Water-in-oil (W/O) fermentation technology has the potential for overcoming the problems related with high broth viscosity in xanthan fermentations. By dispersing the aqueous broth in a continuous organic phase, the broth-thickening mechanisms are confined within the aqueous droplets without significantly increasing the overall viscosity. In this study, xanthan fermentations were made with perfluorocarbon (PFC) or vegetable oil as the organic phase. The results were compared with those obtained previously using n-hexadecane as the organic phase, to evaluate the effects of various properties. PFC provided easy phase separation at the end of fermentation but required higher power input for agitation, a direct result of its high density. The aqueous droplets formed were large (400-450 microm), limiting the cell concentration employable due to the occurrence of oxygen starvation in the inner core. One main advantage of using vegetable oil was its low cost. In addition, vegetable oil provided much finer droplets (<120 microm) and produced high xanthan concentrations (>100 g l(-1)). However, complete phase separation for product recovery was difficult to achieve. Fermentations in both organic phases were terminated by the occurrence of phase inversion to highly viscous O/W dispersions at aqueous-phase volume fractions of 0.53-0.56. The initial fraction was 0.3 but changed due to base addition for pH adjustment and nutrient addition for prolonged production.

pH-sensitive surfactants are potentially beneficial to water-in-oil fermentations. Ideally, the surfactants promote emulsification at fermentation pH (typically ∼7) but, upon pH adjustment, lose surface activity to allow easy phase separation for product recovery. In this study, poly-(methacrylic acid) (PMAA) grafted with poly(ethylene glycol) (PEG) and n-dodecane was synthesized with an initial MAA/EG molar ratio of 1:1 or 20:1 and a MAA/LMA (lauryl methacrylate) ratio of 1:0.16, 1:0.47, or 1:0.78. The polymers' pH sensitivity comes from the complexation between PMAA and PEG at low pH, which turns hydrophilic PMAA and PEG into a hydrophobic complex. The surface activity was confirmed to decrease markedly as pH dropped below ∼6.0. For polymers with 20:1 MAA/EG, the residual surface activity at low pH was still enough to inhibit the desired phase separation. However, the polymers with MAA/ EG/LMA ratios of 1:1:0.47 and 1:1:0.78 showed good emulsification at neutral pH and fast phase separation at pH 4. The polymer with 78% LMA produced the finest droplets, desirable for supporting higher cell concentrations in the fermentation.

For the development of pH‐sensitive surfactants to be used in water‐in‐oil fermentation, the free‐radical terpolymerization of methacrylic acid (MAA), methoxy poly(ethylene glycol) methacrylate (MPEGMA), and lauryl methacrylate (LMA), at a molar ratio of 1.0:0.04:0.76, was studied with two initiators, azobisisobutyronitrile (AIBN) and hydrogen peroxide, at different concentrations. The polymer synthesized with 0.45% AIBN as the initiator was the most promising, giving similar conversions of all three monomers throughout the 10‐h polymerization. The subsequent study on AIBN‐initiated systems indicated that MPEGMA caused an increase‐then‐decrease profile of the MAA conversion with a plateau around an ethylene glycol/MAA ratio of 1–2. This observation was fairly consistent with the well‐known type II template polymerization of poly(ethylene glycol) (PEG)–MAA systems. The reactivity ratios obtained in this study suggested that the polymer synthesized with AIBN as the initiator had a structure of alternating blocks of MAA and LMA, with isolated PEG grafts. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2950–2959, 2004