Black beans also known as turtle beans because of their hard shell-like appearance, are classified as legumes. Beans are actually the edible seeds of the legume plant. Strong antioxidant properties of black turtle beans are largely attributable to their high concentration of anthocyanin's such as delphinidin, petunidin and Maldivian. Overall anthocyanin content of black beans is estimated to be around 214 milligrams per 100 grams. Lets have a look at how adding these to your diet will benefit you. Black beans are a tremendous source of anthocyanin's. Anthocyanins are healthful flavonoid pigments that give foods like blueberries, blackcurrants, raspberries and red grapes their intense colour and good quality antioxidant properties.