Abstract: Transglutaminase (TGase) was employed to catalyze the preparation of glycosylated casein with chitosan (1 kDa). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and reverse phase-high performance liquid chromatography (RP-HPLC) analysis confirmed the occurrence of glycosylation. In vitro digestion with pepsin plus trypsin was used to evaluate the effect of the glycosylation modification on casein digestibility. The results showed TGase catalyzed the acyl-transfer reaction between casein and chitosan and the amount of glucosamine bound to modified casein was 6.86 g/kg protein. After in vitro digestion, the degree of hydrolysis and trichloroacetic acid-soluble nitrogen (TCA-SN) of glycosylated casein were lower than those of native casein, and more macromolecular peptides were found in the glycosylated casein digest. This study showed glycosylation modification with TGase reduced the digestibility of casein.

Key words: transglutaminase, glycosylated protein, casein, in vitro digestion