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| Figure 1: Recommended points of Dextranase addition in a milling train. |
Judicious use of dextranase, applied at the level of the mill, along with attention to biocide application, can help significantly with the dextran problems that are normally seen when the weather is warm and just after a rain. Given dry harvest conditions and cool weather, dextran is not a problem if adequate sanitation procedures are followed. Under conditions where dextranase addition is necessary it is recommended that the addition be at the level of the mill, so the longest residence time possible prior to the juice heaters is achieved. If the first mill juice is separated from the mixed juice, it should also be treated with the enzyme. Figure 1 shows recommended points for dextranase addition in a mill train with compound imbibition.
The dose / dextran removed scales linearly. The actual volume of enzyme used will vary, depending on enzyme source, as the strength of the enzyme varies with supplier. Dosing should start with the manufacturer’s recommendation and be adjusted according to your results. You do not need to use the enzyme unless you see or expect high dextran in the cane. Checking the dextran levels in the crusher juice first thing every morning (before fresh cane deliveries) will give you some idea on whether you need to turn on the dextranase.
Dosing this enzyme at the evaporators or in the syrup may not be cost-effective. The enzyme is inactivated at 131 degrees F and is not active much above pH 6.5. Brix also has an effect, dextranase is only 1/3 as active at 50 Brix as at 30 Brix, and is inactive at 70 Brix.
The following protocol can be used to see if the dextranase is working. Remember, it is not required to reduce dextran to zero, as only about 30% of the dextran in juice passes to the commercial sugar, 1000ppm/Brix in juice will mean about 300 ppm in sugar (and if dextranase is being used the sugar will be around 150 MAU).
Sampling
Because of the wide variation in dextran coming into the mill I suggest taking 4-5 quart size samples over an hour. Samples should be taken at the crusher (or anywhere prior to dextranase addition) and prior to the clarifier (as far downstream from dextranase addition point as possible and preferably post-juice heaters). Samples can be preserved by the addition of 1 drop of concentrated commercial biocide (this will keep the samples from deteriorating until they can be analyzed).
Analysis
Analyze for Brix (refractometer) and dextran (antibody or other method) and calculate dextran in and dextran out on a brix basis. Use the average values from the hourly samples to minimize transient fluctuations in the dextran levels.
If the enzyme is working properly, you should see a reduction in dextran from juice in cane to juice to process. If you don’t see this, first check the sanitation of the mill train. A dirty mill can increase the dextran levels by as much as 4 times. If the mill is clean and there is insufficient drop in dextran, consider upping the dose of the enzyme.