Original article Starch composition, glycemic indices, phenolic constituents, and antioxidative and antidiabetic properties of some common tropical fruits Ganiyu Oboh a , Ayokunle O. Ademosun a , Margareth Akinleye a , Olasunkanmi S. Omojokun a, * , Aline A. Boligon b , Margareth L. Athayde b a Functional Foods and Nutraceuticals Unit, Department of Biochemistry, Federal University of Technology, Akure, Nigeria b Phytochemical Research Laboratory, Department of Industrial Pharmacy, Federal University of Santa Maria, Brazil article info Article history: Received 18 January 2015 Received in revised form 21 January 2015 Accepted 7 February 2015 Available online 20 May 2015 Keywords: African fruits a-amylase a-glucosidase antioxidant glycemic index phenolic constituents abstract Background: Studies have supported the protective effect of high fruit consumption in the management of chronic diseases such as diabetes. Methods: Thirteen fresh tropical fruits were sourced for and the fruits juices were extracted, freeze dried, and then reconstituted for analysis. The sugar, starch, amylose, and amylopectin contents as well as glycemic indices, antioxidant properties, and the ability of the fruits to inhibit starch-hydrolyzing en- zymes were determined. Also, the phenolic constituents of the fruits were characterized using high- performance liquid chromatography coupled with diode array detector. Results: The starch, sugar, amylase, and amylopectin contents were 3.01e3.89 g/100 g, 35.34e60.91 g/ 100 g, 0.84e1.46 g/100 g, and 1.68e2.86 g/100 g, respectively, while the glycemic indices were 28.01 e68.34, with African star apple (28.01) having the lowest and watermelon (68.34) the highest. Furthermore, the fruits exhibited high antioxidant properties as exemplified by their DPPH, ABTSþ,  OH, and NO radical scavenging abilities. Likewise, the fruits also demonstrated a-amylase and a-glucosidase inhibitory property with Soursop (IC 50 ¼ 18.52 mg/mL), guava (IC 50 ¼ 19.77 mg/mL), and African star apple (IC 50 ¼ 20.86 mg/mL) showing the highest inhibitory potential among the 13 fruits. Similarly, the same trend was followed for a-glucosidase inhibitory activity. Conclusion: The fruits' low glycemic indices, strong antioxidant properties, and inhibition of a-amylase and a-glucosidase activities could be possible mechanisms for their use in the management and pre- vention of type-2 diabetes. Copyright © 2015, Korea Food Research Institute, Published by Elsevier. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction Fruits are the edible part of flowering plants commercially available as human food, which is also given as gifts during tradi- tional marriage in Nigeria. Fruits are eaten raw or processed into fruit juices such as orange juice or pineapple juice, or alcoholic beverages such as wine [1,2]. Fruits, however, are enjoyed all year- round, as a large part of Nigeria lies in the tropics, where many fruits are available. Popular fruits consumed in Nigeria include: orange, watermelon, mango, banana, soursop, African star apple, cashew, carrot, breadfruit, pawpaw, and pineapple to mention a few [1] (Figure 1). African star apple (Chrysophyllum albidum) is distributed throughout the southern part of Nigeria, Uganda, Niger Republic, Cameroon, and Ivory Coast [3]. In southwestern Nigeria, the fruit is called agbalumo and popularly referred to as udara in southeastern Nigeria. It is a popular tropical fruit tree found mostly in villages and picked by farmers on their way to farm. Pawpaw is the fruit of the plant Carica papaya native to the tropics. It is eaten as a food or cooking aid and in traditional medicine as it is a sig- nificant source of vitamin C and other polyphenols [4]. Annona muricata L. commonly known as Graviola or soursop is a typical tropical tree with heart shaped edible fruits and widely distributed in most tropical countries [5]. Graviola fruits have been widely consumed in Nigeria in fresh or processed forms for centuries. Cashew (Anacardium occidentale) is a soft fruit widely grown in * Corresponding author. Functional Foods and Nutraceuticals Unit, Department of Biochemistry, Federal University of Technology, Akure, Nigeria P.M.B., 704, Akure 340001, Nigeria. E-mail address: sunjoks@live.com (O.S. Omojokun). Contents lists available at ScienceDirect Journal of Ethnic Foods journal homepage: http://journalofethnicfoods.net http://dx.doi.org/10.1016/j.jef.2015.05.003 2352-6181/Copyright © 2015, Korea Food Research Institute, Published by Elsevier. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/). J Ethn Foods 2 (2015) 64e73