Comparison of free, conjugated, and insoluble-bound phenolics and their antioxidant activities in oven-drying and freeze-drying bamboo (Phyllostachys edulis) shoot tips.

Bamboo(Phyllostachys edulis) shoot was reported to be rich in phenolics. In the present study, free phenolics, conjugated phenolics, and insoluble-bound phenolics of oven-drying and freeze-drying bamboo shoot tips were extracted and separated, of which total phenolic content (TPC), total flavonoid content (TFC), and their antioxidant activities were determined. Phenolics of different binding forms were qualitatively analyzed using HPLC-ESI-QqQ-MS. A total of 22, 41, and 28 compounds were confirmed or tentatively identified in free, conjugated, and insoluble-bound phenolic extraction, respectively. The majority of the identified compounds were organic acids and phenolic acids. Oven-drying samples exhibited higher TPC (10.53-24.92 mg GAE/100 g DW) and TFC (5.80-33.27 mg CE/100 g DW) values, and stronger antioxidant activities (DPPH, ABTS, and FRAP) than freeze-drying (TPC: 1.67-15.28 mg GAE/100 g DW, TFC: 1.43-29.05 mg CE/100 g DW). Insoluble-bound phenolics were the major contributor to the total antioxidant activity. The present study investigated the phenolics composition and antioxidant activities of different binding forms in bamboo shoot tip comprehensively, and provided available information for their high-value deep-processing.