Impact of cooking methods on the chemical and antioxidant composition of some indigenous vegetables used in different food dishes in Southeast Nigeria

Background: Some wild and domesticated vegetables of Ibo ethnic tribe of Southeast, Nigeria, namely Piper guineense, Ocimum gratissimum, Solanum melongena L., Gongronema latifolium, Gnetum africanum and Vernonia amygdalina, have gained interest in food culinary uses due to its nutritional, antioxidant potentials and health benefits. These vegetables are rich in fiber, minerals and phyto-nutrients and have significant health benefits against degenerative disorders. Due to these facts, cooking methods aimed at better retention of nutrients and antioxidant compounds were exploited. Methods: Carefully selected fresh and shredded indigenous vegetables that are commonly used in different food dishes in Southeast Nigeria were cooked (blanched at 98 °C, 2 min and sautéed at 150 °C, 5 min). They were analyzed on a dry weight basis for minerals, vitamins, phytochemicals and antioxidant activity assayed by DPPH, ABTS and FRAP. Results: Results exhibited wild variations showing that Ocimum gratissimum and Solanum melongena L had higher concentrations of functional minerals Zn, Fe, K and Ca. Vitamins B1 and β-carotene had higher concentrations in Solanum melongena L, Gnetum africanum and Vernonia amygdalina. Ocimum gratissimum revealed higher concentrations of TPC and TFC and maintains strong scavenging activity in ABTS and FRAP, while %DPPH manifested stronger activity in Solanum melongena L. Vernonia amygdalina exhibited higher phytochemicals concentrations, especially the alkaloid content. Conclusion: Sautéed cooking retained more nutrients and had stronger antioxidant activity than the blanched method. Overall, these vegetables possess high concentrations of functional constituents that can make them be used to boost human nutrition and benefit the health of consumers. © 2023, The Author(s).