Accessibility of starch granules to fatty acyl amides

Microscopic techniques were used to determine accessible regions in various starches under different swelling conditions. Fatty acyl chlorides of incr easing chain length (C-6-C-16) were reacted with 2-aminopyridine to produce the corresponding fatty acyl amides. Starch granules (common corn, waxy ma ize, potato) were treated with the series of fluorescent amides under a var iety of conditions: anhydrous (hot pyridine), aqueous (no heat), and aqueou s alkali (49 degreesC, with and without swelling-inhibiting salts). isolate d granules were then viewed by confocal laser scanning microscopy to determ ine reagent analog penetration. All populations of granules were heterogene ous with respect to fatty acyl amide penetration, but general patterns coul d be discerned. Observations also indicated that the area surrounding the h ilum was more easily penetrated than was the rest of the granule matrix. No substantial differences in penetration of the fluorescent fatty acyl amide s as the chain length increased (C,C,,) was observed in hot pyridine-swolle n common corn starch granules. Common corn and potato starch granules swoll en in room temperature water showed cutoffs for granular exclusion at C-14 and C-12, respectively. Common corn, waxy maize, and potato starch granules treated under industrial etherification conditions (heat, pH approximate t o 11, swelling-inhibiting salts) were less accessible to C-6, C-8, and C-10 fluorescent amides when sodium citrate was present than when sodium sulfat e was used, and less accessible in either case than in water alone or in ho t anhydrous pyridine. However, appreciable differences between inhibition b y sodium sulfate and sodium citrate were not observed in every case.