Sometimes a betta will do this to either tell you he does not like
     this kind of food, or if his first bite was not good he/she will
     spit it out to get a better bite out of the food.  If your betta
     does this repeatedly with the food you are feeding him consider
     giving him differant food.  The foods your betta was raised on might
     be differant than what you, now that you have him home, are feeding
     him.  Give him a few days to get used to it.