Abstract:Rice bran insoluble dietary fiber （RBIDF） was dried using four methods，namely low-temperature hot air drying，high-temperature hot air drying，vacuum drying，and vacuum freeze drying.The content of free and bound phenolics in RBIDF，as well as their antioxidant activities （DPPH· scavenging capacity and FRAP），was assessed using spectrophotometric techniques.Phenolic compounds were subjected to both qualitative and quantitative analyses using high-performance liquid chromatography （HPLC）.Furthermore，the impact of the four drying methods on the bioaccessibility of phenolic compounds in RBIDF was evaluated through in vitro simulated digestion.The results showed that the content of bound phenolics and their antioxidant activities in the four types of dried RBIDF were higher than those of free phenolics.Epicatechin and vanillin were the predominant free phenolics in RBIDF，accounting for over 90% of the total free monomeric phenolics.Ferulic and p-coumaric acids were the predominant bound phenolics，accounting for over 99% of the total bound monomeric phenolics.Scanning electron microscopy and Fourier transform infrared spectroscopy revealed that different drying methods exerted certain impacts on the structure of RBIDF.In conclusion，compared to hot air drying and vacuum freeze drying，vacuum drying was more conducive to the retention of phenolic compounds during drying and their release during digestion，thereby maintaining relatively higher antioxidant activity and bioaccessibility in RBIDF.