Preparation, characterization and antioxidant activities of derivatives of exopolysaccharide from Lactobacillus helveticus MB2-1

In this study, different derivatives of exopolysaccharides (EPS-2) from Lactobacillus helveticus MB2-1 including acetylated EPS-2 (A-EPS-2), carboxymethyl EPS-2 (C-EPS-2), sulfated EPS-2 (S-EPS-2) and phosphorylated EPS-2 (P-EPS-2) were prepared. Furthermore, the structure, physicochemical properties and antioxidant activities of EPS-2 and its derivatives were compared. The introduction of different chemical groups was confirmed using Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectrogram, and the degrees of substitution (DS) for A-EPS-2, C-EPS-2, S-EPS-2 and P-EPS-2 were 0.439, 0.526, 0.625 and 0.432, respectively. Among four derivatives, the particle size distribution of AEPS-2, C-EPS-2 and P-EPS-2 was in accordance with the molecular weight (Mw) distribution. Besides, the results of scanning electron micrograph, thermogravimetric analysis and differential scanning calorimetry indicated the surface morphology and thermal behavior of EPS-2 had greatly changed after modification. Notably, several derivatives especially S-EPS-2 exhibited improved antioxidant activities when compared with EPS-2, implying the derivatives of EPS-2 might have wide applications as antioxidants in food industry. (C) 2019 Elsevier B.V. All rights reserved.