# Sensory Perception Systems and Machine Learning Methods for Pesticide Detection in Fruits
## 1 Introduction
Therefore, their consumption worldwide has increased considerably in recent years and is crucial to people's health. However, fresh fruits and vegetables contain higher levels of pesticides, mainly fungicides, and insecticides compared to other plant foods, probably due to the short time interval between harvests and market that results in inadequate testing to detect pesticide residues and creates a risk to the health of consumers, as they are often eaten raw or in the form of processed products (juices, jams, pures, etc.) [24]. Furthermore, the concentration of pesticides in fruits and vegetables depends on the amount sprayed on them, the available content in the soil or irrigation water, and the processing of these foods. The above is a way to guarantee safety, prolong shelf life, and maintain or improve the quality of food, which, according to the specifications of the final product, may be subject to different processes [25]. For example, in the food industry, there are several stages such as pre-treatment (washing, rinsing, peeling, grinding, segregation, etc. ), heat treatment (cooking, frying, pasteurization, freeze-drying, baking, sterilization, preservation, etc. ), and final treatment (packaging, bottling, labeling, etc. ), among others, which allow for the concentration of pesticides to be reduced or eliminated [26]. In 2004, the Environmental Working Group (EWG) began publishing the Dirty Dozen list, which identifies some of the fruits and vegetables that contain the highest levels of pesticide residues, according to data obtained from the United States Department of Agriculture (USDA) and the Food and Drug Administration (FDA). The following foods are on the 2022 Dirty Dozen list: strawberry, spinach, kale, nectarine, apple, grape, bell and hot peppers, cherry, peaches, pears, celery, and tomato [27; 28]. Therefore, monitoring and evaluating pesticide levels in fruits and vegetables must be observed. Food industries and stakeholders must ensure that foods comply with legal requirements at all stages of the food chain. To protect human health, legal guidelines have been established to control pesticide levels in food through maximum residue levels, which are set by the Codex AlimentariusCommission (CAC) and the joint FAO/WHO Meeting on Pesticide Residues (JMPR), who have tried to establish, review, and harmonize MRLs for pesticides, where globally, these limits continue to be variable, since many countries have their own regulations [24; 29]. In the case of Colombia, there is the Ministry of Agriculture and Rural Development through the ICA (Colombian Agricultural Institute), which, through resolution 2906 of 2007 issued by the Ministry of Social Protection, stipulates the maximum concentrations of commercial pesticides in the food [30]. To evaluate the levels of pesticides in fruits and vegetables, sensitive, highly selective, and precise analytical instrumental techniques are required. Among these most used techniques are high-performance liquid chromatography (HPLC) and gas chromatography (GC) coupled to mass spectrometry (MS). Other methods, such as enzyme-linked immunosorbent assays (ELISA) and capillary electrophoresis (CE) have been applied in the determination of pesticide residues in real samples [31; 32]. However, these methods have some limitations since they require sophisticated laboratory equipment, preparation, storage, and transportation of samples, which tends to be tedious, high-cost, time-consuming, and require trained personnel. Nowadays, systems based on arrays of gas sensors (E-nose) and chemical electrodes (E-tongue) have been designed to artificially perceive the active molecules of the odor generated from the headspace of the samples and the compounds involved in the flavor of the aqueous solutions [33; 34]. These characteristics of sensory systems have allowed for them to be used in different industries, especially in the food industry, to evaluate the quality of other products through the analysis of odors and flavors [35].