3.2.1. Washing (W)

Washing is the pretreatment in any type of food processing. It was observed that the washing process under tap water reduced the initial concentration of the residues in oranges by 26–84%, and processing factors ranged between 0.173 and 0.776. Consistently with our findings, other studies reported in the literature prevailed that pesticide residue decreased because of the washing of fruits and vegetables [2,27,28].

Li et al. [3] reported that washing of oranges with tap water reduced the residues of carbendazim, abamectin, imidacloprid, prochloraz, and cypermethrin by 43.6–85.4%. Another other study reported by Kwon et al. [29] revealed that the residues of chlorothalonil, oxadixyl, and thiophanate-methyl in tomatoes decreased by 92%, 52%, and 84%, respectively, after washing for 10 s. Acoglu and Yolci Omeroglu [2] investigated the effect of different washing agents on the fate of pesticides in orange. After washing oranges by dipping them into cold water (<10 ◦C) for 20 min, pesticide residues of abamectin, buprofezin, etoxazole, imazalil, and thiophanate-methyl decreased by 3–68%. In the current study, the additional hand rubbing operations eased the removal of pesticides during the washing of oranges.

After the washing step, the highest reduction (84%) was obtained for thiophanatemethyl, which has the lowest octanol/water partition coefficient (LogP) value among the other pesticides (Figure 1). The lowest reduction ratios (31–38%), achieved for abamectin, buprofezin, and etoxazole, can be attributed to their lower water solubility and higher LogP values compared to others. The octanol/water partition coefficient (LogP) of pesticides is the ratio of the solubility of a compound in octanol (a nonpolar solvent) to its water (a polar solvent) solubility [2]. Even though imazalil has a high water solubility (180 g/mL) 26% of the initial concentration was reduced after washing with tap water by hand. Romeh et al. [30] stated that the nature of the harvested crops was effective on the pesticide residue content of the final product. They demonstrated that pesticides can dry on the surface of the fruit and can be absorbed by the outer waxy structure. In this context, although imazalil has a systemic action and should diffuse through the inner part of the fruit, it deposited on the outer oily layer of the peel due to its high octanol–water coefficient as 3.82. In the same context, most of the studies demonstrated that pesticides with low LogP values can be easily washed away from the crop surface compared to the pesticides with high LogP values [2,11]. Polat and Tiryaki [28] observed that the reduction effects of different washing processes for capia pepper was related to the physicochemical properties of the pesticide (including mainly water solubility and an octanol–water coefficient). Similarly, Vass et al. [31] observed that 2% of the imazalil residue in lemon was reduced by washing with cold water.

#### 3.2.2. Peeling: Separation of Peel and Pulp

Peeling is the first step during the processing of many fruits and vegetables. It is an effective method to cut out the outer layers or skins of fruits and some vegetables and to reduce pesticide residues. It is also reported that chemical, mechanical, steam, or freezing peeling processes can provide a significant removal of residues depending on the chemical nature of the pesticides and environmental conditions [9,32].

In the scope of this study, it was concluded that the average initial concentration of the residues increased by 83% to 270% for obtaining the peel (P). As a result of the separation of the orange peels from the fruit pulp (PU), abamectin and etoxazole residues were not detected in the pulp, while a decrease was observed in the concentration of buprofezin, imazalil, and thiophanate-methyl by 57%, 73%, and 86%, respectively. In the same manner, processing factors for peel and pulp ranged between 1.40 and 4.83 and <0.120 and 0.423, respectively. In line with our observations, Yolci Omeroglu et al. [33] reported that the residue concentration of benomyl, which is a systemic fungicide, decreased by 41% to 83% by peeling. Li et al. [3] concluded that immidacloprid, carbendazim, abamectin, and cypermethrin residues were mostly distributed on peel of the orange. They reported that 7.5 to 17.9% of the initial residues diffused through the pulp of the fruit. Kwon et al. [29] observed that peeling process decreased the chlorothalonil, oxadixyl, and thiophanatemethyl concentration in tomato by 96%, 60%, and 93%, respectively.

After the peeling process, the pesticide residues remained on the peel layer of the fruit and mass transfer of the residues from peel to the pulp occurred at a lower diffusivity rate. This can be attributed to the physicochemical properties of the pesticides investigated in the scope of the study. Since thiophanate-methyl, etoxazole, and abamectin are contact and semi-systemic pesticides, they retained on the peel and did not diffuse through the pulp section of the fruit. In the same context, as a systemic pesticide imazalil was expected to diffuse completely through the pulp of the fruits, but its diffusion to the pulp section occurred on a limited scale. This can be attributed to its high octanol-water coefficient. Pesticides with high octanol–water coefficients (logP) (Figure 1) can be easily absorbed by the wax on the orange peel and cannot be removed from the peel easily [28,32]. Similarly, studies reported in the literature emphasize that the peeling process significantly decreased pesticide residues in fruits by peeling, and the reduction ratio was mainly based on the physicochemical properties of the active ingredients [27,32,34,35].

#### 3.2.3. Processing in to Fruit Juice (FJ)

The transition of pesticide residues from fruit to fruit juice depends on the distribution of the residue between peel and pulp in addition to their physicochemical properties. Residues are also reduced by the steps in the fruit juice production process, including clarification steps such as centrifugation or filtration [8,31].

As shown at Table 1, while abamectin and etoxazole residues were not detected in fruit juice, buprofezin, imazalil, and thiophanate-methyl residues decreased by 93%, 79%, and 63% respectively. Processing factor ranged between <0.120 and 0.363. Similarly, Li et al. [3] found that imidacloprid, abamectin, cypermethrin, and prochloraz residues decreased by 46.5%, 46.0%, 94.7%, and 81.0%, respectively, by obtaining orange juice from fresh oranges.

During the processing of oranges into fruit juice it was observed that highest reduction ratio was obtained for the pesticides with low water solubility (abamectin and etoxazole), while most of the residue concentration of the pesticides with higher solubility (thiophanatemethyl and imazalil) transferred into the juice. These findings can be attributed to the distribution of the pesticide residues between fruit peel/pulp and juice, depending on their water solubility [36].
