Metal Chelates of Petunidin Derivatives Exhibit Enhanced Color and Stability.

Peipei Tang,M Monica Giusti

doi:10.3390/foods9101426

Abstract

Anthocyanins with catechol (cyanidin) or pyrogallol (delphinidin) moieties on the B-ring are known to chelate metals, resulting in bluing effects, mainly at pH ≤ 6. Metal interaction with petunidin, an O-methylated anthocyanidin, has not been well documented. In this study, we investigated metal chelation of petunidin derivatives in a wide pH range and its effects on color and stability. Purple potato and black goji extracts containing >80% acylated petunidin derivatives (25 μM) were combined with Al3+ or Fe3+ at 0 μM to 1500 μM in buffers of pH 3–10. Small metal ion concentrations triggered bathochromic shifts (up to ~80nm) at an alkaline pH, resulting in vivid blue hues (hab 200°–310°). Fe3+ caused a larger bathochromic shift than Al3+, producing green colors at pH 8-9. Generally, metal ions increased the color stability and half-life of petunidin derivatives in a dose-dependent manner, particularly at pH 8. Petunidin derivative metal chelates produced a wide range of colors with enhanced stability.

Highlights

Anthocyanins are water-soluble pigments that provide brilliant red, purple and blue colors to vegetables and fruits [1]
This study aimed to investigate the colorimetric and spectrophotometric properties of petunidin derivatives from purple potato and black goji, and to examine the impact of their metal chelation on the color expression and stability
One anthocyanin accounted for 91% of the total peak area at 520nm and was identified as petunidin-3-rutinoside(p-coumaroyl)-5-glucose

Summary

Introduction

Anthocyanins are water-soluble pigments that provide brilliant red, purple and blue colors to vegetables and fruits [1]. They undergo characteristic pH-dependent structural transformations, exerting a diverse color appearance [2]. Anthocyanin color and stability could be influenced by metal complexation [6]. It was reported that anthocyanins with at least two free hydroxyl groups on the B-ring could chelate multivalent metal ions, including, but not limited to, Fe2+ , Fe3+ , Ga3+ , Al3+ , Mg2+ , Sn2+ , Ti2+ , and Cu2+ [7,8,9,10]

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