Hydrothermal induced B → A allomorphic transition in retrograded starches with side chains elongated by amylosucrase to different lengths

Production and characterization of recrystallized linear α-glucans at different temperatures for controllable thermostability and digestibility

Molecular structure of linear α-glucans (LAGs) and crystallization temperature have great effects on the thermostability and digestibility of recrystallized LAGs, but the recrystallization behaviors of LAGs in response to temperature remain unclear. Here LAGs with different lengths were prepared from amylopectin via chain elongation and debranching. Recrystallization of LAGs at 4 °C yielded B-type crystalline structure with relative crystallinity ranged from 23.7% to 46.1%. With a chain length of 40.2, an A-type allomorph was observed for a slow recrystallization at 50 °C. Differential scanning calorimetry suggested that A-type crystal had a higher thermostability than the B-type crystal, and increasing LAGs' chain length improved the dimension of double helices, whose assembly produced starch crystallites that enhanced the thermostability and decreased the in vitro digestibility of recrystallized LAGs. An improved thermostability of recrystallized LAGs preserved their ordered structures and kept the resistance to digestive enzymes, with a RS content up to 75.4%.

Effects of Genotype, Nitrogen, and Sulfur Complex Fertilization on the Nutritional and Technological Characteristics of Buckwheat Flour

The present study investigated the effect of nitrogen fertilization (NF) at the levels of 0, 45, and 90 kg·ha-1 combined with selected sulfur complex fertilization (SCF) levels of 0 and 45 kg·ha-1 on the nutritional and technological characteristics of buckwheat flour from five varieties. The results showed that the genotype was a critical factor affecting the chemical composition and physicochemical properties of buckwheat flour. NF significantly increased protein, total starch, and amylose content as well as mineral composition but decreased particle size, color value, and water hydration properties. However, SCF enhanced the ash content and decreased the protein content but had no significant effect on the pasting temperature. In addition, the combination of NF and SCF significantly reduced granule size, water solubility, viscosity, and rheological properties with increasing fertilization levels. This study can guide the cultivation of buckwheat with the desired physicochemical properties and provide information for buckwheat-based products in the food industry.

Molecular modulating of amylopectin's structure promoted the formation of starch-unsaturated fatty acids complexes with controlled digestibility and improved stability to oxidation

In this study, waxy corn starch (WCS) was modified by amylosucrase and pullulanase, producing linear starch chains with elongated length that favored the complexation with unsaturated fatty acids (uFAs). Compared to native WCS, the amylosucrase-modified WCS with an average chain length of 47.8 was easier to form V-type complexes with oleic acid, while increasing the degree of unsaturation impeded the formation of V-type complexes. The pullulanase treatment hydrolyzed the branching points of amylosucrase-modified WCS and the linear starch chains could forme V-type complexes with oleic acid, linoleic acid, and linolenic acid, with V-type crystallinity decreasing from 38.2 % to 20.1 %. V-type complexes had a lower thermal stability than the B-type starch crystallites, and their peak melting temperature ranged from 67.2 to 79.0 °C. The content of resistant starch in the complexes was in the range of 21.8 %-40.9 % and the formation of V-type complexes decreased the susceptibility of uFAs to oxygen.

Physicochemical Properties of the Rice Flour and Structural Features of the Isolated Starches from Saline-Tolerant Rice Grown at Different Levels of Soil Salinity

Three varieties of saline-tolerant indica rice were grown in soils with salinities of 0.0-0.6% (w/w). The rice grown at salinities of 0.3 and 0.6% had a smaller grain dimension than its counterpart. Salinity stress altered the physiology of plants, leading to changes in the basic chemical compositions for all rice varieties, e.g., increasing the soil salinity improved the content of rice protein (RP). The pasting and rheological properties of the rice flour highly depended on its chemical compositions. An increase of RP inhibited the swelling of starch granules and accordingly decreased the peak viscosity of rice flour, while the aggregation of RP weakened the gel structure of the cooked rice flour. The isolated starches showed polyhedral granules, and they all had an A-type crystalline structure with relative crystallinity varying from 34.16 to 45.40%. Moreover, increasing the soil salinity enhanced the lamellar order and periodic length of the isolated starches.

Impact of crystalline structure on the digestibility of amylopectin-based starch-lipid complexes

In this study, chain-elongated waxy corn starch (mWCS) was complexed with lauric acid (LA) to produce starch-lipid complexes (mWCS@LA) with a mixture of B- and V-type crystalline structures. Results from in vitro digestion showed that mWCS@LA had higher digestibility than mWCS, and the logarithm of slope plots of mWCS@LA revealed a two-stage digestion pattern, with digestion rate of the first stage (k₁ = 0.038 min^-1) being much higher than that of the following stage (k₂ = 0.0116 min^-1). The complexation between the long branch chains of mWCS and LA formed amylopectin-based V-type crystallites that were rapidly hydrolyzed during the first stage. The digesta isolated from the second stage of digestion had a B-type crystallinity of 52.6 %, and starch chains with degree of polymerization of 24-28 mainly contributed to the formation of the B-type crystalline structure. The results from the present study reveal that the B-type crystallites were more resistant to amylolytic hydrolysis than the amylopectin-based V-type crystallites.

Effects of three glutenins extracted in acidic, neutral and alkaline urea solutions on the retrogradation of wheat amylose and amylopectin

Three glutenins (glutenin 1, glutenin 2, and glutenin 2) were extracted in acidic, neutral and alkaline urea solutions respectively. All of the three glutenins are rich in glutamic acid (Glu, >30 %) and proline (Pro, >20 %). Glutenin 1, extracted at pH 5, shows higher contents of hydrophilic amino acids as serine (Ser, 5.25 %), aspartic acid (Asp, 2.99 %), tyrosine (Tyr, 3.11 %), arginine (Arg, 2.09 %) and threonine (Thr, 2.11 %) than the other two glutenins. The retrogradation of three glutenins with amylose/amylopectin indicated that glutenin 1 showed significant inhibition effect on the retrogradation of wheat amylose. The characterizations of amylose retrograded with glutenin 1 by FT-IR, XRD, DSC and solid ¹³C NMR showed that new hydrogen bonds between Glu, Tyr and wheat amylose were formed, which prevented the formation of hydrogen bonds between amylose themselves. Glycosidic bonds between some hydroxyl groups of C6 in wheat amylose and certain hydroxyl groups of Ser and Thr in glutenin with specific chain length were present. The macromolecules with steric hindrance prevented the rearrangement of amylose into regular crystals. The retrogradation of wheat amylose was inhibited in this way. This study provides a key targeting step to control the retrogradation of amylose.