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Ice-binding proteins have attracted the interest of scientists for their unique properties as well as their practical applications. These proteins may be of key importance in the food industry as well as in medicine, according to Õnnela Luhila, PhD student in Food and Biotechnology at Tallinn University of Technology.
Natural defence mechanism against freezing
Organisms from the Arctic have evolved a number of mechanisms to protect themselves from freezing. One solution is the production of special proteins that bind to the surface of ice crystals and prevent them from growing. Originally found in fish, these proteins exist in various organisms. For example, insects that hibernate in frozen soil and plants that can withstand cold nights and night frost. They have also been found in fungi, algae and even micro-organisms such as bacteria.
The proteins can vary widely in size, structure and properties, but they are united by their ability to bind to the surface of microscopic ice crystals and influence their formation, shape or growth. The growth of residual crystals in organisms is dangerous because it can lead to the rupture of cell membranes, water loss and cell death. Therefore, the presence and action of ice-binding proteins is vital.
Protein properties of interest to scientists
Their unique properties have also attracted interest in a wide scope of applications. In medicine, they are seen as a way of prolonging the life of cells, tissues and organs. In agriculture, they could be used to breed more frost-tolerant crops. In the food industry, this stabilisation of ice crystals could be particularly useful for frozen foods, as a lot of frost damage is caused by temperature changes during transport and storage. A good example is improperly stored ice cream that develops large ice crystals on its surface, making its texture icy and unpleasant.
Frost-resistant dough thanks to bacteria
The same problem occurs with frozen dough. Fluctuations in temperature lead to the growth of ice crystals, which can damage yeast cells and the protein structure of the dough. This has a negative effect on the dough rising and ultimately on the quality of the finished bread.
“As part of my PhD, I have been investigating the ice-binding proteins produced by a bacterium found in Scottish coastal waters – Pseudomonas fluorescens. I isolated the proteins in a lab to study their ability to bind to the surface of ice crystals and inhibit crystal growth,” says Õnnela.
“In addition, I tested the effect of adding these proteins to frozen wheat flour dough on the quality of bakery products after freezing. The results showed that the growth of ice crystals in the dough causes significant damage, such as damage to yeast cells, changes in starch structure and breakdown of wheat proteins. As a result of these damages, the dough no longer rises properly and the pastries become dense, hard and drier.”
Adding ice-binding proteins to wholegrain wheat flour dough significantly increased yeast cell survival. This, in turn, ensured a better rising, softer and longer-lasting pastry. The addition of proteins also helped to preserve the pleasant taste and smell of the bread.
It can therefore be said that the addition of ice-binding proteins to frozen dough helps to preserve its quality and extend its shelf life. This discovery could also lead to better preservation of other frozen food products. Research is ongoing to determine exactly which protein is responsible for this effect and how to produce it in larger quantities.
Article “Cryo-protective effect of ice-binding proteins produced by Pseudomonas fluorescens AQP671 on wholegrain wheat bread dough during freezing and frozen storage” was published in JWT.
This article was originally published on the webpage of Tallinn University of Technology (TalTech).
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