Gek1521 - Physics in the Life Sciences

GEK1521 - PHYSICS IN THE LIFE SCIENCES

TERM PAPER

Antifreeze proteins in ice cream production

11/2011

I. Introduction

Freezing is a process during which a substance changes from a liquid to a solid, and it is a common phenomenon in our daily life. This paper will focus on the process of liquid water turning into ice at a sub-zero temperature.

This freezing process obviously poses significant threats to different types of animal, plants that naturally live in cold environments, since the frozen cells are not able to function properly. However, these organisms have found a way to overcome this freezing problem thanks to the presence of antifreeze proteins (AFPs) in their cells. AFPs can be defined as proteins that have an affinity for ice (Peter L. Davies, Jason Baardsnes, Michael J. Kuiper, Virginia K. Walker, 2002), which generally enables these organisms to live under cold ambient conditions by preventing cell’s freezing process.

II. How AFPs stop the formation of ice

1. Formation of Ice

There are two successive phases in this process which are nucleation of ice and crystal growth. Nucleation refers to a process during which a minimum number of crystal and expand in the second phase. The continued expansion of the crystal is known as crystal growth phase. However, impurities and pressure have an effect on the process.

1.1 Nucleation of Ice

Nucleation is the start of process when the solute molecules scattered in the solvent begin to congregate into clusters, then nuclei and become stable (Wikipedia). If these clusters are not stable enough, they will re-dissolve. Therefore,