Cannon-Fenske viscosimeter

The total activity of the enzymatic mixture was determined from the percentage reduction of viscosity [12] during the depolymerization of solutions, buffered at different pH values, containing 1 % (w/v) of the polygalacturonic acid or 0.5% (w/v) of pectin. A Cannon-Fenske viscosimeter, (ASTM series n° 150) kept at the constant temperature of 25 °C, was used to carry out the tests. 

The Cannon-Fenske viscosimeter build according to DIN 51336 (Fig. 3.1c) can be used to measure non-transparent liquids that leave a film on the glass in the area of the measurement points and therefore do not allow for exact time taking. A specialty is the multi-level Ubbelohde viscosimeter shown in Fig. 3.Id, which can be used to investigate the dependence of the viscosity on the shear rate. Because of the various heights of the fluid levels, different pressures and therefore different shear rates affect the liquid. Thus it can be determined if the measured viscosities are independent of the shear stress or the shear rate. 

Pectin lyase (PNL) activity was measured spectrophotometrically by the increase in absorbance at 235 nm of the 4,5-unsaturated reaction products. Reaction mixtures containing 0.25 ml of culture filtrate, 0.25 ml of distilled water and 2.0 ml of 0.24% pectin from apple (Fluka) in 0.05M tris-HCl buffer (pH 8.0) with ImM CaCl2, were incubated at 37 C for 10 minutes. One unit of enzyme is defined as the amount of enzyme which forms Ipmol of 4,5-unsaturated product per minute under the conditions of the assay. The molar extinction coefficients of the unsaturated products is 5550 M cm [25]. Also viscosity measurements were made using Cannon-Fenske viscometers or Ostwald micro-viscosimeter, at 37°C. Reaction mixtures consisted of enzyme solution and 0.75% pectin in 0.05 M tris-HCl buffer (pH 8.0) with 0.5 mM CaCl2. One unit is defined as the amount of enzyme required to change the inverse specific viscosity by 0.001 min under the conditions of reaction. Specific viscosity (n p) is (t/to)-l, where t is the flow time (sec) of the reaction mixture and t is the flow time of the buffer. The inverse pecific viscosity (n p ) is proportional to the incubation time and the amount of enzyme used [26]. Units of enzyme activity were determined for 10 min of reaction. 

For the liquid samples, the viscosity in mmVs has been measured using a capillary viscosimeter (system Cannon-Fenske ASTM D 2515) at 50 °C and 100 °C, according to DIN 51 366. 

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See also in sourсe #XX -- [ ]

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