Total phenolic content and antioxidant capacity of a selection of South African indigenous fruits

Abstract

It has recently been confirmed that people consuming 7+ portions of fruit and vegetables daily have a lower risk of mortality from any cause. With a fifth of the population of South Africa falling below the poverty line, it has been found that rural adults have a very low daily intake of fruit and vegetables; at the same time rural children are consuming a primarily maize-based diet. This low dietary diversity translates into a higher level of infectious diseases in children younger than five years. Interventions at national level included promoting the growing of underexploited traditional indigenous vegetables and fruits in home gardens, in the hope that rural households would help themselves in diversifying their cereal-based diet, while using crops they are accustomed to in their environment. Ten indigenous South African fruits found in the Western Cape were evaluated for their potential to make a positive contribution to the diet of rural communities and were compared with Blueberry and Cranberry, the North American ‘gold standards’. The following determinations were carried out on 12 samples: Total Phenolic Content, Total Flavanols and Total Monomeric Anthocyanins were analysed using the Folin-Ciocalteu, Mazza and pH Differential methods. Total Antioxidant Capacity was assessed using the Trolox Equivalent Antioxidant Capacity (TEAC), DPPH and Molybdenum Reduction assays. The Oxygen Radical Absorbance Capacity (ORACFL) was also determined. Iron Chelating Activity, one of the methods recommended to reflect other antioxidant mechanisms, was also investigated. The fruits possessing the highest concentration of Total Phenolic Content (Mazza) were Christmas berry, Bietou, Wild Olive and Wild Plum, at levels significantly higher than those of the two control berries, Blueberry and Cranberry. The fruits yielding the highest results for the TEAC assay were Wild Plum, Wild Olive, Tortoise berry, Christmas berry and Colpoon. The fruits giving the highest results for the DPPH assay were Wild Plum, Colpoon, Wild Olive, and Christmas berry. The fruits showing the highest results for the Molybdenum Reduction assay were Wild Olive, Wild Plum, Christmas berry, and Tortoise berry. The fruits yielding the highest results for the ORAC Total Antioxidant Capacity assay were Colpoon, Christmas berry, Wild Olive, Crossberry, Wild Plum, Waterberry followed by Blueberry and Cranberry. The results from the Iron Chelating Activity assay revealed a ranking of Christmas berry, Blueberry, followed by Num-num. On combining the results of eight assays, namely TPC (Mazza), TF, TA, TEAC, DPPH, TAC, TPC (FCR), ICA to give an Antioxidant Potency Composite Index, the fruits with the highest iv rankings were (1) Wild Plum, (2) Wild Olive, (3) Colpoon, and (4) Christmas berry. By comparison the northern hemisphere control berries ranked (5) Blueberry and (9) Cranberry. These findings show that by introducing even small servings of indigenous fruits into the diet, an important and inexpensive source of natural antioxidants could be accessed and the mean daily ORAC intake could thereby be boosted significantly by about 4,000 µmol Trolox Equivalents to bring the Total ORAC consumed to within optimum levels (6,000 µmol Trolox Equivalents and above). These bioactive plant compounds have the potential to deliver immense benefits to health to impoverished South African adults, as well as rural children, well beyond basic nutrition.