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Biochemical properties of three sugarbeet root sucrolytic enzymes and their implications for postharvest sucrose loss.

Klotz, K. L.; Finger, F. L.;

Proceedings from the 31st Biennial Meeting (Agriculture) of the American Society of Sugar Beet Technologists, Vancouver, BC, Canada, 28 February-3 March, 2001

2001

บทคัดย่อ

Biochemical properties of three sugarbeet root sucrolytic enzymes and their implications for postharvest sucrose loss.

The major soluble acid invertase [ beta -fuctofuranosidase] isoenzyme and 2 sucrose synthase isoforms (sucrose synthase I and sucrose synthase II) of the roots of sugarbeet hybrid VDH66156 were isolated and their activities under different environmental conditions were determined to assess the ability of the enzymes to degrade sucrose under typical postharvest storage and processing conditions. The optimum temperatures for acid invertase, sucrose synthase I and sucrose synthase II were 35, 50 and 40-45 deg C, respectively. The acid invertase isoenzyme and sucrose II were completely and irreversibly inactivated at temperatures of 60 deg C or greater. Sucrose I was inactivated at temperatures of 65 deg C or greater. All 3 enzymes retained a portion of their activity at temperatures typical of storage. At 5 deg C, the acid invertase isoenzyme, sucrose synthase I and sucrose synthase II, retained, respectively, 16, 8 and 14% of their activity relative to their activity at 35 deg C. Acid invertase exhibited a plateau of activity at pH 5.0 to 5.5, and its activity increased 7.5 times with a decrease in pH from 5.0 to 3.0. Sucrose synthase I was active in the pH range of 5.5 to 8.0; sucrose synthase II was active in the pH range of 5.5 to 7.5.