Perfil químico e caracterização estrutural de metabólitos na polpa do açaí (Euterpe oleracea Mart.) por RMN

Abstract

Acai is a widely consumed fruit in the North Region of Brazil and has gained consumers in other regions of the country and abroad. With the increasing acai pulp demand, quality control measures become necessary to improve its trading; however, there are some problems, such as the fast degradation of the pulp, microbiological contamination and no knowledge on the behavior of the organic compounds present in the pulp of fruits of different origins, growing, seasonality, transport and processing. This study describes the influence of seasonality, growing conditions and genotypic variations on the acai pulp from Belém - PA by 1H NMR combined with chemometric methods, and structural characterization of the chemical constituents by LC-DAD-SPE/NMR. This work was performed in 4 stages: I) Identification of the greatest number of organic compounds by 1D and 2D NMR, without the need for isolation; II) Attainment of the chemical profile by 1H NMR combined with the chemometric treatment of the pulp of the fruits of 31 genotypes cultivated under agronomic control (Embrapa Amazônia Oriental) and also of commercial samples (Belém-PA); III) Verification of the correlation between the 1H NMR chemical profile and the physical-chemical data measured in the same samples; and IV) Identification of the organic compounds present in the commercial acai pulp extracts obtained with an ASETM (accelerated solvent extractor), being the major compounds obtained by 1D and 2D NMR, and the minor ones by LC-DAD-SPE/NMR with time-slice as trapping mode. Tendencies in the distribution of the acai pulp samples were observed according to the type of growing (agronomic control x without control), seasonality (harvest season x inter-harvest season), genetic improvement, and the storage system used by the retailers from Belém, and the compounds responsible for such tendencies were identified. The great variability in the physical-chemical data of the evaluated pulps was verified and, thus, there was no correlation with the 1H NMR spectral data. The ASE provided the best extracts when compared to extracts obtained with the conventional method. Some aromatic compounds were isolated from the acai pulp methanolic extract by LC-DAD-SPE, and their structures were determined based on the analysis of 1D and 2D NMR, UV and MS experiments. This study showed the potential of the high-resolution NMR technique to obtain chemical information from the lyophilized acai pulp. The traditional analysis methods (physical-chemical ones) were not viable, since they did not provide good comprehension of the variations of the acai pulps. The ASE extractor was a good alternative to perform the clean-up and extraction of the organic compounds present in acai and the time-slice mode proved efficient in the isolation of compounds at low concentration present in the acai pulp methanolic extract.