Impact of reagent infiltration time on reaction patterns and pasting properties of modified maize and wheat starches

• A longer reagent infiltration time increased reaction uniformity within granules.
• Amylose (AM) was reacted more than amylopectin (AP) for all infiltration times.
• AM:AP reactivity increased with increasing granular reaction uniformity (wheat starch).
• Pasting viscosity decreased (cross-linking) as the reagent infiltration time increased.
• Granular/molecular reaction locale impacts pasting properties of starch derivatives.

The impact of granular and molecular reaction patterns on modified starch properties was investigated as a function of the length of time allowed for reagent to infiltrate starch granules. A fluorescent reagent [5-(4,6-dichlorotriazinyl)aminofluorescein] was dispersed in aqueous normal maize or wheat starch slurries (35%, w/v) for 0, 5, 10, 30, or 60 min, after which reaction was initiated by increasing the pH to 11.5 and allowing reaction to proceed for 3 h. With increasing lengths of infiltration, the reaction became increasingly homogeneous within the granule interior (matrix) and the AM:AP reactivity ratio increased (wheat starch), as assessed by confocal laser scanning microscopy (CLSM) and size-exclusion chromatography (refractive index and fluorescence detection), respectively. A longer reagent infiltration time also led to a more inhibited (i.e., cross-linked) pasting viscosity, suggesting that both granular and/or molecular reaction patterns were altered by varied reagent infiltration times to ultimately impact modified starch properties.