Influence of calcium on the self-assembly of partially hydrolyzed alpha-lactalbumin.
Self-assembly of alpha-lactalbumin after partial hydrolysis by a protease from Bacillus licheniformis can result in nanotubular structures, which show many similarities to microtubules. Calcium plays a crucial role in this process. The objective of this investigation was to study the role of calcium in more detail. The kinetics of the hydrolysis step and the self-assembly step were monitored by respectively liquid chromatography-mass spectrometry and dynamic light scattering. The microstructure of the gels finally formed was investigated by transmission electron microscopy. This investigation demonstrates that calcium accelerated the kinetics of the self-assembly, but it had no effect on the hydrolysis kinetics. As a result of the accelerated self-assembly kinetics at a high calcium concentration, the time of gelation decreased as well. A minimum concentration of calcium needed to obtain the tubular alpha-lactalbumin structures was determined. Below R = 1.5 (mole calcium/mole alpha-lactalbumin), turbid gels with randomlike structure were obtained. Between R = 1.5 and R = 6, translucent gels with a fine stranded network of tubules were formed, while higher calcium concentrations had a negative effect on the tubule formation, resulting in amorphous structures. The optimum calcium concentration for alpha-lactalbumin nanotube formation seemed to be around R = 3.
NIZO food research, P.O. Box 20, 6710 BA Ede, The Netherlands. joanke.graveland@nizo.nl
Johanna F
JF
Graveland-Bikker
Richard
R
Ipsen
Jeanette
J
Otte
Cornelis G
CG
de Kruif
D002118:Calcium / Q000737:chemistry*; D006868:Hydrolysis; D007768:Lactalbumin / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D013997:Time Factors
D007768:Lactalbumin; D002118:Calcium