Buffer value of milk is due to

Answer: Option A

Buffer value of milk is due to Protein.
The buffer intensity curve of casein determined by difference indicates that the buffer action of casein is exerted principally between pH 4.50 and pH 5.70 with a maximum at approximately pH 5.20. Casein is one of the chief factors in the buffer action of milk in this range.
Buffer value of milk varies with the pH range and is more definite at the range pH 8.5 to 9.0, with an average value of 0.0067.