Shop for prune juice online. Prunes also contain several vitamins and minerals that have bone-protective effects, including vitamin K, phosphorus, magnesium and potassium. Prunes are basically plums that have been dried naturally in the sun without undergoing any fermentation process. A prune is a dried plum of any cultivar, mostly the European plum (Prunus domestica). Searching for high fibre content fruit? Your search is over!!! Its prunes, also called as constipation fruit due to its fibre content.