BIOTECHNOLOGY TECHNIQUES Volume 7 No.7 (July 1993) pp.463-468 Received 14th May XANTHAN FERMENTATIONS IN WATER/OIL DISPERSIONS Lu-Kwang Ju* and Su Zhao Department of Chemical Engineering, The University of Akron Akron, OH 44325, USA SUMMARY Xanthan fermentations in W/O dispersions performed better than the control in both small flasks and a 6.6-L fermentor. The better bulk mixing and oxygen transfer achieved in the dispersion resulted in a still rising xanthan concentration of 65 g/L, compared with 26 g/L in the control. A phase inversion phenomenon was observed when n-hexadecane recovered from previous runs was used as the oil. INTRODUCTION Xanthan gum is an extracellular polysaccharide produced industrially by fermentation of Xadwmonas cam,pestris. Economic analysis has shown t,hat its product,ion costs can be reduced substantially by increasing the gum concentration in the harvested broth (Vincent, 1985). Xanthan broths are, however, highly viscous pseudoplastic fluids having yield st,ress (Galindo et a/., 1989) and lead to a “cavering” phenomenon with the region around the impeller well-mixed and the surrounding fluid st.agna.nt or nearly so (Solomon et al., 1981). The broth rheology presents serious problems to mixing, heat transfer, and oxygen supply and, consequently, limits the maximum gum concentration achievable to 5% (w/v) (Atkinson and Mavituna, 1983). Recognizing this limiting characteristic, Robinson and Wang (1985, 1988) immobilized cells in porous Celite part,icles to preferentially retain the produced gum in particles. Similar techniques were applied to other biopolymer fermentations (Mulchandani et aE., 1989; Wang and Wang, 1989). The technique, however, faced a dilemma: ret,ention of cells and polymers was poor in small support particles; nutrient, especially 02, became limited in larger particles when used to improve the retention of cells and products. On the other hand, emulsion fermentations for xanthan production were described in several patents (e.g. Maury, 198 2; Viehweg, 1989). By confining the thick xanthan broth within emulsified particles in an oil phase, it was shown t,o minimize viscosity problems and significant,ly enhance biopolymer yields with less energy input. However, little fundamental information is available. The use of surfactants further complicated the downstream processingby the difficult emulsion breaking and surfactant removal during product recovery (Schumpe et al., 1991). 463