ISSN:
0178-515X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Abstract Apparent yield stress is a very useful rheological property which is important in determining the extent of mixing in xanthan fermentations as well as the suspending ability of the gum solutions. Using a previously developed stress relaxation technique, three commercial products, one home-made product and one dehydrated-reconstituted fermentation broth (DRFB) were characterized in terms of the apparent yield stress τ y of solutions containing different polymer concentrations and when mono and divalent salts or sucrose were added and also when exposing the samples to heat treatment in the case of DRFB. Sodium, potassium, calcium, magnesium, acetate, pyruvate, the mean molecular weight (MMW) and the molecular weight distribution (MWD) were determined. Although the four products showed differences in their chemical characteristics, the pyruvic acid content and the mean molecular weight played the main role in determining the yield stress patterns. With no salt added, the slope of the τ y vs gum concentration plot was a strong and inverse function of the pyruvate content. With NaCl 0.5%, the mentioned slope correlated linearly with the MMW. The three commercial xanthans showed very similar MWD. Xanthan broths showed an exponential, rather than a linear (as it was the case for end-products) function of τ y in terms of xanthan concentration. No significative differences were found in τ y depending on the type of salt. Sucrose decreased τ y and this effect was more pronounced in DRFB than in a solution of a commercial xanthan.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01112992
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