Amylose content in starches: Toward optimal definition and validating experimental methods

How rheological behaviors of concentrated starch affect graft copolymerization of acrylamide and resultant hydrogel

Corn starches with different amylose/amylopectin ratios were used to explore the effect of rheological behaviors of concentrated system on the graft copolymerization of acrylamide and resultant hydrogels, which sheds a light on their reactive extrusion process. The viscoelastic moduli of starch melts increased with increasing amylose content (AC), leading to a decreased extent of micro-mixing detected by a reduced rheokinetic rate. With increasing AC, the graft efficiency was decreased but with almost similar monomer conversion (about 87.5%) and nearly equivalent graft content. XRD and SAXS spectra revealed that the extent of retrogradation of the starches were increased and two-phase separation was enhanced for hydrogels with increasing AC. Interestingly, microscopic analysis showed the superabsorbent hydrogel from the starch with AC of 50% exhibited a gridding membrane porous structure, resulting in a higher water absorbent capacity of 550 g/g. This was attributed to the moderate crosslinking and the slightly greater graft content.

Molecular structure-property relations controlling mashing performance of amylases as a function of barley grain size

In brewing, amylases are key enzymes in hydrolyzing barley starch to sugars, which are utilized in fermentation to produce ethanol. Starch fermentation depends on sugars produced by amylases and starch molecular structure, both of which vary with barley grain size. Grain size is a major industrial specification for selecting barley for brewing. An in-depth study is given of how enzyme activity and starch structure vary with grain size, the impact of these factors on fermentable sugar production, and the underlying mechanisms. Micro-malting and mashing experiments were based on commercial methodologies. Starch molecular structural parameters were obtained using size-exclusion chromatography, and fitted using biosynthesis-based models. Correlation analysis using the resulting parameters showed larger grain sizes contained fewer long amylopectin chains, higher amylase activities and soluble protein level. Medium grain sizes released most sugars during mashing, because of higher starch utilization from the action of amylases, and shorter amylose chains. As starch is the substrate for amylase-driven fermentable sugars production, measuring its structure should be a prime indication for mashing performance, and should be used as an industry specification when selecting barley grains for brewing.

Characterizing Starch Molecular Structure of Rice

A better understanding of the nutritional properties of rice starch is important because of the rapid rise of diet-related health complications, particularly obesity, type 2 diabetes, and colorectal cancers. Rice starch that is slowly digested to glucose, and where significant quantities of starch which reach the lower gut ("resistant starch"), can mitigate, and also delay the onset of, these diseases. These digestibility properties depend to some extent on starch molecular structure. The characterization of this structure is therefore significant for understanding and developing healthier slower digestible rice. In this chapter, a series of techniques used for characterizing starch structure are reviewed and the procedure for preparing rice starch samples with minimum degradation for characterizing starch chain length distribution (CLD) and overall molecular structure is given. Some methods for choosing or developing plants showing desirable structural characteristics are briefly summarized.

Effects of the Starch Molecular Structures in Barley Malts and Rice Adjuncts on Brewing Performance

Background: Achieving optimal fermentation is challenging when the variation within malt starch structure and enzyme activities are not part of the standard malting specifications. This study explores how the variation of starch and starch amylolytic enzymes in both malts and rice adjuncts affect the mashing and the subsequent yeast fermentation in the laboratory-scale production of beer. Results: The addition of rice adjuncts significantly increased the maltose content whilst reducing the glucose content during mashing. The maltotriose content, released during mashing, was significantly negatively correlated with the total amylose content (r = −0.64, p < 0.05), and significantly negatively correlated with the number of amylopectin longer chains (degree of polymerization 37–100) (r = −0.75, p < 0.01). During fermentation, while the content of maltotriose significantly and positively correlated with both the rate and amount of ethanol production (r = 0.70, p < 0.05; r = 0.70, p < 0.05, respectively), the content of soluble nitrogen in the wort was significantly and positively correlated with both the rate and the amount of ethanol production (r = 0.63, p< 0.05; r = 0.62, p < 0.05, respectively). The amount of amylopectin with longer chains was; however, significantly negatively correlated with the ethanol production (r = −0.06, p < 0.05). Small variations among the ethanol concentration and the rate of ethanol production during fermentation were found with the addition of different rice varieties. Conclusions: The effects of the rice adjuncts on the performance of fermentation depends on the properties of the malt, including the protein modification and malt enzyme activities. This study provides data to improve standard malt specifications in order for brewers to acquire more efficient fermentation, and includes useful molecular structural characterisation.

Banana starch and molecular shear fragmentation dramatically increase structurally driven slowly digestible starch in fully gelatinized bread crumb

The role of native (NB) and extruded (EB) banana starch, and a 1:1 native:extruded banana starch composite (MB), in slowing down the starch digestibility of bread crumb and crust was investigated. During extrusion, the molecular weight of banana starch was reduced from 2.75 × 10⁸ to 4.48 × 10⁶ g/mol (HPSEC-MALS-RI). Results showed a slowly digestible starch (SDS) increase from 1.09% (control) to 4.2, 6.6, and 7.76% in NB, MB and EB crumbs (fully gelatinized), respectively. DSC data attributed this occurrence to the formation of supramolecular structures upon storage involving amylopectin branches (especially those from fragmented amylopectin in EB). The hedonic sensory test showed no differences in overall liking between MB, EB and control, validating feasibility of including banana in the formulation. For the first time, this study shows a molecular size reduction as a strategy to manufacture selected starches that result in highly gelatinized baked products rich in structurally driven SDS.

Ungerminated Rice Grains Observed by Femtosecond Pulse Laser Second-Harmonic Generation Microscopy

As a demonstration that second-order nonlinear optical microscopy is a powerful tool for rice grain science, we observed second-harmonic generation (SHG) images of amylose-free glutinous rice and amylose-containing nonglutinous rice grains. The images obtained from SHG microscopy and photographs of the iodine-stained starch granules indicate that the distribution of starch types in the embryo-facing endosperm region (EFR) depends on the type of rice and suggests that glucose, maltose, or both are localized on the testa side of the embryo. In the testa side of the embryo, crystallized glucose or maltose are judged to be detected by SHG. These monosaccharides and disaccharides play an important role, as they trigger energy in the initial stage of germination. These results confirm SHG microscopy is a good method to monitor the distribution of such sugars and amylopectin in the embryo and its neighboring regions of rice grains.

Ultra-high performance liquid chromatography-size exclusion chromatography (UPLC-SEC) as an efficient tool for the rapid and highly informative characterisation of biopolymers

Starch has a complex molecular structure, with properties dependent on the relative chain lengths and branching structure of its constituent molecules, which varies due to polymorphisms in starch biosynthetic genes, as well as environmental factors. Here we present the application of ultra-high performance size exclusion chromatography to the separation of starch chains from plant seeds. Several methods, have been used to analyse chain length distributions in starch, all with limitations in terms of analysis time, sample preparation and molecular weight range. Here we demonstrate that chain length distributions can be obtained with dramatically reduced analysis time using ultra-high performance size exclusion chromatography. The method may also show improvements in resolution of some fine structural features. Understanding links between starch fine structure and biosynthetic genes will allow bioengineering of starches with tailored properties. This technique may have application to the size separation and resolution of a range of biopolymers of value to the food, drink and pharmaceutical industries.

Effects of palm oil on structural and in vitro digestion properties of cooked rice starches

The glycemic potency of rice depends upon the rate and extent of starch hydrolysis by pancreatic amylase and intestinal alpha-glucosidases. However, complexation of starch molecules with lipids is known to reduce the enzymic hydrolysis. In this study, we elucidated the varietal effect of rice starches on the formation of amylose-lipid complex, after cooking with palm oil, a common cooking oil. The amount of complexed lipid followed the order of black (2.5%), brown (2.5%), white (1.5%) and waxy (0.5%) rice starches. After heating with palm oil, the relative crystallinity of all the rice starches were destroyed whilst a V-type peak at 20° 2θ was increased, indicating the formation of amylose-lipid complex. This is also suggested from the DSC data where the melting enthalpy increased significantly after cooking in palm oil for all rice samples. The formation of amylose-lipid complex reduced the in vitro starch digestibility, enhancing the resistance starch content whilst decreasing the rapid and slow digestion fractions of non-waxy varieties. The rate and extent of in vitro starch hydrolysis seems to be dependent on the presence or absence of amylose fraction. With the mechanistic details, the present study suggests the applicability of palm oil addition during the rice cooking to enhance its nutritional functionality.

Mechanical and barrier properties of maize starch-gelatin composite films: effects of amylose content

BACKGROUND

In order to obtain new reinforcing bio-fillers to improve the physicochemical properties of gelatin-based films, three types of maize starch, waxy maize starch (Ap), normal starch (Ns) and high-amylose starch (Al), were incorporated into gelatin film and the resulting film properties were investigated, focusing on the impact of amylose content.

RESULTS

The thickness, opacity and roughness of gelatin film increased depending on the amylose content along with the starch concentration. The effects of the three starches on the mechanical properties of gelatin film were governed by amylose content, starch concentration as well as environmental relative humidity (RH). At 75% RH, the presence of Al and Ns in the gelatin matrix increased the film strength but decreased its elongation, while Ap exhibited an inverse effect. Starch addition decreased the oxygen permeability of the film, with the lowest value at 20% Al and Ns. All starches, notably at 30% content, led to a decrease in the water vapor permeability of the film at 90% RH, especially Ns starch. Furthermore, the starches improved the thermal stability of the film to some extent. Fourier transform infrared spectra indicated that some weak intermolecular interactions such as hydrogen bonding occurred between gelatin and starch. Moreover, a high degree of B-type crystallinity of starch was characterized in Gel-Al film by X-ray diffraction.

CONCLUSION

Tailoring the properties of gelatin film by the incorporation of different types of maize starch provides the potential to extend its applications in edible food packaging. © 2017 Society of Chemical Industry.

Encapsulation of Ethylene Gas into Granular Cold-Water-Soluble Starch: Structure and Release Kinetics

Ethylene gas was introduced into granular cold-water-soluble (GCWS) starches using a solid encapsulation method. The morphological and structural properties of the novel inclusion complexes (ICs) were characterized using scanning electron microscopy, X-ray diffractometry, and Raman spectroscopy. The V-type single helix of GCWS starches was formed through controlled gelatinization and ethanol precipitation and was approved to host ethylene gas. The controlled release characteristics of ICs were also investigated at various temperature and relative humidity conditions. Avrami's equation was fitted to understand the release kinetics and showed that the release of ethylene from the ICs was accelerated by increasing temperature or RH and was decelerated by increased degree of amylose polymerization. The IC of Hylon-7 had the highest ethylene concentration (31.8%, w/w) among the five starches, and the IC of normal potato starch showed the best controlled release characteristics. As a renewable and inexpensive material, GCWS starch is a desirable solid encapsulation matrix with potential in agricultural and food applications.

The molecular structural features controlling stickiness in cooked rice, a major palatability determinant

The stickiness of cooked rice is important for eating quality and consumer acceptance. The first molecular understanding of stickiness is obtained from leaching and molecular structural characteristics during cooking. Starch is a highly branched glucose polymer. We find (i) the molecular size of leached amylopectin is 30 times smaller than that of native amylopectin while (ii) that of leached amylose is 5 times smaller than that of native amylose, (iii) the chain-length distribution (CLD: the number of monomer units in a chain on the branched polymer) of leached amylopectin is similar to native amylopectin while (iv) the CLD of leached amylose is much narrower than that of the native amylose, and (v) mainly amylopectin, not amylose, leaches out of the granule and rice kernel during cooking. Stickiness is found to increase with decreasing amylose content in the whole grain, and, in the leachate, with increasing total amount of amylopectin, the proportion of short amylopectin chains, and amylopectin molecular size. Molecular adhesion mechanisms are put forward to explain this result. This molecular structural mechanism provides a new tool for rice breeders to select cultivars with desirable palatability by quantifying the components and molecular structure of leached starch.

Role of polysaccharides in food, digestion, and health

Polysaccharides derived from plant foods are major components of the human diet, with limited contributions of related components from fungal and algal sources. In particular, starch and other storage carbohydrates are the major sources of energy in all diets, while cell wall polysaccharides are the major components of dietary fiber. We review the role of these components in the human diet, including their structure and distribution, their modification during food processing and effects on functional properties, their behavior in the gastrointestinal tract, and their contribution to healthy diets.

Instrumental measurement of cooked rice texture by dynamic rheological testing and its relation to the fine structure of rice starch

Increasing demands for better instrumental methods to evaluate cooked rice texture is driving innovations in rice texture research. This study characterized cooked rice texture by descriptive sensory analysis and two instrumental methods (texture profile analysis (TPA) and dynamic rheological testing) using a set of 18 varieties of rice with a wide range in amylose content (0-30%). The panellists' results indicated that hardness and stickiness were the two most discriminating attributes among 13 tested textural attributes. The consistency coefficient (K(*)) and loss tangent (tan δ) from a dynamic frequency sweep were used to compare with hardness and stickiness tested by TPA and sensory panellists, showing that using K(*) to express hardness, and tan δ to express stickiness, are both statistically and mechanistically meaningful. The instrumental method is rationalized in terms of starch structural differences between rices: a higher proportion of both amylose and long amylopectin branches with DP 70-100 causes a more elastic and less viscous texture, which is readily understood in terms of polymer dynamics in solution.

Rice Grain Quality and Consumer Preferences: A Case Study of Two Rural Towns in the Philippines

Hedonic pricing analysis is conducted to determine the implicit values of various attributes in the market value of a good. In this study, hedonic pricing analysis was applied to measure the contribution of grain quality search and experience attributes to the price of rice in two rural towns in the Philippines. Rice samples from respondents underwent quantitative routine assessments of grain quality. In particular, gelatinization temperature and chalkiness, two parameters that are normally assessed through visual scores, were evaluated by purely quantitative means (differential scanning calorimetry and by digital image analysis). Results indicate that rice consumed by respondents had mainly similar physical and chemical grain quality attributes. The respondents' revealed preferences were typical of what has been previously reported for Filipino rice consumers. Hedonic regression analyses showed that grain quality characteristics that affected price varied by income class. Some of the traits or socioeconomic factors that affected price were percent broken grains, gel consistency, and household per capita rice consumption. There is an income effect on rice price and the characteristics that affect price vary between income classes.

The importance of amylose and amylopectin fine structure for textural properties of cooked rice grains

Statistically and causally meaningful relationships are established between starch molecular structure (the molecular distribution of branched starch and the chain length distribution of debranched starch) and texture (hardness and stickiness) of cooked rice grains. The amounts of amylose chains with degree of polymerization (DP) 100-20,000, and of long amylopectin chains, positively correlated with hardness, while amylopectin chains with DP<70 and amylose molecular size both showed negative correlations with hardness (p<0.05). There was also a significant negative correlation between stickiness and the amounts of long amylopectin chains (p<0.01). For rices with similar amylose content, the amount of amylose chains with DP 1000-2000 positively correlated with hardness while size negatively correlated with hardness (p<0.05). This indicates for the first time that, regardless of amylose content, rice varieties with smaller amylose molecular sizes and with higher proportions of long amylose chains have a harder texture after cooking.

Prospects of breeding high-quality rice using post-genomic tools

The holistic understanding derived from integrating grain quality and sensory research outcomes in breeding high-quality rice in the light of post-genomics resources has been synthesized. Acceptance of new rice genotypes by producers and consumers hinges not only on their potential for higher yield but recent emphasis has also been on premium-value genotypes that have the ability to satisfy consumer preferences for grain quality. This review article provides insights into how to link grain quality attributes and sensory perception to support breeding superior rice varieties. Recent advances in quality profiling and omics technologies have provided efficient approaches to identify the key genes and biochemical markers involved in rice quality traits. Emphasis has been given to the upcoming area of holistic understanding of grain quality and attributes derived from sensory evaluation to leverage integrative gene discovery strategies that enable breeding programs to efficiently tap the huge genetic diversity in rice for novel genes that enhance rice food quality.

Roles of GBSSI and SSIIa in determining amylose fine structure

This study examines the relationships between genetics (single nucleotide polymorphisms (SNPs) in GBSSI and SSIIa genes), starch structure (amylose and amylopectin fine structures), and starch properties (relating to gelatinization). GBSSI and SSIIa SNPs did not alter the starch content of rice grains. GBSSI SNPs can affect the amylose content, but they are incapable of altering the chain-lengths of amylopectin and amylose. The amounts of both long and short amylose branches changed with the same trend as amylose content, and they appeared to affect starch gelatinization properties. SSIIa synthesizes intermediate single-lamella amylopectin chains (DP 16-21), and consequently impacts the gelatinization temperature. Mathematical modelling suggests that the reduction in SSIIa activity significantly increases the activity of SBEII, resulting in a decreased activity ratio of SS to SBE in the enzyme set governing an appropriate chain-length distribution range. This application of the genetics-structure-property paradigm provides selection strategies to produce rice varieties with improved qualities.