Tentative characterization of precursor compounds and co-factors of pigment formation in production of 'wu mi' from Vaccinium bracteatum Thunb. Leaves

Mingcong Fan; Yihui Fan; Weiping Huang; Li Wang; Yan Li; Haifeng Qian; Hui Zhang; Xiguang Qi

doi:10.1016/j.foodchem.2018.04.101

Tentative characterization of precursor compounds and co-factors of pigment formation in production of 'wu mi' from Vaccinium bracteatum Thunb. Leaves

Food Chem. 2018 Oct 1:262:199-205. doi: 10.1016/j.foodchem.2018.04.101. Epub 2018 Apr 24.

Authors

Mingcong Fan¹, Yihui Fan², Weiping Huang³, Li Wang⁴, Yan Li⁵, Haifeng Qian⁶, Hui Zhang⁵, Xiguang Qi⁵

Affiliations

¹ School of Food Science and Technology, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China.
² Department of Immunology, School of Medicine, Nantong University, 19 Qixiu Road, Nantong 226001, China.
³ Jiangsu Jiujiu Environmental Science and Technology Co., Ltd., 99 Xinxi Road, Liyang 213300, China.
⁴ School of Food Science and Technology, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China; State Key Laboratory of Food Science and Technology, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China; National Engineering Research Center for Functional Food, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China. Electronic address: wl0519@163.com.
⁵ School of Food Science and Technology, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China; State Key Laboratory of Food Science and Technology, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China; National Engineering Research Center for Functional Food, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China.
⁶ School of Food Science and Technology, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China; State Key Laboratory of Food Science and Technology, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China; National Engineering Research Center for Functional Food, Jiangnan University, 1800 Lihu Avenue, Wuxi 214122, China. Electronic address: qianhaifeng@jiangnan.edu.cn.

PMID: 29751909
DOI: 10.1016/j.foodchem.2018.04.101

Abstract

Vaccinium bracteatum leaves (VBTL) are traditionally used in China to dye rice grains, which assume a deep blue color, named 'Wu mi'. Information on the mechanism of pigment formation is limited. In this study, CIELAB color space parameters were used to represent the color of 'Wu mi'. Precursor compounds of pigments formed during the dyeing process were identified by UPLC Q-TOF MS analysis. The changes in co-factors for pigment formation in VBTL were measured at different growth stages. The L^∗ and b^∗ values of dyed rice increased as the leaves aged, whereas a^∗ values showed irregular changes. Six compounds were tentatively identified as pigment precursors by UPLC Q-TOF MS analysis. The pH and β-glucosidase activity at different growth stages of VBTL were indicated to be crucial co-factors for pigment formation. A tentative hypothesis is presented that iridoid glycosides are hydrolyzed by acids and β-glucosidases to form a dialdehyde structure that binds covalently with amino residues of lysine side chains in rice protein molecules.

Keywords: Co-factors; Color; Precursor compounds; UPLC Q-TOF MS; VBTL.

MeSH terms

China
Food Coloring Agents / analysis
Food Coloring Agents / metabolism*
Food Handling
Hydrolysis
Iridoid Glycosides / analysis
Iridoid Glycosides / metabolism*
Oryza*
Plant Leaves / chemistry*
Plant Leaves / enzymology
Vaccinium myrtillus / chemistry*
Vaccinium myrtillus / enzymology
beta-Glucosidase / metabolism

Substances

Food Coloring Agents
Iridoid Glycosides
beta-Glucosidase