IMPROVED SHAKE-FLASK TEST FOR THE SCREENING OF XANTHAN-PRODUCING MICROORGANISMS

Baffled 500 ml Erlenmeyer flasks were compared with conventional 2800 ml Fernbach flasks for Xanthomonas campestris to produce xanthan. Bacterial growth rates were similar in both types of flask although the Fernbach flasks gave higher biomass concentrations. Xanthan production was similar in both types of flasks but different viscosities were attained. On a weight basis, the xanthan produced in baffled flasks was up to three times more viscous and more pseudoplastic or 'shear thinning'. For screening purposes, baffled flasks are better because the rheological quality of the gum produced in them is more like that obtained in stirred fermentors than the gum from Fernbach flasks and considerably less shaker space is required, thus allowing a larger number of tests to be performed.