Content of minerals, vitamines, and sugars in iceberg lettuce (Lactuca sativa var. capitata L.) grown in the greenhouse dependent on cultivar and development stage

acide ascorbique acido ascorbico ascorbic acid azucares carotenoide carotenoides carotenoids chemical composition composition chimique composition globale contenido de materia seca developmental stages dry matter content etapas de desarrollo gartenbau greenhouses invernaderos lactuca sativa lutein mineralstoffgehalt nitrate nitrates nitratos proximate composition reducing sugars serre sucres sugars variedades varieties