Essais d'optimisation des conditions de cuisson et d'extraction des polyphénols de six légumes et évaluation des activités

Abstract

This study focuses on the optimization of the cooking conditions and the extraction of polyphenols from six vegetables (potato, onion, spinach, aubergine carrot and pepper) and the study of the impact of the cooking method (boiling, steaming and microwaving) on these compounds and their biological activities (antioxidant activity and anticholinesterase activity). To evaluate the quantity of phenolic compounds extracted from raw and cooked vegetables, a experiment design was realized. The factors chosen are (Temperature, time, power) for cooking and (solvent concentration, maceration time, ultrasonication and grinding) for polyphenol extraction . The study was initiated by Plackett-Burmann design to perform the screening of factors and to select the most influential on the Y response (total phenolic) and an optimization by exploiting central composite design. Determination of total polyphenols, flavonoids and LC-MS / MS analysis were performed to monitor the variation of phenolic compounds after cooking. In addition, in this work, we anlyzed antioxidant and anticholinesterase properties of the phenolic compounds of the six raw and cooked vegetables. The results obtained for the six vegetables are different, boiling in water and steam cooking methods have reduced the levels of total polyphenols and flavonoids of the six vegetables. While microwave cooking had different effects on the six vegetables, it had a negative effect on the total polyphenol and flavonoid levels of the potato, spinach, carrot and pepper. However, a positive effect was recorded on the total polyphenols and flavonoids of eggplant. Retention of these compounds has been observed in onions cooked by microwave. The impact of cooking on antioxidant activity varies from one vegetable to another. Cooking caused a decrease in the antioxidant activity of potatoes, onions, carrots, peppers and steamed spinach. A positive effect of cooking was recorded on the antioxidant potential of spinach (cooked in water and by microwave) and eggplant. All three cooking methods showed negative effects on the anticholinesterase activity of potato, spinach and pepper. However, an increase in this activity was recorded for onion, eggplant and carrot. Cooking in water proved to be the worst method for preserving the polyphenols from cooked vegetables and their activities (antioxidant activity and anticholinesterase). The losses of polyphenols are due to their increased solubility in water. However, microwave cooking is suggested as the best method to preserve the polyphenol levels, the antioxidant and anticholinesterase activities of the studied vegetables.