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Advisor(s)
Abstract(s)
The purpose of this research work was to study the proteolytic activity of aqueous crude extracts of
flowers of the plant Cynara cardunculus on the major whey proteins, namely, â-lactoglobulin (â-Lg)
and R-lactalbumin (R-La). These extracts, containing a mixture of cardosins A and B (i.e., two distinct
aspartic proteases), have been employed for many years in traditional cheese-making in Portugal
and Spain. Cow’s milk sweet whey was incubated for up to 24 h at various ratios of addition of crude
enzyme extract, under controlled pH (5.2 and 6.0) and temperature (55 °C). The samples collected
were assayed by gel permeation chromatography and sodium dodecyl sulfate-polyacrylamide gel
electrophoresis. A mechanistic model was proposed for the kinetics of the hydrolysis process, which
is basically a double-substrate, double-enzyme Michaelis-Menten rate expression; the kinetic
parameters were estimated by multiresponse, nonlinear regression analysis. The best estimates
obtained for the specificity ratio (i.e., kcat/Km) of each cardosin within the mixture toward each whey
protein indicated that said aspartic proteases possess a higher catalytic efficiency for R-La (0.42-
4.2 mM-1âs-1) than for â-Lg (0-0.064 mM-1âs-1), at least under the experimental conditions used.
These ratios are below those previously reported for caseins and a synthetic hexapeptide. Cardosins
are more active at pH 5.2 than at pH 6.0 and (as expected) at higher enzyme-to-substrate ratios.
Description
Keywords
Enzymes Dairy products Kinetic Mechanism Plant Proteases
Citation
BARROS, Rui M.; MALCATA, F. Xavier - Hydrolysis Brought about by Enzymes from Cynara cardunculus. Journal of Agricultural and Food Chemistry. ISSN 0021-8561. Vol. 50 (2002), p. 4347-4356
Publisher
American Chemical Society