Effect of Drying Processes on the Fine Structure of A-, B-, and C-Type Starches

Starches isolated from wheat (A-type), potato (B-type), and pea (C-type) are used to investigate the effects of oven drying and freeze drying on fine structure of starches. Freeze drying resulted in more pores and scratches on the surfaces of starch granules. Freeze drying produces lower gelatinization temperatures and enthalpy than oven drying, indicating that freeze dried starch contained less crystallites. Freeze drying lowered relative crystallinity and degraded both short- and long-range molecular order. The order structure of B-type starch is significantly disrupted by freeze drying; B-type starch is transformed into A-type and the crystallinity declined markedly. The characteristic peak at 5.6 degrees (2) of C-type starch also disappeared by freeze drying. Moisture shift changes occurred during both drying processes. Freeze drying removed more bound water, which may have caused disruption to the fine structure of the starches. By contrast, oven drying did not significantly affect the morphology and fine structure of the starches.