Influence of oxidizing and non-oxidizing biocides on enzymatic and microbial activity in sugarcane processing

Authors: Terrell, Evan; Qi, Yunci; Bruni, Gillian; Heck, Emily

Submitted to: Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2023
Publication Date: 9/8/2023
Citation: Terrell, E., Qi, Y., Bruni, G.O., Heck, E. 2023. Influence of oxidizing and non-oxidizing biocides on enzymatic and microbial activity in sugarcane processing. Processes. 11(9). Article 2693. https://doi.org/10.3390/pr11092693.
DOI: https://doi.org/10.3390/pr11092693

Interpretive Summary: Different processing aides are used during raw sugar manufacturing to address issues that result from the presence of unwanted contaminants. These contaminants include polysaccharides (e.g., starch, dextran, fructan) that pose engineering challenges related to sugarcane juice processing and sugar crystallization. Other contaminants include bacteria (e.g., Leuconostoc, Gluconobacter, Pantoea) that consume sucrose as well as produce their own polysaccharides. The management of polysaccharides is achieved through applications of enzymes that can break down polysaccharides. The management of bacteria is achieved through applications of biocides, which can kill bacteria or at least limit their abundance. These biocides can be either "oxidizing" or "non-oxidizing" based on the way they react with other things. One concern when applying oxidizing biocides is that they will non-specifically react with everything in a sugar solution. This may be problematic when enzymes are also present, because the enzymes could lose activity if they react with a biocide. The goal of this study is to explore if these kinds of interactions exist. Results show that the oxidizing biocide sodium hypochlorite (i.e., bleach) can result in diminished residual activity of some enzymes. The biocides were also tested against some bacteria test for susceptibility. These experiments show that in some cases, non-oxidizing biocides (i.e., carbamates) are better than sodium hypochlorite for controlling bacteria growth. These results may have practical implications for how different processing aides can be applied during sugarcane processing for raw sugar production.

Technical Abstract: Processing aides are utilized during raw sugar manufacturing at sugarcane processing facilities to mitigate unwanted contamination from microorganisms and their associated exopolysaccharides (EPS). Microorganisms present in processing facilities contribute to sucrose losses through sugar inversion and consumption, with many bacteria strains subsequently producing dextran and fructan EPS that cause downstream issues related to viscosity and crystallization. Similar issues also result from the presence of unwanted starches from plant material in cane juices. Processing aides include biocides (e.g., sodium hypochlorite, carbamates, hop extracts) for bacterial inhibition, and enzymes (e.g., dextranase, amylase) to break down polysaccharides present in juices. However, oxidizing biocide processing aids (chiefly sodium hypochlorite) may inhibit enzymatic processing aid activity. In this study, biocides and enzymes were simultaneously added to sugarcane juice to measure residual enzymatic activity for dextranase and amylase. The same biocides were also tested to estimate minimum inhibitory concentrations against Leuconostoc, Gluconobacter, Pantoea bacteria strains isolated from Louisiana sugarcane processing facilities. Enzymatic processing aide experiments provide evidence to suggest that sodium hypochlorite may interfere with enzymatic activity, with lesser/limited enzymatic inhibition from carbamates and hop extracts. Further, biocide assays suggest that sodium hypochlorite has limited effectiveness against tested bacterial strains. Hop extract biocide was only effective against Gram-positive Leuconostoc, while carbamate biocide showed more broad-spectrum activity against all tested strains.