ABSTRACT
Microscopic techniques were used to determine accessible regions in various starches under different swelling conditions. Fatty acyl chlorides of increasing chain length (C6–C16) were reacted with 2-aminopyridine to produce the corresponding fatty acyl amides. Starch granules (common corn, waxy maize, potato) were treated with the series of fluorescent amides under a variety of conditions: anhydrous (hot pyridine), aqueous (no heat), and aqueous alkali (49°C, with and without swelling-inhibiting salts). Isolated granules were then viewed by confocal laser scanning microscopy to determine reagent analog penetration. All populations of granules were heterogeneous with respect to fatty acyl amide penetration, but general patterns could be discerned. Observations also indicated that the area surrounding the hilum was more easily penetrated than was the rest of the granule matrix. No substantial differences in penetration of the fluorescent fatty acyl amides as the chain length increased (C6–C16 was observed in hot pyridine-swollen common corn starch granules. Common corn and potato starch granules swollen in room temperature water showed cutoffs for granular exclusion at C14 and C12, respectively. Common corn, waxy maize, and potato starch granules treated under industrial etherification conditions (heat, pH ≈ 11, swelling-inhibiting salts) were less accessible to C6, C8, and C10 fluorescent amides when sodium citrate was present than when sodium sulfate was used, and less accessible in either case than in water alone or in hot anhydrous pyridine. However, appreciable differences between inhibition by sodium sulfate and sodium citrate were not observed in every case.
