Submitted to: American Society of Sugarbeet Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 11/13/2000
Publication Date: N/A
Technical Abstract: The enzymatic conversion of sucrose to invert sugars is responsible for a significant loss of sucrose during postharvest storage and processing. Sucrose catabolism causes sucrose loss directly by the degradation of sucrose and indirectly by the formation of invert sugars that increase the loss of sugar to molasses. The enzymes acid invertase and sucrose synthase have been implicated in postharvest sucrose loss. Some of the biochemical properties of the major soluble acid invertase (AcInv) and two sucrose synthase isoenzymes (SucSynI and SucSynII) were determined to assess their ability to degrade sucrose under conditions typical of storage and processing. Temperature activity profiles revealed that all three enzymes are capable of degrading sucrose at the low temperatures that occur in storage. AcInv, SucSynI and SucSynII retain 16, 8 and 14% of their activity at 5 degree C. Complete inactivation of these enzymes required temperatures of 65 degree C or greater. AcInv and SucSynII were completely inactivated at 60 degree C; SucSynI was completely inactivated at 65 degree C. The sucrose synthase isoenzymes exhibited a surprising degree of heat stability, with a temperature optimum for activity of 50 degree C. AcInv exhibited a plateau of activity at pH 5.0 to 5.5 and activated 7.5-fold with a decrease in pH from 5.0 to 3.0, possibly due to the loss of an inhibitor. SucSynI and SucSynII exhibited maximum activity at pH 6.5 and 7.0, respectively. These studies suggest that potential sucrose loss by these enzymes during sugarbeet root processing can be minimized by control of temperature and pH conditions.