Nutritional, Phytochemical and Antioxidant Evaluation of Fresh and Dried Zanthoxylum zanthoxyloides Leaves: A Traditional Leafy Vegetable Consumed by Some Igbo Clans in Southeast Nigeria

Zanthoxylum zanthoxyloides foliage is utilized as a traditional leafy vegetable by some human populations in clans south east Nigeria. The foliage is dried as a postharvest measure during its seasonal peak usually between late March and April to produce ‘Ukpo Nka’. The impact of air and oven drying at varied temperatures on nutrient, phytochemical and antioxidant potentials of the leaves were evaluated. Results indicated that drying had varied effects on the parameters analyzed. Fresh vegetables had moisture content of 70.80% while it was 14.10% for the air-dried foliage and a range of 10.50 and 12.40% for the oven dried samples. Oven drying at 50 °C increased vitamins and phytochemicals of Z. zanthoxyloides leaves more than the other drying methods adopted in the study. The impact of drying on nutrients and phytochemicals was in this order: oven drying at 50 °C >air drying > oven drying at 40 °C > oven drying at 60 °C > oven drying at 70 °C. Antioxidant activity was evaluated in the methanol and aqueous extracts of the fresh and the various dried vegetable samples using ferric reducing antioxidant power (FRAP). Peak antioxidant activity was slightly higher in the water extracts than in the methanol extracts. Samples oven dried at 40 and 50 °C had higher antioxidant potentials than the other dried samples. It is therefore concluded that oven drying at 50 °C can be adopted to produce “Upko Nka” that will retain nutrients especially vitamins and phytochemicals with good antioxidant potentials to ensure good health, reduce post-harvest losses and ensure food security.