Variability in the Antioxidant Activity of Dietary Supplements from Pomegranate, Milk Thistle, Green Tea, Grape Seed, Goji, and Acai: Effects of in Vitro Digestion Susanne M. Henning,* ,† Yanjun Zhang, † Victoria G. Rontoyanni, †,‡ Jianjun Huang, † Ru-Po Lee, † Amy Trang, † Gloria Nuernberger, † and David Heber † † Center for Human Nutrition, David Geffen School of Medicine, University of California, Los Angeles, California 90095, United States ‡ Epidemiology Department, Office of the Chief Quality Officer, Baylor Scott & White Health, Dallas, Texas 75206, United States ABSTRACT: The antioxidant activity (AA) of fruits and vegetables has been thoroughly investigated but less is known about the AA of dietary supplements (DS). We therefore assessed the AA of three to five DS each from pomegranate, milk thistle, green tea, grapes, goji, and acai using four widely used standard methods. The secondary objective was to determine the effects of in vitro digestion on their AA. The AA of the DS prior to digestion ranked as follows: pomegranate > resveratrol > green tea > grape seed > milk thistle and very low in goji and acai with significant group variability in AA. The AA after in vitro simulated digestion of the mouth, stomach, and small intestine compared to undigested supplement was decreased for green tea and grape seed but increased for pomegranate, resveratrol, milk thistle, goji, and acai to various extents. Although polyphenols provide the major antioxidant potency of the tested supplements, our observations indicate that digestion may alter antioxidant properties depending in part on the variations in polyphenol content. KEYWORDS: pomegranate, antioxidant activity, in vitro digestion, dietary supplements, green tea, milk thistle, acai, goji, resveratrol, grape seed ■ INTRODUCTION Over half of U.S. adults consume at least one dietary supplement (DS) per day as estimated by data from the National Health and Nutrition Examination Survey (NHANES) 1999−2002. 1 According to Yang et al., 2 DS provide 25% of dietary total antioxidant capacity in U.S. adults. Polyphenolic phytochemicals are the most frequently occurring phytochemicals in DS with in vitro antioxidant properties. 3 On the basis of an evaluation of the NHANES 2001−2002 data, flavonoid and proanthocyanidin intake contributes 56% of total antioxidants in the diet. 2 Although polyphenols are principally ingested in the diet, commercially available polyphenolic supplements are numerous and commonly used and may contribute to the antioxidant intake. Typical DS that contain antioxidant polyphenols are derived from pomegranate fruit (Punica granatum L.), green tea (Camellia sinensis), and grapes (Vitis vinifera). Other DS such as milk thistle (Silybum marianum) extract, acai (Euterpe oleracea), and goji berries (Lycium barbarum L.) are commonly consumed for their antioxidant activity (AA) but contain very different phytochem- ical structures (e.g., stilbenes for resveratrol), all of which have some AA. The main phytochemicals held responsible for AA vary considerably in these DS. Pomegranate fruit contains ellagitannins, gallotannins, ellagic acid, and smaller amounts of flavonoids and anthocyanins. 4−6 Green tea extracts contain polyphenols including (−)-epicatechin, (−)-epigallocatechin, and their gallate derivatives (−)-epicatechin-3-gallate and (−)-epigallocatechin-3-gallate, which are distinguished by their potent antioxidant and anti-inflammatory properties, offering cardiovascular and neural protection, and for their effects on fat oxidation. 7 Proanthocyanidins in grape seed extract are the main polyphenolic ingredients responsible for its antioxidant, anti-inflammatory, and antimicrobial effects. 7,8 Resveratrol (3,5,4′-trihydroxystilbene) is a stilbene polyphenol that exerts anti-inflammatory, antioxidant, and estrogenic effects and anticancer properties. 9 Although advertised as a grape extract, it is commonly extracted from the root of Japanese knotwood and occurs as a phytoalexin on the skin of grapes grown in humid conditions, where they are susceptible to fungal infection. The fruit of the milk thistle plant, with its active ingredient and flavonoid complex, silymarin, has been used to promote liver health. Silybin, a flavonolignan, represents about 50−70% of the silymarin extract, among other flavonolignans and flavonoids. Silybin and the rest of the silymarin constituents have demonstrated liver-protective properties under experimental conditions due to their antioxidant and anti-inflammatory properties. 10 In recent years, two berry species rich in polyphenolic phytochemicals, acai berry (Amazonian palm berry) and goji berry, have been widely promoted as having antioxidant properties attributed to their primary active ingredients, β-carotene, β-cryptoxanthin, zeaxanthin, and polysaccharides in goji berry fruit 11 and anthocyanins and other polyphenols in acai berry. 12−15 Received: January 15, 2014 Revised: April 7, 2014 Accepted: April 18, 2014 Published: April 18, 2014 Article pubs.acs.org/JAFC © 2014 American Chemical Society 4313 dx.doi.org/10.1021/jf500106r | J. Agric. Food Chem. 2014, 62, 4313−4321