Physicochemical properties and antioxidant activities of marula fruit (Sclerocarya birrea subsp. Caffra) steamed and boiled before juice extraction

Abstract

Marula fruit is one of the most underutilized fruits in South Africa, and it has been reported to contain a high amount of vitamin C which is regarded as the cheapest antioxidant. The fruit pulp is traditionally extracted and boiled into juice, a process that adversely affects the vitamin C and bioactive phenolic profile of the resulting juice. This study evaluated the effects of boiling and steaming on the physicochemical properties of marula fruit juice. The pH, percentage yield, total titratable acidity (TTA), total soluble solids (TSS), total phenolic content (TPC), radical scavenging capacity, and vitamin C content of the fruit juice were examined. The study also investigated the total carotene, color, and sensory properties of the fruit juice. The results showed that boiling and steaming significantly decreased the Vit C content of the juice (75.67 and 60.05 mg/100 g) compared to control sample (95.11 mg/100 g). The TPC, radical scavenging capacity, and total carotene content of the fruit juice increase because the heating processes softened the matrix of the fruit increasing the extractability of the phenolics and carotene content of the samples. The color of the marula fruit juice was increased by both boiling and steaming, while the sensory properties of the marula fruit juice extracted from steamed marula fruit had the highest scores in all the measured parameters. Steaming of marula fruit before juice extraction improved the nutritional composition, antioxidant activities, and sensory properties of marula fruit juice.