Improving the flavor of oolong tea by-products using an optimized reprocessing process

During oolong tea production, the requirement for highly mature fresh leaves inevitably generates by-products. These include teas with coarse, loose shapes and a yellowish appearance, collectively known as “Huangpian” (HP). HP is usually discarded because of its weak flavor, which leads to a waste of resources and increased production cost of oolong tea. The objective of this study was to elevate the flavor of HP via optimized reprocessing methods. The results demonstrated that the taste thickness and aroma richness of the optimized HP (HP-O) were enhanced after 5 min of steam fumigation, 25 min of rolling, and 45 min of drying. Moreover, non-volatile metabonomics and volatile metabonomics technologies were applied to explore the relevant mechanisms leading to improved HP quality. The improvement in taste was mainly related to flavonoid glycoside degradation and epigallocatechin isomerization, causing gallocatechin and flavonols to accumulate. A total of 19 metabolites were the potential key components contributing to the quality improvement of HP-O tea infusion. Additionally, α-ionone, ( E , E )-2,4-decadienal, dehydrolinalool, and safranal may be the potential key volatiles to enhance the aroma of HP-O. This optimized reprocessing approach could provide a viable strategy for quality improvement of HP, thereby significantly improving the product's market acceptability.