The difference between type A gelatin and type B gelatin

Gelatin is divided into type A gelatin (acid pretreated) and type B gelatin (alkali pretreated) according to the processing. Although they are both extracted from collagen, there are some differences in their properties.

Type A gelatin is extracted from raw material that has undergone acid treatment. The light yellow color of gelatin is due to the Maillard reaction between protein and saccharide. The amino groups are protonated to inhibit the Maillard reaction in acidic solution, resulting in lighter color. The protonated amino groups make the molecules positively charged, so its isoelectric point is between pH 7 and 9. The amino acid of type A gelatin is almost the same as that of the raw material. It has a wide molecular weight distribution: the polypeptide chains are evenly distributed between a dozen KDa and several thousand KDa, with slightly more alpha chains at 100 KDa. It has a higher fat content because fat dissolved by acid cannot be filtered. Type A gelatin is more stable in an acidic environment.

Type B gelatin is extracted from raw material that is pretreated by alkali. The asparagine and glutamine are converted to aspartic acid and glutamic acid. The reduction of amino group and the addition of carboxyl group give its negative charges. Its isoelectric point is between pH 4.7 and 5.2. The amino groups are hydrolyzed partially during alkaline pretreatment, so it contains slightly less nitrogen element than the raw material. The molecular weight distribution is relatively narrow: alpha chains of 100 KDa are the main component with a few larger and smaller molecules. The alkali solution can dissolve some non-collagen protein in raw material, especially albumin and globulin. Fat is removed after saponification by alkali solution, so less fat is left in gelatin B. It is more stable in alkaline environment.