The whiteness on jaggery cubes is a natural occurrence and is typically a result of sugar crystallization. When jaggery is exposed to air or stored for some time, the natural sugars in the jaggery can crystallize on the surface, forming a light, white film. This is completely harmless and does not affect the quality, taste, or nutritional value of the jaggery. If the taste and smell of cubes are perfectly fine, you can enjoy them as you normally would without any second thoughts.