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The effect of particle morphology and concentration on the directly measured yield stress in filamentous suspensions
Author(s) -
Mohseni M.,
Allen D. G.
Publication year - 1995
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.260480312
Subject(s) - volume (thermodynamics) , yield (engineering) , chromatography , fermentation , particle size , chemistry , pulp (tooth) , morphology (biology) , volume fraction , materials science , food science , composite material , biology , medicine , physics , pathology , quantum mechanics , genetics
The influence of concentration (mass and volume fraction) and particle morphology on the yielding properties of filamentous broths of Aspergillus niger and Strepto ‐ myces levoris was investigated using the rotating vane technique and compared with those of pulp suspensions. Two methods were applied to determine the volume fraction of the cells growing in filamentous form: the measurement of interstitial volume using a high molecular weight dye or dextran, and the measurement of dewatered broth filter cake volume by displacement using a pycnometer. The latter method provided the most reliable results. Cell concentrations ranging from 3 to 20 g dw/L, with corresponding volume fractions between 0.005 and 0.05, were obtained with broths generated in stirred tank and shake flask fermentations. The yield stress values obtained using the vane technique (0.1 ≤ τ y ≤ 37 Pa) correlated with biomass concentration ( X , grams dry weight per liter) using the equation τ y = aX b with “ b ” ranging between 2 and 3. Increasing the length of organisms significantly increased the yield stress at a given cell concentration; this morphology effect was described using a “morphology factor” (range 0.016 to 0.11 Pa/[g dw/L] 2.5 ), determined by setting the value of “ b ” to 2.5. The vane yield strain, which is the critical strain or deformation at the yield point, was independent of cell concentration, but increased with increasing length of organisms. Filamentous fermentation broths with highly branched organisms had a greater yield stress than pulp suspensions. © 1995 John Wiley & Sons, Inc.