Effects of cryoprotectants on Nostoc sphaeroides superchilled at low temperature (−3.0°C) and their action mechanisms

Effects of cryoprotectants (NaCl, sucrose and trehalose) on Nostoc sphaeroides (N. sphaeroides) superchilled at −3.0°C as well as their action mechanisms were studied. Prior to storage, N. sphaeroides were immersed into different concentrations (5% and 10%) of NaCl solutions, sucrose solutions, and trehalose solutions for 2 hr. The texture properties, drip loss and low field nuclear magnetic resonance (NMR)-imaging of N. sphaeroides with different treatments were evaluated. The freezing point, solute absorption, water distribution and microscopic structure were also measured to illustrate the action mechanisms of cryoprotectants. Results suggested that cryoprotectants offered an effective method for keeping the texture properties, lowering drip loss, and maintaining the shape of N. sphaeroides. Among all the cryoprotectants used, 5% NaCl exhibited the best effect. The study of their action mechanisms showed that cryoprotectants were efficient in reducing the freezing point, the proportion of free water and microscopic structure destruction of N. sphaeroides. Practical Applications: Considering the higher water content of N. sphaeroides, it is not suitable to be deeply frozen because the formation of numerous ice crystals can cause severe damages to the tissue. To suppress these undesirable changes in superchilling, cryoprotectants including NaCl, sucrose and trehalose are added to the food products. This research contributes to lay a theoretical foundation for the further study of superchilling storage of N. sphaeroides.