Xuan Thang Le

This study examines for the first time the role of xanthan gum (XG) and β-lactoglobulin (βlg) in network formation induced by electrostatic attractive interaction. The gelation processes of βlg–XG mixtures were monitored by viscoelastic measurements as a function of the βlg–XG ratio and βlg and XG concentrations. The structural characterization of the gels was addressed by means of confocal laser scanning microscopy. It was found that the initial tenuous network of XG provided a frame for gel organization, the βlg aggregated along the XG chains and could be regarded as a crosslinking agent, and more elastic gels were obtained at high XG concentrations. The lowest XG concentration at which gelation is possible is estimated to be 4.8 × 10−3 wt%. The βlg–XG ratio strongly affects gelation kinetics and is a main factor controlling the gelation process and the gel structure. The optimal ratio for electrostatic interaction at final pH of gels was estimated to be approximately 3.5. The decreasing repulsive interaction between XG chains and the increasing attractive interaction between βlg and XG with decreasing pH resulted in the formation of soluble complexes followed by the formation of interpolymer complexes. The electrostatic cross-linking of XG chains by βlg results in a sol–gel transition at the point of gelation. This mechanism may be applicable in a wide variety of protein–polysaccharide systems in which the structure of these systems is mainly stabilized by electrostatic attractive interaction.

The activity concentrations of naturally occurring radionuclides 226Ra, 232Th, and 238U were determined in marine sediments, seawaters and seafood along the Gulf of Vietnam to establish baseline data for future environmental monitoring at a surface water depth of 0–3 cm. The concentration of uranium, thorium and radium were determined using a low background gamma spectrum as well as activity ofy of 238U(214Bi), 232Th(228Ac) and 226Ra. The mean radioactivity concentrations of 226Ra, 232Th, and 238U were found to be 8.59 ± 0.54, 1.31 ± 0.15, and 6.91 ± 0.64 Bq m−3, respectively, in seawater samples and 32.96 ± 1.90, 37.64 ± 1.91, and 39.28 ± 1.96 Bq kg−1, respectively, in marine sediments, 0.21 ± 0.03, 0.69 ± 0.11, and 0.19 ± 0.03 Bq kg−1, respectively, in fish samples and 0.23 ± 0.041, 0.41 ± 0.06, and 0.31 ± 0.06 Bq kg−1, respectively, in clam samples. The radioactivity concentrations in seawater are higher than those in sediment and compared with those reported in other countries. The mean values of distribution coefficient (L/kg) is 0.53, 0.13, and 0.23, respectively, in fish samples and 0.19, 0.16 and 0.13, respectively, in clam samples at Hai Phong, Quang Ninh and Ha Tinh. Moreover, the ecological dose at Hai Phong, Quang Ninh and Ha Tinh are 0.03, 0.02 and 0.02 µGy h−1, respectively, in fish and 0.02, 0.03, and 0.03 µGy h−1, respectively, in clams and the mean human’s seafood consumers dose rate is 1.13×10-6 Sv/yrs. Results were discussed and compared with those reported in similar studies and with internationally recommended values within limits recommended by UNSCEAR.