Washing powders usually only contain one type of
enzyme, though some have two or all three; the activity
of these enzymes can be determined using a pH Stat titration
Enzymes are biological molecules that
catalyse (speed up) chemical reactions. Enzymes are
specific - they will only work on particular molecules.
For example, the enzyme sucrase will only bind with
and break bonds in sucrose, not any other type of sugar.
Another characteristic of enzymes is that they can
be re-used over and over again. A single enzyme will
typically catalyse around 10,000 chemical reactions
per second. This means that only a tiny amount of enzyme
is needed to have a huge effect on a reaction.
The rate of enzyme activity depends
on the amount of enzyme present, and also the temperature
and pH of the reaction solution. The most favourable
pH for many enzymes is 6-8, but there are exceptions:
pepsin, a digestive enzyme in the stomach, works best
at pH 2.
People have been experimenting with ways to use the
power of enzymes to clean clothing
for a long time; in fact, the first patent was in 1913.
Because stains are made of different types of molecules,
a range of enzymes are needed to break them down.
- Proteases break down proteins, so are good for blood,
egg, gravy, and other protein stains.
- Amylases break down starches, and lipases break
down fats and grease.
Washing powders usually only contain one type of enzyme,
though some have two or all three.
The activity of these enzymes can be determined using
a pH Stat titration
- The active enzymes to be investigated are weighed
into the sample vessels in the form of aliquots of
the solid substances and these are placed in the sample
beaker. The enzyme sample is first dissolved
by adding a buffer solution.
- Afterwards buffer solution is added (as well as
other auxiliary solutions if required) and the
initial pH value is adjusted, then the reaction
is started by the addition of a defined volume of
substrate solution (0.1-1.0mL).
- In the reaction phase the pH value
is held constant under vigorous stirring (using a
homogenizer) by adding sodium hydroxide solution (pH
stat titration) and the NaOH consumption is recorded
as a function of time.
- The reaction is terminated when either a given conversion
(NaOH consumption) has been achieved, if the reaction
rate (NaOH consumption per unit of time) is too small
or after the maximum permitted reaction time has elapsed.
The Metrohm system used for the automatic
determination of the enzyme activities consists of an
815
Sample Processor, an 842
pH Stat Titrando, and several other 800 Dosinos
for adding the substrate solution and various auxiliary
solutions, etc. The titration
software tiamo™
controls the system.
After each sample has been titrated, the whole electrode
assembly, homogenizer and burette tips are cleaned prior
to the next sample. |
