Metabolomics Analysis Reveals Bitter Taste Formation in off-Season Crab Hepatopancreas Marketed in June of the Lunar Calendar

Crabs marketed off-season in lunar June often have a brown hepatopancreas (BH) that tastes bitter, unlike the nonbitter orange hepatopancreas (OH). We conducted nontargeted and widely targeted metabolomics analyses on both raw and cooked orange and brown hepatopancreas of Eriocheir sinensis. A total of 115 bitter metabolites were identified, including oxylipins, amino acids, small peptides, nucleotides, vitamins, and coenzymes. Targeted quantitative analysis revealed that seven oxylipins were major contributors to the bitterness of BH. The primary metabolic pathways affecting hepatopancreas bitterness involved the production of unsaturated fatty acids and α-linolenic acid metabolism. Furthermore, specific odorants were produced from OH and BH groups during heat treatment, namely ethyl caproate and methional, respectively. Moreover, differential metabolites were found to act as odor precursors, resulting in a brown and bitter hepatopancreas with poor odor quality. This study elucidates the generation of bitter substances in the hepatopancreas of Eriocheir sinensis through metabolic pathways and thermal reaction pathways.