The essential characteristic step in the manufacture of all cheese varieties is coagulation of the casein component of the milk protein. Coagulation may be achieved by a variety of means, but the majority of cheeses are produced by enzymatic (rennet) coagulation.
Rennet can be animal, microbial, or vegetal. The majority of vegetable rennet comes from the cardoon flowers from the genus Cynara (mainly C. cardunculus L., C. scolymus L., and C. humilis L.)
- There is indicating evidence that the Jews were the first to develop the practice of coagulating milk with a thistle bloom. Cheeses prepared with animal enzymes were prohibited under the strict Jewish dietary laws, which forbade religious Jews to cook any animal’s meat in its mother’s milk or other- wise to mix meat with dairy products.
- The stamen of the cardoon plant contain a milk-clotting activity that has been extracted through traditional cheese-making techniques in Portugal and Spain for centuries. Aqueous extracts show proteolytic, lipolytic and amylolytic activities; which means that there are activities that break down proteins, lipids, and converting starch into sugar. The extracts also contain aspartic proteases which are a family of protease enzymes that use an aspartate residue (which can be a carboxylate anion, salt, or ester of an alpha amino acid, aspartic acid) to catalyze peptide substrates.
Scientists have only gained a better understanding of plant aspartic proteases until relatively recently. In 1997, the NC-IUBMB (Nomenclature Committee of the International Union of Biochemistry and Molecular Biology) adopted the name phytepsin – which was introduced to denote all related plant aspartic proteases. While not all phytepsins have been fully investigated, phytepsins from cardoon Cynara cardunculus have been especially well characterized.
Three phytepsins were purified from cardoon flowers and partially characterized and identified as cynarases 1-3. Later, the primary structure of cyprosin was determined and these phytepsins were later renamed cyprosins 1, 2, and 3. Two other phytepsins named cardosin A and cardosin B (cardo is the Portuguese name of the plant), have subsequently been extensively studied from cardoon flowers.
In contrast to the animal rennet enzyme chymosin, which is specific for cleaving only kappa-casein, the aspartic proteases present in plant extracts are very active nonspecific protein cutters. These aspartic proteases cleave alpha, beta, and kappa caseins. However, this causes excessive acidity, bitterness, and potential texture defects in the cheese, thereby limiting their use.
But it is these characteristics that are responsible for the special flavor, smell, and consistency of the cheese varieties produced using plant enzymes.
Many cheeses from the Spanish and Portuguese regions that use vegetable rennet are made with sheep’s milk. Cow’s milk poses problems for use with cardoon coagulants. The enthusiastic cutting activity of the cynarase creates five bitter peptides from cow’s milk proteins that are not formed from the proteins in ewe’s milk. Serendipitously, the rugged Iberian terrain is ill suited to the needs of delicate dairy cattle, but agile browsers like sheep and goats thrive there.
Alan J. Barrett, ed., J. Fred Woessner ed., Neil D. Rawlings ed. Handbook of Proteolytic Enzymes, Volume 1. 2004, Elsevier Academic Press, London
Julio Polaina ed., Andrew P. MacCabe ed. Industrial Enzymes: Structure, Function and Applications. 2007, Springer
Rosa Tovar. Spanish Thistle-Bloom Cheese. Gastronomica: The Journal of Food and Culture, Vol. 2, No. 2 (Spring 2002), pp. 77-82 Published by: University of California Press
Francis and Bronwen Percival. Animal Meets Vegetable: Making Thistle Rennet Cheeses. Culture Magazine, Spring 2010