The effects of heating, UV irradiation, and storage on stability of
the anthocyanin–polyphenol copigment complex
Anna Bc˛cakowska, Alicja Z.Kucharska, Jan Oszmian
´
ski*
Department of Fruit and Vegetable Processing, Agricultural University of Wrocaw, ul. Norwida 25, 50-375 Wrocaw, Poland
Received 27 June 2002; accepted 9 September 2002
Abstract
The influences of temperature, UV irradiation, and 3 months of storage (in the presence and absence of light) on the stability of a
copigmentation complex were investigated.The copigments selected for the study included: quercetin-5
0
-sulphonic acid (QSA),
sodium salt of morin-5
0
-sulphonic acid (NaMSA), rutin, quercetin, chlorogenic acid, tannic acid, and unknown flavones from roots
of the Chinese origin herb Scutellaria baicalensis Georgi.The copigmentation effect increased with the copigment content.UV
irradiation had a stronger degradation effect on the copigmentation complex than heating at 80
C.Direct sunlight was found to be
a significant factor, determining instability of the anthocyanin–copigment complex during storage.The Scutellaria flavones pre-
dominated over other copigments.
# 2002 Elsevier Science Ltd.All rights reserved.
Keywords: Anthocyanin; Copigmentation; Scutellaria baicalensis Georgi; Colour stability
1. Introduction
The anthocyanins (glycosylated polyhydroxy deriva-
tives of 2-phenylbenzopyrylium salts) are natural,
water-soluble, non-toxic pigments responsible for some
colours of fruits, vegetables, flowers, and other plant
tissues (Mazza & Brouillard, 1990).
Aglycones of anthocyanins are bound to sugar at the
C3 and sometimes also at C5, C7 positions and exist in
the glycosylated form.If there is no bound sugar, they
are referred to as anthocyanidins.Anthocyanins may
also exist in the acylated form, with an ester linkage at
the 3
0
glucoside position.Often, among them, are acetyl,
coumaryl, and caffeoyl groups.
The number of hydroxyl groups, the degree of
methylation of these hydroxyl groups, the nature and
number of sugar moieties bound to the molecule, and
the position of linkage, the nature, and number of ali-
phatic or aromatic acids linked to the sugar, determine
the colour of anthocyanins.The same anthocyanin may
have different colours, depending on the pH of the
solution (Dao, Takeoka, Edwards, & Berrios, 1998).At
pH below 2 anthocyanins exist primarily in the form of
red flavylium cations.When the pH increases to 6, the
flavylium cation converts into purple quinonoidal bases.
These compounds are labile and, upon nucleophilic
attack by water, transform to the colourless carbinol
pseudobases and chalcone pseudobases.
So far, anthocyanins have not been broadly used in
foods and beverages, since they are not as stable as
synthetic dyes.In fact, the colour stability of anthocyanin
depends on a combination of various factors, such as
the structure and concentration of the anthocyanin, pH,
temperature, and presence of complexing agents (phenols,
metals) (Mazza & Brouillard, 1990).Recent investigations
(Davies & Mazza, 1993; Mazza & Brouillard, 1987,
1990) have suggested that the molecular copigmentation
of anthocyanins with other compounds (copigments) is
the main colour-stabilizing mechanism in plants.A
copigment alone is usually colourless, but when added to
an anthocyanin solution it greatly enhances the colour of
the solution.A copigment may be one of flavonoids,
alkaloids, amino acids, organic acids, nucleotides, poly-
saccharides, metals, and anthocyanins themselves
(Mazza & Brouillard, 1990).Copigments have electron-
rich pi systems, which are able to associate with the
0308-8146/02/$ - see front matter # 2002 Elsevier Science Ltd.All rights reserved.
PII: S0308-8146(02)00429-6
Food Chemistry 81 (2003) 349–355
www.elsevier.com/locate/foodchem
* Corresponding author.Tel.: +48-71-320-5477; fax: +48-71-320-
5477.
E-mail address: oszm@ozi.ar.wroc.pl (J. Oszmian
´
ski).