The decomposed components are different. Sucrose will produce glucose and fructose after decomposition reaction, while raffinose will be converted into dense disaccharide and fructose. Since sucrose has no aldehyde group and belongs to non-reducing sugar, it cannot produce brick-red precipitate, while dense disaccharide belongs to reducing sugar, so it can produce brick-red precipitate. Therefore, the reason why the brick-red precipitate produced after decomposition of sucrose and raffinose is different is that its decomposition components are different, and the reaction between them is decomposition reaction.