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Title: Stability of yeast invertase in relation to industrial application
Author: Woodward, Jonathan
ISNI:       0000 0001 3572 455X
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1977
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The enzyme yeast invertase (E.C. catalyses the hydrolysis of sucrose to an equimolar mixture of glucose and fructose. Two forms of invertase exist, an extracellular form known as external invertase which is a glycoprotein containing 58% (w/w) mannan, and an intracellular form known as internal invertase which is devoid of mannan. Thermal inactivation of purified external and internal invertases from Baker's yeast was found to occur at 65 C and 50 C respectively, suggesting that the mannan moiety of the external enzyme is responsible for its thermal stability. Removal of mannan from the external enzyme by digestion with ?-mannosidase did nut lower its stability to that of the internal enzyme, indicating its ambiguous role in conferring stability on to the invertase tertiary structure. Candida utilis external invertase has been shown to be much more thermally stable than the corresponding enzyme from Baker's yeast, the latter being used for the production of soft-centred confectionery. The potential usefulness of the C. utilis enzyme to the confectionery industry is discussed. The improvement of the thermal stability of Baker's yeast invertase to that of the C. utilis enzyme has been attempted by chemical modification using bifunctional cross-linking reagents. Only glutaraldehyde was successful, but at the expense of a loss in specific enzyme activity. The chemical modification of Baker's yeast invertase using Fremy's salt, iodine, citraconic anhydride, a water-soluble carbodiimide and toluene diiosocyanate, resulted in the destabilization of the enzyme activity. The possible amino acid interactions involved in maintaining conformational stability of this enzyme are discussed. C. utilis invertase has been stabilized by its chemical modification using dimethylsuberimidate and by heating in the presence of Ca2+. The immobilization of Baker's yeast invertase on to several supports and its effect upon thermal stability is described. Finally, the difference in stability between Baker's yeast and C. utilis invertase, and the role of the mannan moiety in stabilizing the external invertase molecule in conjunction with amino acid interactions, is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available