Susceptibility to trypsinolysis of esterified milk proteins.
Methyl-, ethyl- and propyl-esters of beta-lactoglobulin, alpha-lactalbumin and beta-casein were prepared and then hydrolyzed with trypsin in various conditions. Resulting hydrolysates were analysed by SDS electrophoresis and RP-HPLC. The degree of hydrolysis of esterified samples was generally lower than those of the non-modified proteins. The highest degrees of hydrolysis were obtained at pH 7--8 with native and esterified protein samples. beta-Lactoglobulin propyl ester and beta-casein methyl ester yielded the lowest degrees of hydrolysis. Ethyl- and propyl-esters of beta-casein showed high resistance towards tryptic attack, even after 20 h of hydrolysis. SDS electrophoretic patterns of tryptic hydrolysates of native proteins showed bands corresponding to low molecular weights. Tryptic hydrolysates of esterified proteins showed bands with higher sizes. RP-HPLC profiles of tryptic hydrolysates of esterified samples showed peaks with longer elution times than those obtained with native proteins, indicating the presence of more hydrophobic peptide populations. A peptic pre-treatment improved tryptic action on esterified proteins. It resulted in a better resolution of RP-HPLC profiles and in a complete disappearance of the protein after 20 h tryptic hydrolysis.
Sitohy
M
M
Laboratoire d'Etude des Interactions des Molécules Alimentaires, Institut National de la Recherche Agronomique, B.P. 71627, 44316 Nantes, Cedex 3, France.
Chobert
J M
JM
Haertlé
T
T
D000433:1-Propanol; D000818:Animals; D002364:Caseins / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D004951:Esterification; D000431:Ethanol; D005998:Glycine / Q000031:analogs & derivatives; D006868:Hydrolysis; D007768:Lactalbumin / Q000378:metabolism*; D007782:Lactoglobulins / Q000378:metabolism*; D000432:Methanol; D008894:Milk Proteins / Q000378:metabolism; D012967:Sodium Dodecyl Sulfate; D014357:Trypsin / Q000378:metabolism*
D002364:Caseins; D007782:Lactoglobulins; D008894:Milk Proteins; D012967:Sodium Dodecyl Sulfate; D000431:Ethanol; D007768:Lactalbumin; D000433:1-Propanol; D014357:Trypsin; D005998:Glycine; C100184:tricine; D000432:Methanol