In the Iberian Peninsula, the proteinases present in the flowers of members of the
Cynara genus, C. cardunculus, C. humilis and C. scolymus, have for many years been
successfully used in the manufacture of traditional cheeses from ovine and/or caprine
milk on individual farms (Vieira de Sá & Barbosa, 1972; Trujillo et al. 1994). In
Portugal, C. cardunculus is the species most frequently employed. Although
commercial thistle was tentatively assumed to be pure in taxonomic terms, accurate
analyses have shown that the flowers of C. cardunculus are often mixed with flowers
of C. humilis (Pires et al. 1994). The clotting activity of C. humilis is due to an
aspartic proteinase, currently designated cardosin A and similar to another enzyme
obtained from C. cardunculus. This enzyme is similar in specificity and activity to
chymosin (Pires et al. 1994).
The action of cardosin A from C. cardunculus upon ovine and caprine caseins has
been reported recently (Ramalho-Santos et al. 1996; Simo4es, 1998; Sousa & Malcata,
1998), but as yet there is no information on the proteolytic activity of the proteinase
from C. humilis upon caseins from milks other than bovine. Caseins from small
ruminants' milks are the usual substrates of cardosin during milk coagulation and
cheese ripening, and sodium caseinate represents an intermediate system between
isolated caseins and the cheese matrix that is free from interference by fat. Thus
ovine and caprine caseinates may be useful substrates for investigating the
proteolytic activity of cardosin.
The aim of the present study was to compare the action of pure cardosin A,
obtained from C. humilis, on caprine and ovine caseinates, and to assess the in vitro
contribution of this enzyme to the overall proteolytic action of thistle rennet.