Nutritional value and bioactive properties of Opuntia ficus-indica cladodes

Abstract

Medicinal properties and pharmacological activities of plants have been attributed to their bioactive compounds. However, research has shown that bioactive compound concentrations, biological activities and nutritional profile are influenced by cultivar type. The aim of the study was to characterize the cladodes of 42 spineless cultivars of Opuntia ficus-indica at the Agricultural Research Council in terms of their chemical, nutritional and medicinal properties. The antidiabetic potential of selected extracts was investigated in vitro against alpha-glucosidase enzyme. Aqueous methanol extracts were assayed for total phenolic and flavonoid content, and antioxidant activities using 1,1-Diphenyl-2- picrylhydrazyl (DPPH) and β-carotene linoleic acid system assays. Antibacterial activities of different extracts were assessed against two Gram (-) and two Gram (+) bacteria and their minimum inhibitory concentration (MIC) values recorded. Vitamin C, β-carotene and individual phenolic acid contents were analysed using a Shimadzu HPLC (LC-2030C 3D) equipped with a C18 Luna® column. Quantification was achieved by calibration curve plotted using different standards. Mineral elements were quantified using inductively coupled plasma - optical emission spectrometry. There were variations in the yield depending on the cultivars, however, 50% methanol extracts generally had higher yield as compared to petroleum ether extracts. Significant variation in phytochemical composition, pharmacological activities and nutritional value was observed in the different cultivars studied. The total phenolic content of Berg x Mexican was about 5 times higher than that of Robusta and Montery. Similarly, the flavonoid content of Turpin and Berg x Mexican was about six folds higher than that of Corfu, Montery and Amersfoort. Different cultivars showed different percentage antioxidant activities. Many of the cultivars exhibited antioxidant activity comparable to that of butylated hydroxytoluene (BHT), a synthetic antioxidant usually used as a food additive to prevent the damage caused by free radicals during oxidation processes. Alpha glucosidase inhibitory assay revealed a dose dependent activity with IC50 values ranging from 0.06 - 1.85 mg/ml and 27 of the cultivars showing IC50 values lower than that of acarbose. Noteworthy antibacterial activity was observed against Bacillus subtilis and Escherichia coli with MIC values below 1 mg/ml. The poorest activity was observed against Klebsiella pneumoniae. Petroleum ether extracts generally had the best antibacterial activity when compared to 50% methanol extracts. Compounds profiling indicated that catechin and gallic acid were found to be present in significant quantities in all the cultivars investigated, whilst the least occurring compound was quercetin. Vitamin C content ranged from a lowest of 8.95 mg/100 g to a highest of 124.10 mg/100 g. β-carotene content ranged from a lowest of 3.9 mg/100 g and highest of 31.4 mg/100 g. Potassium and calcium were the most abundant elements present in the Opuntia ficus-indica with a highest of 4980.00 mg/100 g for potassium, whilst iron was found to be the least present with a range of 0.20 to 54.67 mg/100 g. In conclusion, the observed findings indicate that the spineless cladodes of Opuntia ficusindica cultivars are important sources of nutrients and bioactive properties and can be considered as functional foods. Although no cultivar could be singled out as the best as each pharmacological, phytochemical and nutritional trait was different in each cultivar, the observed findings indicate the need for careful cultivar selection when using spineless cactus pear cultivars for product development to ensure product integrity.