Abstract
In recent years, the demand for natural colorants to be used as food additive colors has been increasing. Purple carrot pigment is one of the resources with high potential for use as a natural colorant for food additives. Purple carrot pigment is a type of anthocyanin and has been shown to be highly stable. This anthocyanin is cyanidin 3-[2′′-xylosyl-6′′-(6′′′-sinapoyl or -feruloyl)-glucosyl]- galactoside. Depending on the cultivar and growing conditions, precursors of this structure are also accumulated. It is known that modification with sugars and organic acids contributes to the stability of anthocyanin molecules. The more complex the structure of the anthocyanin molecule, the more stable it is. For this reason, breeding varieties that accumulate only highly modified structures leads to the production of high-quality food additive colors. Therefore, the identification of anthocyanin-modifying enzyme genes will be important for future breeding. The modification of the anthocyanin in purple carrot has been elucidated by recent genome analysis and RNA-seq analysis technology except for the glucosylation. It is generally known that the glycosylation of anthocyanins is catalyzed by uridindiphosho (UDP)-sugar-dependent GTs (UGTs). Some anthocyanin glucosylation is mediated by glycoside hydrolase family 1 (GH1) proteins in acyl-glucose dependently. However, in purple carrot anthocyanins, the glucosylation is not catalyzed by UGT or GH1 protein but by acyl-glucose-dependent GT belonging to the glycoside hydrolase family 3 (GH3) protein. This is the first GH3-mediated glycosyltransferase to be discovered. Here, we describe the anthocyanin modification pathway in purple carrot and its glycosylation, especially by GH3-type glucosyltransferase.
