Does viscosity or structure govern the rate at which starch granules are digested?

• Published in: Carbohydrate polymers Vol. 136; pp. 667 - 675
• Main Authors: Hardacre, Allan K., Lentle, Roger G., Yap, Sia-Yen, Monro, John A.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 20.01.2016
• Subjects: Alkalies - chemistry; Amylases - chemistry; Amylases - metabolism; Amylolysis; Digestion; Gelatinisation; Gels - chemistry; Hydrolysis; Rheology; Shear rate; Starch - chemistry; Starch - metabolism; Starch digestion; Viscosity; P; C; Gelatinisation; Rheology; G; Ck; Starch digestion; Amylolysis; Shear rate
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/j.carbpol.2015.08.060

•Shear rates in the small intestine are sufficient to optimise digestion.•Amylolysis is shear dependent at rates below the commonly reported physiological limits.•Shear rates of 1s−1 and greater did not affect the rate of digestion.•At low shear rate (0.1s−1) and for ungelatinised starch, viscosity was dependent on granule volume.•At higher shear rates and for gelatinised starch viscosity decreased non-linearly during digestion. The rates of in vitro digestion of incompletely or fully gelatinised potato and corn starch were measured at 37°C over 20min in a rheometer fitted with cup and vane geometry at shear rates of 0.1, 1 and 10s−1. Shear rate did not influence the rate of starch digestion provided it was close to physiological levels. However, rates of digestion were significantly reduced when shear rates were below the physiological range (0.1s−1) or when gelatinisation was incomplete. At physiological shear rates the relationship between starch digestion and viscosity was sigmoid in form and following a short initial slow phase a rapid decline in viscosity occurred as starch was digested and the structural integrity of the granules was lost. Conversely, when shear rate was reduced below physiological levels or gelatinisation was incomplete, digestion was hindered, granule integrity was maintained and the relationship between starch and viscosity became linear.