July 8, 2009
By Paul Gross, Ph.D.
In science, the word "super" is accepted for exceptional conditions such as a superconductor or superfluid that can be defined by objective criteria justifying it as superior. Clear definition is missing from the superfruits industry, where, for most consumers, superfruit means a juice product marketed as super by its manufacturer, usually without scientific evidence for anything superlative.
Superfruits are an important category for introducing healthful fruit formats to consumers; yet, there is only a vague definition for what qualifies a fruit with "super" status. During the past five years, almost every novel exotic fruit has been called a superfruit, a total now of about 36 called "super" in industry media. Absence of qualifying criteria defies true nutritional and phytochemical differences among fruits and research progress that may help manufacturers and consumers better differentiate them.
A more grounded way to assess the qualifications of superfruit candidates is using five criteria to screen the whole foods. The criteria are not rigorously quantitative or definitive, but rather are a screen for qualifying superfruits, hopefully stimulating discussion about how to better characterize superfruit products. The proposed scoring system derives from an example in the clinical trials industry in which independent scientific raters scored the quality of clinical trials (Control Clin Trials. 1996 Feb;17(1):1-12).
The criteria lead to accepting only a few fruits actually having exceptional qualitieseight in total, eliminating most others as nutritionally deficient or scientifically undeveloped to warrant calling them true superfruits.
McGraw-Hill, Professional Consumer Group, New York, announced a 240-page book, Superfruits, by Paul Gross, Ph.D., will be published in October 2009. The science-based book will present the top 20 whole food superfruits, their nutrient and phytochemical features, how to shop for and prepare superfruits in a regular diet, and include 75 recipes.
Each of the five criteria is assigned a high score of 5, the total giving a perfect score out of 25, which is not attained by any fruit.
Popularity and sensory appeal of the whole fruit. This is the most important qualifier for calling a fruit super. It should have appealing attributes as a whole food to achieve optimal eating enjoyment and nutrient intake. This criterion includes sensory appeal of appearance, fragrance, taste, color, ease and versatility of uses, availability, reliability of supply and cost-effectiveness. Scores are assigned based on values such as cultivation acreage and volumes produced, and number and diversity of consumer products. Fruits that are not popular for eating as a whole food or use in a variety of formats are automatically eliminated from superfruit status. As another index of appeal, some consumers may apply an approximate ratio of nutrient value/sugar content to estimate caloric burden for fruits of dietary interest.
Nutrient diversity and density. Ideally, a superfruit should contain diverse macro- and micronutrients, with several in particularly rich amounts achieving high percentage of daily value (DV) in one serving, as judged in nutrient assays by an independent third-party contractor or the USDA Nutrient Tables. Nutrient guides allow a comparison of contents per serving, particularly for essential vitamins, minerals and dietary fiber.
Phytochemical diversity and density. This criterion focuses on phytochemicals under active research for potential importance to human health, not simply on antioxidant potential. Most attention in the superfruit market is based on an unproved assumption that antioxidant properties of polyphenols shown in vitro apply in vivo. Instead, scoring looks at the presence of polyphenols, carotenoids and unique phytochemicals, like pomegranate punicalagins.
Basic medical research intensity. In vitro research quickly and inexpensively defines properties relevant to human health. Qualified candidate compounds from fruits may be advanced into animal (in vivo) studies, while mechanism of action, specificity of organ effect, dose-response relationships, receptor identification, pharmacological antagonists and simple disease models are tested in vitro and in vivo. Assessing the number of publications can provide a simple index for breadth, intensity and duration of research inquiry.
Looking at the number of PubMed citations for a research topic, for example, reveals duration and intensity of scientific effort for defining potential health benefits in disease models.
Clinical applications. This shows how advanced science is to proving a superfruit, or specific phytochemical, used regularly in the diet could lead to better human health or disease resistance. It can be assessed by judging where in the research pyramid a product candidate is for accumulating significant scientific agreement needed for FDA approval as a health product.
Emerging from the research pyramid with a successfully validated health claim earns a fruit the full 5 points, but no fruit or fruit extract has yet achieved this level. Grape resveratrol is close, attracting thousands of research studies and numerous clinical trials. Cranberry proanthocyanidins for possible anti-adhesion effects against urinary tract bacteria also are at stage 4.
To summarize, assessing fruits on the five criteria allows the comparison of various candidate superfruits on a continuum of scoring. Approximately, eight fruits achieve relatively high scores across the board, making them Tier 1 Superfruits. Those with less promising research and clinical development would be Tier 2 Superfruits, while fruits with very low scoresoften attributable to needing more independent research and product expansionare Candidate Superfruits. Fruits having poor sensory appeal and popularity, low-nutrient and/or phytochemical content, or insufficient research history are not super, and should be eliminated from the category.
Top of the Tier
Using the five criteria above, there are eight fruits with popularity as mainstream raw fruit or juice products, sound scientific records, exceptional nutrient qualities and potential for clinical progress. These include cranberry (Vaccinium macrocarpon), fig (Ficus carica), goji (Lycium barbarum), mango (Mangifera indica), orange (Citrus sinensis), papaya (Carica papaya), red grape (Vitis vinifera) and strawberry (Fragaria ananassa).
Taking an in-depth look at the scoring for mango and orange provides insight on the value of applying the criteria system. First, mango scored a total of 23 out of 25 possible points. Its popularity/sensory appeal rates a 5, with worldwide distribution and extensive production, as well as consumer popularity and interest in the range of tastes, colors and sensory qualities. Its nutrient and phytochemical content also rate perfect scores, with a broad range of micro- and macronutrients, fiber, carotenoids, polyphenols and the unique xanthone mangiferin. With more than 700 research publications since 1933, mango has been well-studied for potential therapeutic and health applications, and its terpene lupeol appears to exert effects against inflammation, DNA damage and more; therefore, it scores a 4 out of 5. Similarly, mango earns 4 points for clinical applications, as it may be useful in diabetes and to fight malnutrition (J Am Diet Assoc. 2008 Jun;108(6):986-90).
Orange scored 22 points, with perfect scores in popularity/sensory appeal (foods, beverages, flavors and more with global reach) and nutrient content. Its phytochemical content rated a 4 out of 5, with good levels of both carotenoids and polyphenols. The medical research intensity and clinical applications also rated at 4 out of 5, with disease models looking at oranges ability to inhibit inflammation, cancer and cardiovascular disease, and clinical trials examining the effects of mixed citrus fruits on osteoporosis, diabetes and cardiovascular risk factors.
Middling to Not-So-Super
Interestingly, some high-profile superfruits turn out to be less than super when evaluated by objective criteria. Acai (Euterpe oleracea Mart.) scored a 13 out of 25 in this criteria model. Its highest score came in the area of nutrient content (5/5), as it contains protein, prebiotic fiber, minerals, phytosterols, essential fatty acids (EFAs) and lignans. Phytochemical content ranked a 4/5 for its numerous anthocyanins, although it lacks carotenoids. Acai had 3 out of 5 for popularity and sensory appeal, as the powder or 100 percent juice is tart, oily and unpalatable; however, commercially blended or sweetened juices have a popular purple color. Its high fat and fiber content can cause issues in formulation, but acai pulp powder remains a popular smoothie ingredient. It is in the area of research that acai currently falls short, with a score of 1 in basic research intensity (primarily in vitro results, and really only a focus in science since 2004) and 0 in clinical applications, due to its very recent entrance on the global health stage.
Another interesting fruit is amla (Phyllanthus emblica), also known as Indian gooseberry, which scored 11 out of 25 in this exercise. The phytochemical content of polyphenols earned a 4, while nutrient content was only a 2 (high fiber and vitamin C, moderate minerals). Its sensory appeal only came in at 1 out of 5, due to its bitter, astringent taste as a fresh fruit; it is used in the Ayurveda as part of triphala, a combination formula used to address intestinal disorders. There has been some scientific research (2/5) with preliminary evidence for antiviral and antimicrobial properties in vitro, as well as possible effects in rheumatoid arthritis and osteoporosis. Further in vitro work suggests efficacy against inflammation, age-related renal disease, cancer and diabetes. In clinical work (2/5), there has been some evidence for lowering cholesterol levels, but the usage is not developed in Western clinical literature.
Further down on the scoring are mangosteen (Garcinia mangostana) at 9 points and noni (Morinda citrifolia) with a 7 out of 25. Mangosteen scored high on popularity and sensory appeal, but was hampered by the sparse nutrient content, lack of medical research and clinical applications. It does have high levels of certain anthocyanins, xanthones and tannins, but only in the inedible rind; some companies have extracted those compounds to add in to consumer products. With noni, its foul odor and taste resulted in a 0 on sensory appeal, with low scores on nutrient content and phytochemical content (isolated phytochemicals and polysaccharides, vitamin C, fiber). Also, there is a lack of basic and clinical research, with slow progress on exploring its potential health effects.
Using criteria based on sensory appeal, nutrient and phytochemical complexity, and attraction to the global scientific community with significant independent research and development toward understanding potential benefits for human health can help formulators and marketers best target their products in the superfruit arena. The number of Tier 1 Superfruits will likely increase as more research supports the health effects of fruits such as kiwifruit, blueberry, seaberry or sour cherry, for example. However, the industry should consider seriously whether fruits that are not definable as super by reasonably objective criteria warrant carrying the title superfruits.
Paul Gross, Ph.D., received his doctorate in physiology from the University of Glasgow and was trained in neuroscience at the Laboratory of Cerebral Metabolism, National Institute of Mental Health, Bethesda, MD. He was a research scholar for the Heart and Stroke Foundation of Ontario and recipient of the Karger Memorial Award, Switzerland, for publications on brain capillaries. The author wishes to acknowledge Brian Walker, Ph.D., and Ian Crown for their comments and suggestions.
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