You may heard or read following claims from one or the other sources like :
These statements would lead a person to believe that certain juicers are really bad, and produce a juice that is no good. To clear all these points let’s discuss the process of juicing in detail. First, we would need to define the nutrients in juice to see if they would be affected by the juicing process.
Of all these nutrients, Phytochemicals (including Antioxidants and some vitamins) are the most sensitive nutrients in juice.
The two main factors that effect juice quality are: Heat and Oxidation.
Heat can affect the juice mainly by causing enzyme deactivation. Enzyme deactivation occurs only when temperatures exceed 118 degrees fahrenheit. In addition to the heat, there is a time component associated with enzyme deactivation. For example you could probably heat juice to 130 degrees for 1 nano-second with no enzyme deactivation. Passing your finger over a flame is a similar example (this is not advised).
Oxidation occurs when you break open cell walls of the produce and expose it to oxygen. Oxidation occurs when you cut open an apple and it turns brown. In general, oxidation does affect the quality of the juice. Many of the nutrients in the juice are not affected by oxidation, but some are. Oxidation is a natural process. Its best to minimize oxidation.
Oxidation occurs with all juicers. Some juicers create less oxidation in the process of juicing. Oxidation increases, the longer the juice is sitting around. So instead of thinking about that my juicer produce more initial oxidation, drink it immediately when it is made. If you cut open an apple, oxidation is created (it turns brown). You never see the brownining occur if you eat the apple as soon as you cut it!