Effect of Pretreatments on Releasing of Bound Phenolics from Dried Bamboo Shoots during Simulated In Vitro Colonic Fermentation

Salt-dried bamboo shoots (SDBS), steamed dried bamboo shoots (TDBS), fumigation-dried bamboo shoots (UDBS), and fermentation-dried bamboo shoots (FDBS) are four popular types of dried bamboo shoots (DBS) enjoyed by Chinese people. In this work, we aimed at investigating the release pattern of bound phenolics from DBS prepared by different processes on simulated in vitro colonic fermentation. The results showed that nine phenolic compounds were identified from DBS, including seven phenolic acids and two flavonoids. Also, the contents of chlorogenic acid, p-coumaric acid, and ferulic acid were higher. Among the four types of DBS, FDBS exhibited the highest release of bound phenolics during colonic fermentation, with a value of 3.619 mg GAE/g DW. In addition, all the DBS produced four short-chain fatty acids (SCFAs), with the highest content of acetic acid at 7.721 mmol/L, followed by propionic acid and valeric acid, and the lowest content of butyric acid at only 0.023 mmol/L, along with a gradual decrease in their cellulose, hemicellulose, and lignin contents. Concurrently, confocal laser scanning microscopy (CLSM) observation images showed that reduced red fluorescence exhibited a decrease in bound phenolics content, while reduced green fluorescence indicated a decrease in fiber content. A significant positive correlation ( $P$ < 0.05) was observed between the release of bound phenolics and total SCFA production during colonic fermentation of SDBS, TDBS, UDBS, and FDBS, with correlation coefficients of 0.632, 0.844, 0.717, and 0.916, respectively, and a significant negative correlation ( $P$ < 0.05) with the IC50 values for the inhibition of α-amylase and α-glucosidase, with correlation coefficients of −0.643, −0.613, −0.823, and −0.839, respectively. The four DBS were ranked in descending order of bound phenolic release, SCFA production, dietary fiber reduction, and inhibitory activity associated with the metabolic syndrome: FDBS, TDBS, SDBS, and UDBS. DBS released large amounts of bound phenolics and produced SCFAs during colonic fermentation, which might be potentially beneficial for maintaining intestinal microbiota balance.