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

Abstract

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 τ 0 – N [ P ( t )]·ln ẏ 0 , leading to a dimensionless power‐law equation valid over the entire fermentation: (τ/τ 0 ) = (ẏ/ẏ 0 ) N [ P ( t )] . The resulting power‐low from[(τ/τ 0 ) = [ẏ/ẏ 0 ] N ( t )] indicates that all related samples will exhibit power‐low plots passing through the common point, (τ 0 γ 0 ). 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 P B , 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.