Effect of alkali treatment and natural fermentation on the residue behaviour of malathion and malaoxon during table olive production

Pesticide use is indispensable for combating diseases occurring during olive cultivation. However, this has led to challenges of pesticide residues in consumer products as a result of pesticide application errors and the methods used during processing and preservation. This work aimed to identify the effects of table olive processing and preservation techniques on the concentrations of malathion and its degradation product malaoxon. For this purpose, olive trees in an experimental olive orchard were sprayed homogeneously with malathion at a dose of 975 mg L−1 and processed as (i) vacuum-packed, (ii) alkali treated and (iii) directly brined for natural fermentation. The changes in microbial growth, pH-acidity and pesticide (malathion and malaoxon) concentrations were monitored regularly during the experiment. Lactic acid bacteria, yeast and mould growth were not detected in any of the treatments. Mesophilic aerobic bacteria and enterobacteria were the dominant microbial groups in all non-sprayed treatments, but no enterobacteria growth was detected in sprayed treatments. Lower pH values were observed in the brines of natural fermentation treatments of both sprayed and non-sprayed olives. The independent effects of time and processing method and their interactions on malathion and malaoxon concentrations were found significant (p < .05). During the experiments, the highest reduction in malathion concentration was observed in alkali treated samples (95–99%), followed by naturally fermented (77–88%) and vacuum-packed samples (74–76%). Processing factors for all treatments were lower than 1.