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.

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.1However, 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:https://epublications.uef.fi/pub/urn_isbn_978-952-61-1360-9/urn_isbn_978-952-61-1360-9.pdf. Accessed October 29, 2014.