Abstract
Microbial-infected sugarbeets with rot along with associated soil microbes are carried into factory processing streams during raw sugar extraction. These microbes consume sucrose and commonly cause downstream processing issues. In particular, bacterial exopolysaccharides often cause operational challenges by clogging filters, increasing viscosity, and interfering with clarification and sucrose crystallization. Therefore, isolation and identification of the microbes and key phenotypes are central toward ongoing efforts to reduce microbial-related sucrose losses. This study was conducted in order to obtain relevant microbial isolates from sugar beet factories to facilitate further investigation into impacts on processing as well as to determine optimal antimicrobial dosing. To this end we conducted a microbial isolation study from juice and biofilm material broadly sampling from eighteen sugarbeet processing factories across North America. Juice and biofilm material was collected by factory operators into cryovials containing glycerol to produce a cryostock that could be frozen while preserving microbial viability until samples could be shipped to the research laboratory in New Orleans, LA and cultured for identification. This effort resulted in 612 isolates. In total, 379 isolates, belonging to 22 genera, were obtained from 33 diffuser tower juice samples, and 233 isolates, belonging to 26 genera, were obtained from 21 biofilm samples. Susceptibility testing of key groups of microbial isolates by microdilution assay has been used to assess the minimum inhibitory concentration (MIC) values of conventional antimicrobial agents to prevent microbial growth. The MIC value of sodium hypochlorite for most Leuconostoc, Weissella, Bacillus, and Peribacillus isolates was typically 250 ppm with a few Leuconostoc outliers showing increased resistance at significantly higher doses. Pantoea and Rahnella typically had higher MIC values near 500 ppm of sodium hypochlorite. MIC doses of Hydritreat 2216 with peracetic acid active ingredient ranged from 63-250 ppm for Leuconostoc, Weissella, Bacillus, Peribacillus, Pantoea, Rahnella, and Acinetobacter isolates. Hops Betastab XL was tested against Gram-positive isolates and showed MIC values typically in the range of 16-31 with a few outlier MIC values for more resistant strains of Leuconostoc above 1000 ppm. Avancid GL50 (glutaraldehyde) showed relatively lower effectiveness against isolates with MIC value ranges of 250-1000+ ppm. Magnacide D showed better inhibition of Gram-negative isolates at MIC values between 16-250 ppm whereas it was generally less effective against Gram-positive isolates. These studies also indicate that high temperature of 50 ℃ or more is advantageous for controlling growth of key microbial contaminants and may be more impactful for processing than some antimicrobial agents.