Mónica Hernández-López

Effects of chitosan and plant extracts on growth of Colletotrichum gloeosporioides, anthracnose levels and quality of papaya fruit

The objectives of this research were to evaluate the in vitro fungicidal effect of chitosan and aqueous extracts of custard apple leaves, papaya leaves and papaya seeds, and the combination of chitosan and plant extracts on the development of Colletotrichum gloeosporioides, which causes anthracnose on papaya. Chitosan at 2.0% and 3.0% had a fungicidal effect on C. gloeosporioides. Extracts alone did not show any fungicidal effect while the combination of 2.5% chitosan with all the tested extracts had a fungistatic rather than fungicidal effect. Changes in the conidial morphology of C. gloeosporioides were observed with 1.5% chitosan concentration after 7 h incubation. For in situ studies, control of anthracnose disease was obtained with 1.5% chitosan applied before C. gloeosporioides inoculation. Phomopsis was most frequently isolated from the non-inoculated fruit. Chitosan applications did not influence the content of total solid solubles or percentage weight loss during the storage of papaya fruit. However, there was a tendency toward greater firmness in fruit treated with the papaya seed extract alone or combined with chitosan.

Morphological and Ultrastructural Modifications of Chitosan-Treated Fungal Phytopathogens

Summary A number of studies have confirmed the in vitro fungicidal effect of chitosan on various phytopathogenic fungal families including among others, Mucoraceae, Pleosporaceae, and Glomerellaceae. Investigations of the morphology and ultrastructure of the chitosan-treated fungi in in vitro studies and during the plant-pathogen interaction of various pathosystems have been carried out by using conventional optical/light microscopy and with other advanced instruments including SEM, TEM, and confocal microscopy. The electrostatic interaction between chitosan and the microorganism is noted by dramatic alterations observed from the damaged structure of the cell wall and plasma membrane. The integrity of organelles including vacuoles was seriously affected, leading in some cases to lysis of the fungal cell. During the host-pathogen interaction, formation of structural barriers by the host, mainly through inter- and intracellular synthesis of phenolic-lignin-like material that stops fungal invasion, was also observed. Fungal growth was not beyond the outer cortical area of the infected tissues, while damage on fungi was similar to those observed in in vitro studies. Microscopic examinations have confirmed the fungicidal and eliciting properties of chitosan.

Evaluation of Physical Properties and Antibacterial Activity of Bioactive Compounds-Loaded Chitosan Nanoparticles

Bioactive compounds such as essential oils (EO), botanical extracts and natural resins are well known to have beneficial properties. Among these properties are their antibacterial activity. A disadvantage of these compounds is that they are volatile. Therefore, encapsulation is a good way to overcome this problem. In this study, the morphology, particle size distribution, Zeta potential and microbiological activity of chitosan nanoparticles incorporated with three different bioactive compounds having antimicrobial properties: ethanol extract of propolis, thyme essential oil and ethanol extract of Byrsonima crassifolia (L.) Kunth were evaluated. Nanoparticles were synthesized using the nanoprecipitation method. The morphology was observed using transmission electron microscopy (TEM). Also, particle size distribution and Zeta potential were measured. Results show spherical in shape nanoparticles. Thyme essential oil-loaded chitosan nanoparticles (TEO-CSNPs) showed the smallest particle size and highest stability as assessed by Zeta potential measurement, followed in stability by ethanol extract of propolis-loaded chitosan nanoparticles (EEP-CSNPs), ethanol extract of Byrsonima crassifolia (L.) Kunth (EEBC-CSNPs) and finally by chitosan nanoparticles (CSNPs). The antibacterial activity of the bioactive compounds-loaded chitosan nanoparticles was evaluated against Staphylococcus aureus. The highest antibacterial activity was observed for TEO-CSNPs with an inhibition halo (IH) value of 10.54±0.78 mm, followed by EEP-CSNPs (8.10±1.19 mm). EEBC-CSNPs and CSNPs did not show zone of inhibition. Bioactive compounds-loaded chitosan nanoparticles represents a good alternative for bacterial control of food borne pathogens in applications for fruits and vegetables conservation.

Synthesis and Characterization of Chitosan Nanoparticles Loaded Botanical Extracts with Antifungal Activity on Colletotrichum gloeosporioides and Alternaria species

In this study, chitosan nanoparticles (CSNPs) and chitosan nanoparticles- botanical extracts: EEA-CSNPs (ethanolic blueberry extract added chitosan nano-particles) and EMN-CSNPs (extract methanol of nanche added chitosan nano-particles) were characterized and evaluated in vitro ongrowth of Alternaria alternata isolated from Fig and Rosemary and Colletotrichum gloeosporioides isolated from Papaya and Soursop. From particle size distribution characteriza-tion, the size of nanoparticles increased after EEA incorporation. On the other hand, the smallest value of Z-average particle size was for the EMN-CSNPs. Zeta potential value decreased for CSNPs and EEA-CSNPs. However, when EMN is incorporated to CSNPs, the value is increased. From the results, it can be seen that the most stable suspension was EMN-CSNPs. After incorporation of Byrsonima crassifolia to CSNPs, no changes were observed in characteristic absorption bands for the FTIR spectra. However, after Vaccinium corymbosum incorporation to the CSNPs, changes were seen. For in vitro evaluation, CSNPs without EEA caused the total germination and sporulation inhibition of A. alternata from Rosemary. Incorporation of EMN to CSNPs improved the control of C. gloeosporioides with amycelial growth inhibition of 79% isolated from papaya and 82% isolated from soursop. In both isolated there were total germination inhibition. Overall, a synergistic effect between the chitosan and EMN was observed.