Pacheco Palencia, Lisbeth A. (2010-07). Chemical Characterization, Bioactive Properties, and Pigment Stability of Polyphenolics in Acai (Euterpe oleracea Mart.). Doctoral Dissertation.
Thesis
Phytochemical composition, antioxidant activity, pigment stability, bioactive properties, and in-vitro absorption of polyphenolics in acai fruit (Euterpe oleracea Mart.) were investigated. Detailed characterization of phenolic compounds present in acai fruit, acai fruit pulp, and a polyphenolic-enriched acai oil were conducted by HPLCESI- MSn analyses and their stability and influence on antioxidant capacity determined. Anthocyanins were predominant in acai fruits, which also contained several flavone and flavonol glycosides, flavanol derivatives, and phenolic acids. In-vitro absorption and antiproliferative effects of phytochemical extracts from acai pulp and acai oil were determined as a function of chemical composition. Polyphenolic mixtures from both acai pulp and acai oil extracts significantly inhibited HT-29 colon cancer cell proliferation, also inducing the generation of reactive oxygen species. In-vitro intestinal absorption using Caco-2 cell models demonstrated that phenolic acids and monomeric flavanol derivatives are readily transported through cell monolayers in-vitro. The influence of polyphenolic cofactors on the stability of anthocyanins in acai fruit under varying conditions of temperature and pH was evaluated. Significant time, temperature, and pH-dependent anthocyanin losses were observed in all models, yet the presence of phenolic acids, procyanidins, and flavone-C-glycosides had a positive influence on anthocyanin stability. External addition of flavone-C-glycosides significantly enhanced visual color, increased anthocyanin stability during exposures to high pH or storage temperatures, and had comparable effects to those of a commercial anthocyanin enhancer. Anthocyanin polymerization reactions occurring during storage of acai fruit juice models were investigated and potential mechanisms and reaction products identified. Polymeric anthocyanin fractions contained several anthocyanin-flavanol adducts based on cyanidin or pelargonidin aglycones and their presence was related to increased anthocyanin sulfite bleaching resistance and to the appearance of large, unresolved peaks in HPLC chromatograms. A reaction mechanism involving the nucleophilic addition of anthocyanins in their hydrated form to flavanol carbocations resulting from cleavage of interflavanic bonds was proposed for the formation of flavanol-anthocyanin adducts in acai fruit juices. Antiproliferative activity and in-vitro absorption of monomeric and polymeric anthocyanin fractions were also evaluated. Both fractions inhibited HT-29 colon cancer cell growth in a similar, concentration-dependent manner, yet in-vitro absorption trials using Caco-2 intestinal cell monolayers indicated the presence of anthocyanin polymers may influence anthocyanin absorption in acai fruit products.
