ASTM E723-13 (2019). Standard Practice for Evaluation of Antimicrobials as Preservatives for Aqueous-Based Products Used in the Paper Industry (Bacterial Spoilage).
Test accredited by ENAC (Spanish National Accreditation Entity).
The ASTM E723 standard defines a test procedure used to determine if an antimicrobial prevents deterioration caused by bacteria in water-based processed products used in the paper industry (pigment suspensions, dye solutions, pulps, starch solutions, polymers, gluing agents, latex emulsions…etc.).
To perform the test, the aqueous material to be preserved is inoculated with an appropriate bacterial inoculum, depending on the purpose of the test. As inoculum, a material contaminated by bacteria, any of the following bacteria or a pool of them can be used: Pseudomonas aeruginosa, Burkholderia cepacia, Escherichia coli, Staphyloccus aureus and Enterobacter gergoviae. The antimicrobial under test is then added to the inoculated samples at the desired concentrations. Each test must include a minimum of five concentrations of the antimicrobial and a control, without antimicrobial. Subsequently, the samples are incubated at the storage temperature of the product, generally between 28°C and 37°C. The incubation time of the samples should be set according to the conservation time of the aqueous material and the acceptable level of contamination of the material. Samples can be taken at 3, 8, 24, 48, 72 hours, or weekly, depending on how rapidly and to what extent the inoculum needs to be killed. In addition, if the material can be re-inoculated during preservation or to determine the number of re-inoculations that one concentration of antimicrobial can control, samples can be re-inoculated on a weekly or biweekly interval. After the incubation time, the number of viable bacteria present in the sample is determined and compared with the number obtained from the control without antimicrobial to calculate the percentage of percent kill. The proper level of antimicrobial is one that reduces and keeps the microorganisms to an acceptable level in the aqueous material. Typically, the level of microorganisms should be reduced by 99.99% in a 7-day period of time. In addition, the bacterial count detected must not increase during the duration of the test (if longer than 7 days) or during the storage time of the material. The degree of preservation obtained can also be judged by evaluating visual deterioration and other signs of degradation, such as changes in pH, colour, odour, etc.