Cloud point extraction applied to casein proteins of cow milk and their identification by mass spectrometry.
This work describes the optimization of a cloud point extraction (CPE) method for casein proteins from cow milk samples. To promote phase separation, polyoxyethylene(8) isooctylphenyl ether (Triton X-114) and sodium chloride (NaCl) were used as nonionic surfactant and electrolyte, respectively. Using multivariate studies, four major CPE variables were evaluated: Triton X-114 concentration, sample volume, NaCl concentration, and pH. The results show that surfactant concentration and sample volume were the main variable affecting the CPE process, with the following optimized parameters: 1% (w/v) Triton X-114 concentration, 50 microL of sample volume, 6% (w/v) NaCl concentration and extractions carried out at pH 7.0. At these conditions, 923+/-66 and 67+/-2 microg mL(-1) of total protein were found in the surfactant-rich and surfactant-poor phases, respectively. Finally, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) was then used to evaluate those target proteins (alpha(s1)-casein, alpha(s2)-casein and beta-casein) separation as well as to check the efficiency of the extraction procedure, making a fingerprint of those target proteins possible.
Lopes
Aline Soriano
AS
Universidade Estadual de Campinas, Institute of Chemistry, Spectrometry, Sample Preparation and Mechanization Group, P.O. Box 6154, 13084-862 Campinas, São Paulo, Brazil.
Garcia
Jerusa Simone
JS
Catharino
Rodrigo Ramos
RR
Santos
Leonardo Silva
LS
Eberlin
Marcos Nogueira
MN
Arruda
Marco Aurélio Zezzi
MA
D000818:Animals; D002364:Caseins / Q000032:analysis*; D002417:Cattle; D008892:Milk / Q000737:chemistry*; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
D002364:Caseins; D011092:Polyethylene Glycols; D012965:Sodium Chloride; D017830:Octoxynol; C010615:Nonidet P-40