Changes in structure and phenolic profiles during processing of steamed bread enriched with purple sweetpotato flour

Purple-fleshed sweetpotato is a rich source of antioxidants such as polyphenols. Chinese steamed bread (CSB) is a popular food product for many people. The effect of CSB making process on the structure and phenolic profiles of CSB enriched with purple sweetpotato flour (PSPF) at different concentrations was investigated. The mixing process greatly reduced the gluten strength due to the incorporation of PSPF. The addition of PSPF induced extensive structural modification on CSB due to the starch-polyphenol and protein-polyphenol interactions. The total phenolic contents, in vitro antioxidant activity, and the contents of hydroxycinnamic acid derivatives were decreased by fermentation and proofing, but they were increased after steaming and storage. The anthocyanins were significantly degraded during the CSB making process. The textural and structural properties of CSB were significantly affected by the PSPF substitutions. The results of this study are useful to develop functional CSB with improved nutritional quality and phenolic profiles.