4. Summary and further discussion
In the US, most commercial dextranases are from a fungal (Chaetomium) source and are available in ‘‘nonconcentrated’’ or ‘‘concentrated’’ forms. An approximate 8to 10-fold difference in activity exists between the two forms, and activity variations exist among dextranases within each form. Currently, there is no uniform method to measure dextranase activity used by commercial dextranase vendors, which has meant that direct comparison of activities is not possible. A simple titration method to determine the relative activity of dextranases has been identified and modified for easy factory use. This method will allow factory staff to compare commercial dextranases and make more informed decisions on which dextranase to use, as well as monitor the stability of the dextranases stored across the grinding season, as some have been shown to change. Under factory storage conditions over the typical length of a Louisiana grinding season, the activity of a ‘‘concentrated’’ dextranase decreased only slightly (9%). In strong contrast, the activity of a ‘‘non-concentrated’’ dextranase had approximately halved ( 46%) and even reduced in activity when stored under refrigeration.Overall, applications of dextranases to juice were much more efficient and economical than adding them to evaporator syrups, and application of ‘‘concentrated’’ dextranase was more economical than application of ‘‘non-cocnentrated’’. Some sugar technologists [10] have advocated dextranase addition to syrup rather than juice because it is ‘‘wasteful to treat contaminated material before its clarification’’. However, recent large factory studies [4] have shown that dextran removal is very dependent on the clarification system in use, and if no pre-heating of the juice occurs as in cold liming, dextran can even form. Furthermore, Eggleston et al. [4] found much less dextran removal across factory clarification processes than DeStefano [10] reported in three samples. Application of ‘‘nonconcentrated’’ dextranases to final evaporator syrups is not economical and confirms initial factory studies. However, ‘‘concentrated’’ dextranase can be applied at levels as low as 10 ppm/solids (equivalent to 45 ppm/juice), and although this is higher than levels required for addition to juice, factory staff could consider adding it to both syrup and juice when severe dextran problems are occuring after a severe freeze or storm. Heating the juice to 50.0 8 C, dramatically removed more dextran from a juice than at the current ambient temperature of application (32.2 8 C) and was more economical. In practice at the factory, to bring the juice temperature up to 48.9 8 C (or at least in the optimum temperature range of 43.3–54.4 8 C), heated juice could be recirculated into small tanks with as little as 5 min R
for the ‘‘concentrated’’ dextranase to work at < 4 ppm/juice levels. Such tanks could include tanks which were previously used for cold liming. Accurate temperature control of the juice must be maintained to preventinactivation of the dextranase. Leuconostoc and Lactobacillus growth does not occur readily at or above a temperature of 50 8 C [6]; therefore, the possible problem of simultaneous dextran formation and breakdown is expected to be limited. This is further evidenced by the formation of dextran being catalyzed by an exogenous enzyme dextransucrase, compared to the endogenous mechanism of dextranase to breakdown dextran. Moreover, dextranase was shown to work in the presence of biocide (dithiocarbamate) injuice. Nevertheless, factory studies are being planned to check that no adverse dextran formation is occurring at 50.0 8 C, as well as optimize conditions for factory conditions as extrapolation from the laboratory to the factory is not always simple.