engleski

Biooxidation kinetic in reaction systems of low water activity

Kinetics of D-glucose and D-sorbitol oxidation catalysed by biocatalytic system of Gluconobacter suboxydans S-22 in reaction media of low water activity were studied. The shake flask cultivation experiments at different temperatures were performed applying reaction systems with intact and disintegrated microbial cells suspended in sterile water solutions of different D-glucose or D-sorbitol concentration. Values of input parameters adequately reflected on experimental results. The increase in substrate concentration caused an adequate decrease of volumetric oxygen transfer rate coefficient (KLa). Specific biocatalytic activity of washed whole intact cells was much higher than that of corresponding amount of disintegrated cells, only in the substance concentration range below 500 g/L. In general, specific biocatalytic activities were decreasing with increasing substrate concentration. However, the fall down of activity of intact cells as a function of substrate concentration appeared to be of sigmoidal form, while that of disrupted cells showed to be approximately linear. A lower temperature (30 oC) was more convenient for reaction systems of lower substrate concentration (100 g/L), while a higher temperature (37 oC) showed to be more favourable for reaction systems of higher substrate concentration. Temperature increase caused the specific biocatalytic activity to decrease in dependence on water activity increase. Data agree with expectation, if taking into account findings of others (1) for other reaction systems. Based on the obtained results and our previous observation (2), it could be concluded that mass transfer phenomena play an important role in biooxidation kinetics. In substance concentration range below 500 g/L the "gas-liquid interface" appears to be more relevant, while at higher substance concentration the "cell-liquid interface" and the activity of biocatalyst become more important and influence the process kinetics more. Findings of this work support our previous observation and suggest the application of higher biooxidation temperature, in cases when water activity in reaction systems falls down below 0.4 (e.g. when applying high yielding prolonged fed batch culture or two-compartment fed batch culture). 1. E. Barzana, M. Karel, A. M. Klibanov, Biotechnol. Bioeng. 34 (1989) 1178-1185. 2. M. Bošnjak, K. Mihaljević, Med. Fac. Landbouw. Univ. Gent, 58/4b, (Proc. 7th FAB, Gent 30 Sep.-1 Oct., 1993) pp. 1939-1948

Biooxidation kinetics; D-glucose; D-sorbitol; water activity

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