Optimization of phenolic compounds extraction from Tetrapleura tetraptera and Aframomum citratum and biological assessments

This thesis explores the optimization of phenolic compounds extraction and the biological activities of two non woody forest products (Tetrapleura tetraptera and Aframomum citratum fruit extracts) spread in three agro-ecologic zones in Cameroon in a home food consumption context. The fruits are used for seasoning traditional recipes and in the traditional pharmacopeae. The general objective of this study was to contribute to a development of a therapeutic and preventive dietary supplement rich in dietary antioxidant to fight against oxidative stress on diabetic patents. As they are geographically harvested in many agro-ecologic areas, the various specific objectives were to investigate on their chemical and biological variabilities; on the impact of heat treatment (roasting) on their properties; to define the optimum conditions for total polyphenol recovery of a mix of the spices; and to administer a beverage obtained under optimum extraction conditions to diabetic rats in other to study their antidiabetic capabilities.
The first trials results showed that for T. tetraptera, samples from the bimodal forest zone (BFZ) possess more sugars, calories, minerals and phenolic compounds. Gallic acid, chlorogenic acid, benzoic acid, 2-OH cinnamic acid, salycilic acid, flavone, gallocatechin, epigallocatechin gallate, naringin, phlorizin were among the predominant phenolic compounds identified in aqueous extract. Concerning A. citratum, samples from the BFZ contain more protein, fiber, phenolic and minerals (especially samples from the East region). A total of six dominant phenolic acids (Gallic, chlorogenic, protocatechuic, 2-OH cinnamic, caffeic, p-coumaric) and five flavonoids (epigallocatechin gallate, resveratrol, phlorizin, rutin, epicatechin, luteolin) were observed on the extracts. All the aqueous extracts biological activities (antioxidant, anti-inflammatory) of spices from the BFZ are dose dependent and more effective. Heat treatment significantly reduces fat, raw proteins and total sugars but improves raw fibre, phenolic contents and the biological activities of all the spices. For the total polyphenols recovery, the optimal conditions were: roasting temperature of 150°C, roasting time of 12.6 min, a brewing time of 11.9 min. After in vivo test on rats, the effect of the beverage alone is significantly the same as the conjoined administration of the beverage and the antidiabetic drug (Glibenclamide) reference and the administration the α-glucosidase inhibitor (Acarbose) after 4hrs when assessing the anti-hyperglycemic test on diabetic rats. The Glibenclamide effect is significantly improved by the beverage administration on hypoglycaemic assay and this synergy reduces diabetes complications on diabetic rats. As conclusion, the best areas to harvest are in the BFZ and the heat treatment applied has to be controlled. The beverage obtained with 95/5 Tetrapleura tetraptera/Aframomum citratum formulation possesses antoxidant, anti-nflammatory and hypoglycaemic activities. However there is a need for additional in vivo tests in order to confirm the different in vitro biological activities observed and to determine the human relevance of the beverage at the dose used.