The answer is carbohydrates, reducing sugar specifically (such as glucose, sucrose etc) are present.
Benedict's solution is for testing for the presence of reducing sugar, and positive would result in color change of solution from blue to orange/red, which small amount would result in color change to green.
Therefore, if the solution changes from blue to orange, it means that the white grape juice contains reducing sugar, which is the simple form of carbohydrates, the biological molecule.
