NC State
J. Mentu, T. Pirttijärvi, H. Lindell and M. Salkinoja-Salonen. Microbiological control of pigments and fillers in paper industry. In The Fundamentals of Papermaking Materials, Trans. of the XIth Fund. Res. Symp. Cambridge, 1997, (C.F. Baker, ed.), pp 955–993, FRC, Manchester, 2018.


Microbial contaminants will decrease the quality of pigments and fillers in paper and board industry . Microbe-caused spoilage of these raw materials as well as indirect deteriorative effects of these spoiled
additives on the machine housekeeping, production and hygienic properties of paper products are well-known problems at the mills.

The traditional analysis of colony forming units helps both the manufacturer ofraw material and his client to understand, what are the major contaminants and their densities in the raw material studied.
These methods, unfortunately, are unsatisfying when rapid microbiological analyses are needed in urgent situations (trouble shooting, prevention of process contamination) . Their shortage as indicators of the effects of biocides on the activity of microbes is also evident . Three “rapid methods” were regarded as promising alternatives of colony count analyses in the control of paper and board
machine’s processes: detection of microbial growth by impedance method or turbidity test and measurement of biomass by luminometric ATP assay . When tested for mineral additive control, difficulties were arisen in every case: inhibitive effect of sedimentation of the sample in direct impedance measurement, poor interpretation of slow growth responses in indirect impedance method and the adsorptive effects of turbidity on the light emission (ATP assay) or on the background
absorbance (turbidometry) . For these reasons, strong dilutions of samples were needed and only high microbial densities (over 1000000 CFU/ml) were practically measurable by these methods. Integration of total impedance change may help to estimate low microbial densities by impedance methods, and more effective extraction and fractioning of microbial ATP may increase the sensitivity of ATP assay . Turbidometry seems to be a rather finished method, but its weak point is the long incubation period needed. Some efforts to develop all methods for the control of mineral additives seems thus to be necessary.

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