Dear student,
The white powder is Baking powder .the ingredients are sodium bi carbonate and citric acid
On heating the sodium bi carbonate the following changes taken place :
NaHCO3 Na2CO3 + H2O + CO2
Evolution of carbon di oxide gas makes small pore in the food items in which air is filled and make them fluffy
the effect of the formation of washing soda while heating of baking soda the citric acid is added as it combines with the sodium carbonate and forms salt , water and more carbon dioxide
Regards