Structural features of α-glucans in the very early developαmental stage of rice endosperm

Young cereal grains as a new source of healthy and hypoallergenic foods: a review

Young cereals contain higher quantities of nutrients such as sterols, γ-oryzanols, tocols and phenolic compounds than mature grains. They are more easily digested with low allergenic potential. Applications of young cereals include plant-based milk substitutes, substitution of wheat flour, malting, fructose and pigments production. Research on young cereals is scarce and mainly focused on botanical studies. This review focused on major young cereals (wheat, rice and corn) compositions, bioactive compounds and applications that will benefit future research in plant-based food and functional ingredients. During grain maturity, amylose content increased, whereas amylopectin content and its structure varied depending largely on grain type. In rice, non-significant differences in average chain length of amylopectin during grain maturity were reported, with protein contents of young rice and wheat higher than at their mature stages. High digestibility of the flowery-to-milky stage rice protein indicated lower allergen levels. Immune-reactive gluten was not found in young wheat. Young wheat contained high essential amino acids with a more balanced profile, particularly for lysine. The angiotensin-converting enzyme inhibitory effect of milky stage protein hydrolysate was higher than mature protein. Young grains contained less starch with more fiber and sugar. Antioxidant activity in young rice was high as it contained gamma-oryzanol, ascorbate, glutathione tocopherols and phenolic compounds. This review of the available information concerning the composition, properties and functional ingredients of immature cereals will assist future research in plant-based food and functional ingredients.

Effects of BEIIb-Deficiency on the Cluster Structure of Amylopectin and the Internal Structure of Starch Granules in Endosperm and Culm of Japonica-Type Rice

It is known that one of starch branching enzyme (BE) isoforms, BEIIb, plays a specific role not only in the synthesis of distinct amylopectin cluster structure, but also in the formation of the internal structure of starch granules in rice endosperm because in its absence the starch crystalline polymorph changes to the B-type from the typical A-type found in the wild-type (WT) cereal endosperm starch granules. In the present study, to examine the contribution of BEIIb to the amylopectin cluster structure, the chain-length distributions of amylopectin and its phosphorylase-limit dextrins (Φ-LD) from endosperm and culm of a null be2b mutant called amylose-extender (ae) mutant line, EM10, were compared with those of its WT cultivar, Kinmaze, of japonica rice. The results strongly suggest that BEIIb specifically formed new short chains whose branch points were localized in the basal part of the crystalline lamellae and presumably in the intermediate between the crystalline and amorphous lamellae of amylopectin clusters in the WT endosperm, whereas in its absence branch points which were mainly formed by BEI were only located in the amorphous lamellae of amylopectin. These differences in the cluster structure of amylopectin between Kinmaze and EM10 endosperm were considered to be responsible for the differences in the A-type and B-type crystalline structures of starch granules between Kinmaze and EM10, respectively. The changes in internal structure of starch granules caused by BEIIb were analyzed by wide angle X-ray diffraction, small-angle X-ray scattering, solid state ¹³C NMR, and optical sum frequency generation spectroscopy. It was noted that the size the amylopectin cluster in ae endosperm (approximately 8.24 nm) was significantly smaller than that in WT endosperm (approximately 8.81 nm). Based on the present results, we proposed a model for the cluster structure of amylopectin in WT and ae mutant of rice endosperm. We also hypothesized the role of BEIIa in amylopectin biosynthesis in culm where BEIIb was not expressed and instead BEIIa was the major BE component in WT of rice.

Analysis of malto-oligosaccharides and related metabolites in rice endosperm during development

Linear glucans with degree of polymerization of up to 23 were detected in rice endosperm at the very early developmental stage of endosperm and considered to play an important role in the de novo synthesis of branched glucans. Little is known concerning the contribution of malto-oligosaccharides (MOS) and longer linear glucans to the starch biosynthesis in cereal endosperm. In the present study, the changes in the amount of major metabolic intermediates including MOS and linear glucans with a degree of polymerization (DP) of ≤ 9 and ≥ 10, respectively, in rice endosperm were measured during the development. Significant amounts of linear glucans of at least DP23 were present in the endosperm at 3 and 5 days after pollination (DAP), whereas most MOS of DP up to 8 were detected in the endosperm throughout the development up to 20 DAP. It was also found that a significant amount of simple sugars such as sucrose, glucose, and fructose, and organic acids such as malic acid, citric acid, and succinic acid were present in the developing endosperm. Although the levels of metabolites are not directly related to the extent of the metabolic flux, the present results suggest that MOS and linear glucans as well as these sugars and organic acids are involved in starch biosynthesis of rice endosperm. It is thought that linear glucans might play a role in starch biosynthesis in rice endosperm, presumably as the precursor for the subsequent synthesis of branched glucans involved in the initiation process that is possibly active in the endosperm at the very early developmental stage.

Effects of BEIIb-Deficiency on the Cluster Structure of Amylopectin and the Internal Structure of Starch Granules in Endosperm and Culm of Japonica-Type Rice

It is known that one of starch branching enzyme (BE) isoforms, BEIIb, plays a specific role not only in the synthesis of distinct amylopectin cluster structure, but also in the formation of the internal structure of starch granules in rice endosperm because in its absence the starch crystalline polymorph changes to the B-type from the typical A-type found in the wild-type (WT) cereal endosperm starch granules. In the present study, to examine the contribution of BEIIb to the amylopectin cluster structure, the chain-length distributions of amylopectin and its phosphorylase-limit dextrins (Φ-LD) from endosperm and culm of a null be2b mutant called amylose-extender (ae) mutant line, EM10, were compared with those of its WT cultivar, Kinmaze, of japonica rice. The results strongly suggest that BEIIb specifically formed new short chains whose branch points were localized in the basal part of the crystalline lamellae and presumably in the intermediate between the crystalline and amorphous lamellae of amylopectin clusters in the WT endosperm, whereas in its absence branch points which were mainly formed by BEI were only located in the amorphous lamellae of amylopectin. These differences in the cluster structure of amylopectin between Kinmaze and EM10 endosperm were considered to be responsible for the differences in the A-type and B-type crystalline structures of starch granules between Kinmaze and EM10, respectively. The changes in internal structure of starch granules caused by BEIIb were analyzed by wide angle X-ray diffraction, small-angle X-ray scattering, solid state ¹³C NMR, and optical sum frequency generation spectroscopy. It was noted that the size the amylopectin cluster in ae endosperm (approximately 8.24 nm) was significantly smaller than that in WT endosperm (approximately 8.81 nm). Based on the present results, we proposed a model for the cluster structure of amylopectin in WT and ae mutant of rice endosperm. We also hypothesized the role of BEIIa in amylopectin biosynthesis in culm where BEIIb was not expressed and instead BEIIa was the major BE component in WT of rice.