Laundry. I always thought it was a piece of cake, until I had to start doing it by myself. Of course I’ve been through the mystery of the disappearing socks, the whites turning pink or the tissue in a pocket, but the real deal came when I became a mom. I mean kids are absolute experts in putting on dirt! Stains were now not as easy to remove as before and there’s of course the endless loads, I mean, it seems like unless you do it naked, you are actually never done!!!. As a scientist, I just had to find out how to improve my laundry and I’ve learned a lot of interesting things. Apart from seeing how the whole process has improved over time, it is amazing to see how the biotech industry is making laundry so much simpler.
First of all, what are detergents made of?
Despite coming in different brands and prices, most detergents share the same components:
Surfactants: Also called ‘surface active agents’, they are the heart of laundry detergent formulation. These chemicals change the properties of water by lowering its surface tension, allowing clothes to wet more quickly so soil can be readily loosened and removed. They also emulsify oily soils and keep them dispersed and suspended so they do not settle back on the clothes surface.
Builders: They are water softeners. They enhance or “build” the cleaning efficiency of the surfactant. Their primary function is to reduce the water hardness by sequestrating or chelating water minerals by precipitation or even by exchanging ions. Chelation is necessary since it can deactivate surfactants and typical sequestering anions are polyphosphates and sodium citrate. Typical precipitating builders is sodium silicate. An ion exchange builder is sodium aluminosilicate (Zeolite).
Enzymes: Their function is to break up different forms of dirt such as proteins, starches and lipids. The use of enzymes allows lower temperatures to be used and also shorter periods of washing. Major detergents enzymes include proteases, amylases, lipases, cellulases and miscellaneous enzymes such as peroxidases and pullulanase.
Many other ingredients are added depending on specific applications and may include optical brightners, fabric softeners, perfumes and dye transfer inhibitors.
How did enzymes end up in my washing machine?!
The original idea of using enzymes as detergents came from Dr Otto Röhm, a very clever guy and the first chemist who isolated and applied enzymes in technical applications. Röhm patented in 1913 the use of crude pancreatic extracts in laundry pre-soak compositions to improve the removal of biological stains. He then sold the enzyme formulation ‘Burnus’, containing the protease trypsin extracted from pig pancreas, which was sold in European markets… but it wasn’t so successful. The problem with this first enzymatic detergent was that activity and stability of trypsin are not too good in the presence of typical detergent ingredients. So, all in all the concept of “detergent enzyme” did not really catch on.
Despite of the failure, this first attempt of enzymatic detergents underscored the importance of measuring parameters such as enzyme activity and stability as part of the development process, even more in early steps.
Since then, new and better enzyme-containing detergents came into the fast-growing market, until 1970 when its use was discontinued due to allegations about enzymes causing allergic reactions, specifically in some workers during the production of formulations who started having asthmatic attacks. But as science is the expert in succeeding the unsuccessful, this problem was overcome in 1975 by a great idea: encapsulating the granules of enzymes thus making them heavier and more likely to fall to the floor instead of blowing around. Of course improvements in industrial hygiene practices also made a difference.
From the 1980s, great advances in the detergent industry have taken place, such as the development of concentrated heavy-duty power detergents, softening through the wash and the addition of new enzymes. Moreover, washing conditions gradually changed towards lower temperatures and water quantities were reduced. Soon, new enzymes, better adapted to these new conditions became available: Novozymes created the first detergent Celluzyme, a multicomponent cellulose; through protein engineering techniques, Gencore developed Maxapem, the first bleach-compatible protease and Lipolase appeared as the first detergent lipase, which was also developed by Novozymes.
The importance of enzyme stability for use in laundry
Of course not all enzymes capable of degrading stains are suitable to be added into detergents. To do so, they must accomplish several criteria:
1. They must have broad substrate specificity.
2. They must be active at the pH of detergent solutions (between 7 and 11)
3. They must be active at several wash temperatures (4 to 60°C).
4. They must be stable in the presence of other detergent ingredients during the wash process as well as in storage when incorporated to the detergent.
Thus, every new candidate enzyme must undergo a characterization process before being added to detergents and stability is a major factor to consider. Once released from it encapsulated form, enzymes must withstand soaps, oxidants, brighteners, all at pH values between 7 and 11. And although one effect of incorporating enzymes is that lower washing temperatures may be employed, enzymes must remain stable and retain activity up to 60°C. Loss of enzyme activity also happens during storage, what has become a prime concern to enzyme manufacturers. The loss of enzyme activity occurs mainly due to partial unfolding. In order to protect enzyme against denaturation, adding stabilizers has proved successful, such as calcium salts, borate and sodium formate. Protein engineering has also made possible to improve enzyme stability.
An example of the importance of enzyme stability is that most detergent proteases are stable during wash in the presence of oxygen-based bleach systems, but their storage stability in detergents containing bleach may be a problem. This happens because methionine present in the protease molecule can be oxidized by the bleach, inactivating the enzyme. That’s why many protein-engineered proteases replace methionine close to the active site with other amino acids insensitive toward oxidation, thus increasing storage stability. Another example comes from a-amylases, an enzyme that degrades starch-containing stains and the starchy glue that bind other types of stain to fabric. The stability of some calcium-dependent a-amylases can be improved by adding calcium salts to the detergent formulation. Or subtilisin, a protease that requires at least one calcium ion to mantain the 3D structure of the enzyme. Calcium-sequestering agents used to control water hardness in laundry, decrease subtilisin stability, but this can be corrected by the introduction of negatively charged residues near the calcium-binding site, which increases the binding affinity of enzyme for calcium and improved stability.
Nowadays, technological advances allow to obtain information of protein stability, as is the case of nanoDSF, which performs a label free thermal unfolding assay for protein stability analysis of candidate enzymes.
Science has given me some tips to do my laundry in a more efficient and environmentally friendly way. My advice is, pay attention to what you buy and use, and choose wisely. I now use enzyme-containing detergents which also allow me to use cold water. Since as much as 90% of the energy used by washing clothes goes just to heat the water, I’m also becoming more friendly with the environment.
The contribution of enzymes in detergents has improved laundry big time…. They are very much welcome in my washing machine.