## 4 Discussion  
The color results showed the lower \(L^{*}\), higher \(a^{*}\), and lower \(b^{*}\) values in the ZSS-Pi group. \(L^{*}\) indicates lightness, \(a^{*}\) represents redness (+) and greenness (-), and \(b^{*}\) indicates yellowness (+) and blueness (-). Combined with the actual process of _P. interpunctella_ infesting ZSS, the insects usually firstly break through the purple-red testa first and infest the pale-yellow cotyledons internally, resulting in an increase in purple-red testa proportions and a decrease in pale-yellow cotyledons proportion in samples. Therefore, the redness deepened, the yellowness lightened, and the lightness darkened in the ZSS-Pi samples. Figure 8: Metabolic pathway enrichment maps of differential metabolites in positive (**A**) and negative (**B**) modes. The horizontal coordinate was the enrichment significance \(p\)-value and the vertical coordinate was the KEGG pathway. The size of bubbles in the graph represented the number of metabolites enriched to the metabolic set in that pathway. Figure 9: Differential metabolite abundances in ZSS and ZSS-Pi groups. (*: \(p\leq 0.05\), **: \(p\leq 0.01\), ***: \(p\leq 0.001\), ***: \(p\leq 0.001\), ***: \(p\leq 0.0001\)). TFC in the ZSS-Pi group significantly decreased by 31.5% (_p_ < 0.05), indicating that insect infestation can decrease the quality of ZSS. Flavonoids are the main active ingredients in ZSS with various pharmacological activities, such as calming, anti-anxiety, anti-depression, enhancing memory, and protecting the brain and nerves [8]. The significant decrease in TFC will inevitably lead to a decrease in the clinical efficacy of ZSS. It was reported that TFC of hawthorn berries was significantly decreased after insect infestation relative to no insect-infested samples, and TFC was significantly lower in high insect density than those in low insect density, which might be due to the destruction of the cell structure of products by insects [16, 17]. Previous research has indicated that insect infestation can alter the levels of active compounds and reduce the quality, nutritional value, and health benefits of the material. After infestation, the active compounds of neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid, epicatechin, hyperoside, and isoquercitrin decreased relative to the no insect-infested hawthorn samples [46]. When Farfarae Flos was infested by insects, the levels of active compounds such as chlorogenic acid, isochlorogenic acid, and tussilagone were reduced, inevitably compromising its quality and clinical efficacy [47]. Likewise, insect infestation in ZSS-Pi samples led to a decrease in the content of four active compounds with the HPLC results, suggesting a decline in both quality and medicinal value. This might be due to the absorption and metabolism of saponins in ZSS by _P. interpunctella._  
ZSS was abundant with fatty acids. The results of HS-SPME-GC-MS showed that the content of 2,3-butanediol and tetradecane decreased in the ZSS-Pi group, and the content of the other seven differential compounds, including all the methyl ester, increased. It was speculated that when _P. interpunctella_ infested ZSS, fatty acids were ingested and metabolized into ester compounds with related enzymes in the body of _P. interpunctella._ Therefore, the content of ester compounds increased, which provided a basis and reference for the identification of insect-infested ZSS. In view of this, it was thought that methyl esters could be chosen as the characteristic marker of ZSS infested by _P. interpunctella_ and used to identify whether ZSS was infested. It was speculated that sucrose was ingested and metabolized with related enzymes in the body of P. interpunctella for life activities [48]. The increase in organic acids' abundance might have resulted from the metabolization of _P. interpunctella._ For example, uric acid was the final product of insect nitrogen metabolism. It had been reported that the uric acid level could be used to judge the degree of insect infestation [49, 50].