Extracellular microbial polysaccharides. II. Evolution of broth Power‐law parameters for xanthan and pullulan batch fermentation

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Abstract
The shear viscosities of xanthan batch fermentation broths obey a power‐law relation τ = K (P)[ẏ]N(P), where the power‐law parameters are functions of xanthan concentration P. within the shear rate range of 1.15 to 384.0 sec−1. Cell‐free solutions prepared from these samples exhibit the same values of K and N as the corresponding cell‐bearing broth. Further, in the course of the fermentation time, t, it was found that K(P) and N(P) were related by an equation of the form ln K[P(t)] = ln τ0 – N[P(t)]·ln ẏ0, leading to a dimensionless power‐law equation valid over the entire fermentation: (τ/τ0) = (ẏ/ẏ0)N[P(t)]. The resulting power‐low from[(τ/τ0) = [ẏ/ẏ0]N(t)] indicates that all related samples will exhibit power‐low plots passing through the common point, (τ0γ0). These equations have previously been observed with other polysaccharide solution. They are also shown here to be applicable to the pullulan fermentation data of Leduy et at. The parameter K is related to polymer concentration (P) with the correlation K = A PB, where B = 1.75 ± 0.25 for xanthan solutions. With X(t), S(t), and P(t) available from paper I, the correlations of this paper (hereafter referred to as II) [K(t) = f(P)(t) and N(t) = g(K(t))] provide a predictive description of the shear viscosity evolution of polysaccharide‐producing fermentation broths.
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