Survival from the Cold Winter: Freezing and Ice Crystallization Inhibition by Antifreeze Proteins - Bioinspiration: From Nano to Micro Scales - page 58

most accurate estimation of the ice-water interfacial energy, and the homogeneous
nucleation barrier, genuine homogeneous ice nucleation may hardly take place even
below 80 ı C[ 12 ]. This implies that if we can eliminate the influence of foreign
bodies, freezing may never occur [ 12 ].
As freezing is mediated by minute foreign particles, i.e., dust particles, bacterial
epiphytes, which cannot be removed completely, in theory, the most effective way
to block freezing is to inhibit the promoting effect of foreign bodies on nucleation.
In this regard, the understanding of ice nucleation under the influence of minute
foreign particles is particularly important for the identification of novel technologies
in controlling freezing and antifreeze in general.
Due to the fact that crystallization involves nucleation and growth, the inhibition
of the growth of ice crystallites becomes important if the nucleation inhibition fails.
We notice that many antifreeze proteins (AFPs) are capable of modifying the growth
habit of ice crystallites. As the habit modification is attributed to the retardation of
some particular orientations in the crystal growth form [ 13 - 17 ], we therefore can
consider the habit modification as a special case of the growth inhibition.
Many plants, fish, insects, and other organisms have evolved with unique
adaptive mechanisms that allow them to survive in harsh environments at the
extremes of temperature [ 18 - 21 ]. Scholander [ 22 , 23 ] and DeVries [ 24 , 25 ]werethe
first to investigate the mechanisms by which polar fish are able to survive. Analysis
of the blood plasma of these fish showed that while the concentrations of salts
and small ions in the body fluids are somewhat higher relative to fish in temperate
waters, these salts are only responsible for 40-50% of the observed freezing point
depression. The remainder of the protective effect was attributed to the presence of
a series of relatively high molecular mass glycoproteins and proteins [ 26 - 29 ].
The eminent antifreeze effect results from AFPs found in the blood and tissues
of organisms that live in freezing environments [ 2 ]. In these organisms, the effect of
freezing proteins is retarded, or the damage incurred upon freezing and thawing is
reduced [ 2 - 4 ]. Applications of the antifreeze effect of these AFPs, the capacity to
inhibit ice crystallization, have been sought for maintaining texture in frozen foods,
improving storage of blood, tissues and organs, cryosurgery, and protecting crops
from freezing [ 4 ].
AFPs and antifreeze glycoproteins (AFGPs) have since been identified in the
body fluids of many species of polar fish. The study of annual cycle of AFP
production and secretion into the blood in polar fish such as winter flounder
indicates that plasma AFP levels correlate closely with the annual cycle of seawater
temperatures. AFP appears in the plasma as the water temperature declines, reaches
peak levels of 10-15 mg/mL during winter, and clears from the plasma as the
temperature rises above 0 ı C[ 30 ]. Peak levels of AFP during winter reduce the
plasma freezing temperature of winter flounder to approximately 1.7 ı C.
In this chapter, we will review the latest works on freezing kinetics and the
antifreeze mechanism of AFP and AFGPs. This includes the effect of a trace amount
of foreign nanoparticles on ice nucleation in ultrapure microsized water droplets
and its implications for freezing and antifreeze in general. As highlighted earlier,
how AFPs change the surface characteristics of foreign bodies so as to inhibit ice