1. A method of preparing a concentrated spinach extract in liquid or in dry form, with a polyphenol content of greater than or equal to 50%, comprising the step of purifying an untreated spinach extract in liquid form by a liquid extraction method with a liquid — edible oil, preferably selected from the group comprising olive oil, sunflower oil, grape seed oil, fish oil and mixtures thereof. 2. The method according to claim 1, characterized in that it comprises the following steps: - add edible oil to the untreated extract in liquid form to obtain a liquid untreated extract with the addition of edible oil； - subject said liquid untreated extract with the addition of edible oil to a concentration stage in vacuum and with stirring to obtain a pop-up oil phase containing chlorophyll pigments and carotenoids, and an aqueous phase containing water-soluble compounds, and individually separate the oil and water phase. 3. The method according to claim 2, wherein the oil phase is captured, then subjected to one or more washing steps with water and, if necessary, dried to obtain a coloring powder. The method according to claim 2, wherein the aqueous phase is captured, then subjected to a purification step to obtain a concentrated purified extract. The method according to claim 4, wherein the purification step is performed by passing the concentrated extract through a chromatographic resin, more specifically through an ion exchange resin or adsorption / desorption resin, or by extracting a liquid with a liquid using a water-immiscible solvent, preferably selected from the group consisting of ethyl acetate and butanol .6. C1. Способ приготовления концентрированного экстракта шпината в жидкой или в сухой форме, с содержанием полифенолов выше или равным 50%, включающий стадию очистки необработанного экстракта шпината в жидкой форме способом экстракции жидкости жидкостью - пищевым маслом, предпочтительно выбранным из группы, включающей оливковое масло, подсолнечное масло, масло из
