Microstructural Changes and In Vitro Digestibility of Maize Starch Treated with Different Calcium Compounds Used in Nixtamalization Processes

Maize starch dispersions (5 g/100 mL water) are treated with Ca(OH)(2)(0.2 g/100 g starch), emulating the traditional nixtamalization process, and with CaCl(2)or Ca(CO)(3)(1.0g/100 g starch) salts, emulating ecological nixtamalization processes. The effect of these calcium compounds upon the in vitro digestibility of maize starch is evaluated in comparison to an untreated starch dispersion used as control. The Ca(OH)(2)treatment significantly increases the rapidly digestible starch (RDS) fraction (from approximate to 33 to 64%) and significantly decreases the slowly digestible starch (SDS) fraction (from approximate to 63 to 30%), while both salt treatments lead to significant decreases in the RDS fraction (from approximate to 33 to 17%) and significant increases in the SDS fraction (from approximate to 63 to 76%), and resistant starch (RS) fraction (from approximate to 2.8 to 6.8%), compared to the untreated control. The mechanisms responsible for causing changes in the digestible starch fractions are not fully elucidated. Optical micrographs and different analytical methods (rheology, attenuated total reflection Fourier transform infrared, X-ray photoelectron spectrometry and nuclear magnetic resonance) are used to explore the molecular organization of untreated and the different calcium-treated samples. It is found that the disruption of insoluble remnants (ghosts) by alkali treatment and the formation of calcium-mediated cross-linking structures play an important role in the in vitro digestibility and microstructural changes of maize starch.