Our lab has conducted a systematic and multi-faceted investigation into sweet tea (Lithocarpus litseifolius or Lithocarpus polystachyus). Our research spans from optimizing extraction techniques and characterizing key bioactive compounds (dihydrochalcones and polysaccharides) to evaluating their health benefits and exploring novel food applications. This body of work establishes sweet tea as a valuable natural source of functional ingredients with significant therapeutic potential.

1.     Optimization of Extraction and Characterization of Bioactive Compounds

A primary focus of our research has been to develop efficient and green methods for extracting sweet tea's main bioactive components. We have systematically optimized and compared various advanced extraction techniques. For extracting key antioxidant dihydrochalcones in sweet tea, we optimized microwave-assisted extraction (MAE), achieving high antioxidant capacity under specific conditions (58% ethanol, 25 min) (Shang et al., 2020). We also developed a DPPH-spiking HPLC method to precisely screen for the main antioxidants in sweet tea, identifying isoquercitrin, phloridzin, and trilobatin. We then optimized an ultrasound-assisted extraction (UAE) protocol that yielded high concentrations of these compounds (e.g., 163 mg/g trilobatin) and significantly higher antioxidant capacity compared to traditional maceration (Liu et al., 2021).

For sweet tea polysaccharides (STPs), we have explored a wide array of pre-processing and extraction methods. We investigated the impact of drying methods on bioactive compounds of sweet tea, and found that hot-air drying and freeze-drying of sweet tea leaves yielded STPs with higher total phenolic content and superior bioactivities compared to other drying methods (Guo et al., 2022). In addition, by comparing eight different extraction technologies, we found that deep-eutectic solvents and diluted alkali solutions yielded STPs with the most favorable biological properties, which were strongly correlated with the total phenolic content of the crude extracts (Guo et al., 2021). We further optimized pressurized hot water extraction (PHWE), achieving a 4.64% yield of STPs (Lei et al., 2022), and developed a microwave-assisted deep eutectic solvent extraction (MDAE) method that yielded STPs with lower molecular weight and higher uronic acid content, resulting in stronger in vitro antioxidant and anti-diabetic effects compared to hot water extraction (Wu et al., 2022). Our foundational work also includes a comprehensive review that identifies the principal dihydrochalcones in sweet tea, including phlorizin, phloretin, and trilobatin, and summarizes their multiple health benefits (Shang et al., 2022).

2.     Elucidation of Health Benefits and Gut Microbiota Interaction

Our research provides strong evidence for the health-promoting effects of sweet tea, particularly in the context of inflammatory diseases and gut health. In a key in vivo study, we demonstrated that sweet tea extract significantly prevented dextran sulfate sodium (DSS)-induced ulcerative colitis (UC) in mice. The extract suppressed pro-inflammatory mediators (e.g., MPO, TNF-α), upregulated tight junction proteins to restore gut barrier integrity, and modulated the gut microbiota profile. Specifically, it increased the abundance of beneficial bacteria like Akkermansia and Lachnospiraceae, leading to a significant increase in butyric acid. We elucidated the mechanism as the activation of butyrate-GPR-mediated anti-inflammatory signaling and simultaneous inhibition of the HDAC3/NF-κB inflammatory pathway (He et al., 2022).

Furthermore, our investigation into STPs revealed their potential as prebiotics. In vitro fecal fermentation experiments showed that STPs could be effectively utilized by gut microbiota (54% fermentability), promoting the growth of beneficial microbes and enhancing the production of beneficial short-chain fatty acids (Lei et al., 2022).

3.     Development of Novel Sweet Tea-Based Food Products

Building on our fundamental research, we have explored the development of new functional foods from sweet tea. We successfully created instant sweet tea powders using freeze-drying and spray-drying methods. Our analysis showed that the instant powders had higher concentrations of proteins, polysaccharides, and total phenolics compared to the original raw tea leaves. Freeze-dried instant tea made from young leaves exhibited the highest TPC, TFC, and antioxidant capacities (Liu et al., 2021). However, GC-MS and sensory analysis revealed that while the instant tea developed a desirable caramel-like attribute, it lost some of the woody, green, and floral notes present in the original tea, indicating a need for further aroma improvement (Liu et al., 2022).

4.     Significance and Novelty of Our Work

The significance of our research lies in its comprehensive, "source-to-product" approach that establishes a strong scientific foundation for the use of sweet tea. The novelty is evident in several key areas:

(1) Technological Innovation: We are pioneers in applying and systematically optimizing a diverse range of modern, green extraction techniques (UAE, MAE, PHWE, MDAE) specifically for sweet tea's different bioactive components, providing clear guidance for industrial application.

(2) Comprehensive Characterization: Our lab has uniquely focused on both the phenolic (dihydrochalcones) and polysaccharide fractions of sweet tea, providing a holistic understanding of its chemical composition and multifaceted health benefits.

(3) Mechanism-Driven Health Research: Our work on ulcerative colitis provides a clear, evidence-based mechanism linking sweet tea consumption to gut microbiota modulation, butyrate production, and specific anti-inflammatory signaling pathways (GPRs, HDAC3/NF-κB).

(4) From Bioactives to Functional Foods: We have successfully translated our fundamental knowledge into tangible product development, creating and characterizing novel foods like instant sweet tea, and providing critical insights into their quality and sensory profiles.

In summary, our lab's research has not only characterized the rich bioactives in sweet tea but has also demonstrated their concrete health benefits and pioneered methods for their extraction and application in novel functional foods, positioning sweet tea as a promising resource of novel food ingredients for the health and wellness industry.

Acknowledgement

We would like to thank the hard work and collaboration of all my team members and collaborators involved in this work.

Our Publication List

Guo, H., Fu, M. X., Zhao, Y. X., Li, H., Li, H. B., Wu, D. T., & Gan, R. Y. (2021). The Chemical, Structural, and Biological Properties of Crude Polysaccharides from Sweet Tea (Lithocarpus litseifolius (Hance) Chun) Based on Different Extraction Technologies. Foods, 10(8), 1779. http://dx.doi.org/10.3390/foods10081779

Guo, H., Fu, M. X., Zhao, Y. X., Wu, D. T., Liu, H. Y., Li, H. B., Ayyash, M., & Gan, R. Y. (2022). Effect of different drying techniques on structural characteristics and bioactivities of polysaccharides extracted from (Lithocarpus litseifolius [Hance] Chun) sweet tea leaves. Journal of Food Measurement and Characterization, 16(5), 4050-4063. http://dx.doi.org/10.1007/s11694-022-01510-2

He, X. Q., Liu, D., Liu, H. Y., Wu, D. T., Li, H. B., Zhang, X. S., & Gan, R. Y. (2022). Prevention of Ulcerative Colitis in Mice by Sweet Tea (Lithocarpus litseifolius) via the Regulation of Gut Microbiota and Butyric-Acid-Mediated Anti-Inflammatory Signaling. Nutrients, 14(11), 2208. http://dx.doi.org/10.3390/nu14112208

Lei, J., Li, W., Fu, M. X., Wang, A. Q., Wu, D. T., Guo, H., Hu, Y. C., Gan, R. Y., Zou, L., & Liu, Y. (2022). Pressurized hot water extraction, structural properties, biological effects, and in vitro microbial fermentation characteristics of sweet tea polysaccharide. International Journal of Biological Macromolecules, 222, 3215-3228. http://dx.doi.org/10.1016/j.ijbiomac.2022.10.094

Liu, H. Y., Liu, Y., Li, M. Y., Mai, Y. H., Guo, H., Wadood, S. A., Raza, A. L., Wang, Y., Zhang, J. Y., Li, H. B., & Gan, R. Y. (2022). The chemical, sensory, and volatile characteristics of instant sweet tea (Lithocarpus litseifolius [Hance] Chun) using electronic nose and GC-MS-based metabolomics analysis. LWT-Food Science and Technology, 163, 113518. http://dx.doi.org/10.1016/j.lwt.2022.113518

Liu, H. Y., Liu, Y., Mai, Y. H., Guo, H., He, X. Q., Xia, Y., Li, H., Zhuang, Q. G., & Gan, R. Y. (2021). Phenolic Content, Main Flavonoids, and Antioxidant Capacity of Instant Sweet Tea (Lithocarpus litseifolius [Hance] Chun) Prepared with Different Raw Materials and Drying Methods. Foods, 10(8), 1930. http://dx.doi.org/10.3390/foods10081930

Liu, Y., Liu, H. Y., Xia, Y., Guo, H., He, X. Q., Li, H., Wu, D. T., Geng, F., Lin, F. J., Li, H. B., Zhuang, Q. G., & Gan, R. Y. (2021). Screening and process optimization of ultrasound-assisted extraction of main antioxidants from sweet tea (Lithocarpus litseifolius [Hance] Chun). Food Bioscience, 43, 101277. http://dx.doi.org/10.1016/j.fbio.2021.101277

Saimaiti, A., Huang, S. Y., Xiong, R. G., Wu, S. X., Zhou, D. D., Yang, Z. J., Luo, M., Gan, R. Y., & Li, H. B. (2022). Antioxidant Capacities and Polyphenol Contents of Kombucha Beverages Based on Vine Tea and Sweet Tea. Antioxidants, 11(9), 1655. http://dx.doi.org/10.3390/antiox11091655

Shang, A., Liu, H. Y., Luo, M., Xia, Y., Yang, X., Li, H. Y., Wu, D. T., Sun, Q. C., Geng, F., Li, H. B., & Gan, R. Y. (2022). Sweet tea (Lithocarpus polystachyusrehd.) as a new natural source of bioactive dihydrochalcones with multiple health benefits. Critical Reviews in Food Science and Nutrition, 62(4), 917-934. http://dx.doi.org/10.1080/10408398.2020.1830363

Shang, A., Luo, M., Gan, R. Y., Xu, X. Y., Xia, Y., Guo, H., Liu, Y., & Li, H. B. (2020). Effects of Microwave-Assisted Extraction Conditions on Antioxidant Capacity of Sweet Tea (Lithocarpus polystachyus Rehd.). Antioxidants, 9(8), 678. http://dx.doi.org/10.3390/antiox9080678

Wu, D. T., Fu, M. X., Guo, H., Hu, Y. C., Zheng, X. Q., Gan, R. Y., & Zou, L. (2022). Microwave-Assisted Deep Eutectic Solvent Extraction, Structural Characteristics, and Biological Functions of Polysaccharides from Sweet Tea (Lithocarpus litseifolius) Leaves. Antioxidants, 11(8), 1578. http://dx.doi.org/10.3390/antiox11081578