Phytochemicals and antioxidant activity of different fruit fractions (peel, pulp, aril and seed) of Thai gac (Momordica cochinchinensis Spreng)

Abstract

Three fractions (peel, pulp and aril) of gac fruit (Momordica cochinchinensis Spreng) were investigated for their phytochemicals (lycopene, beta-carotene, lutein and phenolic compounds) and their antioxidant activity. The results showed that the aril had the highest contents for both lycopene and beta-carotene, whilst peel (yellow) contained the highest amount of lutein. Two major phenolic acid groups: hydroxybenzoic acids and hydroxycinnamic were identified and quantified. Gallic acid and p-hydroxybenzoic acid were found in all fractions. Ferulic acid and p-hydroxybenzoic acid were most evident in pulp. Myricetin was the only flavonoid found in all fractions. Apigenin was the most predominant flavonoid in pulp (red), whereas rutin and luteolin gave the highest content in aril. The extracts of different fractions exhibited different levels of antioxidant activity in the systems tested. The aril extract showed the highest FRAP value. The greatest antioxidant activities of peel and pulp extracts were at immature stage, whereas those in the seed extracts increased from mature stage to ripe stage. The contents of total phenolic and total flavonoid in peel and pulp decreased during the fruit development stage (immature > ripe fruit) and subsequently displayed lower antioxidant capacity, except for the seed.

Introduction

Momordica cochinchinensis Spreng is a tropical plant grown in many countries in tropical regions. It may be called by different name such as Gac (in Viet Nam), Fak kao (in Thailand), Bhat kerala (in India), Moc Niet Tu (in China) and Mak kao (in Laos). It is botanically classified in the Cucurbitaceae family and has long been used as a food and traditional medicine in East and Southeast Asia (Iwamoto et al., 1985). As a medicinal plant, in Viet Nam, the seed membranes are used to aid in the relief of dry eyes, as well as to promote healthy vision. Similarly, in traditional Chinese medicine the seeds of gac, known as mubiezi, are employed for a variety of internal and external purposes (Ishida, Turner, Chapman, & Mckeon, 2004). In Viet Nam, gac fruit is very popular because it has been shown to be especially high in lycopene and beta carotene content (Aoki, Kieu, Kuze, Tomisaka, & Chuyen, 2002). Lycopene has been reported to be associated with reduced risk of certain types of cancer, such as prostate cancer, digestive-tract cancers and lung cancer (Goula & Adamopoulos, 2005). Beta-carotene converts to vitamin A in the body (Kim, Giraud, & Driskell, 2007). This is essential for the health and proper development of the cell membranes.

Gac has been consumed in different ways among different cultures. In Viet Nam, gac is used as a colourant for cooking red glutinous rice (Aoki et al., 2002) or xoi gac, served at festive occasions such as new years and weddings (Ishida et al., 2004). In Thailand, the gac fruit (green fruit) is used in cooking, especially immature gac which is commonly consumed as vegetable. The fruit meat has flavours like papaya, is cooked or boiled to consume with chili paste, or used to cook a curry. The reports mentioned above have demonstrated the difference of cultural consumption between societies. Recently, in Thailand the gac fruit entered the commercial production as a functional food e.g. functional drink. However, there has been little information regarding the phytochemicals composition and antioxidant activity of different parts of the gac fruit (mostly reported on fruit) in Thai cultivar. We collected gac fruits from three development stages, namely immature (green), mature (yellow) and ripe (red). Therefore, the purpose of this present study was to investigate the phytochemicals of different parts of the gac fruit and to evaluate the antioxidation activity by using DPPH radical-scavenging activity and ferric reducing/antioxidant power assay.