The degree of modification of casein derivatives, a number of linoleic acid bound
to sodium caseinate, was determined by measuring the number of free amino groups
using OPA reagent. Twenty-five milliliters of sodium tetraborate buffer (pH 9.5)
was mixed with 2.5 mL OPA dissolved in methanol (16.4 mg/2.5 mL) followed by
addition of 5 mL of 20% SDS to sodium tetraborate buffer/OPA mixture. Then, 400
μL of 2-ME was added to sodium tetraborate buffer/OPA/SDS mixture and
final volume of mixture was adjusted to 100 mL with deionized water. To
determine the number of amino groups, 50 μL of unmodified (standard) or
hydrophobically-modified sodium caseinate was mixed with 1 mL of OPA reagent.
Measurement of the number of amino acids groups at 340 nm was performed using a
UV-VIS spectrophotometer (GENESYS10-S, Thermo Spectronic, Rochester, NY,
USA).
to sodium caseinate, was determined by measuring the number of free amino groups
using OPA reagent. Twenty-five milliliters of sodium tetraborate buffer (pH 9.5)
was mixed with 2.5 mL OPA dissolved in methanol (16.4 mg/2.5 mL) followed by
addition of 5 mL of 20% SDS to sodium tetraborate buffer/OPA mixture. Then, 400
μL of 2-ME was added to sodium tetraborate buffer/OPA/SDS mixture and
final volume of mixture was adjusted to 100 mL with deionized water. To
determine the number of amino groups, 50 μL of unmodified (standard) or
hydrophobically-modified sodium caseinate was mixed with 1 mL of OPA reagent.
Measurement of the number of amino acids groups at 340 nm was performed using a
UV-VIS spectrophotometer (GENESYS10-S, Thermo Spectronic, Rochester, NY,
USA).
