Page 126 - Advances in Textile Biotechnology

Enzymatic modifi cation of polyacrylonitrile and cellulose acetate fi bres 107

main chain. For cellulose acetate, the hydrolysis of its side chains releases
acetic acid to the reaction media and the hydroxyl group is located on the
polymer backbone (Fig. 5.5).
The evaluation of enzyme activity on these textile substrates can be per-
formed by measuring either the chemical changes at the solid substrate or
the amount of the soluble product released into solution.

Both ammonia and acetic acid can be easily quantified using enzymatic

assays that are very specific, are simple to perform, and require only common
laboratory equipment such as a UV/visible spectrophotometer. There are
several diagnostic kits for both ammonia and acetic acid commercially
available. By measuring the decrease or increase in absorbance at 340 nm,
as the reduced nicotinamide adenine dinucleotide (NADH) is consumed or
formed, respectively, the amount of ammonia and acetic acid are calculated,
according to the stoichiometry of the reaction. Minor sample preparation
is necessary and this consists of protein removal using strong acids and
subsequent neutralization.
Other methods based on chemical reactions exist for ammonia determi-
nation. The most common is the direct nesslerization method which involves
the reaction of ammonia with an alkaline solution of mercury (II) iodide
in potassium iodide–Nessler reagent to produce an orange–brown product
(Greenberg et al., 1992, pp. 4.75–4.80). Banerjee et al. (2003) described

a fluorimetric assay based on the reaction of ammonia with buffered
o-phthaldialdehyde-2-mercaptoethanol solution (pH 7.4). The product is a
fluorescent complex, whose intensity is measured with excitation and emis-

sion wavelengths of 412 and 467 nm, respectively. Acetic acid can also be
determined by non-enzymatic assays. Gas chromatography is one of the
most used methods to quantify acetic acid for which several columns are
commercially available. A titration can also be used, but it is not specifi c
for this acid. When assessing both soluble products (ammonia or acetic acid/
acetate), it is important to verify the stability of the solutions during treat-
ment of the fibres and possible interferences, such as from the protein

content, which can alter or mask the real concentration of these compounds.
Controls with an inhibited/deactivated enzyme are important to eliminate
background interferences; the use of biocide compounds during enzymatic

treatment; or the acidification of aliquots from the treatment solutions
containing ammonia (to prevent its volatilization) are some examples
of what can be done to control as much as possible the quality of the
measurements.
For the evaluation of chemical changes on the solid material, analytical
methods that have a good surface sensitivity and depth resolution should
have an advantage because enzymes act mainly at the fi bre surface. When
comparing controls and samples from a particular enzymatic treatment, the

© Woodhead Publishing Limited, 2010