When whole blood or a suspension of erythrocytes (red blood cells) is frozen and thawed, the majority of the erythrocytes are lysed, which means they are destroyed or burst open. This can have detrimental effects on the blood and its ability to perform its functions effectively.
However, if glycerol is present in the suspension in a concentration of about two molar, then the erythrocytes are able to remain intact after freezing and thawing, appearing to be uninjured. Glycerol acts as a cryoprotectant in this case, helping to preserve the integrity of the erythrocytes during the freezing and thawing process.
To understand what happens when blood freezes, let's dive into the details. When blood is subjected to extremely low temperatures during freezing, ice crystals start to form. These ice crystals can cause damage to the delicate cellular structures within the blood, including the erythrocytes. As the ice crystals expand, they can rupture the cell membranes of the erythrocytes, leading to their lysis.
The process of freezing and thawing can also result in the formation of sharp ice crystals, which can physically puncture and damage the erythrocytes. The rapid changes in temperature during thawing can further exacerbate this damage, leading to the destruction of a significant portion of the erythrocytes.
However, the addition of glycerol to the blood suspension changes the dynamics of freezing and thawing. Glycerol is a cryoprotectant because it has the ability to lower the freezing point of water and reduce the formation of ice crystals. When glycerol is present in a concentration of about two molar, it helps to prevent the formation of large ice crystals that can cause severe damage to the erythrocytes.
Moreover, glycerol has the ability to penetrate the cell membranes of the erythrocytes and protect their internal structures. It acts as a type of “antifreeze” for the cells, preventing the formation of sharp ice crystals that could puncture the membranes and cause lysis.
Personal experience-wise, as a sommelier and brewer, I haven't directly dealt with freezing blood, but I have encountered the concept of cryoprotectants in the context of winemaking and brewing. In winemaking, for example, glycerol is sometimes added to wines to improve their mouthfeel and texture. It helps to enhance the overall sensory experience by providing a smoother and more rounded mouthfeel. This, in a way, parallels its role as a cryoprotectant in blood, where it helps to preserve the integrity of the erythrocytes.
To summarize, when blood freezes without the presence of a cryoprotectant like glycerol, the erythrocytes are susceptible to lysis and damage due to the formation of ice crystals. However, when glycerol is present in the blood suspension, it acts as a cryoprotectant, preventing the formation of large ice crystals and protecting the erythrocytes from damage. This allows the erythrocytes to remain intact after freezing and thawing, ensuring their functionality and overall preservation.