Starch is the main storage carbohydrate in plants and an important natural resource for food, feed and industrial raw materials. However, the details regarding the pathway for starch biosynthesis and the diversity of biosynthetic enzymes involved in this process are poorly understood. This study uses a comprehensive phylogenetic analysis of 74 sequenced plant genomes to revisit the evolutionary history of the genes encoding ADP-glucose pyrophosphorylase (AGPase), starch synthase (SS), starch branching enzyme (SBE) and starch de-branching enzyme (DBE). Additionally, the protein structures and expression patterns of these four core genes in starch biosynthesis were studied to determine their functional differences. The results showed that AGPase, SS, SBE and DBE have undergone complicated evolutionary processes in plants and that gene/genome duplications are responsible for the observed differences in isoform numbers. A structure analysis of these proteins suggested that the deletion/mutation of amino acids in some active sites resulted in not only structural variation but also sub-functionalization or neo-functionalization. Expression profiling indicated that AGPase-, SS-, SBE- and DBE-encoding genes exhibit spatio-temporally divergent expression patterns related to the composition of functional complexes in starch biosynthesis. This study provides a comprehensive atlas of the starch biosynthetic pathway, and these data should support future studies aimed at increasing understanding of starch biosynthesis and the functional evolutionary divergence of AGPase, SS, SBE, and DBE in plants.

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Particle-size distribution, granular structure, and composition significantly affect the physicochemical properties, rheological properties, and nutritional function of starch. Flow cytometry and flow sorting are widely considered convenient and efficient ways of classifying and separating natural biological particles or other substances into subpopulations, respectively, based on the differential response of each component to stimulation by a light beam; the results allow for the correlation analysis of parameters. In this study, different types of starches isolated from waxy maize, sweet maize, high-amylose maize, pop maize, and normal maize were initially classified into various subgroups by flow cytometer and then collected through flow sorting to observe their morphology and particle-size distribution. The results showed that a 0.25% Gelzan solution served as an optimal reagent for keeping individual starch particles homogeneously dispersed in suspension for a relatively long time. The bivariate flow cytometric population distributions indicated that the starches of normal maize, sweet maize, and pop maize were divided into two subgroups, whereas high-amylose maize starch had only one subgroup. Waxy maize starch, conversely, showed three subpopulations. The subgroups sorted by flow cytometer were determined and verified in terms of morphology and granule size by scanning electron microscopy and laser particle distribution analyzer. Results showed that flow cytometry can be regarded as a novel method for classifying and sorting starch granules. © 2017 International Society for Advancement of Cytometry.

To investigate the applicability of high-amylose corn grits (HACG) to the process for extruded products, a single screw extruder was used to produce extrudates under feed rate of 220 g/min, barrel temperature of 120°C, and screw rotational speed of 150 rpm. The nutritional, physical and sensory properties were investigated in the HACG extrudate and normal corn grits (NCG) extrudate acting as control. The results indicated that the HACG extrudate had higher (P≤ 0.05) protein (7.07%), fiber (5.41%), lipid (1.48%), ash (0.76%), resistant starch (2.89%), zein (4.65%), calcium (22.34 mg/kg), magnesium (718.63 mg/kg), iron (19.47 mg/kg), zinc (22.73 mg/kg) contents and 16 of 17 types of amino acids compared to the NCG extrudate. In regards to physical properties, the bulk density (BD), radial expansion index (REI) and water solubility index (WSI) values of the HACG extrudate, which were 57.94 mg/ml, 45.47 and 43.25, respectively, were significantly lower (P≤ 0.05) than those of the NCG extrudate. However, the HACG extrudate had a higher special length (SL), indicating a higher axial expansion, water absorption index (WAI), frangibility and cohesiveness (7.34 cm/g, 3.69, 68.79 and 0.32, respectively), and a more sponge-like structure. A sensory analysis indicated that the HACG extrudate had higher values for frangibility, cohesiveness, chewiness and overall taste with a lower coarseness and adhesiveness (to teeth).