Acai, a Potent Antioxidant Superfruit
By Dr. Paul Gross
Berrydoctor.comJust by its deep violet color, you know there is something special about açaí, the tropical palmberry (Euterpe oleraceae Mart.). With pigmentation so dense, its juice stains anything it touches – skin, cowhide, containers, even teeth when frequently taken undiluted.
Used for food, beverages, medicines and dyes by Amazon peasants over centuries, açaí has blazed its way into popularity on the US market over recent years as one of Nature's superfruits with a delicious taste and versatility of beverage and food applications.
Until recently, however, this reputation was based on assumptions that such a legendary and richly pigmented fruit would be nutritious and have exceptional antioxidant properties. Due to the remoteness and obscurity of açaí, and its highly perishable nature, no contract laboratory assays were available and there were few scientific studies in the medical or food science literature.
Even at the end of 2006, there were only 10 medical reports on açaí listed in PubMed, the online database of medical publications by the US National Library of Medicine (http://pubmed.gov).
However, two recent research publications and one contract assay have supplied new information about açaí that allows comparisons with other better-known nutritious, antioxidant fruits -- in this example, goji (“wolfberry”) and blueberry. Below is a summary of these new findings.
Nutrient Content
Upon review of the tables below are several new facts about the nutrient content of açaí. As the assessment of this berry's nutritional composition comes from two sources (4,7) whose açaí samples were not identical, average or approximated data are presented:
1. the caloric value of a single serving (approximately 600 calories per standard 100 g) is exceptional among comparative berry fruit such as goji (“wolfberry”, Lycium barbarum L.) and lowbush blueberry (Vaccinium angustifolium L.), apparently due to its remarkably high fat content
2. the total fat content for açaí berry is highly unusual for fruit, some 40% of dry weight
3. it has a very high fiber content, approximately 35%
4. relative to the National Academy of Sciences (NAS) Dietary Reference Intakes (DRI) and the micronutrient-dense goji berry, açaí has remarkable contents of several essential minerals – calcium, copper, iron, magnesium, phosphorus, potassium and zinc
5. lipid-soluble antioxidant vitamins A and E are rich in concentration, 1000 IU and 45 mg per 100 g, respectively. 67% of the total tocopherols in açaí pulp are alpha-tocopherol (4).
Table 1. Macronutrients
(1) Laboratorio Catarinense SA, Joinville, Brazil, ref. 4
(2) Schauss et al., ref. 7
(3) Gross et al., ref. 3
(4) ref. 1
By comparison with the two other berry species shown - goji and blueberries - the new açaí analyses demonstrate a much higher energy, fat and fiber yield. By comparison to most plant foods, goji berry is also a high-calorie, nutrient-dense fruit, whereas blueberry is relatively lean in caloric value and nutrients.
Analysis of the fat composition by both sources (4,7) revealed the precise origins of açaí's exceptional lipid density. Nearly all of the saturated fatty acid content in açaí is from palmitic acid (IUPAC hexadecanoic acid, approx. 23%), monounsaturated fat is from oleic acid (approx. 58%, an omega-9 fat,18:1 ?-9), and polyunsaturated fats result from linoleic acid (12%, an omega-6 fat, 18:2 ?-6). These three fatty acids, therefore, make up 93% of the total lipids in açaí. The oleic acid content of açaí is the same as in olive oil.
A similar compartmental analysis of fiber sources was not completed in either study. Previously, analysis of high-fiber plant foods like Rubus and goji berries showed that pectins, lignans, cellulose and polysaccharides comprise the high fiber content of these fruits (3). It would be valuable to have such an assay done on açaí pulp as this fruit appears to be truly exceptional as a dietary fiber source.
Both assays included data for several phytosterols, plant-derived lipids with structure similar to mammalian cholesterol. Phytosterols have considerable promise as cholesterol-lowering and anticancer agents in human therapies (5). In each study, beta-sitosterol was the dominant element, comprising some 85% (average) of the total for all sterols (Table 2). These results reveal açaí as an enriched food source of this valuable phytosterol.
In summary, açaí fruit displays unusually high contents of calories, diverse fats, fiber and phytosterols, particularly beta-sitosterol.
The density of several minerals in açaí is a significant percentage of the DRI, especially for copper and zinc which equal or exceed the DRI (Table 2). In one assay (4), vitamin E content was 3-times the DRI (Table 2).
Table 2. Essential Micronutrients
(1) Laboratorio Catarinense SA, Joinville, Brazil, ref. 4
(2) Schauss et al., ref. 7
(3) Gross et al., ref. 3
(4) ref. 1
* not considered a micronutrient; x, no RDI established; ^ demonstrated in fruit, roots and leaves of Lycium barbarum L. or Lycium chinense (3); ? no reportsPhenolic Antioxidants
Attention of food chemists is drawn readily to açaí by its rich color, a subjective indication of high concentration of phenolic pigments with antioxidant properties that may convey health benefits for numerous human disease conditions (8,9).
Both studies (4,8) analyzed açaí pulp for phenolic compounds, finding levels of anthocyanins were1% of sample mass (4) and total phenolics unexpectedly moderate (1.4 g per 100 g, ref. 8). It is likely that phenolics not yet identified are present in açaí, indicating a need for further analysis of pigments in this intriguing berry.
In the study by Schauss and coworkers (8), measurements of oxygen radical absorbance capacity (“ORAC”, antioxidant strength) were performed on freeze-dried açaí pulp and skin powders in vitro for each of four reactive oxygen species (ROS) - superoxide, peroxynitrite, hydroxyl radical and peroxyl radical for both hydrophilic- and lipid-soluble species.
The assay for superoxide, considered perhaps the most representative determination of antioxidant capacity (as it is involved in formation of other ROS and circulates systemically in blood), revealed a value of 161,400 units per 100 g, the highest result yet found for superoxide radical among plant foods (8). Total ORAC (against peroxyl radical) determined from both hydrophilic and lipophilic sources was 102,700 units per 100 g, again the highest value found to date among edible fruits and vegetables for this radical (8). Additional evidence showed that açaí pulp significantly inhibited the formation of all ROS in vitro (8).
Research Directions, Commercial Development and Potential Health Effects
To date, there has been limited research interest in açaí mainly due its novelty in food science, but this is certain to change in coming years. Appealing exotic foods with high antioxidant strength and rich nutrient content will undoubtedly attract scientific attention and find diverse applications in the functional food industry.
A potential problem in developing açaí for broader commercial purposes as a functional food is susceptibility to oxidation due to its exceptional fat content. This will be a significant challenge to prevent spoiling during post-harvest handling, processing and shipping. Freeze-drying of the fresh pulp is one solution that appears to effectively preserve nutrients (7,8).
Dozens of diseases have a component of oxidative stress at their origins, such as chronic inflammation, atherosclerosis, diabetes and cancer (8,9), and so may be prevented or inhibited by high-antioxidant fruit like açaí.
For example, a recent study showed that açaí antioxidants could induce more rapid death (apoptosis) of leukemia cells in vitro (2). This preliminary research indicates a possible anti-cancer effect of anthocyanins and other açaí pigments, similar to promising laboratory results examining phenolics in the black raspberry as a chemopreventive food source (6).
References
1. Blueberry Nutrients, World's Healthiest Foods,
http://whfoods.com/genpage.php?tname=nutrientprofile&dbid=84
2. Del Pozo-Insfran D, Percival SS, Talcott ST. Acai (Euterpe oleracea Mart.) polyphenolics in their glycoside and aglycone forms induce apoptosis of HL-60 leukemia cells. J Agric Food Chem. 2006 Feb 22;54(4):1222-9.
3. Gross PM, Zhang X, Zhang R, Wolfberry: Nature’s Bounty of Nutrition and Health, Booksurge Publishing (Amazon.com), 2006.
4. Laboratorio Catarinense SA, Joinville, Brazil and Markan Global Enterprises, http://thesuperberry.com/constituents.htm
5. Ling WH, Jones PJ. Dietary phytosterols: a review of metabolism, benefits and side effects. Life Sci. 1995;57(3):195-206.
6. Lu H, Li J, Zhang D, Stoner GD, Huang C. Molecular mechanisms involved in chemoprevention of black raspberry extracts: from transcription factors to their target genes. Nutr Cancer. 2006;54(1):69-78.
7. Schauss AG, Wu X, Prior RL, Ou B, Patel D, Huang D, Kababick JP. Phytochemical and nutrient composition of the freeze-dried amazonian palm berry, Euterpe oleraceae mart. (acai).
J Agric Food Chem. 2006 Nov 1;54(22):8598-603.8. Schauss AG, Wu X, Prior RL, Ou B, Huang D, Owens J, Agarwal A, Jensen GS, Hart AN, Shanbrom E. Antioxidant capacity and other bioactivities of the freeze-dried amazonian palm berry, Euterpe oleraceae mart. (acai). J Agric Food Chem. 2006 Nov 1;54(22):8604-10.
9. Valko M, Leibfritz D, Moncol J, Cronin MT, Mazur M, Telser J. Free radicals and antioxidants in normal physiological functions and human disease. Int J Biochem Cell Biol. 2006 Jan;39(1):44-84.
About the Author
Paul M. Gross, PhD, received his doctorate in physiology from the University of Glasgow, Scotland and was a post-doctoral fellow in neuroscience at the Laboratory of CerebralMetabolism, National Institutes of Health, Bethesda, MD. A Research Scholar for the Heart and Stroke Foundations of Ontario and Canada, he published 85 peer-reviewed journal reports and book chapters over his 25 year career in medical science, and was recipient of the Karger Memorial Award, Switzerland, for publications on brain capillaries. Dr. Gross is senior author of a 2006 book on the goji berry entitled Wolfberry: Natures Bounty of Nutrition and Health (Booksurge Publishing, Amazon.com) and publisher of The Berry Doctor's Journal at http://berrydoctor.com where readers can obtain free information on berry science and nutrition.
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