How a clarification aid can affect polarimetric analysis of sugarcane juices

The use of clarification/filter aids for polarimetric measurements of cane products is still an acute problem in many countries due to the toxicity and environmental concerns of lead acetate, the availability of other non-lead aids, and concerns with any metal salts advocated as lead acetate substitutes. A systematic study was undertaken comparing various amounts of two commercial clarification aids (Octapol and Clearpol) and Diatomaceous Earth (DE) on the filtration of Louisiana factory juices through coarse filter paper (27 µm pore size) for their effect on the accuracy of polarimetric measurement at 589 nm, and how they compare to HPLC (high-performance liquid chromatography) values. Octapol had a significantly (P < 0.05) higher density (0.615 g/cm3) than Clearpol (0.440 g/cm³); thus, for the same volume, slightly less mass of Clearpol is added. The amounts of total salts (av. 17.6%) in Octapol were higher (P < 0.05) than in Clearpol (av. 5.3%), with a much greater batch-to-batch variability. Excess amounts of Octapol caused an increase in the filtrate dry substance content and decreased polarimetric and HPLC sucrose contentss; this phenomenon also occurred for Clearpol but to a much lesser extent. The dry substance increase in the filtrate juice was due to soluble mineral salts from the aids dissolving. Overall, this study highlights the importance of standardizing clarification aids for polarimetric measurement and the need for batches or lots of such aids to be monitored for critical components affecting the polarimeter readings, e.g., total salts. A greater risk is being taken when using aids that contain relatively high amounts of salts (>~6%) because results are more susceptible to inaccuracy when excessively dosed.