DSC and optical investigation of Spirulina platensis suspension and wet mass subjected to rapid freezing at − 20 °C, − 80 °C, and − 196 °C
摘要
The objectives of this study were: (i) to assess the growth and survival of the Spirulina platensis after exposure of its suspension to − 20 °C, − 80 °C, and − 196 °C, (ii) to determine the influence of rapid freezing of the suspension and wet biomass at the abovementioned temperatures on thermodynamic stability of the phycobilisome complex (PBSc) in vivo, and (iii) to identify freezing temperature conditions that minimize the unfolding/denaturation of the algal biomass and its PBCc. Our findings indicate that PBCc containing C-phycocyanin (C-PC) and C-allophycocyanin (C-APC) in Spirulina platensis suspension at weight-to-volume ratio (W/V) of 1/100 to 1/50, and wet mass at W/V of 1/3.5 to 1/5 unfolds cooperatively at temperature (Td) of 57.5 ± 2.0 °C with a transition interval (∆Td) of 3.0 ± 0.5°, and melting enthalpy (∆Hd) of 40.0 ± 2.8 Jg−1. The rapid freezing of small portions of the wet mass followed by thawing initiates a partial unfolding of the biomass, including PBCc that has a two-step transition at 51.0 ± 2.0 °C and 57.5 ± 2.0 °C, comprising the denaturation interval of 36 °C to 72 °C, which resembles the unfolding of purified C-PC. The recultivation after freezing initiates full recovery of biophysical features of Spirulina platensis. The obtained data can be considered during the initial step of isolating native C-PC and C-APC by destruction of cell membrane using rapid freezing and thawing of small portions of Spirulina platensis. We have demonstrated that freezing of the wet mass to − 196 °C helps the highest yield of unfolded PBCc. In the case of sediment freezing at − 196 °C and − 80 °C, the PBCc minimally unfolds.