Quantification of Total Phenolics, Flavonoids and Antioxidant Activities of Three Selected Tropical Fruits Grown In Nigeria

Abstract

Antioxidant activity, total phenolic and flavonoid contents of tissues of three tropical fruits (pineapple, soursop and African bush mango) grown in Nigeria were determined. Samples of pineapple peels and pulp, soursop and African bush mango pulp and seeds were freeze-dried and methanolic extracts prepared using ultrasound assisted extraction method. Qualitative phytochemical screening for antioxidants was carried out in addition to quantification of total phenolics and flavonoids using Folin–Ciocalteu and aluminium chloride colorimetric methods, respectively. Antioxidant activity of the fruit tissue extracts was determined using FRAP and DPPH assays. Data obtained were analysed using ANOVA at p<0.05. Qualitative screening showed the presence of phenolics, flavonoids, saponins, tannins, alkaloids, glycosides and carbohydrates in all the samples. Total phenolic content ranged from 61.5±0.12 mg GAE/g dw in African bush mango pulp to 550.7±0.33 mg GAE/g dw in Soursop pulp. Soursop pulp exhibited the highest flavonoids content (224.7±3.48 mg QE/g dw) while African bush mango pulp (43.1±2.91 mg QE/g dw) had the lowest. DPPH assay showed that Soursop pulp had the highest free radical inhibition (84.3%±0.26), while the lowest inhibition (52.1%±1.75) was obtained in African bush mango pulp. FRAP values ranged from 7.19±1.83 μM in African bush mango pulp to 28.59±0.18 μM in pineapple peels. The peels, seeds, and pulps of the selected tropical fruits contain substantial antioxidant activity and several bioactive substances that could serve as functional foods with the potential to be utilised in nutraceutical industries that could thereby have positive influence on the health of consumers.

Keywords: Phytochemical, Pineapple, African bush mango, Soursop, Tropical fruits