Selective oxidation of colour-inducing constituents in raw sugar cane juice with potassium permanganate

Authors: FANG, YIDA - Colorado School Of Mines; ELLIS, ANDERSON - Colorado School Of Mines; Uchimiya, Sophie; STRATHMANN, TIMOTHY - Colorado School Of Mines

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2019
Publication Date: 6/18/2019
Citation: Fang, Y., Ellis, A., Uchimiya, M., Strathmann, T.J. 2019. Selective oxidation of colour-inducing constituents in raw sugar cane juice with potassium permanganate. Food Chemistry. 298:125036. https://doi.org/10.1016/j.foodchem.2019.125036.
DOI: https://doi.org/10.1016/j.foodchem.2019.125036

Interpretive Summary: Removal of color-inducing constituents produced during sugar cane juice processing represents a major cost and it is one of the most important parameters monitored during sugar refining. While many current decoloring technologies are based upon physical methods, these methods require addition of capital-intensive unit operations (e.g., adsorber beds). Other available chemical treatment methods like sulphitation can also introduce potentially toxic byproducts. As a result, new technologies for decoloration are desired that can be directly applied within existing refinery unit operations (e.g., clarification steps) while being selective for color-inducing constituents without negatively affecting sugar yields. The work reported here represents the first ever report on the decoloration of real raw sugar cane juice solutions using potassium permanganate (KMnO4), a selective chemical oxidizing agent that is available commercially in bulk and already widely applied at drinking water treatment utilities. Results show that the chemical selectivity of permanganate acts to oxidize color-inducing constituents (e.g., phenolics) while being unreactive with the desired sucrose components in the sugar cane juice. In addition, during reactions the permanganate is converted to solid phase Mn(IV/III) products that can be readily removed by existing clarification steps within the sugar refining process stream. Thus, findings indicate a promising new strategy for decoloration of sugar cane juice that can potentially be applied within the existing sugar refining infrastructure.

Technical Abstract: Color removal in produced raw sugar represents a crucial but expensive process in the sugar industry and current technologies are only focused on physical separation methods. In this report, permanganate (MnO4-) oxidation is explored as an alternative method to remove color-inducing constituents in sugar cane juice or produced raw sugar. Results of oxidant screening experiments showed permanganate to be most effective at 70C, and alum, an inexpensive coagulant, was able to remove residual Mn species, which otherwise would produce artificial absorbances in ICUMSA color measurements, after MnO4- treatment. The optimal dosages of MnO4- and alum for decoloration of a 17 wt% raw sugar solution (70C) was found to be 4 mM and 2 g/L, respectively, resulting in a 92% reduction in color. Color removal was further improved (95%) by permanganate treatment at ambient temperature, and removal of residual Mn was improved from 70% to 88%. Sugar analysis confirmed sucrose, the major component of raw sugar, was not oxidized or otherwise degraded during treatment with MnO4- and alum. Two-phase kinetic behavior was observed, where an initial rapid oxidation phase (10 min) is followed by a second slower reaction phase that continues for up to 110 min. Collectively, these results suggest that permanganate oxidation is a promising alternative for accomplishing the decoloration of raw sugar solutions.