## 3 Results and Discussion  
Effect of Sterilization Methods on the C6 Aldehydes Key Aromas and Aroma Profile of Red Raspberry Juice  
The concentrations of all aroma-active compounds identified in variously processed red raspberry juices are detailed in Table S1 of the Supplementary Materials. Specifically, the contents of two key C6 aldehyde compounds are presented separately in Figure 1a,b. Notably, in both HHP and HTST red raspberry juices, the content of hexanal decreased by 16.77% and 13.15%, respectively, while (Z)-3-hexenal dropped by 16.48% and 26.13%, respectively. These results indicated that both sterilization methods caused varying degrees of loss in the aromas of C6 aldehydes in red raspberry juice, consistent with our previous findings from studies on pasteurization and HHP sterilization of mango juice [15]. QDA is a powerful method to investigate the effect of aroma compound losses on the overall aroma profile of foods [28]. As illustrated in Figure 1c, most of the sensory attribute scores of fresh, HHP, and HTST red raspberry juices are similar, particularly for the floral,  
Figure 1: The contents of C6 aldehyde key aroma compounds (**a,b**) and aroma profiles (**c**) of red raspberry juices after different sterilization treatments. Different lowercase letters (a–c) denote a significant difference (\(p<0.05\)). sweaty, medicinal, woody, and fruity notes. However, the grassy odor in HHP and HTST red raspberry juice was significantly lower than that in the fresh sample, aligning with the observed changes in the contents of these two key C6 aldehydes post-sterilization. Therefore, it is speculated that the aroma deterioration of red raspberry juice induced by sterilization is primarily due to the loss of C6 aldehydes. Effects of Different Sterilization Methods on Key Enzymes in the Fatty Acid Metabolism Pathway of Red Raspberry Juice  
Aldehyde compounds are primarily derived from the fatty acid metabolism pathway; thus, monitoring and analyzing the activity of key enzymes in this pathway is crucial for understanding how sterilization affects C6 aldehyde compounds. As depicted in Figure 2, the enzymatic activities of LOX, ADH, HPL, and AAT significantly decreased in both HHP and HTST red raspberry juices compared to the control group, suggesting that the reduction in C6 aldehydes may be linked to the diminished enzymatic oxidation of unsaturated fatty acids due to these treatments [29]. Nevertheless, the residual enzyme activities of ADH and AAT in HHP-treated red raspberry juice still reached 68.44% and 87.13%, respectively, indicating that enzymatic conversion of relevant substrates during HHP sterilization is feasible [30]. For instance, (Z)-3-hexenal could be converted to (Z)-3-hexenol and (Z)-3-hexyl acetate by the action of ADH and AAT, potentially explaining the loss of (Z)-3-hexenal in HHP-treated juice. Additionally, the residual enzyme activity of LOX in the HTST raspberry juice was 49.78%, with ADH, HPL, and AAT activities all exceeding 25%, showing that HTST has a stronger inactivating effect on these enzymes than HHP. These findings were consistent with the previous studies on melon juice [31] and longan juice [32], which attributed to the reversible nature of enzyme structure damage caused by HHP, allowing partial or complete recovery of their activities during storage. Effect of Different Sterilization Methods on Aroma Compounds Downstream of the Fatty Acid Metabolism Pathway in Red Raspberry Juice  
Among the fatty acid metabolism pathway, substrates such as linoleic and linoleic acids are converted to fatty acid hydroperoxides by LOX and subsequently transformed  
Figure 2: The key enzyme activities of LOX (**a**), ADH (**b**), HPL (**c**), and AAT (**d**) in red raspberry juices after different sterilization treatments. Different lowercase letters (a–c) denote a significant difference (\(p<0.05\)). into aldehydes, alcohols, and esters by HPL, ADH, and AAT [33].