RESUMO
High hydrostatic pressure (HHP) promotes the release of bioactive compounds from their intracellular compartments making them more bioaccessible. Our aim was to propose a schematic tissue model to explain the release mechanisms of betalains and phenolic compounds in vegetable cells submitted to HHP by analyzing cell microstructure, cell morphology, cell viability and the localization of bioactive compounds in prickly pear fruits. Prickly pear slices were pressurized at 100, 350 and 600 MPa at 20 °C. Chlorenchyma cells (in peels) and parenchyma cells (in pulps) were analyzed by transmission electron microscopy, confocal laser scanning microscopy and optical microscopy. After pressurization, the respiration and ethylene production of processed fruits were measured every 6 h (during storage at 16 °C and 75% RH for 24 h). In chlorenchyma cells, HHP ruptured betalain-storing vesicles in the cytoplasm and possibly increased the activity of endogenous enzymes. Contrarily, HHP released betalains from the vacuoles of parenchyma cells due to breaking of the tonoplast where they presented higher stability. In both tissues, phenolic compounds were released from cell walls with increasing pressure and enhanced by cell wall ultrastructural modifications (100 MPa), rupture (350 MPa) and the rearrangement of microfibrillated cellulose (600 MPa). Prickly pears submitted to HHP presented advanced senescence marked by considerable ethylene increase and the gradual loss of CO2 production after 6 h. Cells were viable at 100 MPa by conserving intact cell membranes and after 24 h their respiration rates presented no significant differences compared to controls therefore indicating the possibility of synthesis of bioactive compound as a response to abiotic stress. We have proposed a new approach for analyzing the effects of HHP and have identified the storing of betalains in vesicles located in the cytoplasm of chlorenchyma cells for the first time. This study is the first to fathom the dynamic morphological changes and release mechanisms of bioactive compounds in vegetable cells subjected to HHP.
Assuntos
Opuntia/química , Opuntia/ultraestrutura , Compostos Fitoquímicos/análise , Compostos Fitoquímicos/química , Extratos Vegetais/análise , Extratos Vegetais/química , Betalaínas/química , Frutas , Pressão Hidrostática , MicroscopiaRESUMO
Lucuma is a starchy orange-yellow fruit native to the Andean region. It is widely consumed in Latin America and has been recently adapted to the agronomical characteristics of the south region of Spain. However, its carotenoid profile has never been reported. The aim of this study was to characterize the carotenoid and carotenoid ester composition of lucuma pulps (var. Molina and Beltran) and assess their bioaccessibility with an in vitro simulated gastrointestinal digestion according to the INFOGEST® methodology. The carotenoid profile in lucuma pulps revealed a high qualitative diversity composed of 33 compounds, corresponding to 9 free xanthophylls, 9 hydrocarbon carotenes and 15 xanthophyll esters. (13Z)-violaxanthin, (all-E)-violaxanthin and (all-E)-antheraxanthin were the most abundant carotenoids in lucuma fruits and were naturally present as xanthophyll esters: (all-E)-antheraxanthin 3-O-palmitate, (all-E)-violaxanthin laurate and (all-E)-violaxanthin palmitate. Carotenoids were stable during in vitro digestion; however, their release from the food matrix was limited which contributed to their low bioaccessibility.