Physical characterisation of amylopectin gels

Main Characteristics of Processed Grain Starch Products and Physicochemical Features of the Starches from Maize (Zea mays L.) with Different Genotypes

To understand the relationship between the genotype of maize plants and differences in their origin and the ploidy of the genome, which carry gene alleles programming the biosynthesis of various starch modifications, the thermodynamic and morphological features of starches from the grains of these plants have been studied. This study investigated the peculiarities of starch extracted from subspecies of maize (the dry matter mass (DM) fraction, starch content in grain DM, ash content in grain DM, and amylose content in starch) belonging to different genotypes within the framework of the program for the investigation of polymorphism of the world collection of plant genetic resources VIR. Among the starch genotypes of maize studied, four groups comprised the waxy (wx), conditionally high amylose ("ae"), sugar (su), and wild (WT) genotypes. Starches with an amylose content of over 30% conditionally belonged to the "ae" genotype. The starches of the su genotype had fewer starch granules than other investigated genotypes. An increase in amylose content in the investigated starches, accompanied by a decrease in their thermodynamic melting parameters, induced the accumulation of defective structures in the starches under study. The thermodynamic parameters evaluated for dissociation of the amylose-lipid complex were temperature (T_aml) and enthalpy (H_aml); for the su genotype, temperature and enthalpy values of dissociation of the amylose-lipid complex were higher than in the starches from the "ae" and WT genotypes. This study has shown that the amylose content in starch and the individual features of the maize genotype determine the thermodynamic melting parameters of the starches under study.

Effect of starch concentration and resistant starch filler addition on the physical properties of starch hydrogels

Corn starch-based hydrogels are safe and biodegradable polymers with a wide array of applications in food science. The aim of this study was to investigate the effects of starch and natural filler resistant starch type 2 (RS2) particles concentration on the textural properties of corn starch hydrogels. Native starch (NS) hydrogels of 8%, 10%, 12%, and 15% w/v were prepared; in each of these dispersions, part of the NS was substituted with RS2 to a concentration of 2% or 10%. NS hydrogels with the highest concentrations had the maximum hardness, cohesiveness, and gumminess values, whereas the addition of RS2 particles did not affect gel textural properties. Native and substituted RS2 hydrogels showed close similarities in their rheological and textural characteristics. Water-holding capacity greatly decreased with increasing starch concentration, suggesting that the hydrogels with the highest NS concentration had the densest network as depicted by SEM micrographs. Subsequently, hardness, gumminess, and consistency coefficient were linearly correlated to starch concentration and storage time. Fluid release was exponentially dependent on starch concentration. The degree of crystallinity by X-ray diffraction (XRD) indicated that by increasing starch concentration and substitution level, crystallinity increased. Consequently, NS concentration determined the textural properties of corn starch hydrogels. On the other hand, RS2 substitutions did not affect any of these parameters, indicating their potential role as inactive fillers with a beneficial effect on the maintenance of normal blood glucose levels. Therefore, the consistency of a food gel can be optimized by changing the ratio of inactive filler to starch gel matrix.

Physicochemical studies of nanocrystals of starches from two rice (Oryza sativa L.) types and their characteristics using various modern instrument techniques

BACKGROUND

Starch nanocrystals have received considerable attention, due to their biodegradability, nontoxicity and renewable and abundant sources. The objective of this research is to compare the morphology, physicochemical characteristics and rheological properties of native (NSNC) and waxy rice starch nanocrystals (WSNC).

RESULTS

Both NSNC and WSNC exhibited a platelet-like shape, and they tended to show square-like platelet morphology with increasing initial amylopectin content. Compared to native starches, three weight loss stages of NSNC and WSNC in thermogravimetric analysis curves were observed, while the thermal depolymerization of NSNC started earlier than that of WSNC. The relative crystallinity of NSNC and WSNC was 38.6% and 48.3%, respectively, which were markedly higher than that of native starches. Fourier transform infrared spectra revealed that NSNC presented the highest ratio of 1045/1014 cm^-1 bands among the tested samples, which was probably due to the re-association of retrograded amylose to double-helices structure in NSNC. Moreover, the introduction of sulfur atoms on the surface of NSNC and WSNC was confirmed from the results of X-ray photoelectron spectroscopy. At 5% (w/v) and 10% (w/v) concentration levels, all SNC suspensions exhibited a shear-thinning behavior as the shear rate increased from 0.1 to 100 s^-1 .

CONCLUSIONS

Starch nanocrystals obtained from native and waxy rice starch can be potentially used as reinforcement in biodegradable nanocomposites for packaging, fat replacers, thickening agents and emulsion stabilizers. © 2020 Society of Chemical Industry.

Effects of limited moisture content and storing temperature on retrogradation of rice starch

The objective of this study is to investigate the effects of limited moisture content and storing temperature on the retrogradation of rice starch. Starch was gelatinized in various moisture contents (30-42%) and rice paste was stored at different temperatures (4 °C, 15 °C, 30 °C, -18/30 °C and 4/30 °C). X-ray diffraction (XRD) analysis revealed that after retrogradation, the crystalline type of rice starch changed from A-type to B + V type. The B-type crystallinity of retrograded rice starch under 30 °C was the highest among the five temperature conditions, and an increase in B-type crystallinity with increasing moisture content was observed. Differential scanning calorimetry (DSC) results revealed that rice starch retrogradation consists of recrystallization of amylopectin and amylose, and is mainly attributed to amylopectin. The higher moisture content was favorable for amylopectin recrystallization, whereas the moisture content had little effect on the amylose recrystallization. The optimal temperature for amylopectin and amylose recrystallization was 4 °C and 15 °C, respectively. The amylopectin recrystallization enthalpy of rice starch stored at 4/30 °C was mediated between 4 °C and 30 °C but always higher than that at -18/30 °C. On the whole, after being heated at 42% moisture content and stored at 4 °C, rice starch showed the maximum total retrogradation enthalpy (8.44 J/g).

Combination of Poly(lactic) Acid and Starch for Biodegradable Food Packaging

The massive use of synthetic plastics, in particular in the food packaging area, has a great environmental impact, and alternative more ecologic materials are being required. Poly(lactic) acid (PLA) and starch have been extensively studied as potential replacements for non-degradable petrochemical polymers on the basis of their availability, adequate food contact properties and competitive cost. Nevertheless, both polymers exhibit some drawbacks for packaging uses and need to be adapted to the food packaging requirements. Starch, in particular, is very water sensitive and its film properties are heavily dependent on the moisture content, exhibiting relatively low mechanical resistance. PLA films are very brittle and offer low resistance to oxygen permeation. Their combination as blend or multilayer films could provide properties that are more adequate for packaging purposes on the basis of their complementary characteristics. The main characteristics of PLA and starch in terms of not only the barrier and mechanical properties of their films but also of their combinations, by using blending or multilayer strategies, have been analyzed, identifying components or processes that favor the polymer compatibility and the good performance of the combined materials. The properties of some blends/combinations have been discussed in comparison with those of pure polymer films.

Formation of crystalline complexes between amylomaize dextrin and ceramide

Complexes between amylomaize dextrin (average DP 311) and ceramide were prepared by using two different blending systems: an aqueous batch system containing ethanol and a two-phase system of isopropyl ether and water. The organic solvents and complex formation temperature (50-90°C) were important in determining the level of complex formation and its crystalline structure. Under X-ray diffraction analysis, the solvents as well as ceramide could form complexes with dextrin as weak V6I type crystals. However, the crystallinity of complexes was much higher in the presence of ceramide, which would enhance complex formation by forming ternary co-inclusion complexes of dextrin-solvent-ceramide. Compared to the two-phase system, the batch system yielded much higher crystallinity of complexes. With a minor use of ethanol (0.5 mL) in the batch system, aqueous blending of dextrin and ceramide at 50°C for 2 days followed by a storage at 25°C for 1 day produced well-defined V6I crystal particles as precipitates. The isolated particles had rectangular shapes with a size of 1 μm or less, and contained about half of the ceramide initially added. The ceramide-dextrin complex exhibited enhanced water dispersibility, up to 45% based on the ceramide content in complex.

Improving the performance of starch-based wood adhesive by using sodium dodecyl sulfate

Sodium dodecyl sulfate (SDS) was used to improve the performance of starch-based wood adhesive. The effects of SDS on shear strength, viscosity and storage stability were investigated. It was shown that, although the addition of 1.5-2% (dry starch basis) SDS resulted in a slight decrease in shear strength, the mobility and storage stability of adhesive were significantly enhanced. Possible mechanisms regarding specific action of SDS were discussed. It was proved, using blue value or differential scanning calorimetry (DSC) analysis, that the amylose-SDS complexes were formed in the adhesive. The complex formation or simple adsorption of SDS with starch molecules might hinder the aggregation of latex particles, as shown by scanning electron microscopy images, and inhibit starch retrogradation, as observed by DSC analysis. As a result, in the presence of SDS, the adhesive had higher mobility and storage stability, indicating that SDS could be used to prepare starch-based wood adhesives with high performance.

In situ crosslinkable hydrogel formed from a polysaccharide-based hydrogelator

In situ crosslinkable hydrogel formed from an amphiphilic amylopectin-based hydrogelator in aqueous solution was investigated with respect to its viscoelasticity, structure as well as protein encapsulation and release. Different from the physical hydrogel formed from an aqueous amylopectin system of sufficiently high concentration, such a hydrogel could be formed rapidly at room temperature and exhibit enhanced viscoelastic properties, mechanical strength, and shear thinning behavior. In addition, it has a more complex network structure with a higher fractal dimension due to intermolecular hydrophobic interactions and macromolecular chain entanglements. By circular dichroism analyses and in vitro release experiments, this hydrogel material was found to have a great potential as new matrix for the entrapment and sustained release of bovine serum albumin.