In addition to volatile compounds, metabolites also have a great effect on the flavour of food. Fresh finger citron cannot be eaten directly because of its spicy and bitter taste, so it is made into a preserved fruit product known as Laoxianghuang (LXH). To investigate the metabolites that have an effect on the flavour of LXH, untargeted metabolomics was performed using an ultrahigh-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS), and the metabolites of the Laoxianghuang samples from different locations in the Chaoshan area were compared and analysed. A total of 756 metabolites were identified and distinct differences were revealed among the different Laoxianghuang samples. A total of 33 differential metabolites with the most significant changes were screened through further multivariate analytical steps, and each group of samples had unique metabolites. For instance, pomolic acid had the highest content in the JG sample, while L-glycyl-L-isoleucine was rich in the QS sample. Moreover, flavonoid metabolites made the greatest contribution to the unique flavour of Laoxianghuang. The metabolic pathways involved are the biosynthetic pathways of flavonoids, isoflavonoids, flavones, and flavonols. This study can provide some creative information for distinguishing the quality differences of Laoxianghuang from the perspective of metabolites and offer preliminary theoretical support to characterise the formation of flavour substances in Laoxianghuang.

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Fruit can use its structural characteristics to stabilize the excess electrons of free radicals and prevent cell aging, which is the main source of antioxidants supplementation. In the current study, the expression of antioxidant metabolic genes was evaluated in fruit extract. Seventy mice were divided into one control group and six experimental groups. Six experimental groups were fed 0.1g of grape extract daily for 3, 7, 10, 14, 21, 24 and 30 days, respectively. The antioxidant activity of fruit extract was tested by antioxidant metabolic enzyme gene expression in the liver and kidney of different experimental groups. The results showed that grape extract could effectively enhance SOD activity, LPL relative expression and FAS relative expression in mice liver tissue; grape extract could effectively increase SOD relative expression, TrxR2 relative expression and CAT relative expression in mice kidney tissue; grape extract could effectively reduce MDA activity in mice liver tissue, and increase and decrease the extent of MDA activity and the duration of feeding in mice. The proportion of fruit extracts showed that fruit extracts could effectively improve the antioxidant performance of the body.