Short communicationPhenolic profiles and antioxidant activity of litchi pulp of different cultivars cultivated in Southern China
Highlights
► Phenolic and flavonoid contents in litchi pulp had significant varietal difference. ► Phenolics and flavonoids existed mainly in free form in litchi pulp. ► Six phenolic compounds were detected in litchi pulp by HPLC. ► Some litchi cultivars (Feizixiao and Nuomici) showed potent antioxidant activity.
Introduction
Many chronic diseases, such as cardiovascular diseases and cancer, are the leading causes of death in many developed and developing countries. Epidemiologic evidence has suggested that diets rich in fruits and vegetables are associated with reduced risk of these diseases. Phytochemicals in fruits and vegetables are known to be associated with many health benefits. One could be that the potent antioxidant properties of phytochemicals may decrease oxidative stress in consumers. Previous research showed that phenolic compounds contribute most to the antioxidant capacity of fruits and vegetables (Eberhardt, Lee, & Liu, 2000).
Litchi (Litchi chinensis Sonn.), which originates in China, is now cultivated widely in warm climates around the world. It becomes one of the world’s most popular fruits due to its delicious flavor and attractive appearance. As good sources of minerals, dietary fibre, and phytochemicals (Mahattanatawee et al., 2006), litchi has been employed in traditional Chinese medicine for its benefits on heart, spleen and liver. However, little is known about the possible bioactive compounds contributing to the health benefits of litchi.
Previous studies on the phenolic content and antioxidant activity of litchi fruit were mainly focused on its by-products, pericarp (Sarni-Manchado, Le Roux, Le Guerneve, Lozano, & Cheynier, 2000) and seeds (Nagendra Prasad et al., 2009). In contrast, the most commonly consumed part, litchi pulp, was rarely mentioned in the literature. Both qualitative and quantitative knowledge of phenolics and their antioxidant activity in the pulp are limited and incomplete. Amitabye et al. investigated the total phenolic content and antioxidant activity of litchi pulp in northern Mauritius (Luximon-Ramma, Bahorun1, & Crozier, 2003). Mahattanatawee et al. (2006) detected glycosides of quercetin and kaempferol in litchi pulp from southern Florida. However, these studies only reported the free phenolics on the basis of the solvent-soluble extraction, while the bound phenolics and their contribution to antioxidant activity were not involved. In fact, it was reported that approximately 24% of total phenolics in fruits were presented in the bound form (Sun, Chu, Wu, & Liu, 2002). As indicated in previous studies (Chandrasekara and Shahidi, 2010, Madhujith and Shahidi, 2009), there will be an underestimation of the phenolic content and antioxidant activity if the bound fraction was not included. Furthermore, many litchi cultivars mature in different time periods. Their phenolic compositions and activities are assumed to differ due to the differences in cultivation environment and varieties. However, only a certain litchi cultivar was analysed in previous research. It will greatly enhance our knowledge in terms of the nutritive values of these diverse cultivars if the differences in phenolic distribution and antioxidant activity among them are available.
Therefore, 13 representative litchi cultivars in southern China were analysed in the present investigation to determine (1) the contents of free and bound phenolics and their antioxidant activities; (2) the compositions and contents of individual phenolics in both free and bound forms; (3) the correlation among phenolic contents and antioxidant activities.
Section snippets
Chemicals and reagents
Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), DPPH (2,2-diphenyl-1-picrylhydrazyl), TPTZ (2,4,6-tripyridyl-s-triazine), gallic acid, chlorogenic acid, (+)-catechin, caffeic acid, (−)-epicatechin, rutin and Folin–Ciocalteu’s phenol reagent were purchased from Sigma Chemical Co. HPLC-grade acetic acid and acetonitrile were obtained from Fisher (Suwanee, GA, USA). All other chemicals used were of analytical grade or above.
Litchi fruit preparation
Different Litchi cultivars at commercial maturation
Total phenolic contents
The free and bound phenolic contents in pulp of 13 litchi varieties and their percentage contributions to the total phenolic contents are presented in Table 1. The free and bound phenolic contents of 13 litchi varieties ranged from 66.17 (Chanchutou) to 226.03 (Feizixiao) mg GAE/100 g, and from 11.18 (Heiye) to 40.54 (Yuhebao) mg GAE/100 g, respectively. The percentage contribution of free fractions to the total was from 63.1% (Yuhebao) to 91.4% (Heiye). Total phenolic contents of 13 litchi
Discussion
It is well-known that genetic and environmental factors play important roles in the composition and content of phenolic compounds. Significant varietal differences in phenolic contents were found in 13 litchi cultivars tested in this study. These varietal discrepancies may be partly attributed to the different genotypes of these litchi cultivars and to different growing conditions. In fact, similar phenomena were reported in other fruits such as guava (Thaipong, Boonprakob, Crosby,
Acknowledgements
This work was supported by Special Prophase Project on The National Basic Research Program of China (973 Project) (2012CB722904), National Nature Science Foundation of China (31171680), National 948 plan (2012-S18), Guangdong international cooperation project (2010B050600005) and Major Science and Technology Special Projects of Guangdong Province (2009A080209002).
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These authors contributed equally to this work.