Evaluation of the trend of changes in olive oil quality at different levels of olive fruit fly Bactrocera oleae (Dip.: Tephritidae) infestation

The olive fruit fly (Bactrocera oleae) is one of the country's most important pests of olive products. The present study was designed to investigate the effect of olive fly damage on the quality of olive oil "Zard" cultivar across two years of storage from 2018 until 2020. Treatment levels including control and 10, 20, 30, 40, and 50% of olive fruit fly infestation were prepared manually. Then important quality indices of oil, including peroxide value, free acidity, and K232 and K270 extinction coefficients, were measured during nine stages at intervals of three months. The experiment was performed using a statistical design of repeated measures with three replications. The results showed that the differences between samples with different infestation percentages were significant in terms of peroxide and free acidity indices. Also, significant differences were observed between sampling time stages in each treatment level (control, 10, 20, 30, 40, and 50% of olive fly infestation). However, in contrast, the difference between the samples was not significant for the extinction coefficients of 232 and 270 wavelengths. Based on the results, after 24 months, the acidity level in the sample with 50% of olive fly infestation increased by 57.58% and, in terms of peroxide value, was associated with a significant increase (more than 13 times increase). It should be noted that the value of peroxide for infestation percentages of 30, 40, and 50 percent in August 2020 and November 2020 exceeded the standard allowable. The results of this study indicate significant differences in peroxide value between control samples and samples infested with olive fly and different storage times. Hence, as infestation and storage time increases, the quality of olive oil decreases.