As a popular health ingredient, grape seed extract contains a high level of proanthocyanidins (PACs). Apart from grape seed, PACs are also present in a wide range of food sources, including peanuts, pine barks, hazelnuts, cinnamon, whole cranberries and apples. Because of similar PACs break down to grape seed, cheaper sources like peanut become a potential substitute for PAC extraction. It is well known that peanut is a very dangerous potential allergen. Up to now, however, there are no standardized criteria for the quality of grape seed extract, which arising a serious concern of the commercial grape seed supplement composition.
A recent joint study published in Food Chemistry revealed the rampant adulteration in grape seed extracts. While grape seed is rich in B-type PACs, as well as catechin and epicatechin, peanut skin is principally composed of A-type PACs and a low amount of catechin and epicatechin. The study, “Chemical investigation of commercial grape seed derived products to access quality and detect adulteration” used a TLC method, to analyze 21 commercial available Grape Seed extract supplements (purchased from a variety of suppliers) through fingerprint comparison to standard extract of grape seed and peanut skin. Few samples contained the active ingredients at an amount level comparable to the authentic Grape Seed Extract Standard. 9 out of 21 samples were considered to be adulterated by peanut skin extract.
The authors studied the relationship between the grape seed supplement price and its quality as well. As put in the paper, “(The results) suggesting there is no correlation between price and quality as determined by HPLC”, and “consumers are paying an arbitrary price with regards to quality”.
As part of its drive to clean up the market, Skyherb, a China-based manufacturer of grape seed extract, initiated a project with Alkemist Labs to develop a High Performance Thin Layer Chromatography (HPTLC) method for rapid and simultaneous identification of Peanut Skin adulteration in Grape Seed. The fingerprints of the grape seed and peanut skin extracts showed a different profile of bands and can be distinguished from each other. The method is applicable to raw materials, extracts and commercially available dietary supplements. Using it, as low as 5% peanut skin adulteration was visually detectable. A number of commercial grape seed extract samples bought from different suppliers were tested for the adulteration. The results turned out 6 out of 10 samples were adulterated by peanut skin.
Apart from the HPTLC method, an HPLC method for detection of grape seed extract adulteration was also developed, together with Zhejiang University. The peak of A-type PACs from peanut skin, which are barely found in grape seed, can act as a feature peak for the adulteration identification. If the standard of A-type PACs could be available, that will be the easiest way for the industry to conduct the adulteration identification work. Skyherb expects to introduce the rapid identification method to the industry within the first quarter of 2015.