Improvement of Emulsifying Properties of Casein at Isoelectric Point by Glycosylation Modifications

• 1、Food Science and Technology School, Jiangnan University, Wuxi 214122

Abstract：[Objective] In order to solve the problem of poor emulsifying property of the casein in the vicinity of its isoelectric point (pH 4.6), it was glycosylated by Maillard reaction. [Method] We used dextran as the glycosyl donor and investigated the effects of the preparation parameters (pH, temperature, time, mass ratio, and relative humidity) on the copolymer\'s degree of grafting、browning index.We focused on the evaluation of the improvement of the emulsifying activity (EAI) and stability (ES) of the copolymer at pH 4.6.The process was optimized by response surface method. The copolymers were characterized by SDS-PAGE, amino acid analyzer, high performance liquid chromatography(HPLC), and Fourier infrared transform spectroscopy(FT-IR). [Results] Optimum conditions were as follow: pH 6.9、60℃、24 h、casein-dextran mass ratio of 5:1 and relative humidity of 79%. Under this condition, the degree of grafting was 27.80%, the browning index was 0.07, the EAI was 0.74, and the ES was 98.24. SDS-PAGE showed that the band of the copolymer became shallower at 29000 Da and obvious band appeared at the top of the separation gel. Compared with the original casein, the content of the copolymer in the range of relative molecular weight>240000 Da increased by 10.63%, the content of lysine and arginine decreased significantly, and the FT-IR spectrum was enhanced at 3700-3200 cm-1 and 1260-1000 cm-1. [Conclusion] Casein and dextran form high molecular weight polymers by Maillard reaction, in which lysine and arginine are the main reaction amino acids. The covalent grafting of dextran and casein introduced hydrophilic hydroxyl groups, which improved the casein emulsifying property at pH 4.6 and expanded its application range.

Keywords： food biotechnology casein Maillard reaction isoelectric point emulsifying activity emulsifying stability