Altering functional attributes of proteins through cross linking by transglutaminase – A case study with whey and seed proteins

The effect of cross linking of the major whey protein b-lactoglobulin (b-Lg) and major protein fractions
(11S) of soybean (Glycinin) and sesame seed (a-globulin) with the microbial enzyme transglutaminase
(EC 2.3.2.13) was studied. The formation of polymerized proteins was followed by poly acrylamide gel
electrophoresis, gel filtration high pressure liquid chromatography (HPLC) and evaluation of functional
properties. Cross linked proteins were less turbid on heating to higher temperature as compared to
untreated samples and the temperature at which the protein turns turbid also increased in the treated
samples. In case of b-Lg and a-globulin of sesame seed when the control showed turbidity at 60 �C,
the enzyme treated sample indicated at 65 �C and higher. Similar results were obtained in the case of soybean
also. The treated samples showed higher emulsifying activity when compared to the control. The
control showed an emulsifying activity of 0.55 ± 0.02, and the treated sample showed an emulsifying
activity of 0.72 ± 0.02 (optical density at 500 nm is taken as emulsifying activity). Foaming capacity
did not improve significantly with the enzyme treatment. The complex formed was investigated by gel
filtration chromatography. Nearly 30% of the proteins (11S protein fractions and b-Lg) formed the complex
and increase in the concentration of the proteins or the enzyme did not show any increase in the
complex formation. The changes in the fluorescence intensity indicated changes in the microenvironment
of the chromophores induced by the enzymatic cross linking.