Biofunctionality assessment of α-lactalbumin nanotubes

Abstract

The functional properties α-LA nanotubes and the gels formed during their synthesis were studied to evaluate their potential applications. The bioactivity of α-LA was improved by the synthesis of nanotubes, with significantly (p < 0.05) higher ACE-inhibitory (IACE) and antioxidant activity (μmol TE/mg protein). The IC50 (protein concentration to inhibit 50% of ACE activity) of α-LA nanotubes was 281 ± 21 μg mL−1 and the antioxidant activity 1.28 ± 0.01 μmol TE mg−1 protein. Besides, the IACE-value was significantly higher (p < 0.05) when the α-LA fragments incorporated into the nanotube’ structure were considered, and not only the low MW peptides formed during the nanotube synthesis (not incorporated into the nanotube’ structure).This study also analysed how different ion ratios in the synthesis of α-LA nanotubes changed their functionality. Thus, gels formed by long and regular α-LA nanotubes (2 mol of Mn2+/mol of α-LA) showed fluid−gel characteristics, with some time-dependent shear-thinning flow (thixotropy). At fixed recovery time, a less thixotropic behaviour was found in these fluid gels (high percentage −71.6 ± 7.4%− of structural regeneration). Additionally, they stayed in gel form at high temperatures and even increased their stiffness up to 65 °C. The increase in the ion ratio (3 mol of Mn2+/mol of α-LA) during nanotube synthesis modified the α-LA nanotubes' microstructure nanotubes resulting in short and branched nanotubes. These gels showed a higher level of pseudo-plasticity, higher consistency and thixotropy. These are characteristics of a more complex and dense network with greater time dependence and lower structural regeneration (18.6 ± 2.0%).