Characterization of the physicochemical and thermal properties of unexplored starches with potential industrial uses from six Brazilian maize landraces

Starches isolated from six maize landraces from Brazil were investigated for their physicochemical, morphological, structural and thermal properties and compared to a commercial maize starch (COM). Similarities (chemical composition) and differences (structural characteristics) were observed. The crystallinity of starches ranged between 18.5 and 25.0%. The swelling power at 65°C ranged between 3.00 g/g Pires (PIR) and 4.82 g/g Mato Grosso (MT), whereas at 90°C varied between 18.8 g/g (PIR) and 23.9 g/g (MT), differing from COM, i.e., 14.6 g/g. The starch granule's morphology and size determined by SEM showed polyhedral and spherical shapes and a heterogeneous size distribution between 1.7 and 25 µm. The gelatinization process studied by DSC showed that transition temperatures (T0, Tp, Tc) ranged between 61.0–65.9, 67.5–71.7, and 75.2–76.8°C, respectively, and enthalpies (ΔHgel) between 11.4 and 13.3 (J/g). The retrogradation properties were analyzed after storage for 7, 14, and 40 days at 4°C; the retrogradation degree changed with the time and among the different starches, as well as the transition temperatures and enthalpies, which were lower than those observed for the gelatinization process. Other parameters like gelatinization and retrogradation temperature range (Rgel, Rret) and PHI were analyzed. Rgel was faster for BR and slower for MT, while Rret was broader than the corresponding gelatinization and PHI was not significantly different among the studied starches, except for the BR (slightly higher value).