Mix cornflour in a half a cup of water and keep aside. Cut chicken breasts into small pieces and cook in four cups of boiling chicken stock or water for five minutes. Add sweet corn and continue to boil. Add salt and white pepper powder. Boil for two minutes. Reduce heat and add the cornflour mixture. Stir continuously and bring the mixture to a boil again. Add the egg whites, gently stir and serve hot.