Identification of phenolic compounds in soursop (Annona muricata) pulp by high-performance liquid chromatography with diode array and electrospray ionization mass spectrometric detection

https://doi.org/10.1016/j.foodres.2014.05.051Get rights and content

Highlights

  • Soursop fruit pulp was analyzed with HPLC-DAD/ESI-MS.

  • Sixteen phenolic compounds were separated and tentatively identified.

  • Prevalent compounds were a cinnamic acid derivative and p-coumaric acid.

Abstract

Soursop (Annona muricata L., Annonaceae) is a neotropical fruit species producing large fruits that can be consumed fresh and mainly processed. While the leaves, roots and stems of this species have been the subject of reiterated phytochemical studies, their fruits have received less attention. Phenolic compounds were extracted from the pulp of ripe soursop fruits and separated into two fractions by solid phase extraction. The first was eluted with water and HCl (0.01%), while the second was obtained with ethyl acetate. Their characterization was conducted with high-performance liquid chromatography with diode array and electrospray ionization mass spectrometric detection. The analytical system allowed the separation and tentative identification of 16 phenolic compounds, mainly based on MS fragmentation patterns. Prevalent compounds were a cinnamic acid derivative and p-coumaric acid, together with several other minor compounds that may have health benefits due to antioxidant characteristics. To the best of our knowledge, this is the first study on the phenolic composition of soursop fruit pulp based on a mass spectrometric method.

Introduction

The soursop (Annona muricata L.) is a tropical evergreen tree of the Annonaceae family yielding large fruits of 0.9 to 10 kg weight, with spiny peel and fibrous sour flesh, usually carrying more than one hundred seeds of 1–2 cm length. It most likely originates from Central America, the Antilles or Northern South America, where it is known as “guanabana”. In some other countries it is named “graviola”. In Latin America, soursop is popular in Mexico, Central America, Cuba and several South American countries. Mexico, Venezuela and Brazil are the major producing countries. It is also cultivated in Sri Lanka, China and Polynesia. In the USA, it is grown in southern Florida and Puerto Rico. Soursop fruits are occasionally consumed fresh, but are more commonly used for preparing juices, refreshing drinks, nectars, ice creams, sherbets and desserts. Due to its exotic taste and appealing aroma, resembling a mixture of pineapple and mango, soursop has been considered to be the most delicious fruit of the Annona genus, including its suitability for both industrial processing and commercialization. The processed pulp can be preserved by pasteurization or freezing (Pinto et al., 2005).

Some studies have been conducted on the composition as well as nutritional, medicinal and functional potentials of soursop fruit pulp (Dai et al., 2011, de Souza et al., 2012, Hasrat et al., 1997, Márquez Cardozo, 2009, Onimawo, 2002, Ragasa et al., 2012, Ramírez-Méndez et al., 2012). According to Pinto et al. (2005), the pulp of annonas generally has little nutritional importance, despite being rich in some minerals and vitamins (Gyamfi et al., 2011). In addition, the pulp of this fruit has been proposed as a potential source of dietary fiber (up to 50% w/w dry basis) (Ramírez & Pacheco de Delahaye, 2009).

On the other hand, more studies have focused on the roots, stems and leaves of this species, which have shown antitumor activity (Gomes de Melo et al., 2010, Hamizah et al., 2012, Paul et al., 2013, Torres et al., 2012) among other benefits (Correa Gordillo et al., 2012, Grzybowski et al., 2013, Hamid et al., 2012, Nwokocha et al., 2012, Pinto et al., 2005). The Annonaceous acetogenins from the seeds exerting cytotoxic activity without harming healthy cells have been extensively investigated (Onimawo, 2002, Rieser et al., 1991).

Phenolic compounds, i.e. molecules possessing an aromatic ring bearing one or more hydroxyl groups and with structures ranging from simple molecules to high-molecular mass polymers, are one of the most widely spread groups of phytochemicals. Besides having important physiological functions in the plants, e.g. acting as phytoalexins, antifeedants, and attractants for pollinators, and functioning as sunscreen against UV light, some potential health beneficial properties for humans have been proposed for these compounds (e.g., serving as antioxidants and protecting against chronic diseases such as cancer, brain dysfunction and atherosclerosis). Therefore, much effort has been undertaken aiming at the characterization of phenolic compounds in different plant tissues, especially in under-utilized, less-known and indigenous plant species, usually being of local relevance (Ignat, Volf, & Popa, 2011).

To the best of our knowledge, detailed analysis of the phenolic compounds in the pulp of A. muricata, the edible part of this plant, applying modern analytical methods for their unambiguous identification, has been conducted for the first time. Therefore, considering the variety of interesting phytochemicals with potential health benefits found in other organs of this species, the aim of the present work was to characterize the phenolic composition of the soursop fruit pulp by means of high-performance liquid chromatography with diode array and electrospray ionization mass spectrometric detection.

Section snippets

Materials

Reagents and solvents of analytical and HPLC grade were purchased from VWR (Darmstadt, Germany). C18 reversed-phase cartridges (Chromabond, 1000 mg) were obtained from Macherey-Nagel (Düren, Germany). p-Coumaric acid was obtained from Carl Roth, Karlsruhe, Germany. Commercially-ripe soursop (A. muricata L.) fruits were purchased in local markets in San José, Costa Rica.

Sample preparation

Fruit pulp was manually separated from seeds and peels, subsequently freeze-dried (ALPHA 1-2/LD, Christ, Osterode, Germany), and

Results and discussion

In this study, 16 phenolic compounds extracted in two fractions from soursop freeze-dried fruit pulp samples were at least partially characterized by HPLC with diode array and mass spectrometric detection. Based on existing data, additional peaks could not be identified. Despite the growing interest in this plant, to the best of our knowledge, the polyphenol composition of the fruit pulp has so far not been studied with mass spectrometric methods.

LC–MS analysis of fraction I in the negative

Conclusions

Despite the growing interest into several plant parts of the soursop in terms of their phytochemical composition and their assumed health benefits, the fruit pulp has so far not been comprehensively investigated. Only its proximate nutrient composition and the presence of isoquinoline alkaloids have been subject to some research. The present HPLC–DAD–MS investigation of the polyphenol composition of the edible portion of soursop revealed the prevalence of cinnamic acid derivatives and p

Acknowledgments

P.E. and V.M.J. acknowledge funding from the German Academic Exchange Service (DAAD).

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