Sodium Metabisulfite in food is used as a preservative and antioxidant. The effective form as a preservative is an undissociated sulfite acid and usually forms at the acidity (pH) level. 3. In the process of processing food, sodium metabisulphite is added to the foodstuff to prevent the enzymatic browning of the fruit before it is processed, and the bitterness of cassava, in addition to maintaining the color to remain attractive.