Scientifically, this tart-tasting fruit is Citrus paradisi
[DOC] [TLE] Grapefruit - Wikipedia [PAR] The grapefruit (Citrus  paradisi) is a subtropical citrus tree known for its sour to 
semi-sweet fruit ... Scientific classification .... of the substances which has a strong 
influence on the taste and odor of grapefruit, compared with other citrus fruits.