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Antimicrobial properties of residues from olive industry treated by ionizing radiation
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Resumo(s)
Olive pomace is a recalcitrant waste of the olive oil industry and is also an abundant source of
bioactive compounds. Aiming to reduce its environmental impact and increase the value of industrial
waste through the incorporation of bioactive compounds in added value products, the present work’s
goal was to evaluate the bioactive potential of extracts from non-irradiated and irradiated olive pomace
(electron beam). In this work, the ionizing radiation was not used as a potential treatment process, but
instead, to increase the bioactivity of olive pomace, considering that possibly the amount of compounds with bioactive potential extracted is greater.
Thus, the antioxidant, antimicrobial and antitumoral/proliferative properties of solutions extracted from two types of olive pomace samples were evaluated. One before the extraction of oil from
olive pomace, designated "Crude Olive Pomace" (COP) and the other after that extraction, "Extracted
Olive Pomace" (EOP). COP and EOP were irradiated at two different doses (6 and 11 kGy) and nonirradiated samples were used as control.
Results of the antioxidant activity suggested an irradiation’s effect at the evaluated doses. Antioxidant activity was evaluated using the free radical scavenging method (DPPH) and the Ferric Reducing Antioxidant Power method (FRAP). Results obtained through DPPH indicated that EOP extracts irradiated at both doses presented antioxidant activity values similar to non-irradiated COP extracts. Non-irradiated EOP extracts had lower antioxidant activity compared to non-irradiated COP
extracts. Based on the FRAP method, COP extracts showed, globally, higher valuesthan EOP extracts,
with no significant differences between irradiated and non-irradiated samples.
Results for antimicrobial activity were expressed based on the Minimum Inhibitory Concentration (MIC) and on the Minimum Bactericidal Concentration (MBC). All extracts showed the same
MIC for all Gram-negative bacteria studied (Escherichia coli, Salmonella enterica serotype Typhimurium and Pseudomonas fluorescens). MBC values were the highest for EOP extracts against all
Gram-negative bacteria. Bacillus cereus and Enterococcus faecalis presented the same MIC and MBC
values for both extracts and the values were the lowest and highest within Gram-positive bacteria,
respectively. Overall, the olive pomace extracts were more effective against Gram-positive than
against Gram-negative bacteria, and the effect of irradiation was not detected.
The cell proliferation assay (WST-1 reagent) was used to assess the potential cytotoxicity or
anti-proliferative activity of various concentrations (4-400 µg/mL) of the extracts using non-tumoral
(HEK293T, RAW264.7) and tumoral (A549, Caco-2) cell lines. All extracts from non-irradiated and
irradiated olive pomace at the highest concentration induced a decrease between 44 and 89% in cell
viability of the lines under study, which translates into a cytotoxic effect of the extracts on the cells
while lower concentrations did not show a significant cytotoxic effect. Regarding tumoral cell lines
(A549 and Caco-2), we can suggest that high extract concentrations could promote antitumoral activity. Electron beam irradiation of olive pomace had no effect on the viability of the cell lines studied,
suggesting that bioactive compounds extracted from these residues after irradiation do not show cytotoxicity.
Overall, the results suggested that irradiation could increase the antioxidant activity of Extracted Olive Pomace; highlighting the potential of valorizing both types of pomace residue with preserved bioactive properties. This work is part of a broader project aiming the valorization of agroindustrial waste that uses ionizing radiation to promote the extractability of bioactive compounds with
potential use in the food, cosmetic or nutraceutical industry.
Descrição
Tese de mestrado, Microbiologia Aplicada, 2021, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
bagaço de azeitona irradiação por feixe de eletrões compostos bioativos propriedades bioativas Teses de mestrado - 2021