Influence of cooking methods and times on purple eggplant (Solanum melongena L.) bioactive compounds

In several countries of Africa, purple eggplants are added in cooking meals. However, during cooking, high temperature and long time can affect the nutrients and the bioactive compounds. Thus, a study has been conducted to assess the cooking methods and time which better preserve purple eggplant nutrients losses. So, purple eggplant samples were cooked and steamed for 10, 20 and 30 minutes. The analyses were focused on the determination of physicochemical parameters, macro and micronutrients, phytochemical compounds and antioxidant activity. The results showed that protein content, initially 14.11% in fresh eggplants, rosed to 14.73% and 15.60% in eggplants boiled and steamed for 20 mins, respectively. Total carbohydrate content increased from 63.75% in fresh eggplant to 68.17% in eggplant steamed for 20 mins. The fiber content of fresh eggplant (24.75%) rosed to 28.95% and 29.84% in eggplant cooked in water and steamed for 20 mins, respectively. Polyphenol content in fresh eggplant which was about 47.84 mg EAG /100mg increased to 60.57 and 62.85 mg EAG /100 mg in eggplant cooked in water and steamed during 20 mins, respectively. The antioxidant inhibitory concentration of 50% DPPH activity (IC50) was about 0.42 mg/mL for purple eggplants boiled and steamed during 20 mins. These IC50 revealed an antiradical power of 238.09 µmol of reduced DPPH/mg of sample. Morever, purple eggplant steamed during 30 minutes present an antiradical power of 400 µmol of reduced DPPH/mg of sample. Steaming purple eggplant favored nutrient preservation and high antioxidant potentialities.