Optimal application of dextranase in a Louisiana sugarcane factory to mitigate severe processing problems after a freeze

Abstract

A Louisiana (LA) state-wide severe freeze occurred from 23–26 December 2022, which was followed by warm weather and occasional fog causing severe deterioration of all sugarcane varieties in the fields. Dextranase was applied to break down dextran (glucose polysaccharide) into smaller, more manageable molecules, which can improve processing. The efficiency of dextranase application depends on the pH, dry solids content rds (Brix), temperature, retention time, and agitation, type, activity and dosage of the applied dextranase as well as the enzyme/substrate ratio. Dextranase applications to juice are more efficient and economical than adding to syrup because the high temperature and dry solids content of syrups impede its action. Heating juice to 50 °C and pre-liming to pH 5.9 is optimal for dextranase application, but after 50 °C the activity falls off quickly. One LA factory built a new juice liming system that was quickly modified for optimal dextranase application after the freeze. Optimum conditions for concentrated dextranase (92700 DU/mL) applied were: rds <25%, temperature 50 °C, juice pH = 5.90, 1:10 working solution of concentrated dextranase up to 5 mg/L dosage; retention time = 10 min; 0.624 s–1 agitation. These conditions were successful with >80% breakdown of Haze dextran and minimized processing problems associated with the freeze. Retention time was not as important as temperature and the pH of the juice. The use of dextranase allowed this factory to (i) process all the field sugarcane from the growers even when sucrose concentrations were very low (down to ~56% juice purities on the last day of cane delivery), (ii) continue to crystallize sugar at acceptable crystallization rates, (iii) keep crystal elongation factors to only 2.3 and largely prevent needle formation, and (iv) allow the production of raw sugar with no dextran penalties from the refinery.