## 3 Results and Discussion
### Metabolite Analysis  
A total of 23,545 substance peaks were detected using metabolomics methods for subsequent comparative analysis of the differential metabolites (Figure 4A). The unsupervised PCA model and supervised PLS-DA model were used to distinguish the differences in the metabolites between the samples. Among them, the cumulative variance contribution rate of PC1 (63.5%) and PC2 (28.1%) was 91.6% (Figure 4B), indicating sufficient sample information [28]. The PLS-DA score plot demonstrated inter-group differences and intra  
Figure 3: Changes in microbial communities in three types of cheddar cheese with varying salt concentrations: Chao1 index OTU Venn diagram (**A**); principal coordinate analysis (PCoA) of all the samples by the weighted UniFrac distance (**B**); cluster heatmap at the genus level (**C**); relative abundance at the genus level (**D**). group consistency (R\({}^{2}\)X = 0.916, R\({}^{2}\)Y = 0.990, Q\({}^{2}\) = 0.983) (Figure 4C). The results of the permutation test [R\({}^{2}\) = (0.0, 0.46), Q\({}^{2}\) = (0.0, \(-\)0.93)] (Figure 4D) indicate that the model in this study has good predictability and reproducibility, without overfitting. Based on different levels of importance (VIP \(\geq\) 1) and \(p\)-values (\(p\) < 0.05), a total of 54 differential metabolites were screened and were subsequently clustered into a heatmap (Figure 5A) and a Z-score plot (Figure 5B), to summarize the changes in the metabolites present in cheese with varying salt concentrations. These metabolites primarily consist of amino acids, fatty acids, carbohydrates, and organic acids, as well as their respective derivatives. From a holistic perspective, amino acids and their derivatives, including gamma-aminobutyric acid, L-lysine, and L-ornithine, are more abundant in the HS group, enhancing the flavor of the cheese. The HS group exhibits a higher abundance of fatty acids and derivatives, including lysophosphatidylcholine, palmitoleic acid, and oxopentanoate. The accumulation of lysophosphatidylcholine may stem from phospholipase-catalyzed phospholipid hydrolysis caused by _Pseudomonas_[29]. Conversely, the abundance of carbohydrates, specifically sucrose and lactose, is significantly lower in the HS group. This observation may correlate with the higher abundance and diversity of the microbial communities in low-salt environments, which promote carbohydrate consumption, subsequently generating metabolites like alcohols and acids [30]. Regarding organic acids and their derivatives, the concentrations of oxaloacetic acid, erucic acid, and citric acid are higher in  
Figure 4: Metabolomic analysis of three types of cheddar cheese with varying salt concentrations: total ion chromatogram (**A**); PCA score plot (**B**); PLS-DA score plot (**C**); PLS-DA permutation test plot (**D**). the HS group, which aligns with previous findings that low-salt treatment increases organic acids [31]. At an individual level, notable elevations (Z-score > 25) in L-lysine, cadaverine, oxaloacetic acid, and L-ornithine in the HS group suggest that a low-salt environment promotes an increase in these specific metabolites. The analysis of metabolite pathways can further elucidate the inter-group differences [32]. Based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database for enrichment analysis [33], and a comprehensive consideration of the \(p\)-values and impact values, the ten most significant metabolic pathways were selected (Figure 6), most of which are related to amino acid metabolism. This suggests that amino acid metabolism appears to be the main pathway responsible for metabolic differences in cheese caused by salt reduction. Integrated analysis of the pathways reveals a metabolic network diagram (Figure 7), where the same metabolite participates in multiple pathways simultaneously, indicating its significant impact. L-lysine has been identified as a key metabolite involved in six pathways. In recent years, the metabolic pathways of fermented foods have gradually attracted increasing attention. [PERSON] et al.