Abstract:
Polar organisms produce antifreeze proteins (AFPs) that bind ice, modifying and inhibiting the growth of large ice crystals, and thereby protecting the host from freeze damage. This phenomenon has huge potential and AFPs are ideal candidates for cryopreservation applications ranging from biomedical to food technologies. In this thesis, a biomimetic approach to control ice crystal growth is proposed, based on AFPs from polar fish and insects. In the first part of this thesis, a range of AFP analogues based on those produced by polar fish and insects were synthesized and systematically studied for their effects on ice crystal shape with and without a small-molecule enhancer. The results highlighted some important structure-activity relationships of the AFPs and illustrated the effect of length, amino acids, and intra-coil bridging mechanisms on the ice-shaping behaviour of the peptides. The effects ranged from no shape modification and no thermal hysteresis to a strong shape modification and a significant thermal hysteresis. The results were then related to a general AFP ice binding model. CD spectroscopy was undertaken to determine the conformation of the peptides in solution. In the second part of this thesis, the general principles of crystal growth modification using peptides as additives (described in Part I) were used to explore the potential application of AFPs in frozen food. AFPs were used as an antifreeze treatment for frozen food that successfully modified the growth of ice crystals within the food structure. The effects of these AFPs on the ice crystal size, drip loss, texture, volatile compounds, total phenol content, total anthocyanins content, and total antioxidant properties of frozen fruits and vegetables were investigated. The results showed a significant positive effect of AFPs in frozen food applications. Based on the results, future work to develop efficient peptides for cryopreservation applications is suggested.
