An Enzyme Often Used in Laundry — Alkaline Protease

1) What is a laundry protease? Which part of the work does it do in a detergent?

A detergent protease is an enzyme used specially tohydrolyse protein stains. It cuts the protein’speptide bondsinto smaller peptides / amino acids, so the stain is more easilydissolved or dispersedand carried away in the wash.NCBE Reading+1

In household and commercial detergents, protease is usuallythe most common class of enzyme, and the one whose dose is also most clearly felt(because the density of everyday protein stains is high: sweat, skin flakes, food protein, blood and so on).Creative Enzymes+1

2) What type is a common “laundry protease”? Why are most of them alkaline, serine proteases?

The laundry environment is mostly on the alkaline side (there is a builder-alkali and surfactant system), so mainstream laundry proteases are mostly designed asalkaline proteases, and commonly belong to theserine endoproteases, represented for example by the subtilisin class.NCBE Reading+2ScienceDirect+2

Taking Savinase (a subtilisin type), often used as teaching material in publicly available sources, as an example:

• It is a serine-type endo-protease with a broad substrate range, and can hydrolyse most of the peptide bonds inside a protein

• The suitable detergent pH range is about pH 8–12(the optimum often falls around pH 10)

• The working temperature range is about 20–60°C(above that, activity drops clearly)NCBE Reading+1

A “one-sentence” version for consumers:
What protease is best at is snipping the “protein soil stuck to the fibres” into pieces, so it is more easily washed off.

3) Which stains most need protease?

Typical protein-type stains include:

• Blood, egg liquid, milk / whey, gravy, and the protein components of soups

• Sweat stains / mixed sebum soils (sweat itself + skin-flake protein / keratin fragments)

• The protein components of grass stains / mud stains (often mixed with chlorophyll and dirt)
  Publicly available detergent-enzyme materials often use blood, egg, sweat, grass and the like as example stains for protease.Creative Enzymes+1

4) The wash and the operation: “when is protease most effective,” and how to use it without stepping on a mine

(A) Temperature: a common mine with protein stains is “high heat setting them first”

Stains such as blood and egg white readily coagulate / denature when they meet high heat, and stick to the fibres even more.
A practical suggestion:First wash / soak at a medium-to-low temperature to let the enzyme act, then, if needed, raise the temperature for a later cleaning stage (especially in a commercial process).

(B) pH: a laundry protease is usually more favoured in an alkaline bath

Mainstream laundry proteases are designed to work in the alkaline environment common in detergents (for example a pH 8–12 window).NCBE Reading+1

(C) Time and contact: a heavy stain should first have “its surface opened”

An enzyme is only effective if itcomes into contact with the substrate. For a thick layer of dried protein stain, it is suggested that you first wet / brush the surface open with water and a little detergent, then let the protease work in the bath; the success rate will be much higher.

• A practical reminder for the operation: In an industrial washer, if dosing is fully automatic, it is usually suggested that the “enzyme agent (auxiliary)” and the “bleach (hydrogen peroxide / sodium percarbonate)” bedosed in stages, or a few minutes apart.

• Although modern enzymes have been engineered for oxidation resistance, a high concentration of active oxygen will still cut enzyme activity. Letting the enzyme run for 5–10 minutes first, and then adding the bleach, usually gives the best result.

5) The logic of pairing with other enzymes / chemicals

(A) A multi-enzyme division of labour: protease is often used together with lipase / amylase

Real stains are often a “compound type”: for example a food sauce = protein + grease + starch / colloid.
So in a formula it is common to have:

• Proteaseto take the protein apart

• Lipaseto take the grease apart

• Amylaseto take the starch apart
  Mannanaseto take the thickening colloid apart
  This division of labour is a typical structure in detergent-enzyme reviews and industry materials.A.I.S.E.+1

(B) Compatibility with oxygen bleach (sodium percarbonate / peroxides): look at the “oxidation-resistant” design

An oxidising bleach (or its active species) may harm ordinary protease activity, so industry has done a great deal of engineering to giveproteases oxidation resistance / alkali resistance / heat resistance(the subtilisin family is especially typical).ScienceDirect+1

If the formula contains an oxygen bleach, the protease should be an “oxidation-resistant type,” or a system design should be used to bring the conflict between the two to a minimum.

6) Material compatibility: protease is a high-risk point for wool / silk (this must be written clearly)

This is a very important risk-management point for the laundry trade:

• Wool and silk belong to thenatural protein fibres(wool is mainly keratin; silk is the fibre protein fibroin).

• Research and professional chapters both point out that a detergent containing protease may causeclear damageto wool and silk. So if a protease is to be used on a protein fibre, a design that “limits the depth of the enzyme’s action / acts only on the surface” usually has to be made.repositorium.sdum.uminho.pt+1

• A “general powerful laundry detergent / powder that contains protease” is not recommended forwool or silk; for these materials one should choose asilk-and-wool speciality (usually containing no protease, or with a milder enzyme system)。

7) Safety and occupational health: an enzyme is not a “poison,” but inhalation must be strictly prevented (respiratory sensitisation)

Industry and occupational-health documents emphasise again and again: cleaning enzymes (including protease) as a whole are usually not highly toxic, but theyare indeed respiratory sensitisers; the risk is highly correlated with the amount of exposure to “inhalable enzyme particles / aerosols.”A.I.S.E.+2media.acihq.org+2

The suggested points of emphasis are:

• Prefer alow-dust form(a liquid, coated granules, low-dust granulation)

• When dosing, avoid raising dust / spraying; if necessary, use local extraction and personal protection

• Product labelling and training (especially for concentrated enzymes on the professional side)media.acihq.org+2amfep.org+2

8) The environmental side: why enzymes are often seen as a tool for an “environmentally friendly formula”

Industry-association materials point out that an enzyme is aprotein, and is therefore generally regarded asbiodegradable; at the same time, an enzyme can raise stain-removal efficiency at a lower temperature, and indirectly support an energy-saving wash.A.I.S.E.+1

9) Notes on choosing a protease

• **A protease can deal with:** blood, egg liquid, milk / gravy, sweat soils and other protein stains (it snips the protein into pieces and takes them away).NCBE Reading+1

• The “golden SOP” for treating bloodstains (a practical application)

• The mnemonic: cold first, then heat; enzyme first, then bleach.

• Why this way? If the first step is to put on hot water at once, the albumin in the blood will coagulate in an instant (like frying a sunny-side-up egg) and become a denatured protein. At that point, even a strong enzyme can no longer cut it, and it will become a permanent yellow mark.

• Cold water (<30°C) + protease:First soak or brush with cold water and a pre-wash (or a stain remover aimed at blood) that contains protease. Give the enzyme time to cut the haemoglobin and the plasma proteins.

• Rinse: Rinse away the soil that has been cut into pieces.

• Main wash / bleach (>60°C): After the first step, if pigment still remains, then raise the temperature, and use sodium percarbonate (oxygen bleach) to deal with the remaining pigment.

• **Best use:** first let the enzyme act at a medium-to-low temperature, then do the later wash; wet a thick stain open first, then wash.

• **Materials not recommended:** wool, silk (protein fibres may be harmed by the enzyme).repositorium.sdum.uminho.pt+1

• The nature of wool and silkis protein。

• Wool = keratin (the same as human hair and nails).

• Silk = fibroin.
  
  

• The consequence: If you wash a woollen garment with a powerful protease, the enzyme cannot tell “stain protein” from “garment protein”; it will cut them all the same.

• Slight damage: The garment becomes thinner, the lustre disappears, the hand becomes coarser.

• Serious damage: The structure collapses; the garment gets holes or is “pulverised.”

• **A safety reminder (professional side):** avoid inhaling dust / mist, because an enzyme may cause respiratory sensitisation.media.acihq.org+1