Formation mechanism of blue pigment in boiled lotus rhizome discs: Insight into the chelation of polyphenols and iron.

[Display omitted] • The blue change of boiled lotus rhizome discs (BLRDs) was non-enzymatic browning. • The blue pigment may be mainly due to the complexation of iron and polyphenols. • The main polyphenols that caused bluing of BLRDs were L-dopa and gallocatechin. • L-dopa-iron and catechin-iron were chelated in form of bis-complexes in this study. Boiled lotus rhizome discs (BLRDs), as common processed products of lotus rhizome, have gained increasing attention from consumers and food manufacturers. However, the blue pigment formed during boiling affects its appearance and reduces the appetite of BLRDs. In this study, the effects of polyphenols and iron contents on blue pigment formation in BLRDs in different regions and months were investigated. Results revealed that blue variation was more serious in March and April of the second year in Wuhan, and polyphenols and iron contents in these two months were significantly higher than those in other months. Then, UPLC and UV–Vis analysis showed that polyphenols causing the formation of blue pigment in BLRDs were L -dopa, gallocatechin, catechin, epigallocatechin, chlorogenic acid and epicatechin, among which L-dopa (52.450 mg/100 g in fresh lotus rhizome (FLR)) and gallocatechin (36.210 mg/100 g in FLR) possessed the greatest effect. Moreover, the ESI-Q-TOF-MS analysis of L -dopa-iron chelate and gallocatechin-iron chelate suggested that the blue pigment of BLRDs was mainly in the form of bis-complexes under boiling conditions. The study on formation mechanism of blue pigment in BLRDs can provide a reference for lotus rhizome processing. [ABSTRACT FROM AUTHOR]