The mucous secretion differs from the secretion of serous as former has:
The mucous secretion differs from secretion of serous in two important respects: 

They have little or no enzymatic activity and probably serve mainly for lubrication and protection of the oral tissues
The ratio of carbohydrate to protein is greater and larger amounts of sialic acid acid and occasionally sulfated sugars are present.
Little or no enzymatic activity.
The ratio of carbohydrate to protein is greater.
A larger amount of sialic acid.
All of the above.