Effects of processing conditions on the caseinolytic activity of crude extracts of Cynara cardunculus L

Four processing parameters (time of grinding, pH of buffer, salt concentration of buffer, and homogenization time) involved in the liquid extraction of proteinases from flowers of the wild thistle (Cynara cardunculus), were studied for their effects on final caseinolytic activity by a surface response method. The caseinolytic activity was assayed spectrophotometrically using o-phthal-dialdehyde. An empirical quadratic model was applied to experimental data pertaining to the average enzymatic activity and equations describing the optimal conditions were obtained. Simultaneous solution of these equations for the local maxima indicated that, within the range tested, the maximum (estimated) specific caseinolytic activity (around 9.5 mu mol of equivalent leucine/min.g of thistle flower) was obtained by grinding the flowers for 36 s, using an extraction buffer with a pH of 5.9 and a salt content of 0% (w/w), and homogenizing the ground flower/buffer suspension for 15 min. These data are of use in the optimization of extraction procedures, which are of relevance to the production of standardized plant rennets suitable for the large scale manufacture of ewe's milk cheese.