## 1 Introduction  
Strawberry is a fruit that is loved by a wide range of consumers due to its juicy taste, unique tangy-sweet taste, and wealth of nutrients, vitamins, and minerals. Nevertheless, strawberry is soft and, therefore, very vulnerable to mechanical damage during the post-harvest supply chain. Impact, compression, and vibration are the main mechanical forces that can cause fruit damage [1; 2]. When fruit is mechanically damaged, its physiological metabolism becomes abnormal, such as quick softening [3], water losses [4], and oxidation browning [5]. Moreover, the mechanically damaged fruit is also more susceptible to infection by bacteria and fungi, which can easily cause fruit decay and affect fruit safety [6]. Therefore, mechanically damaged fruit is not suitable for further storage and sale, which, in turn, leads to a significant decline in the market value of the product. In a competitive market, accurate and timely detection of whether the fruit is damaged by mechanical forces or not is important to provide information for post-harvest storage, transportation, and retail sale to optimize storage, transportation, and sales strategies. Retailers, sellers, and consumers usually identify the damaged fruit with the naked eye. For inspection purposes, digital vernier calipers are often used to measure the bruisedarea of fruits. Nevertheless, both visual inspection and the evaluation with digital verniers are inefficient, subjective, tedious, labor-intensive, and selected [7; 8]. On the other hand, compared with manual inspection, spectroscopic and imaging technologies such as visible and near-infrared spectroscopy and hyperspectral imaging are non-invasive and allow for more rapid detection and have been used to detect the mechanical damage of fruits [9; 10]. Nevertheless, the fruits are usually packaged in cardboard boxes or plastic boxes and then placed in a dark environment during supply chains, and, in some cases, the fruits are even wrapped with paper or foam nets, resulting in the inability to detect mechanical damage by spectroscopic and imaging methods. Moreover, when the fruit is damaged by impact, there might be no apparent brwise on the surface of the fruit immediately; when the brwise becomes evident, in most cases, the fruit is already placed in the packages, which makes the visual or imaging detection impossible. Volatile organic compounds (VOCs) are a key indicator for fruit quality assessment and are also an important consideration for customers [11]. Previous studies have shown that VOCs of fruit can change after the fruit is damaged [12; 13]. Therefore, analyzing the VOCs of fruit provides a possible way to detect the fruit with mechanical damage. The electronic nose (e-nose) is a widely used bionic olfactory system and a widely used technology for detecting VOCs [14; 15; 16]. It has obtained much attention because of its advantages of rapid and straightforward operation, non-destructive detecting, and cost-effectiveness. Previously, the e-nose systems have been used to classify fruit grades and predict fruit quality in peach [17], apple [18], apricot [19], mandarin [20], Goji berries [21], sweet cherries [22], and mango [23]. Especially for strawberries, the e-nose shows its capability of determining the freshness of strawberries [24], detecting fungal disease in strawberries in the early stage [25], and characterizing processed strawberry juices [26]. However, to the best of our knowledge, e-nose technology is seldom used to study the detection of mechanical damage to fruits. Moreover, it should be noted that many previous works on investigating fruit quality using e-nose technology are based on a destructive process of sampling, in which the fruit was cut or sliced to obtain more VOCs [27; 28]. However, in the actual fruit supply chain, the detection of VOCs must be carried out on the intact fruit, and no destructive sampling can be carried out.