Theaflavins (TFs), natural orange-red tea pigments formed during tea fermentation and characterized by a benzophenone structure, are known for their multiple potential health benefits. However, their low content in black tea and instability pose challenges for the industrial production of high-purity TF products, limiting their broader application. A comprehensive understanding of current methods for synthesizing TFs is crucial for their industrialization. This review highlights the formation mechanism and the biomimetic synthesis of TFs, particularly the enzymatic approach and its various influencing factors. Additionally, recent advances in enhancing the stability of TFs are briefly introduced. Although significant breakthroughs have been realized in the in vitro enzymatic synthesis of TFs, enzymatic methodologies still face substantial challenges in scaling up for commercial production, while the directed synthesis of specific TF monomers remains technically constrained. As a result, exploring targeted synthesis processes for TFs is still a focal point for future research. Furthermore, the search for novel and efficient delivery systems to enhance the bioavailability of TFs is imperative for expanding the utilization and application scope of TFs.

Insomnia is associated with neurotransmitters and intestinal dysbiosis. Though studies have demonstrated the ameliorative effects of milk hydrolysates on insomnia, the underlying mechanisms require further exploration. In this study, we investigated how papain hydrolysates of goat casein (CPH) and whey protein (WPH) affected mice’s sleeplessness. Here, we show that CPH effectively improved the total sleep time in 12 h and restoring neurotransmitters (5-hydroxytryptamine (5-HT), γ-aminobutyric acid (GABA), dopamine (DA), and norepinephrine (NE)) in mice. Further gut microbiota analysis revealed a significant increase in the relative abundance of Helicobacter and Escherichia-Shigella and a decrease in the relative abundance of Lactobacillus in the insomnia model mice (Model). Compared to the Model group, both CPH and WPH significantly increased the relative abundance of Akkermansia and Lactobacillus while lowering the relative abundance of Helicobacter and Escherichia-Shigella. Notably, while diazepam (DZP) increased mouse sleep duration, it also increased the relative abundance of Colidextribacter, Parasutterella, Muribaculaceae, and Prevotella. Additionally, the gene expression and protein expression of GABA_A receptor, cAMP-response element binding protein (CREB), and brain-derived neurotrophic factor (BDNF) were upregulated in the hypothalamus. We also discovered a link between intestinal gut microbiota and neurotransmitters. Overall, our results suggest that goat milk hydrolysates, especially CPH, can effectively improve insomnia, providing a theoretical basis for further experimentation and individualized designs.