## 3 Results and Discussion  
### Volatile Substance Analysis  
As shown in Figure S1, the main peak shapes and peak emergence times of the GC-MS spectra of egg yolk remained the same under different ozone treatment times. Table S1 showed that a total of 18 volatile components were identified in the egg yolk from five groups with different ozone treatment times. Quantities of 18, 17, 16, 14, and 14 volatiles were identified from egg yolks treated with ozone for 0 min, 10 min, 20 min, 30 min, and 40 min, respectively. The identified 18 volatiles were n-hexane, hexadecane, 2-nonen-1-ol, cedrene, pentanal, hexanal, heptanal, octanal, 2,5-dihydroxybenzaldehyde, nonanal, decanal, undecanal, 6-methyl-5-hepten-2-one, geranyl acetone, 3-methyl-1-butanol, nonen-1-ol, 2-cyanoacetamide, and dibutyl amine. Nonanal and octanal accounted for 20.48% and 27.35% of the yolk volatiles and were the main contributing components to the yolk's flavor [17]. The identified egg yolk volatiles were mainly classified into alkanes, terpen, aldehydes, alcohols, ketones, and amines, among which aldehydes and alcohols accounted for a higher proportion [18]. In addition, it could be seen from Table S1 that the types of yolk volatiles decreased significantly (\(p<0.05\)) with the increase in ozone treatment time, and the types of yolk volatiles decreased by 5.6%, 11.1%, 22.3%, and 22.3% after 10 min, 20 min, 30 min and, 40 min of ozone treatment, respectively.  
[PERSON] et al. [18] explored the effect of bioactive terpen on egg yolk volatiles, and a total of 111 different volatile compounds were identified by using GC-MS. The addition of bioactive terpen significantly (\(p<0.05\)) reduced the content of some ketones, amines, and nitro and organic acid compounds and thus improved the flavor of egg yolks [18]. It is noteworthy that the contents of hexane, hexadecane, heptanal, and dibutyl amine decreased significantly (\(p<0.05\)) with the increase in ozone treatment time. No alkane volatiles were detected in the egg yolk after 40 min and 30 min of ozone treatment, while the content of aldehydes in the egg yolk increased significantly (\(p<0.05\)). Egg yolks produced the highest content and the most diverse range of volatiles in aldehydes. Aldehydes had a low threshold and made an important contribution to flavor [19]. The highest content of nonanal had a strong oily and sweet orange odor. And its ethanolic solution had a vanillin odor, which is used as a food additive, and is also used in the preparation of rose, orange blossom, fragrant violet, and scented flavors [20]. The odor of nonanal played a dominant role in the egg yolk's volatiles.  
Figure 1 showed that the percentages of aldehydes in egg yolk treated with ozone for 0 min, 10 min, 20 min, 30 min, and 40 min were 78.08%, 91.40%, 93.11%, 94.63%, and 93.12%, respectively. It could be assumed that ozone oxidation promoted the degradation of fatty acids in egg yolks, thus producing more aldehyde volatiles. The aldehyde volatiles had a certain fruit flavor, so with the increase in aldehydes substantially improved the flavor of egg yolks [21]. In addition, it was found that the content of dibutyl amine, which had a strong ammonia taste and irritation, decreased in the yolk with the increase in ozone treatment time. It could be concluded that ozone treatment might be beneficial to improving the effects of undesirable flavors in the yolk.