Physicochemical, pasting, crystallinity, and morphological properties of starches isolated from maize kernels exhibiting different types of defects.

The present study aims to evaluate the physicochemical, rheological, and safety properties of starches isolated from maize kernels with different types of defects. Starch isolation showed to be a valuable alternative to defective yellow maize kernels, since the presence of the evaluated kernel defects (broken, fermented, rotten, moldy, germinated, insect-damaged, and shrunken and immature kernels) did not provide significant changes on starch purity and colour. Only starch isolated from shrunken and immature kernels exhibited reduced extractability. Starch obtained from germinated kernels exhibited the greatest solubility. While flour from moldy kernels showed 7.5 ppb of aflatoxin A1, 25.0 ppb of aflatoxin A2, and 1229.4 ppb of fumonisin B1, any of these mycotoxins were detected in isolated starch. In sum, minor changes in pasting, thermal, crystallinity, and morphological properties of the isolated starches from defective kernels were determined, which does not impair its use in industrial processes.

Effect of lime concentration on gelatinized maize starch dispersions properties.

Maize starch was lime-cooked at 92 °C with 0.0-0.40% w/w Ca(OH)2. Optical micrographs showed that lime disrupted the integrity of insoluble remnants (ghosts) and increased the degree of syneresis of the gelatinized starch dispersions (GSD). The particle size distribution was monomodal, shifting to smaller sizes and narrower distributions with increasing lime concentration. X-ray patterns and FTIR spectra showed that crystallinity decreased to a minimum at lime concentration of 0.20% w/w. Lime-treated GSD exhibited thixotropic and viscoelastic behaviour. In the linear viscoelastic region the storage modulus was higher than the loss modulus, but a crossover between these moduli occurred in the non-linear viscoelastic region. The viscoelastic properties decreased with increased lime concentration. The electrochemical properties suggested that the amylopectin-rich remnants and the released amylose contained in the continuous matrix was firstly attacked by calcium ions at low lime levels (<0.20% w/w), disrupting the starch gel microstructure.