Alkaloid changes in the capsule of the poppy (Papaver somniferum L.) during maturation and storage
Creators: name: Hofman, PJ
Publisher: name: University Of Tasmania
Year: 2023

description: Many research workers have observed the changes in the morphine percentage and yield from the capsules of Papaver somniferum L. with maturity, and there are conflicting results reported in the literature. The general trends observed are for a continually increasing percentage and yield until 20 to 40 days after flowering, followed by little change, or a decrease. It is generally assumed that variety and environment exert the greatest influence. Thus experiments were conducted to determine the pattern of the morphine, codeine, and thebaine changes in the capsule during the maturation of a commercial variety grown under Tasmanian conditions. The factors reportedly contributing to alkaloid losses in the mature capsule in the field were also studied with the aim of reducing such losses. In addition, preliminary experiments were conducted into artificial drying and storage of the capsule material. Alkaloid percentages in the capsules were followed in two seasons, and also under glasshouse conditions. In all three situations the morphine and codeine percentages and yields - increased until 35 to 42 days after flowering, when the capsule dry matter content was approximately 50%. The thebaine percentage and yield decreased with maturity, particularly within the first 21 days after flowering. Morphine and codeine losses from the mature capsule occurred in one season only, during a period of persistent rain. This coincided with the appearance of brown water droplets on the capsule surface, and increased fungal colonization and capsule discolouration. Thus three mechanisms for alkaloid losses were suggested; leaching, and degradation by fungi and capsule enzymes (biodegradation). Greater integrity of the waxy bloom on the pericarp was associated with reduced alkaloid losses, suggesting a partial dependence of these mechanisms on the rate of water entry into the capsule, either directly, or indirectly through the sample moisture content. It was observed that the undamaged-waxy bloom covering the pericarp consisted of a layer of rod-shaped wax crystals sufficiently thick to completely cover the cuticle. This layer produced very high contact angles, suggesting a high water repellency. Under normal field conditions the waxy bloom, and thus the integrity of the wax structure, decreased during maturation, such that, by about 60 days after flowering, the bloom was restricted to the protected areas of the capsule; at the base and the apex. Associated with these changes, water repellency decreased and the ease of water entry and translocation increased. This was not solely a result of a waxy bloom loss, since the effectiveness of the intact wax layer also decreased with maturity. Interplant abrasion was the major cause of surface damage, since the waxy bloom on the capsules from staked plants changed little over a 90 day period. Interplant abrasion apparently did not result in a removal of wax from the capsule, but more a rubbing of the wax crystals to form a smooth layer. Capsule alkaloid losses by leaching were determined by analysing the leachate collected from glasshouse and field grown capsules subjected to simulated rain. Under these conditions the mature capsule lost up to 80% of the morphine and codeine, and 50% of the thebaine to the leachate. From the field-grown material it was observed that leaching losses of less than 10% occurred from the immature capsule. At 42 days after flowering however, morphine and codeine losses increased dramatically and continued to increase thereafter. Thebaine losses were not substantial until 56 days after flowering. An intact waxy bloom, achieved by plant staking, significantly reduced leaching losses, but only in the mature capsule. Complete wax damage, produced by artificial rubbing, greatly increased the losses. These results are in accordance with the results from the staked plants noted above. The ability of capsule enzymes to effect alkaloid losses was demonstrated by incubating acetone powder extracts with the alkaloids. Losses in the order of 10% for morphine and codeine, and 50% for thebaine were observed, but only in the presence of p-cresol, a substrate for the enzyme polyphenoloxidase. Warburg analysis indicated that the alkaloids are not enzyme substrates themselves, but do increase the rate of gas uptake of an enzyme - p-cresol reaction mixture. These, and other observations, suggested the involvement of polyphenoloxidase in alkaloid losses, but only through the reaction products of the phenolic substrates. Since enzyme activity was detected in extracts from the mature capsule, this mechanism may operate on remoistening of the dry capsule. Support for this was obtained by the incubation of surface-sterilized, mature, remoistened capsules. In addition to the fungi commonly associated with the poppy, Dendryphion penicillatum, AZternaria alternata, and Cladosporium cladosporioides, the fungus Dthellisia sp. was also identified. D. penicillatum was capable of degrading morphine and thebaine, as demonstrated by using nutrient solutions, while anbellisia sp. caused losses of codeine also. Losses of morphine and thebaine were fairly similar in magnitude, but greater than codeine losses. When intact capsules were inoculated with the fungi, only EWoellisia sp. (25%) and A. aZternata (45%) caused morphine losses. Codeine and thebaine were not affected. Based on these results, and bearing in mind the artificial nature of the experiments conducted, the roles of the three mechanisms in producing alkaloid losses in the field situation is discussed. It was concluded that leaching was the most important, and losses become potentially large at and following capsule maturity. On account of this, 42 day old capsules were artificially dried to a moisture content of approximately 15% and stored under commercial conditions. Field dry (56 day old) material was also similarly stored. Although the former decreased in morphine content (8%) during drying, it's final content was still higher than that of the 56 day old material, thus illustrating the potential of this technique to provide a higher quality product. Over a 35 week storage period a 5% and 10% decrease in the morphine and thebaine percentage respectively occurred. This was restricted mainly to the first 12 weeks of storage. It is stressed that, although the results indicate the potential advantages of this technique to both the producer and the processor, further work is required with regard to the drying procedures, and the economics of the process. The sorption isotherm of the commercially stored capsules was determined. It was found that, for safe storage, the moisture content of the product should be no greater than 16%, and preferably below 15%.