The Role Played by Acetyl Group Distribution Patterns in Substituted Starch Toward Enzymatic De-acetylation and Chain Fragmentation
Résumé
The nature and distribution of the acetylated groups were evaluated by 13C-NMR and 1H-NMR. The starch substrate with a DS of 1.5 comprises only two patterns: α-(1→4)-d-glucopyranose and 2,3,6-tri-O-acetyl-α-(1→4)-d-glucopyranose. The starch with a DS of 3.0 also comprises two patterns: 2,3,4,6-tetra-O-acetyl-α-(1→4)-d-glucopyranose and 2,3,6-tri-O-acetyl-α-(1→4)-d-glucopyranose; whereas starch (DS = 1.9) contains 4 patterns: 2,3,6-tri-O-acetyl-α-(1→4)-d-glucopyranose, 2,3,4,6-tetra-O-acetyl-α-(1→4)-d-glucopyranose terminal, 2,6-di-O-acetyl-α-(1→4)-d-glucopyranose, and 3,6-di-O-acetyl-α-(1→4)-d-glucopyranose. Using esterase from Viscozyme, it has been possible to hydrolyze up to 7% of the DS 3.0 starch. An α-amylase (Fungamyl 800) was then added to these acetylesterases. With a 2.4 FAU/mL fraction of α-amylase and 2.4 U/mL from the Viscozyme's acetylesterase, 28% of the acetylated end groups were hydrolyzed for the starch substrates with DS 3.0. Moreover, a synergic action between α-amylase and acetylesterase was noticed, allowing fragmentation of 32% for DS 1.5, 30% for DS 1.9, and 11% for DS 3.0.
