THE ROLE OF SUGAR-BEET INVERTASE AND RELATED ENZYMES DURING GROWTH, STORAGE AND PROCESSING

In a collaborative project between British Sugar pie and Sucros Ltd, f our sucrose inverting enzyme activities were identified in sugar beet: soluble acid invertase, insoluble acid invertase, soluble alkaline in vertase and soluble sucrose synthetase. The activities of these enzyme s were measured in the growing crop, during beer storage and through t he extraction process. Crop sample results confirmed many of the previ ous understandings on the phasing of plant growth and sucrose accumula tion. It is likely that the enzymes active in sugar beet before harves t are necessary in their entirety for healthy plant development. Durin g clamping and storage, a relationship between beet invertase and sucr ose synthetase activities? and invert sugar content was observed. Two distinct physiological pathways influencing these activities are propo sed. Clamping and storage trials were performed both in U.K, and Finla nd under very different climatological conditions. Typical late autumn and early winter freezing and thawing in Finland caused significant i nvertase activity increase in beet starting to deteriorate. Microbial invertases analysed showed significantly higher thermostability compar ed to beet invertases. Results from healthy beet process sampling indi cated that only a small fraction of the difference between sugar beet and raw juice invert sugar concentration was due to sugar beet derived invertase enzymes. While processing frozen and thawed beet material, the invert sugar difference was higher, but still only partially expla ined by elevated invertase enzyme activities in the beet material. The results emphasized the importance of rapid temperature increase in ex traction. It is possible to estimate the considerable financial impact of invert sugar formation during clamping and processing. This report provides information useful in the reduction of this cost.