| Summary: | To enhance the utilization of summer–autumn tea, a water-soluble polysaccharide (D1N1) was isolated through a series of techniques including hot water extraction, ethanol precipitation, and column chromatography. The structure of D1N1 was determined through the utilization of ultraviolet, Fourier-transform infrared, high-performance anion-exchange chromatography, gas chromatography–tandem mass spectrometry, and nuclear magnetic resonance. The results revealed that glucose was the predominant component of D1N1, accounting for 95% of its composition. Additionally, D1N1 also contained galactose, arabinose, and rhamnose. The molecular weight (Mw) of D1N1 was determined to be 224.71 kDa. The backbone of D1N1 consisted of →4)-α-D -Glc<i>p</i> (1→, →3,4)-α-D-Gal<i>p</i>-(1→, →4,6)-α-D -Glc<i>p</i> (1→ at a molar ratio of 35:1:1, and branching at the O-3 position of →3,4)-α-D-Gal<i>p</i>-(1→ and O-6 position of →4,6)-α-D-Glc<i>p</i> (1→ with α-D -Glc<i>p</i> (1→. In addition, the antioxidant activity of D1N1 was also evaluated. D1N1 exhibited excellent antioxidant bioactivity against the DPPH, superoxide anion radical, and ABTS<sup>+</sup> radical. These findings provide a theoretical basis for the application of summer–autumn tea polysaccharide as a potential functional food.
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