Enzyme Technology
Use of immobilised invertase
Invertase was probably the first enzyme to be
used on a large scale in an immobilised form (by Tate & Lyle). In the period
1941 -1946 the acid, previously used in the manufacture of Golden Syrup, was
unavailable, so yeast invertase was used instead. Yeast cells were autolysed and
the autolysate clarified by adjustment to pH 4.7, followed by filtration through
a bed of calcium sulphate and adsorption into bone char. A layer of the bone
char containing invertase was included in the bed of bone char already used for
decolourising the syrup. The scale used was large, the bed of invertase-char
being 2 ft (60 cm) deep in a bed of char 20 ft (610 cm) deep. The preparation
was very stable, the limiting factors being microbial contamination or loss of
decolourising power rather than loss of enzymic activity. The process was cost-effective but, not surprisingly, the product did not have the subtlety of
flavour of the acid-hydrolysed material and the immobilised enzyme process was
abandoned when the acid became available once again. Recently, however, it has
been relaunched using BrimacTM, where the invertase -char mix is stabilised by
cross-linking and has a half-life of 90 days in use (pH 5.5, 50°C). The
revival is due, in part, to the success of HFCS as a high-quality low-colour
sweetener. It is impossible to produce inverted syrups of equivalent quality by
acid hydrolysis. Enzymic inversion avoids the high-colour, high salt-ash,
relatively low conversion and batch variability problems of acid hydrolysis.
Although free invertase may be used (with residence times of about a day), the
use of immobilised enzymes in a PBR (with residence time of about 15 min) makes
the process competitive; the cost of 95% inversion (at 50% (w/w)) being no more
than the final evaporation costs (to 75% (w/w)). A productivity of 16 tonnes of
inverted syrup (dry weight) may be achieved using one litre of the granular
enzyme.
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This page was established in 2004 and last updated by Martin
Chaplin on
6 August, 2014
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