Modeling and optimizing the changes in physical properties of olives in response to attacks of olive fruit fly (Bactrocera oleae (Gmelin))

Abstract

Response Surface Methodology (RSM) was used to establish a predictive model for the effects of olive fruit fly attacks on the physical properties of olives at different orchard altitudes and harvesting periods. The physical properties investigated included the maturity index, fruit removal force, and change ratios of weight, density, hardness, and crushing force of olives. This study was conducted using the Ayvalik olive cultivar at three orchards in the Edremit district, Balikesir (Turkey), at altitudes of 84, 126, and 168 m. The olives were harvested at 50-day intervals during the months of September to December for three years repeatedly (2016-2018). A Box-Behnken experiment design (BBD)-based optimization model was used to minimize the responses and obtain the optimum factors. Using the desirability function method, the ratio of damaged olives was 0.10, the harvesting time was 72 days after the first harvest, and an altitude of 168 m was found to be the optimal condition. In this condition, the dependent variables were predicted as follows: the maturity index, 3.56; fruit removal force, 2.73 N; the change ratio of weight, -0.0767; density, -0.1989; hardness, 0.0504; and crushing force, 0.0205. The results indicated that the losses in the physical properties were severely affected by the damage caused by the attacks of the olive fruit fly. These losses were also caused by orchard altitude and harvesting dates. The results demonstrated that the change ratios of the physical properties of olives can be used as ripening criteria.