Effect of amylolysis on the formation, the molecular, crystalline and thermal characteristics and the digestibility of retrograded starches.

This study evaluated the effect of amylases on the formation, and characteristics of retrograded starches using sweet potato (SPS), cassava (CAS) and high amylose maize (HAS) starches. The starches were gelatinized, hydrolyzed with fungal or maltogenic α-amylase, de-branched and retrograded. The modified starches were then analyzed for digestibility, chain size distribution, relative crystallinity and crystallite size, thermal properties and the proportion of double helices. CAS was the most susceptible and HAS the most resistant to the action of both enzymes. Amylolysis was efficient in forming resistant starch type 3 (RS3) and high levels (> 60%) were found for all starches. RS3 content was highly correlated with the proportion of chains with degrees of polymerization between 13 and 30 for all starches, especially for the root starches, while for HAS, the high amylose content and reduction in the size of amylose chains and very long amylopectin chains also deeply contributed for the RS3 formation. These sizes (DP 13-30) are best suited for the formation of a more crystalline, more perfect, and more strongly bonded structure, composed of larger crystallites, and with a higher concentration of double helices. High correlation coefficients were found between RS3, relative crystallinity, crystallites size, and enthalpy change.

Structural, thermal, and morphological characteristics of cassava amylodextrins.

BACKGROUND: Amylodextrins from cassava starch were obtained by acid hydrolysis, and their structural, thermal and morphological characteristics were evaluated and compared to those from potato and corn amylodextrins. RESULTS: Cassava starch was the most susceptible to hydrolysis due to imperfections in its crystalline structure. The crystalline patterns of amylodextrins remained unchanged, and crystallinity and peak temperature increased with hydrolysis time, whereas thermal degradation temperature decreased, independent of treatment time and starch source. Cassava amylodextrins had similar structural and morphological characteristics to those from corn amylodextrins due to their A-type crystalline arrangements. A-amylodextrins were structurally and thermally more stable than potato amylodextrins (B-type). Starch nanocrystals (SNC) were observed by transmission electron microscopy from the third day of hydrolysis in cassava amylodextrins, whereas potato and corn amylodextrins displayed SNC only on the fifth day. A-SNC displayed platelet shapes, whereas B-SNC were rounded. The SNC shape was related to the packing form and geometry of unit cells of allomorphs A and B. CONCLUSION: Microstructures (agglomerated crystalline particles) and nanostructures (double helix organization) were observed for amylodextrins. Cassava starch was shown to be a promising material for SNC production, since it requires less hydrolysis time to obtaining more stable crystals. © 2017 Society of Chemical Industry.