Identification of management of malodour from odour-producing bacteria in natural rubber

The rubber industry in Thailand is affected by the problem of malodours caused by volatile fatty acids (VFAs) produced by various bacteria in natural rubber (NR). In this study, we aimed to identify the bacteria in NR and rubber serum and to inhibit the unpleasant odours produced by the bacteria. Six notable bacteria, Enterobacter cloacae, Klebsiella pneumoniae, Kurthia gibsonii, Lysinibacillus fusiformis, Lysinibacillus pakistanensis, and Proteus mirabilis were identified by 16S rRNA gene analysis. The lowest concentration of substances that inhibited the growth of bacteria by 100% was determined by the minimum bactericidal concentration (MBC) method. The obtained MBC ranges of acetic acid, citric acid, and sodium benzoate were 6.25–25 mM, 3.13–25 mM and 12.5–200 mM, respectively. Moreover, NR was prepared to verify the bactericidal properties using six formulations. The results of the colony plate count method together with bacterial copy number analysis by quantitative polymerase chain reaction showed that two of the formulations, 200 mM sodium benzoate in 5% (v/v) formic acid (SB-FA) and 200 mM sodium benzoate in 5% (v/v) sulfuric acid (SB-SA), could decrease bacterial growth in natural rubber. The reduction of malodours produced by various bacteria was confirmed by sensory tests and gas chromatography–mass spectrometry. These findings may be useful to the rubber industry in the identification of a novel strategy to reduce unpleasant odours in NR preparation without affecting physical properties.