Cynara cardunculus L.: chemical composition and soda-anthraquinone cooking

This paper presents results about the determination of chemical composition of a new annual plant (Cynara cardunculus L. or Cardoon in English) growin g in Portugal at experimental scale. Two raw materials were studied. The fi rst one concerns over mature crops collected in 1996, whereas the second on e was collected at the right time in 1997. The Klason lignin content of the first raw material was found to be relatively high (about 30%), whereas th at corresponding to mature material was found to be around 20%. This result clearly showed the importance of the time of collection of this annual pla nt. The polysaccharides content, for both raw materials, was found to be as high as 60% of which 30% was hemicelluloses, the rest, i.e. 70% being cell ulose. The quantity of water and ethanol/toluene extractives was also very high, i.e. around 10 and 5%, respectively. The conditions of soda-anthraqui none pulping were varied in order to establish the optimal condition of coo king this material. The criteria used were the obtention of good yield with low kappa and an acceptable pulp viscosity. Thus, the following conditions were retained, alkali active of 20 and anthraquinone of 0.25%, with respec t to oven dried material, the time of cooking was 90 min of heating up to 1 60 degrees C and maintaining this temperature during 120 min. The pulps obt ained from both the original materials had a yield of about 35%, a kappa nu mber of 17 and a viscosity of about 900 cm(3)/g. For mature crops it was fo und that only 30 min of cooking (after 90 min of heating up) gave pulps wit h properties as good as those corresponding to pulps from over mature mater ial cooked during 2 h. (C) 2000 Elsevier Science B.V. All rights reserved.