Effects of different monosaccharides on thermal stability of phycobiliproteins from Oscillatoria sp. (BTA-170): Analysis of kinetics, thermodynamics, colour and antioxidant properties

Abstract

Phycobiliproteins (PBPs) are natural colourants and antioxidants derived from cyanobacteria. The purity indexes of extracted C-phycocyanin (C-PC), allophycocyanin (A-PC), and phycoerythrin (PE) were 0.98-1.23, 0.78-0.0.96, and 0.85-0.99, respectively. To investigate thermodynamic characteristics, degradation kinetics, colour, and antioxidant capabilities of Oscillatoria sp. (BTA-170) extract powder, the PBPs were thermally treated with various monosaccharides such as glucose, fructose, glucose, and lactose. In comparison to other monosaccharides that can stabilize the degradation of C-PC, A-PC, and PE at higher temperatures, glucose was found to be the most essential supplement. At 85 °C, glucose enhanced the half-life of C-PC from 2.09 to 5.37 h, whereas glucose increased the half-life of A-PC from 4.9 to 13.51 h and PE from 5.57 to 15.77 h. While glucose was added, entropy (S) for C-PC was reduced from −177.82 to −183.25 J/Mol K, for A-PC from −178.24 to −169.61 J/Mol K, and for PE from −176.28 to −170.97 J/Mol K. However, the value of enthalpy (H) was enhanced from 52.37 to 53.20 KJ/Mol, while the values of A-PC and PE were raised from 40.63 to 40.56 KJ/Mol and 40.32 to 41.43 KJ/Mol, respectively. Gibbs free energy (G*) was found in the range of 111.48–118.81KJ/Mol for C-PC, 94.49–101.28 KJ/Mol for A-PC, and 95.79–102.63 KJ/Mol for PE when glucose was added, showing a higher degree of protein stability. When fructose was added, the ΔE values of PBPs were reduced from 13.31 to 6.62 at 85 °C, with the least amount of colour degradation among the monosaccharides. At 85 °C, glucose reduced the IC 50 of PBPs from 30.45 mg/ml to 17.33 mg/ml. The thermal tolerance of monosaccharides for PBPs suggested that they could be a potential source of PBP stabilization in the food industry.