EVALUATION OF THE INTERACTION OF MICROALGAL PROTEINS WITH BOVINE SODIUM CASEINATE BY FLUORESCENCE SPECTROSCOPY

SANCHEZ, MARÍA FLORENCIA; RISSO, PATRICIA H.; INGRASSIA, ROMINA

BIOCELL

INST HISTOL EMBRIOL-CONICET

Año: 2022

0327-9545

Spirulina protein derivatives (SPD) present antioxidant properties that may be stabilized by encapsulation by using biopolymers. The objective of this work was to study the interaction of SPD and sodium caseinate (NaCAS) to evaluate the use of the latter, derived from dairy casein, as wall material. Spirulina extract (10% W/V) was prepared in 1.5% CaCl2, stirred for 7.5 h, and centrifuged at 1,000×g for 20 min. The antioxidant capacity of the SPD was measured by the 2,2´-azino-bis-(3-ethylbenzothiasoline-6-sulfonic acid) radical capture method (ABTS+) at 0, 48, and 96 h after storing at -18°C or 3°C. The results were expressed as a function of the percentage of inhibition of the ABTS+ radical. NaCAS was prepared at 3% (%W/W) in 10 mM Tris-HCl buffer pH 7. The interaction between SPD and NaCAS was evaluated by measuring the fluorescence intensity (FI) in an Aminco-Bowman spectrofluorometer. The FI of NaCAS was measured in a range of 300-400 nm with an excitation wavelength (λexc) =288 nm, in the absence and the presence of increasing concentrations of SPD (NaCAS+SPD). In the same way, FI of SPD was determined in the absence and the presence of increasing concentrations of NaCAS (SPD+NaCAS). Also, the FI of SPD was measured in a range of 630-700 nm with λexc=620 nm, in the absence and the presence of increasing concentrations of NaCAS. The SPD presented an antioxidant capacity of 48.0±0.6%, but at 48 h, the samples stored at 3°C and -18°C decreased the inhibition percentage by 15% and 14%, respectively. At 96 h, the percentage inhibition was reduced by 9% and 28% for samples stored at -18°C and 3°C, respectively. Therefore, although the antioxidant capacity was more preserved at -18 °C, it is demonstrated that it is essential to implement a methodology to achieve the stabilization of the SPD. For NaCAS/SPD interaction studies, in NaCAS+SPD and SPD+NaCAS assays, the FI increased as the added protein concentration increased, without evident changes in the maximum emission wavelength. This would be due to an increase in the concentration of intrinsic protein fluorophores (tyrosine and tryptophan), without appreciable changes in their environment. In the assays at λexc=620 nm, where the prosthetic group of the major protein of SPDs is excited, a decrease in FI was observed as the concentration of NaCAS increased, along with a blue shift of the maximum emission wavelength. These results reveal a conformational change with the insertion of the prosthetic group in a more hydrophobic environment. Future studies with other complementary techniques are required to deepen our knowledge about these interactions, such as infrared spectroscopy and differential scanning calorimetry.