# E-Nose Quality Evaluation of Extra Virgin Olive Oil Stored in Different Containers
## 1 Introduction  
Virgin olive oil is considered to be of great importance among the agricultural products that make up the Mediterranean diet. It is characterized by a high nutritional value and sensory qualities [1]. Currently, the quality of olive oil is regulated by European legislation (EC), the International Olive Oil Council (IOC), and the Codex Alimentarius. The Commission Regulation [2] has established different categories of olive oil, with extra virgin olive oil (EVOO) considered to be of the highest quality based on analytical parameters and sensory criteria and is, therefore, placed in the highest commercial category. The quality of olive oil and its shelf life is greatly influenced by different aspects such as astronomical conditions, raw materials, harvesting, and fruit storage [3]. In addition, storage time and packaging type are two further critical factors that determine quality [4]. Quality decreases during storage, and one of the principal factors to affect it is oxidation, the intensity of which depends on the antioxidant activity of the product [5]. Auto-oxidation, photo-oxygenation, or photo-oxidation are processes that are difficult to control. Auto-oxidation takes place when oxidation occurs in the absence of light, which follows a free radical mechanism, where hydroperoxides are formed due to the absorption of oxygen. Once EVOO is exposed to light, photo-oxidation occurs through natural photosensitizers that react with triplet oxygen to form singlet oxygen in the excited state [6]. Flavor, aroma, and quality can be affected as a result of the oxidation of lipids to hydroperoxides. Thisresults in ketones, aldehydes, acids, and alcohols. The influence of light transmission and the effect of temperature on physico-chemical quality parameters, sensory attributes, and the shelf life of EVOO has been studied [5; 7; 8; 9]. The deterioration of EVOO is caused by different variables such as oxygen, light, and temperature that cause oxidative and hydrolytic reactions. This research has shown that EVOO can have a shelf life of between 12 and 18 months if the different variables are controlled [10]. Thus, to minimize oxidation processes, different containers have been proposed to protect olive oil from both oxygen and light. Industrialists use different types of containers made from dark packaging that can prevent the penetration of light and, in turn, prevent the oxidation process [5; 6; 7; 9]. As a result, the Royal Decree 760/2021 of 31 August [11], which approves the quality standard for olive and olive-pomace oils, advises to protect oils from oxidative processes with regard to the product within which it is packaged. The most commonly used techniques to identify and quantify volatile compounds are a panel test and gas chromatography. These procedures of analysis require specialized technical personnel and long laboratory analysis times to determine the quality of the stored oil. Therefore, an alternative to these traditional methods is an artificial olfactory system such as the electronic nose (E-nose). This non-destructive device represents a powerful sensory tool that enables the successful qualitative and quantitative evaluation of the volatile compounds of the product. An E-nose has been used during the elaboration process or in the final product in several industrial sectors. There are some references of its use related to olives and table olive products [12; 13] in the olive sector. In the case of olive oil, this tool has previously been used to discriminate VOO with varying qualities with high accuracy (67-77%) [14] and to differentiate between VOO with different sensory qualities obtained from healthy and infested olives [15]. With the use of an E-nose, [PERSON] et al. [16] predicted the olive oil quality based on the fruit characteristic after harvest. Moreover, studies have demonstrated the capability of the E-nose in the monitoring of the evolution of volatile compounds during storage [17].