## 3 Results and Discussion
### VOCs  
Volatile organic compounds (VOCs) are closely related to the flavor quality of fresh-cut products, which greatly affects the consumers' sensory evaluation. A total of 37 VOCs were detected in peeled potatoes during storage period, and they could be categorized as alcohols, aldehydes, ketones, esters, furans and hydrocarbons (Table 2), which was  
Figure 5: Radar chart (**a**) and PCA score plot (**b**) and loading plot (**c**) from the E-nose data of vacuum-packaged peeled potato samples during storage. similar to the results of [PERSON] et al. (2018). Among these VOCs, alcohols, aldehydes and hydrocarbons, which accounted for the major proportion, showed significant upward trends and reached 5304.19 \(\upmu\)g/kg, 3638.29 \(\upmu\)g/kg and 1415.60 \(\upmu\)g/kg at the end of storage, respectively. It is worth noting that esters were only detected in peeled potatoes on day 0, and the content was 17.92 \(\upmu\)g/kg. Losses of esters, as an early response to the loss of freshness, have also been reported in fresh-cut cantaloupe (2017, 2018). In addition, some VOCs (ethanol, 1-pentanol, 3-methyl-1-butanol, 2-methyl-1-butanol, benzyl alcohol, hexanal, (E)-2-hexanal, heptanal, (E)-2-heptanal, (E, E)-2,4-heptdiagnal, (E)-2-octenal, decanal, 1-penten-3-one, 1-octen-3-one and tetradecane, 2-pentyl-furan) were also found in raw potatoes, as reported by previous studies (2018, 2018,  
During the whole storage, total content of VOCs exhibited an increasing trend and reached 10,658.68 \(\upmu\)g/kg at the end of storage (12 d), which was about 4.9-times that of day 0. This may have been because that spoilage microorganisms produced VOCs under anaerobic conditions by participating in carbohydrate metabolism, amino acid metabolism and other metabolic pathways [41]. Several studies have reported the relationship between microorganisms and the formation of VOCs. For instance, _Erwinia_ has the ability to produce short chain alcohols and carbonyl compounds in raw potatoes [51]. Ethanol can originate from the hetero-fermentation of sugar metabolism by _Leuconstoc_[41]. 2-ethyl-1-hexanol may be produced by the action of mold [52]. 3-methyl-1-butanol and 2-methyl-1-butanol, which form off-odors with a fermentative character, are the products of amino acid metabolism under the action of _Panttoea_[35; 53; 54]. Furthermore, physical damage can result in the mixing of enzymes and nonvolatile precursors in cells to produce VOCs. For example, an intrinsic lipid attacked by enzymes in cut or sliced potatoes could produce a large number of aldehydes and alcohols, such as heptanal, 1-penten-3-one, 1-pentanol, 2,4-heptadienal and 2-pentyl furan [46]. A partial least-squares discriminant analysis (PLS-DA) was used to clarify the effects of storage time on the changes of VOCs in potato samples and to screen for potential spoilage markers. The PLS-DA score plot, loading plot and permutation test at 200 times are displayed in Figure 6. The PLS-DA is a supervised model which can filter system noise and extract variable information. The model fit parameters of R2X, R2Y and Q2 were 0.916, 0.962 and 0.919, respectively, which indicated a good fit and acceptable predictability of the PLS-DA model. Using the PLS-DA model, potato samples in different storage periods were clearly distinguished (Figure 5(a)). In order to screen for the potential spoilage markers, VOCs related to time evolution were extracted for further analysis (Figure 7). The spoilage markers were defined as VOCs with a variable importance in projection (VIP) \(\geq\) 1. Based on the criterion, _p_-mentha-1,8-dien-7-ol, (E)-2-hexenal, heptanal, ethanol, (Z)-2-octen-1-ol, (Z)-3,7-dimethyl-3,6-octadian-1-ol, 3-ethyl-4-methylpentan-1-ol, (E)-2-heptanal, 4-ethylcyclohexanol and methyl salicate were selected. Among these compounds, ethanol was the most abundant, with a steady increasing content starting from 1517.1 \(\upmu\)g/kg on day 4 and reaching 3843.27 \(\upmu\)g/kg on day 12.