Sensory and metabolite migration from tilapia skin to soup during the boiling process: fast and then slow

Animal skin soup, a traditional Chinese food, is considered beneficial for beauty, skin, and health. Tilapia skin, a common by-product in tilapia processing, is currently underutilized. While explored for applications like xenografts and collagen extraction, its potential as a soup ingredient and the associated sensory and metabolite migration during boiling have not been investigated. Mass spectrometry-based untargeted metabolomics offers a powerful tool to analyze food components. This study aimed to analyze sensory and metabolite migration during tilapia skin boiling by assessing content changes, sensory changes (using electronic nose and tongue), and metabolite migration via metabolomics analysis. The researchers hypothesized that the sensory and metabolite migration would occur rapidly initially and then slow down.

Existing literature demonstrates the use of tilapia skin in various applications, such as xenografts for burn treatment and collagen extraction for food and medical use. However, there's a lack of research on tilapia skin soup and the sensory and metabolite changes during its preparation. Mass spectrometry-based untargeted metabolomics has been successfully applied to analyze metabolites in various foods like tea, wine, and sea cucumbers, demonstrating its potential for food component analysis and aroma profile comparison. This study builds upon this existing research by applying metabolomics to understand the dynamic changes in tilapia skin soup during the boiling process.

Tilapia skins were thawed, cleaned, and cut into pieces. Two grams of skin were boiled in 10 mL of ultrapure water at 100 °C for 10, 30, and 60 minutes. Content analysis included measurements of mass loss ratio, moisture content, ash content, soluble solid content, and protein content. Sensory analysis was performed using an electronic nose (E-nose) to assess odor changes and an electronic tongue (E-tongue) to evaluate taste changes. Metabolomics analysis involved metabolite extraction from tilapia skin and soup using a methanol:acetonitrile:water solvent. UHPLC-MS/MS and GC-TOF-MS were used for metabolite detection. Data analysis included PCA and OPLS-DA to identify differential metabolites and metabolic pathways. Univariate analysis (UVA) was used to identify differential chemicals and metabolites, and cluster heat maps visualized these differences. Statistical significance was determined using p-values and VIP scores from OPLS-DA.

Content analysis revealed that the major changes in tilapia skin and soup occurred within the first 30 minutes of boiling. E-nose analysis showed distinct volatile component changes within the first 10 minutes, with less change after 30 minutes. E-tongue analysis showed that bitterness, richness, and saltiness were the dominant tastes, with sweetness showing slight changes. Metabolomics analysis identified 783 and 761 chemicals in tilapia skin and soup samples respectively. PCA and OPLS-DA analyses demonstrated significant differences in metabolite profiles across different boiling times, confirming the rapid initial migration of metabolites. Univariate analysis and cluster heat maps further highlighted the significant changes within the first 10 minutes. Key differential metabolites were identified (six in tilapia skin and seven in soup) using VIP scores >1 and p-values <0.05. These included adenine, gingerol, terephthalic acid, vanillin, pentanenitrile, and 2-pyrrolidinone (skin); butyramide, lysope(0:0/20:4(5z,8z,11z,14z)), lysope(22:6(4z,7z,10z,13z,16z,19z)/0:0), linoleic acid, N-acetylneuraminic acid, L-threose, and benzoin (soup). Metabolic pathway analysis showed that the initial 10 minutes were key for metabolite changes, primarily involving amino acid, lipid, and carbohydrate metabolism.

The findings strongly support the hypothesis that sensory and metabolite migration from tilapia skin to soup is initially rapid and then slows down. The significant changes observed within the first 10 minutes highlight the importance of precise boiling time control for optimizing the flavor and nutritional content of tilapia skin soup. The identification of specific key metabolites provides valuable insights into the flavor and taste profiles of the soup. The study's metabolomics approach offers a novel and robust method for analyzing metabolite migration in food processing. This detailed characterization can be used to improve the production and quality control of tilapia skin soup, enhancing its value as a food product.

This study provides a comprehensive understanding of the sensory and metabolite migration during the boiling of tilapia skin. The initial 10 minutes of boiling proved to be the most impactful period for metabolite changes. Specific key metabolites influencing flavor and taste were identified, suggesting that carefully controlled boiling times are crucial for optimizing the final product. The findings contribute to a better understanding of food processing and offer a valuable metabolomic methodology for studying metabolite migration in other food systems. Future research could focus on exploring the detailed reaction mechanisms and further characterizing the identified metabolites to enhance flavor and nutritional value.

While this study offers a thorough analysis, the use of untargeted metabolomics limits the identification of all metabolites, and some compounds remain unidentified. The study focuses on a specific boiling method; other methods may yield different results. Further research is needed to explore the detailed reaction mechanisms and fully elucidate the roles of identified metabolites in flavor and taste.