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Effects of processing conditions on the caseinolytic activity of crude extracts of Cynara cardunculus L/Efectos de las condiciones de extracción sobre la actividad caseinolítica de los extractos de Cynara cardunculus L

Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr António Bernardino de Almeida, 4200 Porto, Portugal

F.X. Malcata

Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr António Bernardino de Almeida, 4200 Porto, Portugal

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 µmol of equivalent leucine/min.g of thistle flower) was obtained by grinding the flowers for 36 s, using an extrac tion 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 proce dures, which are of relevance to the production of standardized plant rennets suitable for the large scale manufacture of ewe's milk cheese.

Key Words: Cynara cardunculus • wild thistle • plant rennet • proteinases • caseinolytic activity • surface response method

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