Defatted Green Tea Seed Extracts as a Functional By‐Product With Antioxidant and Antimicrobial Activities

Green tea exhibits multifunctional effects owing to its bioactive compounds. These effects were mainly demonstrated in green tea leaves. Therefore, they are expected in green tea seeds (GTSs). This study aimed to explore the potential use of by‐products from defatted GTSs (DGTS) by comparing the bioactive compounds and antioxidant and antimicrobial activities of water (DGTSW) and ethanol (DGTSE) extracts, to identify their nutritional and functional applications. DGTSW and DGTSE were prepared and investigated. The bioactive compounds in DGTSW and DGTSE were analyzed, and their antioxidant and antimicrobial activities were investigated. DGTSW exhibited a higher extraction yield, crude protein content, and crude lipid content than those of DGTSE, indicating greater nutritional value. In contrast, DGTSE contained high levels of bioactive compounds, including epigallocatechin gallate, flavonoids, and alkaloids, as well as high free‐sugar content. Free amino acid composition showed that DGTSW was rich in umami‐related free amino acids, such as glutamic and aspartic acid, whereas DGTSE had higher levels of bitter‐related free amino acids, such as valine, leucine, and isoleucine. Antioxidant activity was significantly higher in DGTSE, which may be attributed to the presence of potent bioactive compounds, including polyphenols, flavonoids, and alkaloids. In addition, DGTSE exhibited strong antimicrobial activity against Pichia membranifaciens with an inhibition zone and microbial growth inhibition rate of 96.5% at 20 mg/mL. These findings suggest that the nutritional and functional properties of DGTS could be affected by the appropriate extraction solvent, with water extraction favoring nutritional components and ethanol extraction enhancing functional activity through abundant bioactive compounds.