Particle Geometry for Reduced Glycaemic Impact ^†

Against a backdrop of the global epidemic of diabetes, reducing glycaemic impact has become a priority for the food industry. Starch is the major source of glycaemic carbohydrate in the human diet. One approach to reducing the glycaemic impact of human diets is to ingest starch in the form of dense structures that require predominantly superficial enzymolysis to be converted to absorbable digestion products. Then, rate of digestion will depend on surface area, allowing the geometry of simple shapes to be used to configure particles of defined glycaemic impact, using equations relating the proportion (P) of particle digested after T minutes of digestion to initial particle diameter (D₀ mm) and average rate of superficial volume erosion (E mm³/min) over time T:

(a)

Spherical particles:

P = 6TE/(π D_o³)

(b)

Cylindrical particles of initial length L₀:

P = 4TE/(πL₀ D_o²)

(c)

Flat structures of depth D, length L and width W:

P = TE/(LD_oW)

By using spreadsheets based on the equations, erosion rate may be continuously adjusted from its initial value in response to the shape-dependent, non-linear, progressive reduction in surface area during digestion. Then for a given digestibility particle dimensions required to yield time-dependent nutritionally distinct carbohydrate fractions—rapidly digested (RDS), slowly digested (SDS) and inaccessible digestible (IDS) starch, or a simulated glycaemic response curve, may be determined.

The functionality of the spreadsheets was tested by in vitro digestion of spherical (sago), cylindrical (spaghetti) and flat (lasagna) particles, which provided digestion curves that matched spreadsheet predictions.