3.4. Dextranase studies on factory syrups and juices
3.4.1. Application of dextranases to last evaporator effect syrup
Because of the lack of adequate residence times for the addition of juices in US factories, dextranases have been added to the last evaporators mostly because of the availability of up to 20 min calculated R
[20]. However, the syrup temperatures and 8 Brixes occurring in last evaporators have been shown not be very conducive to applications of ‘‘non-concentrated’’ and ‘‘concentrated’’ dextranase here (Figs. 2 and 3).
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In raw sugar factories, solids are concentrated from approximately 15.0 8 Brix in juice to 65.0 8 Brix in final evaporator syrup. As a consequence, the dextranase has to act upon 4.5 times as much dextran in syrup than in juice. For this reason, dextranase were added to syrups as ppm on solids (i.e., equivalent to 4.5 times as much as if it had
been added on juice). Dextran removal was measured using a modified haze dextran method because of its ease of use and because it gives a reliable estimate of high MW dextrans which are responsible for the major processing difficulties associated with this polysaccharide [6]. However, the haze method is a reflection of all haze forming material, and although proteins are precipitated with trichloroacetic acid (TCA) and starch is removed with amylase, other polysaccharides such as indigenous cane polysaccharide could have contributed to the haze. Therefore, although results are relative, they are most likely underestimations of dextran removal. Viscosity was monitored as well as percentage dextran removal, to ensure that processing efficiency was definitely improved upon by degrading dextran in syrup with dextranases. The effect of various concentrations of a ‘‘nonconcentrated’’ dextranase to a final evaporator syrup containing dextran (7230 ppm/8 Brix) at 63 8 C are shown in Fig. 4. It can be seen in Fig. 4a that 20 ppm/solids dextranase had very little effect on dextran degradation, with only 7.4% being removed after 20 min. Slight improvements occurred at 40 ppm (Fig. 4a) with 15.8% dextran removal after 20 min. Dextran degradation with 80 ppm/solids dextranase was better, with 13.5 and 25.2% dextran removal after 15 and 20 min, respectively. However, ‘‘non-concentrated’’ dextranase at 80 ppm/solids is equivalent to 360 ppm/juice, and for such a limited breakdown in dextran at this high level, it is not economically viable to add ‘‘non-concentrated’’ dextranase to syrup. The effect of the ‘‘nonconcentrated’’ dextranase onviscosity reduction in the syrup is illustrated in Fig. 4b. At 0 ppm dextranase, the viscosity increased slightly across 20 min R
, most likely because of
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