Residue from star fruit as valuable source for functional food ingredients and antioxidant nutraceuticals Guanghou Shui, Lai Peng Leong * Food Science & Technology Programme, Department of Chemistry, National University of Singapore, Singapore 117543, Singapore Received 20 September 2004; accepted 23 March 2005 Abstract Our previous study has indicated that star fruit (Averrhoa carambola L.) is a good source of natural antioxidants and that poly- phenolics are its major antioxidants. In this study, the residue of star fruit, which is normally discarded during juice drink process- ing, was found to contain much higher antioxidant activity than the extracted juice using several methods for assessing antioxidant activity. Under optimized extraction conditions, the residue accounted for around 70% of total antioxidant activity (TAA) and total polyphenolic contents, however only contributed 15% of the weight of whole fruit. Freeze-dried residue powder, which accounted for around 5% of total weight, had total polyphenolic content of 33.2 ± 3.6 mg gallic acid equivalent (GAE)/g sample and total anti- oxidant activity of 3490 ± 310 and 3412 ± 290 mg L-ascorbic acid equivalent antioxidant capacity (AEAC) or 5270 ± 468 and 5152 ± 706 mg trolox equivalent antioxidant capacity (TEAC) per 100 g sample obtained by 2,2 0 -azino-bis-(3-ethylbenzthiazo- line-6-sulfonic acid) free radical (ABTS +Å ) and 1,1-diphenyl-2-picryl-hydrazyl (DPPH Å ) scavenging assays, respectively. It was also found to have 510.3 ± 68.1 mol ferric reducing/antioxidant power (FRAP) per gram sample. The residue extract also shows strong antioxidant activity in delaying oxidative rancidity of soya bean oil at 110 °C. Antioxidant activity and polyphenolic profile of res- idue extracts were compared with extracts of standardized pyconogenol. High performance liquid chromatography coupled with mass spectrometry (HPLC/MS) shows that major proanthocyanidins in star fruit were different from their isomers in pyconogenol. The high content of phenolics and strong antioxidant activity of residue extracts indicate that residue powder may impart health benefits when used in functional food products and that residue extracts should also be regarded as potential nutraceutical resources in future. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Star fruit; Antioxidants; Anti-rancidity; Phenolics; Residue; Functional food; Nutraceuticals 1. Introduction Fruits and vegetables are good dietary sources of nat- ural antioxidants for dietary prevention of degenerative diseases. The main contribution to the antioxidant capacity of a fruit or vegetable is likely to come from a variety of phytochemicals other than vitamin C (Leong & Shui, 2002). Fruits and vegetables contain many antioxidants such as phenolics, thiols, carotenoids and tocopherols, which may protect us against chronic diseases. Antioxidants could reduce oxidative damages to biomolecules by modulating reactive free radicals. Therefore, increased consumption of fruits and vegeta- bles has been recommended. An increasingly growing market for nutraceuticals and functional foods has trig- gered the study on natural sources of antioxidants and their potential for nutraceutical and functional foods (Cevallos-Casals & Cisneros-Zevallos, 2003; Lachance, 2002; Lachance, Nakat, & Jeong, 2001). 0308-8146/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2005.03.048 * Corresponding author. Tel.: +65 6874 2917; fax: +65 0065 677 57 895. E-mail address: laipeng@nus.edu.sg (L.P. Leong). www.elsevier.com/locate/foodchem Food Chemistry 97 (2006) 277–284 Food Chemistry