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) growing in Portugal at experimental scale. Two raw materials were studied. The first one concerns over mature crops collected in 1996, whereas the second one 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 that corresponding to mature material was found to be around 20%. This result clearly showed the importance of the time of collection of this annual plant. 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 cellulose. The quantity of water and ethanol/toluene extractives was also very high, i.e. around 10 and 5%, respectively. The conditions of soda-anthraquinone pulping were varied in order to establish the optimal condition of cooking this material. The criteria used were the obtention of good yield with low k and an acceptable pulp viscosity. Thus, the following conditions were retained, alkali active of 20 and anthraquinone of 0.25%, with respect to oven dried material, the time of cooking was 90 min of heating up to 160°C and maintaining this temperature during 120 min. The pulps obtained from both the original materials had a yield of about 35%, a k number of 17 and a viscosity of about 900 cm/g. For mature crops it was found that only 30 min of cooking (after 90 min of heating up) gave pulps with properties as good as those corresponding to pulps from over mature material cooked during 2 h. © 2000 Elsevier Science B.V. All rights reserved.