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Adulteration of Pomegranate Products — A Review of the Evidence

Editor’s note: This article was produced as part of the ABC-AHP-NCNPR Botanical Adulterants Program’s continuing coverage of adulteration-related issues.

Introduction

Pomegranate (Punica granatum, Lythraceae) fruit juice has enjoyed considerable market growth and commercial success as a popular beverage in the United States and internationally for more than a decade. The consumption of pomegranate juice in the United States went from roughly 75 million eight-ounce servings in 2004 to about 450 million servings in 2008 — a 500% increase.1 One review indicates that sales of pomegranate juice grew dramatically from $84,500 in 2001 to $66 million in 2005.2 According to 2014 estimates, 150,000-200,000 metric tons of fresh pomegranates and 3.7 million gallons of pomegranate juice concentrate are sold annually (A.R. Rejaei, director of clinical regulatory affairs at POM Wonderful, email to M. Blumenthal, April 7, 2015).

As the popularity of pomegranate has increased, many suppliers of herbs and other plant-based materials have begun to produce a variety of dried pomegranate materials (e.g., dried juice concentrates and extracts) for use as ingredients with health-promoting properties in the burgeoning global market for natural products.* These concentrates and extracts are produced by various means from pomegranate juice, whole pomegranate fruit, or selected parts of the fruit.

Many manufacturers produce botanical extracts standardized to a chemical compound or a class of compounds (marker compounds) for quality control purposes and/or to help ensure consistent, reproducible biological activity. Following this trend, some manufacturers of pomegranate fruit extracts (PFEs) are standardizing their PFEs to ellagic acid (EA), a common phenolic compound widely distributed in nature. EA has a number of reported beneficial physiological activities, with much work focusing on the compound’s antioxidant activity.3 (EA was recently found to have pro-oxidant properties as well.) The antioxidant activities of EA metabolites formed in the intestinal tract (“colonic metabolites,” such as urolithin A) are thought to be responsible for the therapeutic effects attributed to EA.4,5

A number of PFEs are marketed with claims of high levels of EA (ca. 40-70%), but industry experts have questioned the practice of standardizing PFEs to such high levels of EA. A concern raised by some experts — and a central question in this paper — is whether such high EA levels are endogenous in the pomegranate fruit source of these extracts, or if they are the result of added, non-pomegranate-sourced (i.e., exogenous) EA.

Other pomegranate products have been the subject of adulteration reports as well. A 2009 article describing pomegranate juice adulterated with other fruit juices suggests that there may be several forms of adulteration that exist in the marketplace.6

This article briefly reviews the chemistry and reported health benefits of pomegranate, the evidence for adulteration of pomegranate juice and extract, the pharmacology and safety of EA, and the issues surrounding standardizing PFEs to EA content.

Background

Pomegranate is believed to have originated in an area encompassing what is now Iran, Afghanistan, and northern India. Pomegranate played a prominent role in Greek mythology, symbolism, and ceremonies, as well as in numerous religions, including Zoroastrianism, Buddhism, early Christianity, Hinduism, and Islam.7,8 All parts of the pomegranate plant (root, bark, leaves, flowers, and fruit) have been used in Ayurvedic medicine in India for a variety of purposes, including as an antiparasitic agent and blood tonic, and for the treatment of ulcers, canker sores, and diabetes.7 The antitumor, antidiabetic, cardioprotective, antioxidant, and antimicrobial properties of pomegranate preparations have taken on a more prominent role in current use.2,9-12

The chemistry of pomegranate is dominated by phenolic compounds of differing complexity, including benzoic and cinnamic acid derivatives, flavonoids, ellagitannins, and anthocyanins.10 Lignans were reported in pomegranate for the first time in 2009, adding to the family of phenolics found in this species.13 Two analyses of pomegranate juice using ultra high-performance liquid chromatography-mass spectrometry (UHPLC-MS) have cataloged 67 and 75 different secondary metabolites, respectively, most of them phenolics.14,15 Triterpenes have also been reported in pomegranate.16 Pomegranate seed oil contains phytosterols and has a fatty acid profile dominated by punicic acid, an omega-5 linolenic acid isomer with the carbon-carbon double bonds at positions 9, 11, and 13.17

The majority of pomegranate dietary supplements are reportedly manufactured from dried extracts. The materials of commerce discussed in this review are all derived from the fruit, whether from the seed, juice, or rind/husk/peel.18 Pomegranate dietary supplements are typically produced from either dehydrated pomegranate juice (also known as juice concentrate, not an extract) or compounds extracted from pomegranate fruit and/or fruit parts by using a solvent (e.g., water, ethanol, methanol, or combinations thereof), often after the juice has been removed by mechanical pressing. Depending on the methods used and the desired chemical profile of the finished material, manufacturers often try to preserve the bioactive phenolic compounds19 of pomegranate that have been the subject of numerous chemical, pharmacological, and clinical studies.

As a conventional food, pomegranate juice remains a popular beverage for its antioxidant activity. A recent review summarizing the impact of processing on the bioactive constituents, flavor, and aroma of pomegranate juice noted that temperature, pH, pressure, and time all affect the final concentration and ratios of different juice constituents.20

Evidence of Adulteration

At least three different forms of adulteration have been reported in pomegranate products in the global marketplace: pomegranate juices made with juice(s) from other fruits; pomegranate extracts spiked with additional EA or polyphenols; and products made mostly from unknown or unidentified source materials, with little to no pomegranate constituents.

Juice

Increased demand for an agricultural commodity in relatively fixed supply usually drives up the cost of the raw material, which can tempt less scrupulous suppliers and manufacturers to dilute or substitute the actual commodity with lower-cost, more readily available materials. The addition of lower-cost, readily available juices to more expensive juices in limited supply has been an issue in the food and beverage industry for some time.21 Both pomegranate juice and extracts thereof appear to have been subject to this form of economically motivated adulteration.

In 2009, Zhang et al.6 evaluated 45 juice samples from 23 US manufacturers, all purchased in local markets. First, they adapted criteria for determining the identity of genuine pomegranate juice from the databases of Krueger Food Laboratories, Inc., and the Association of the Industry of Juices and Nectars of the European Economic Community.22-24 After examining the profiles of anthocyanins, ellagitannins, sugars, and acids in those juice samples, they found that only approximately 35% of the tested juices had complete profiles appropriate for or representative of pomegranate juice. (The researchers also tested the samples for mannitol and tartaric acid content, and used stable isotope ratio analysis [SIRA] to test for any added sugars.) This seminal study established that adulteration of pomegranate juice was pervasive at the time, and offered a multi-parameter profile to determine if juice products are adulterated.

Numerous methods and criteria have been used previously to identify adulterated juice products. In 2011, concern about fruit juice adulteration led the Grocery Manufacturers Association to conduct an HPLC-MS analysis of various fruit juices, including pomegranate, apple (Malus spp., Rosaceae), orange (Citrus sinensis, Rutaceae), red grape (Vitis vinifera, Vitaceae), white grape (V. vinifera), and cranberry (Vaccinium macrocarpon, Ericaceae), to determine their levels of tartaric, quinic, malic, and citric acids.25 The researchers used the unique ratio of acids in each juice to determine if other juice(s) were present. This study also confirmed the presence of low levels of tartaric and quinic acids in pomegranate. A group in Spain subsequently evaluated pomegranate juice to measure the contents of organic acids, sugars, minerals, proline, and volatile flavor/aroma compounds. The analyses revealed adulteration with varying amounts of grape or peach (Prunus persica, Rosaceae) juice.26 Furthermore, Tezcan et al. in Turkey used a chiral micellar electrokinetic chromatography laser-induced fluorescence (MEKC-LIF) method to develop a fairly complete amino acid profile of pomegranate juice. The results suggested that asparagine (L-Asn) could serve as an effective indicator of adulteration with apple juice, since it is six- to 13-fold more abundant in juices made from certain varieties of apples.27

Borges et al. used HPLC with multiple detectors in two studies of products advertised to contain “100% pomegranate juice.” In one study,28 HPLC coupled with a photodiode array and tandem mass spectrometers (HPLC-PDA-MS2) was used to analyze the polyphenolic profiles of 36 commercially sold juices, including six labeled to contain 100% pomegranate juice and 20 pomegranate juices blended with other fruit juices. (The remaining 10 juices were composed of other fruits.) Three of the “pure” pomegranate juices exhibited typical pomegranate profiles and the highest ellagitannin contents of the tested juices, but only one of these contained significant concentrations of anthocyanins. The other three juices advertised as “pure pomegranate juice” displayed aberrant HPLC profiles relative to the expected pomegranate fingerprint, which suggested blending with other fruit juices or the addition of exogenous polyphenols.

In the second study by Borges et al., fluorescence detection (FD) was combined with the previously used HPLC-PDA-MS method to compare the polyphenolic profiles of a known pure pomegranate juice to red wine and three other juices claiming to be pure pomegranate juice.29 The red wine and the authentic pomegranate juice both exhibited the expected anthocyanin profiles and were readily distinguished by the analytical methods used (pomegranate juice also produced peaks for its ellagitannins, while the red wine, in contrast, gave peaks for flavan-3-ol monomers and procyanidin dimers and trimers). Notably, the three supposedly pure pomegranate juices had the expected ellagitannins, but they also exhibited anthocyanin profiles indicative of a mixture of both source fruits (pomegranates and grapes), as well as the procyanidins and flavan-3-ols seen in grape-derived juices. These results suggested that grape juice might be used to dilute more expensive pomegranate juice, while maintaining an appropriate color.

Krueger Food Laboratories followed up its aforementioned work22,23 with a three-year study of more than 500 juice samples.30 With this large dataset, researchers were able to use an iterative statistical analysis to reduce the sample set to a group of compositionally consistent juices. This was accomplished by calculating a mean and standard deviation of various juice components for the whole set of samples, then excluding any samples that were three or more standard deviations from the mean. The process was repeated on the remaining samples until a stable set of 263 juices was obtained — the presumptive authentic pomegranate juice samples. The report includes a table of 14 pomegranate juice components, mostly sugars and organic acids (with mean content and standard deviation), and a representative HPLC-UV profile of the anthocyanins. A number of patterns of adulteration were observed, including the addition of up to seven fruit juices, sugars, anthocyanin colorants from many natural sources, and artificial colors. Ten references are provided for the analytical methods used, six of which are official AOAC International methods.

In 2016, researchers from Italy demonstrated the use of a DNA-based method, Sequence Characterized Amplified Regions (SCAR), to detect as low as 1% adulteration of pomegranate juice by 10 other botanical sources of anthocyanins reported as potential adulterants of pomegranate products. The SCAR marker selected as a positive control for pomegranate, designated ScPg231, correctly identified eleven different accessions** of P. granatum. The marker also identified pomegranate in four product mixtures: two herbal teas containing 2% and 20% pomegranate, respectively; a jam containing pomegranate, lemon (Citrus limon, Rutaceae), agave (Agave spp., Agavaceae), and pectin; and a juice mix containing 3.5% pomegranate juice concentrate. These results indicate that relatively short-length SCAR markers may be highly useful for identifying pomegranate components with partially degraded DNA.32

Extracts

While pomegranate juice adulteration is generally the result of addition of other fruit juices, adulteration of pomegranate extracts predominantly involves the addition of exogenous polyphenolic material. Pomegranate extracts not standardized to a particular marker, but instead to a non-specific estimation of antioxidant capacity or total phenolics, may be particularly prone to the addition of inexpensive polyphenols (e.g., EA) or tannins to increase antioxidant activity, or to the addition of anthocyanins to adjust color. In an extreme case, a non-pomegranate-based material could be similarly augmented with polyphenols to resemble a pomegranate-derived product.

An analysis of the ellagitannin content and antioxidant capacity of 27 commercially available pomegranate extracts found that only five extracts contained significant amounts of punicalin and punicalagins (pomegranate-specific ellagitannins). Seventeen of the samples contained mostly EA, currently the most used marker compound for standardization of these extracts, while the remaining five had little or no EA or ellagitannins and weak antioxidant activity.33

Another analysis of 19 commercially available pomegranate extracts by a different research group provided similar results.34 Qualitative analysis indicated that only seven of the 19 tested extracts produced polyphenolic profiles indicative of pomegranate, while 13 of the extracts had EA levels exceeding what should be found in the arils (seed coverings) and rind of pomegranate, and six of those had little or no pomegranate ellagitannins present. The extracts that contained some pomegranate ellagitannins but no pomegranate anthocyanins, the authors noted, were likely produced by extraction of the press cake (rinds and arils) after juice production. Two possible explanations were presented for the extracts with high levels of EA but no pomegranate ellagitannins: (1) The extraction and/or associated processing methods were so harsh that the ellagitannins were all decomposed, or (2) no pomegranate was present, and exogenous EA was added.

In addition to the HPLC analyses described above, thin-layer chromatography (TLC) may also be helpful in determining whether an unknown sample matches authentic pomegranate reference samples.

Ellagic Acid

EA Standardization

The issue of standardizing PFEs to EA content is complex, sometimes even problematic, for a number of reasons, discussed below.

1. Free EA is not the most abundant phenolic compound in pomegranate.19 Table 1 summarizes the EA content of various pomegranate parts from several geographic regions, illustrating that EA yields from experimental pomegranate extracts are not likely to exceed 10%. Furthermore, the data suggest that considerable variation of EA (and other polyphenols) may be observed in different varieties of pomegranate, as well as in accessions of the fruit from different ecological niches and geographic regions. Further complicating the matter is the fact that different processing methods for the juice or extracts can result in partial hydrolysis of EA esters (ellagitannins), leading to higher observed levels of free EA in the resulting extract. Considering the experimental conditions used in various publications cited in Table 1, it would be exceedingly difficult, if not practically impossible, to achieve the high levels of EA (40-70%) advertised in products claiming to contain only pomegranate fruit. 

One report has described the preparation of a processed extract of pomegranate rinds containing a remarkable 90% EA, as measured by HPLC analysis.35 The process was described as a triple extraction with hot 50% ethanol, followed by boiling those extracts in hydrochloric acid (HCl) for six hours, and drying the resulting reaction mixture solids. An extract processed in this manner could be used to augment the EA content of pomegranate extracts and products derived therefrom. However, extracts produced using these methods would be unlikely to retain the chemical fingerprint of pomegranate polyphenols.

2. EA is also available in substantial quantities from other sources of ellagitannins (e.g., chestnut [Castanea spp., Fagaceae] bark or fruit36 or gall nuts), offering a potentially lower-cost alternative source for “enhancing” pomegranate extracts. Moreover, the last dozen years have seen a surge of interest in producing free EA through the biotransformation of tannins (i.e., the enzymatic degradation of complex polyphenols to EA by microbial cultures).37-41

3. EA is not the primary or foremost bioactive compound in pomegranate. In fact, the compounds responsible for many of the pharmacological benefits attributed to pomegranate have not been adequately identified. It is possible, even likely, that different compounds may be associated with various bioactivities.

Punicalin and punicalagins A and B are more abundant than EA in pomegranate and have been reported to account for 89% of the antioxidant activity of pomegranate juice.19,42 Although standardizing PFEs to EA content may be convenient from an analytical chemistry standpoint, it would be more logical to standardize PFEs to punicalin and punicalagins A and B, which are more abundant and distinctive markers for pomegranate. The availability of high-quality reference standards to analyze for these potential markers might be a short-term issue, but there is clearly a market need for such reference standards.

4. EA is poorly soluble in aqueous media, particularly under acidic conditions, and it is not significantly bioavailable when consumed as the free acid.43,44 However, hydrolysable ellagitannins (e.g., punicalin and the punicalagins) not only are more soluble than EA in physiological media, but also yield bioavailable EA during metabolism in the human gut.44 Ironically, higher EA content in various commercial products would thus seem likely to result in lower blood levels of EA, relative to the complex of authentic, unaltered pomegranate polyphenolic compounds.

EA Bioavailability

A single human volunteer, after fasting overnight, took a dose of 180 mL of pomegranate juice containing 25 mg of EA and 318 mg ellagitannins. Blood samples were drawn prior to dosing and at 30 minutes, one, two, three, four, and six hours after dosing, and they were processed and analyzed by HPLC. The peak EA concentration, 31.9 ng/mL (0.106 µM), was observed in the one-hour sample, and EA was undetectable by the fourth hour. The ellagitannins were not detected at any time point.52

In another small pharmacokinetic study, 11 human volunteers consumed 45 g of freeze-dried black raspberries (Rubus spp., Rosaceae) each day for seven days. Blood and urine samples were collected and analyzed for four anthocyanins and free EA.53 The research team found that less than 1% of the compounds of interest were absorbed and eliminated in urine. Maximum levels of the anthocyanins and EA occurred between one and two hours after dosing, while the highest levels in urine were found up to four hours after consumption. No adverse effects were noted.

In a different study, 11 volunteers fasted overnight before consuming two capsules, each containing 400 mg of pomegranate extract. The combined dose contained 21.6 mg of EA and 330.8 mg of ellagitannins. Blood was drawn at 30 minutes, one, two, four, six, eight, and 24 hours after dosing, and subsequently analyzed by HPLC-MS. Significant variation in blood levels was observed among the 11 subjects, but the average peak EA concentration, 33.8 ng/mL, was recorded at the one-hour time point.54 These results compare remarkably well with the one-person study reviewed above,52 even though the pomegranate products used were in different dosage forms (juice vs. capsule) and were produced by different manufacturers.

An additional study involved 16 adults who consumed, sequentially, eight ounces of pomegranate juice from a first-press squeezing of whole fruit, a teaspoon of a concentrated liquid extract of the fruit material left after first press squeezing in eight ounces of water, and a capsule containing 1,000 mg of a dried powder obtained by a solid phase extraction of the concentrated liquid extract described above. Consumption of each of these doses was separated by a one-week washout phase. Blood samples were drawn prior to dosing and at 30 minutes, one, two, three, four, six, and 24 hours after dosing. The three test materials had similar gallic acid equivalent values, but no analyses for punicalagins or EA were provided in the paper. The times to maximum concentration (Tmax) of EA for the juice and extract dissolved in water were similar to previously reported times, roughly one hour. The Tmax for the encapsulated dry powder was considerably longer, about 2.6 hours, but this may have been related to dissolution time of the gelatin capsule. All three dosage forms gave similar areas under the curve (i.e., integration of the plot of EA concentration vs. time after dosing).55

EA Safety

A search of the scientific and toxicological literature revealed no reports of adverse effects or significant toxicity associated with EA. The poor bioavailability of EA likely makes establishing a lowest-observed adverse effect level (LOAEL) for EA difficult.

In an effort to determine an LD50 level (a measure of acute toxicity that is based on the lethal dose that produces mortality in 50% of test animals) in mice, the animals were given a single dose of 25-1,500 mg/kg of EA orally or 25-1,000 mg/kg intraperitoneally and observed for 14 days. No animals died within 24 hours, meaning that an LD50 was not reached. No animals died after 14 days, nor were any irreversible signs or symptoms observed in the test animals.56

In a subchronic toxicity study, rats were given an EA oral dose of 10, 30, or 100 mg/kg. Thirty days after dosing, hematological and biochemical tests were conducted on blood samples and histopathological profiles were observed for vital organs. The only deviation from normal observed was reduced uric acid levels at the 30 and 100 mg/kg doses. Thus, this study found that free EA exhibited quite low toxicity.56

In another, longer subchronic toxicity study, rats were fed a powder basal diet for 90 days that included EA at dose levels of 0, 1.25, 2.5, and 5​% (0, 9.4, 19.1, 39.1 g​/kg body weight, respectively, in males, and 0, 10.1, 20.1, 42.3 g​/kg body weight, respectively, in females).57 No mortality, histopathological changes, or treatment-related clinical signs were observed, except for decreased weight gain in female rats fed the three actual doses of EA. From these results, the authors calculated an estimated no-observed adverse effect level (NOAEL) dose for EA in females of 3,254 mg/kg/day and estimated no-observed effect level (NOEL) values in males (3,011 mg/kg/day) and females (778 mg/kg/day).

This relatively small but consistent pool of data, along with the widespread presence of EA in the human diet and the low bioavailability of EA, suggest that high levels of EA in a supplement may not be a safety issue, but rather a possible regulatory, efficacy, and/or ethical matter.

Conclusion

The evidence reviewed above indicates that some pomegranate juice products are adulterated by blending with other fruit juices and/or colorants. Furthermore, some pomegranate juice concentrates and extracts (and resulting products) are likely adulterated by the addition of non-pomegranate EA sources. In either case, the consumer may not receive the expected benefits of consuming pure, high-quality pomegranate juice or extracts.

Suppliers, buyers, and manufacturers of finished products need to be aware of this issue and should take steps to ensure that their materials are not adulterated. This report indicates that a single analytical method will most likely not be able to determine all of the possible adulterants (and approaches to adulteration) of pomegranate juice, juice concentrate, and extract, but there is an array of available methods that can be applied for quality control purposes. Ongoing research in various laboratories will likely provide additional tools and methods in the near future.

*Natural products may be referred to as functional foods, dietary supplements (in the United States), natural health products (in Canada), therapeutic goods (in Australia), or food supplements (in Europe), depending on where they are sold.

**According to the US Department of Agriculture, an accession is “a genetically unique plant sample from a particular geographic location.”31

References

  1. Packer R. Pomegranate juice adulteration. Food Safety Magazine. February 2013.
  2. Johanningsmeier SD, Harris GK. Pomegranate as a functional food and nutraceutical source. Annu Rev Food Sci Technol. 2011;2:181-201.
  3. Tomás-Barberán FA, García-Conesa MT, Larrosa M, et al. Bioavailability, metabolism, and bioactivity of food ellagic acid and related polyphenols. In: Recent Advances in Polyphenol Research. Vol 1. Daayf F, Lattanzio V, eds. Hoboken, NJ: Blackwell Publishing Ltd.; 2008:263-267.
  4. Espin JC, Larrosa M, Garcia-Conesa MT, Tomas-Barberan F. Biological significance of urolithins, the gut microbial ellagic acid-derived metabolites: the evidence so far. Evid Based Complement Alternat Med. 2013(2013):270418. doi:10.1155/2013/270418.
  5. Saha P, Yeoh BS, Singh R, et al. Gut microbiota conversion of dietary ellagic acid into bioactive phytoceutical urolithin A inhibits heme peroxidases. PLoS One. 2016;11:e0156811. doi:10.1371/journal.pone.0156811.
  6. Zhang Y, Krueger D, Durst R, et al. International multidimensional authenticity specification (IMAS) algorithm for detection of commercial pomegranate juice adulteration. J Agric Food Chem. 2009; 57:2550-2557.
  7. Bhandari PR. Pomegranate (Punica granatum L). Ancient seeds for modern cure? Review of potential therapeutic applications. Int J Nutr Pharmacol Neurol Dis. 2012;2:171-184.
  8. Ruis AR. Pomegranate and the mediation of balance in early medicine. Gastronomica. 2015;15:22-33.
  9. Miguel MG, Neves MA, Antunus MD. Pomegranate (Punica granatum L.): A medicinal plant with myriad biological properties — A short review. J Med Plants Res. 2010;4:2836-2847.
  10. Jasuja ND, Saxena R, Chandra S, Sharma R. Pharmacological characterization and beneficial uses of Punica granatum. Asian J Plant Sci. 2012;6:251-267.
  11. Katz SR, Newman RA, Lansky EP. Punica granatum: Heuristic treatment for diabetes mellitus. J Med Food. 2007;10:213-217.
  12. Jurenka J. Therapeutic applications of pomegranate (Punica granatum L.): A review. Alt Med Rev. 2008;13:128-144.
  13. Bonzanini F, Bruni R, Palla G, Serlataite N, Caligiani A. Identification and distribution of lignans in Punica granatum L. fruit endocarp, pulp, seeds, wood knots and commercial juices by GC-MS. Food Chem. 2009;117:745-749.
  14. Calani L, Beghe D, Mena P, et al. Ultra-HPLC−MSn (poly)phenolic profiling and chemometric analysis of juices from ancient Punica granatum L. cultivars: A nontargeted approach. J Agric Food Chem. 2013;61:5600-5609.
  15. Mena P, Calani L, Dall’Asta C, et al. Rapid and comprehensive evaluation of (poly)phenolic compounds in pomegranate (Punica granatum L.) juice by uHPLC-MSn. Molecules. 2012;17:14821-14840.
  16. Jiang HZ, Ma QY, Fan HJ, et al. Fatty acid synthase inhibitors isolated from Punica granatum L. J Brazilian Chem Soc. 2012;23:889-893.
  17. Kaufman M, Wiesman Z. Pomegranate oil analysis with emphasis on MALDI-TOF/MS triacylglycerol fingerprinting. J Agric Food Chem. 2007;55:10405-10413.
  18. Gardner Z, McGuffin M, eds. American Herbal Products Association’s Botanical Safety Handbook. 2nd ed. Boca Raton, FL: CRC Press; 2013:155-159.
  19. Gil MI, Tomás-Barberán FA, Hess-Pierce B, Holcroft DM, Kader AA. Antioxidant activity of pomegranate juice and its relationship with phenolic composition and processing. J Agric Food Chem. 2000;48:4581-4589.
  20. Nuncio-Jáuregui N, Calín-Sánchez A, Vázquez-Araújo L, Pérez-López AJ, Frutos-Fernández MJ, Carbonell-Barrachin AA. Processing pomegranates for juice and impact on bioactive components. In: Processing and Impact on Active Components in Food. Preedy VR, ed. Amsterdam, Netherlands: Elsevier Inc.; 2015:629-636.
  21. US Food and Drug Administration Guide to Inspection of Foods, Section 10, Orange and Other Juices. Available at: www.fda.gov/ora/Inspect_ref/igs/foodspa.html. Accessed September 22, 2016.
  22. Krueger DA. Composition of commercial pomegranate juice. Abstracts, 122nd Annual Meeting of the AOAC, 2008.
  23. Krueger DA. Composition of pomegranate juice. J AOAC Int. 2012;95:163-168.
  24. Association of the Industry of Juices and Nectars from Fruits and Vegetables of the European Economic Community (AIJN). Draft Reference Guideline for Pomegranate Juice, Code of Practice for Evaluation of Fruit and Vegetable Juices. March 18, 2008.
  25. Ehling S, Cole S. Analysis of organic acids in fruit juices by liquid chromatography-mass spectrometry: An enhanced tool for authenticity testing. J Agric Food Chem. 2011;59:2229-2234.
  26. Nuncio-Jauregui N, Calin-Sanchez A, Hernandez F, Carbonell-Barrachina AA. Pomegranate juice adulteration by addition of grape or peach juices. J Sci Food Agr. 2014;94:646-655.
  27. Tezcan F, Uzaşçi S, Uyar G, Oztekin N, Erim FB. Determination of amino acids in pomegranate juices and fingerprint for adulteration with apple juices. Food Chem. 2013;141:187-1191.
  28. Borges G, Mullen W, Crozier A. Comparison of the polyphenolic composition and antioxidant activity of European commercial fruit juices. Food Funct. 2010;1:73-83.
  29. Borges G, Crozier A. HPLC-​PDA-​MS fingerprinting to assess the authenticity of pomegranate beverages. Food Chem. 2012;135:1863-1867.
  30. Krueger Food Laboratories. Composition of pomegranate juice. J AOAC International. 2012;95(1):163-168. Available at: www.kfl.com/pom.html. Accessed June 2, 2016.
  31. Definitions: What is an accession? United States Department of Agriculture – Agricultural Research Service website. Available at: www.ars.usda.gov/plains-area/fort-collins-co/center-for-agricultural-resources-research/plant-germplasm-preservation-research/docs/ncgrp-faq/. Accessed October 10, 2016.
  32. Marieschi M, Torelli A, Beghé D, Bruni R. Authentication of Punica granatum L.: Development of SCAR markers for the detection of 10 fruits potentially used in economically motivated adulteration. Food Chem. 2016;202:438-444.
  33. Zhang Y, Wang D, Lee RP, Henning SM, Heber D. Absence of pomegranate ellagitannins in the majority of commercial pomegranate extracts: implications for standardization and quality control. J Agric Food Chem. 2009;57:7395-400.
  34. Madrigal-Carballo S, Rodriguez G, Krueger CG, Dreher M, Reed JD. Pomegranate (Punica granatum) supplements: Authenticity, antioxidant and polyphenol composition. J Funct Food. 2009;324-329.
  35. Yoshimura M, Watanabe Y, Kasai K, Yamakoshi J, Koga T. Inhibitory effect of an ellagic acid-rich pomegranate extract on tyrosinase activity and ultraviolet-induced pigmentation. Biosci Biotechnol Biochem. 2005;69:2368-2373.
  36. Vekiari SA, Gordon MH, Garcia-Macias P, Labrinea H. Extraction and determination of ellagic acid content in chestnut bark and fruit. Food Chem. 2008;110:1007-1011.
  37. Vattem Dam Shetty K. Ellagic acid production and phenolic antioxidant activity in cranberry pomace (Vaccinium macrocarpon) mediated by Lentinus edodes using a solid-state system. Proc Biochem. 2003;39:367-379.
  38. Shi B, He Q, Yao K, Huang W, Li Q. Production of ellagic acid from degradation of valonea tannins by Aspergillus niger and Candida utilis. J Chem Technol Biotechnol. 2005;80:1154-1159.
  39. Juang W, Ni J, Borthwick AGL. Biosynthesis of valonia tannin hydrolase and hydrolysis of valonia tannin to ellagic acid by Aspergillus SHL 6. Process Biochem. 2005;40:1245-1249.
  40. Robledo A, Aguilera-Carbó A, Rodriguez R, Martinez JL, Garza Y, Aguilar CN. Ellagic acid production by Aspergillus niger in solid state fermentation of pomegranate residues. J Ind Microbiol Biotechnol. 2008;35:507-513.
  41. Sepúlveda L, Ascacio A, Rodríguez-Herrera R, Aguilera-Carbó A, Aguilar CN. Ellagic acid: Biological properties and biotechnological development for production processes. African J Biotechnol. 2011;10:4518-4523.
  42. Tzulker R, Glazer I, Bar-Ilan I, Holland D, Aviram M, Amir R. Antioxidant activity, polyphenol content, and related compounds in different fruit juices and homogenates prepared from 29 different pomegranate accessions. J Agric Food Chem. 2007;55:9559-9570.
  43. Lei F, Xing D-M, Xiang L, et al. Pharmacokinetic study of ellagic acid in rat after oral administration of pomegranate leaf extract. J Chromatogr B. 2003;796:189-194.
  44. Seeram NP, Henning SM, Zhang Y, Suchard M, Li Z, Heber D. Pomegranate juice ellagitannin metabolites are present in human plasma and some persist in urine for up to 48 h. J Nutr. 2006;136:2481-2485.
  45. Ben Nasr C, Ayed N, Metche M. Quantitative determination of the polyphenolic content of pomegranate peel. Z Lebensm Unters Forsch. 1996;203:374-378.
  46. Zhou B, Wu Z, Li X, Zhang J, Hu X. Analysis of ellagic acid in pomegranate rinds by capillary electrophoresis and high-performance liquid chromatography. Phytochem Anal. 2008;19:86-89.
  47. Panichayupakarananta P, Issuriya A, Sirikatitham A, Wang W. Antioxidant assay-guided purification and LC determination of ellagic acid in pomegranate peel. J Chromatogr Sci. 2010;48:456-459.
  48. Fischer UA, Carle R, Kammerer DR. Identification and quantification of phenolic compounds from pomegranate (Punica granatum L.) peel, mesocarp, aril and differently produced juices by HPLC-DAD–ESI/MSn. Food Chem. 2011;127:807-821.
  49. Jimenez Del Rio M, Ramazanov A, Sikorski S, Ramazanov Z, Chkhikvishvili I. A new method of standardization of health-​promoting pomegranate fruit (Punica granatum) extract. Georgian Medical News. 2006;140:70-77.
  50. Calín-Sánchez Á, Figiel A, Hernández F, Melgarejo P, Lech K, Carbonell-Barrachina ÁA. Chemical composition, antioxidant capacity, and sensory quality of pomegranate (Punica granatum L.) arils and rind as affected by drying method. Food Proc Biotechnol. 2013;6:1644-1654.
  51. Gómez-Caravaca M, Verardo V, Toselli M, Segura-Carretero A, Fernández-Gutiérrez A, Caboni MF. Determination of the major phenolic compounds in pomegranate juices by HPLC-DAD-ESI-MS. J Agric Food Chem. 2013;61:5328-5337.
  52. Seeram NP, Lee R, Heber D. Bioavailability of ellagic acid in human plasma after consumption of ellagitannins from pomegranate (Punica granatum L.) juice. Clin Chim Acta. 2004;348:63-68.
  53. Stoner GD, Sardo C, Apseloff G, et al. Pharmacokinetics of anthocyanins and ellagic acid in healthy volunteers fed freeze-​dried black raspberries daily for 7 days. J Clin Pharmacol. 2005;45:1153-1164.
  54. Mertens-Talcott SU, Jilma-Stohlawetz P, Rios J, Hingorani L, Derendorf H. Absorption, metabolism, and antioxidant effects of pomegranate (Punica granatum L.) polyphenols after ingestion of a standardized extract in healthy human volunteers. J Agric Food Chem. 2006;54:8956-8961.
  55. Seeram NP, Zhang Y, McKeever R, et al. Pomegranate juice and extracts provide similar levels of plasma and urinary ellagitannin metabolites in human subjects. J Med Food. 2008;11:390-394.
  56. Beserra AMSS, Souza MdC, Colodel EM, et al. Toxicological evaluation of ellagic acid in rodents. Rev Bras Farm. 2010;91:16-24.
  57. Tasaki M, Umemura T, Maeda M, et al. Safety assessment of ellagic acid, a food additive, in a subchronic toxicity study using F344 rats. Food Chem Toxicol. 2008;46:1119-1