Focus on Anthocyanins
Reviewed: Yamamoto M, Yamaura K, Ishiwatari M,
et al. Degradation Index for quality evaluation of commercial dietary
supplements of bilberry extract. J Food Sci.
2013;78(3):S477-S483.
A
group from Chiba University (Chiba, Japan) investigated the heat stability of bilberry
(Vaccinium myrtillus, Ericaceae) or
blueberry (V. angustifolium [lowbush blueberry]; V. corymbosum [highbush blueberry]; possibly other Vaccinium spp.) anthocyanins in solid dosage forms (soft
capsules, tablets, and granules). Three commercial samples were exposed to 70°C
for five days without humidity control. The individual anthocyanins and
anthocyanidins were analyzed by ultra high-performance liquid chromatography
(UHPLC) using detection in the visible range at 535 nm. Stability was also
monitored by UV/Vis spectrophotometry.
The
heat treatment led to a cleavage of glycosidic bonds in all three formulations,
and the anthocyanidin-arabinosides were more easily hydrolyzed than the
galactosides. The anthocyanidin-glucosides were the most stable in all three
formulations. The extracts in the tablets were more stable than those in the
soft capsules or the granules, but a direct comparison is difficult since the
tablets contained black currant (Ribes nigrum,
Grossulariaceae) extract in addition to blueberry extract, while the soft
capsules contained bilberry extract and the granules blueberry extract only.
Based on their findings, the authors looked for high levels of anthocyanidins
as a sign of degradation in 17 additional commercial products. Five samples had
a more than three times higher ratio of cyanidin and delphinidin/cyanidin-3-O-arabinoside and delphinidin-3-O-arabinoside
than the standard material and were considered partly degraded. One sample did not
contain any of the labeled blueberry extract but was entirely made up of black
currant extract. A comparison between the UHPLC-Vis and UV/Vis approaches
showed that the UHPLC-Vis method not only was able to detect the single case of
adulteration, but it also allowed to get a better read on the stability of the
products, since the occurrence of hydrolysis went undetected by UV/Vis.
Comment: It is well known that anthocyanins are not very stable
and manufacturers of such products have to be very careful to avoid degradation
of the material. The results of the paper, indicating a loss of over 50% of
delphinidin-, cyanidin-, peonidin- and malvidin-3-O-arabinosides
after five days in a solid formulation at 70°C, provide additional data to show
that anthocyanins are a major stability challenge and may warrant that
manufacturers consider additional label information to caution against excessive
heat exposure.
Since
the authors have chosen to compare the stability of a bilberry extract in soft
capsules to a tablet containing a blueberry/black currant combination and a
granule with blueberry extract, conclusions on a particular ingredient are
difficult to make. In addition, the confusion between bilberries and
blueberries in some parts of the manuscript (e.g., “the product label of sample D indicates the
presence of black currant in addition to blueberry extract … thus, the
ingredient in sample D was surmised to be black currant, and consequently, no
constituents of bilberry were regarded to be present.”) makes the interpretation of
the findings very challenging. Nevertheless, the authors clearly demonstrated
that UV/Vis is neither a suitable method for authentication nor for monitoring
the stability of anthocyanin-containing ingredients and products.
Reviewed: Lee J. Marketplace analysis
demonstrates quality control standards needed for black raspberry dietary
supplements. Plant Foods Hum Nutr. 2014;69(2):161-167.
This publication from the United
States Department of Agriculture (USDA) focuses on the authenticity of
commercially available black raspberry (Rubus occidentalis,
Rosaceae) supplements and dried fruit. Just based on the labels, it seems that
manufacturers have difficulties in distinguishing black raspberry from its
cousin, the blackberry (R. fruticosus),
since four out of 19 samples of black raspberry purchased via Amazon.com
actually showed an image of blackberry. The HPLC-UV/Vis analysis of authentic
black raspberry indicated cyanidin-3-O-rutinoside to be the most abundant anthocyanin, followed
by cyanidin-3-O-xylosylrutinoside and cyanidin-3-O-glucoside.
The same HPLC-UV method was used
to analyze anthocyanins in the 19 commercial products. The results showed that
12 samples contained black raspberry (between 0.1 and 145.2 mg/capsule), while four
samples contained anthocyanins from species other than black raspberry and three
samples did not contain any anthocyanins at all. The identity of the
anthocyanin-containing adulterants is not known, although in one instance, the
author hypothesizes that the sample contained a freeze-dried blackberry powder.
In addition, two samples may have included a pink-colored filler. As a
conclusion, she indicates that there is a need for dietary supplement quality
control standards and suggests that anthocyanin profiling of black raspberry
products by HPLC-UV/Vis is a suitable approach to detect adulteration of this
ingredient.
Comment:
The adulteration of anthocyanin-rich bilberry extracts has been extensively
documented.1 However, the publication by Lee provides evidence that
the issue with adulteration of anthocyanin-containing extracts is much broader,
and substitution with cheaper materials can be expected to occur in other
ingredients, in particular those where the supply is limited (as in the case of
black raspberry). When picking the whole fruit, black raspberries can be
distinguished from blackberries by the fact that the fruit stem (torus or
receptacle) stays with the plant, leaving a hollow core in the black raspberry
fruit (this also happens with ripe red raspberries [R. idaeus]).
For powdered material and extracts, many analytical methods to distinguish
berry species based on the anthocyanin pattern have been described in the
literature, and tables with specific markers for various fruit extracts, like
the one published in the doctoral thesis by Primetta,2 are available
to the manufacturer. The use of such methods will ensure the correct identity
of the ingredient in question.
References
1. Foster S, Blumenthal M. The adulteration of commercial bilberry extracts. HerbalGram.
2012;(96):64-73.
2. Primetta A. Phenolic compounds in
the berries of the selected Vaccinium
species: the potential for authenticity analyses.
PhD thesis. Dissertations in Forestry and Natural Sciences.
Kuopio, Finland: Publications of the University of Eastern Finland; 2014.
Available at: http://epublications.uef.fi/pub/urn_isbn_978-952-61-1360-9/urn_isbn_978-952-61-1360-9.pdf. Accessed
October 29, 2014.
