Nutrition and Food Kiwifruit Overview of Potential Health Benefits Keith Singletary, PhD Kiwifruit belongs to the genus Actinidia (Actinidiaceae) and is derived brought to New Zealand in the early 20th century, where it from a deciduous woody, fruiting vine. It is composed of different was eventually domesticated, renamed, and sold world- species and cultivars that exhibit a variety of characteristics and sen- wide. Currently, commercial growth of the fruit has spread sory attributes. Kiwi plants have been grown for centuries in China, to many countries including the United States, Italy, Chile, where they are known as mihoutau. Kiwi plant seeds were brought 3Y5 to New Zealand in the early 20th century, where it was eventually France, Greece, Brazil, and Japan. 6 domesticated and sold worldwide. Currently, commercial growth of There are dozens of species comprising the genus Actinidia. the fruit has spread to many countries including the United States, Although the designation kiwifruit applies mainly to both Italy, Chile, France, Greece, and Japan. Kiwifruit extracts have been Actinidia deliciosa and Actinidia chinensis, the A deliciosa reportedly used in traditional Chinese medicine for relief of symptoms Hayward cultivar is the most popular variety marketed com- of numerous disorders. In light of growing consumer acceptance of kiwifruits worldwide, there has been an increased attention given to mercially. Whereas A deliciosa fruit has translucent, green identifying health benefits associated with its consumption. Potential flesh with rows of edible, black seeds covered by a brown, benefits include a rich source of antioxidants, improvement of gas- hairy skin, the closely related variant A chinensis (Hort 16A) trointestinal laxation, lowering of blood lipid levels, and alleviation of may have yellow flesh that is surrounded by hairless skin. skin disorders. Some individuals report allergic symptoms to kiwifruit, The ZESPRI GOLD kiwifruit cultivar of A chinensis has bright and a considerable research effort is being focused on characterizing kiwifuit’s allergenicity among various populations of people. Kiwifruit yellow flesh, and other variants have been produced with 3,5 not only is rich in vitamin C but also is a good source of other nutrients reddish flesh. A third unique species Actinidia arguta or such as folate, potassium, and dietary fiber. This fruit’s content of nu- ‘‘hardy kiwifruit’’ can actually be eaten whole, because it is trients and biologically active phytochemicals has stimulated investi- grape-sized (weighing 5Y15g) and is covered by a smooth, gations into its antioxidant and anti-inflammatory actions that might hairless, edible skin. Its flavor has been described as more then help prevent cardiovascular disease, cancer, and other degener- intense, sweet, and aromatic, in part due to its composition ative disorders. Nutr Today. 2012;47(3):133Y147 of multiple volatile compounds.7 Like A arguta, Actinidia kolomikta and Actinidia polygama have been developed as frost-resistant varieties and have been grown as ornamental iwifruit belongs to the genus Actinidia (Actinidiaceae) plants in some northern regions. and is derived from a deciduous, woody fruiting vine. The chemical composition among kiwifruit cultivars is not K It is composed of different species and cultivars that uniform and may influence palatability. Whereas the A exhibit a variety of physical characteristics and sensory deliciosa and A chinensis genotypes have roughly similar attributes. Kiwi plants were originally grown in mountain- sugar content, composed of equal amounts of glucose ous, forested regions of China (as Chinese gooseberry), 1,2 and fructose and relatively less sucrose, in A arguta the where it is also known as mihoutau. Its seeds were ratio of sucrose to glucose and fructose is much higher. Furthermore, A arguta has 4- to 6-fold higher levels of Keith Singletary, PhD, is professor emeritus of nutrition in the Department myoinositol compared with A deliciosa and A chinensis, of Food Science and Human Nutrition at the University of Illinois. From 2001 making it one of the richest dietary sources of this sugar to 2004, he was the director of the Functional Foods for Health Program, an 3 interdisciplinary program between the Chicago and Urbana-Champaign cam- alcohol. Myoinositol is a cyclic polyol found in many puses of the University of Illinois. Dr Singletary received bachelor’s and mas- ter’s degrees in microbiology from Michigan State University and his PhD in foods, particularly in fruits. Inositol is an important nutri- nutritional sciences from the University of Illinois. Dr Singletary’s primary ent for cells within the body. The balance of sugar and research interests are in molecular carcinogenesis and cancer chemopre- vention, specifically identifying and determining the mechanism of action of organic acids in kiwifruits contributes greatly to their phytochemicals in fruits, vegetables, and spices as cancer protective agents. sensory qualities. In this regard, most kiwifruits have citric He also investigated the biological basis behind the role of alcohol intake in enhancing breast carcinogenesis. He has been recognized with the Senior acid as a predominant organic acid, and, in contrast to Faculty Award for Excellence in Research by the College of Agricultural, other common fruits, the acid-tasting quinic acid predom- Consumer, and Environmental Sciences at the University of Illinois and with inates as well. Quinic acid is an important metabolite the Outstanding Graduate Mentor/Advisor award from the Department of 8 Food Science and Human Nutrition. Dr Singletary currently resides in Florida. associated with the shikimate pathway in plants. Some Funding for this article was provided in part by the California Kiwifruit kiwifruit constituents may make important contributions Commission and the International Kiwifruit Organization. to human nutrient requirements.2 Notably Actinidia fruits The author has no conflicts of interest to disclose. are exceptionally high in ascorbic acid (vitamin C), al- Correspondence: Keith Singletary, PhD, University of Illinois, 260 Bevier Hall, 905 S Goodwin Ave, Urbana, IL 61801 ([email protected]). though amounts may vary considerably among cultivars. DOI: 10.1097/NT.0b013e31825744bc Amounts of vitamin C in the 3 main species generally vary R Volume 47, Number 3, May/June 2012 Nutrition Today) 133 Copyright © 2012 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. from 50 to 430 mg/100 g fresh weight,3,9 with levels in A ISSUES OF KIWIFRUIT SAFETY AND ALLERGENICITY chinensis generally being somewhat higher than in A The allergenicity of kiwifruit constituents has been rec- deliciosa, 100 mg and 85 mg/100 g fresh weight, respec- ognized for over 2 decades. Furthermore, there have been tively. Kiwifruits are good sources of folate and potassium an increasing number of reported kiwifruit allergies as and contain large amounts of vitamin E in the seed, al- consumption of this fruit continues to expand world- though the bioavailability of this fat-soluble vitamin may wide.156,157 In general, the prevalence of kiwifruit allergy be potentially diminished because of limited human di- needs to be more fully characterized and may differ gestibility of the seed. This fruit also contains about 2% to geographically, with 1 study suggesting that it may be as 3% dietary fiber. Sensory acceptance of kiwifruit is also common as peanut allergy among French school-aged dependent on the presence of calcium oxalate in all va- children.158 It is purported to be among the top 10 food rieties, although variation in oxalate content among spe- 10Y12 allergy sources based on studies in France, Finland, and cies has been noted. Oxalates can cause oral irritation Sweden.159 A recent report suggests that ethnic differ- when certain kiwifruit-derived products are eaten. Depend- ences among children may explain some of the variability ing on the species and cultivar, kiwifruit also contains dif- in incidence of food allergies within populations as well as ferent pigments including chlorophylls, carotenoids, lutein, variations noted in the age at onset of symptoms.160 2,3,13Y16 and anthocyanins. Free galactose, myosmine, water- It should be mentioned that, compared with other com- soluble vitamins, serotonin, alkaloids, and saponins also mon food allergies, such as those to tree nuts and pea- 2,3,17Y22 have been quantitated in kiwifruit. Moreover, kiwi- nuts, the allergic response to kiwifruit in general appears fruit is known to contain appreciable amounts of proteases, to be considerably less severe. The allergic response in 3 principally the cysteine protease actinidin (Act). It should adults is often a mild localized oral allergy syndrome that be pointed out that various aspects of kiwifruit cultivation, is characterized by oropharyngeal itching and swelling.161 harvesting, storage, and processing may affect the chem- Nonetheless, systemic reactions are not uncommon, es- 3,14,23Y30 ical and nutritional properties of this fruit. pecially in children, and may include anaphylaxis, urticaria, and gastrointestinal (GI) symptoms following kiwifruit in- OVERVIEW OF HEALTH BENEFITS take. Sublingual immunotherapy has been attempted to lessen these symptoms.156,161Y166 Differences in systemic In ancient China, Actinidia plants were used for symptom responses to kiwifruits have been documented and, in relief of numerous disorders, such as digestive problems, part, may depend on the species