), n08, spiking level020 mg/kg and agreement of the experimental protein estimate for butter, 0.611 (0.044)g/100 g, n03 lots, with a published value 0.6/100 g], and analyte selectivity (baseline resolution of FMOC-arginine and FMOC-aspartic acid from the FMOC derivatives of other common amino acids). The method provides for a reliable estimation of the protein content of anhydrous milk fat, when present at concentrations >2 mg/kg. Keywords Anhydrous milk fat . Arginine . Aspartic acid . HPLC determination . Method validation . Protein
P. W. Johns (*) : D. J. Schmitz Abbott Nutrition Division, Abbott Laboratories, 3300 Stelzer Road, Columbus, OH 43219, USA e-mail: [email protected]
Introduction The insolubility of proteins in non-aqueous solvents was demonstrated by Pace et al. (2004), who suggested that “most proteins will be almost completely insoluble in most organic solvents” and that “proteins will be essentially insoluble in non-polar solvents such as cyclohexane”. This leads one to expect protein insolubility in fats and oils (many of which exhibit lower water solubility than cyclohexane), and this expectation is supported by experimental data, e.g., a study of 35 olive oils found ≤0.5 mg of protein/ kg of olive oil (Hidalgo et al. 2001) and a study of plant and fish oils found
Data Loading...
