Les Copeland

Starch Retrogradation: A Comprehensive Review

Starch retrogradation is a process in which disaggregated amylose and amylopectin chains in a gelatinized starch paste reassociate to form more ordered structures. Starch retrogradation has been the subject of intensive research over the last 50 years, mainly due to its detrimental effect on the sensory and storage qualities of many starchy foods. However, starch retrogadation is desirable for some starchy food products in terms of textural and nutritional properties. To better understand the effect of starch retrogradation on the quality of starchy foods, measurement methods of starch retrogradation and factors that influence starch retrogradation have been studied extensively. This article provides a comprehensive review of starch retrogradation including the definition of the process, molecular mechanisms of how it occurs, and measurement methods and factors that influence starch retrogradation. The review also discusses the effect of retrogradation on the in vitro enzyme digestibility of starch. Spectroscopic methods such as FTIR and Raman are considered to be very promising in characterizing starch retrogradation at a molecular level, although more studies are needed in the future.

Molecular disassembly of starch granules during gelatinization and its effect on starch digestibility: a review

Starch is the most important glycemic carbohydrate in foods. The relationship between the rate and extent of starch digestion to produce glucose for absorption into the bloodstream and risk factors for diet-related diseases is of considerable nutritional interest. Native starch is attacked slowly by enzymes, but after hydrothermal processing its susceptibility to enzymatic breakdown is greatly increased. Most starch consumed by humans has undergone some form of processing or cooking, which causes native starch granules to gelatinize, followed by retrogradation on cooling. The extent of gelatinization and retrogradation are major determinants of the susceptibility of starch to enzymatic digestion and its functional properties for food processing. The type and extent of changes that occur in starch as a result of gelatinization, pasting and retrogradation are determined by the type of the starch, processing and storage conditions. A mechanistic understanding of the molecular disassembly of starch granules during gelatinization is critical to explaining the effects of processing or cooking on starch digestibility. This review focuses on the molecular disassembly of starch granules during starch gelatinization over a wide range of water levels, and its consequential effect on in vitro starch digestibility and in vivo glycemic index.

Effect of Acid Hydrolysis on Starch Structure and Functionality: A Review

Acid hydrolysis is an important chemical modification that can significantly change the structural and functional properties of starch without disrupting its granular morphology. A deep understanding of the effect of acid hydrolysis on starch structure and functionality is of great importance for starch scientific research and its industrial applications. During acid hydrolysis, amorphous regions are hydrolyzed preferentially, which enhances the crystallinity and double helical content of acid hydrolyzed starch. This review discusses current understanding of the effect of acid hydrolysis on starch structure and functionality. The effects of acid hydrolysis on amylose content, chain length distribution of amylopectin molecules, molecular and crystalline organization (including lamellar structure) and granular morphology are considered. Functional properties discussed include swelling power, gelatinization, retrogradation, pasting, gel texture, and in vitro enzyme digestibility. The paper also highlights some promising applications of acid hydrolyzed starch (starch nanocrystals) in the preparation of biodegradable nanocomposites, bio-hydrogen, and slowly digestible starch-based healthy foods.

Enzymes of carbohydrate metabolism in soybean nodules

Abstract The activities of enzymes of carbohydrate metabolism have been measured in the plant and bacteroid fractions of soybean ( Glycine max ) nodules and in roots of non-nodulated soybeans. The plant fraction of the nodules contained the enzymes required to convert sucrose to pyruvate and to oxaloacetate as well as enzymes of starch synthesis and degradation. In contrast, the bacteroids had only limited capacity for carbohydrate metabolism and appeared to lack the complete glycolytic pathway. The distribution of enzymes of carbohydrate metabolism between the cortical tissue and central infected zone of the nodules was investigated. The conversion of sucrose to organic acids may take place to a large extent in the cortical tissue of the nodules.

THE IMPORTANCE OF DIETARY CARBOHYDRATE IN HUMAN EVOLUTION.

We propose that plant foods containing high quantities of starch were essential for the evolution of the human phenotype during the Pleistocene. Although previous studies have highlighted a stone tool-mediated shift from primarily plant-based to primarily meat-based diets as critical in the development of the brain and other human traits, we argue that digestible carbohydrates were also necessary to accommodate the increased metabolic demands of a growing brain. Furthermore, we acknowledge the adaptive role cooking played in improving the digestibility and palatability of key carbohydrates. We provide evidence that cooked starch, a source of preformed glucose, greatly increased energy availability to human tissues with high glucose demands, such as the brain, red blood cells, and the developing fetus. We also highlight the auxiliary role copy number variation in the salivary amylase genes may have played in increasing the importance of starch in human evolution following the origins of cooking. Salivary amylases are largely ineffective on raw crystalline starch, but cooking substantially increases both their energy-yielding potential and glycemia. Although uncertainties remain regarding the antiquity of cooking and the origins of salivary amylase gene copy number variation, the hypothesis we present makes a testable prediction that these events are correlated.

Structural and functional properties of starches from field peas

Starch was isolated from seven varieties of field peas (Pisumsativum L.) and characterised using a combination of physical, chemical and functional tests. The total starch content of the peas ranged between 34% and 42.7% of dry matter, and the amylose content of the starch was between 35% and 38%. Average particle diameter of the seven starches varied between 21.4 and 26.1μm. All of the pea starches gave a typical C-type X-ray diffraction pattern, with relative crystallinity ranging between 36% and 55% and the proportion of B-type crystallites between 3.8% and 30.4%. Although there were only small differences between the starches in amylose content, they displayed significant variability in functional properties, including swelling power, pasting characteristics, thermal transition temperatures in the differential scanning calorimeter, and in susceptibility to invitro attack by α-amylase. The results indicate the importance of structural characteristics of starch molecules, particularly amylopectin, as determinants of the properties of native starch granules.

The wheat-grain proteome as a basis for more efficient cultivar identification.

The wheat‐grain proteome was investigated, as a basis for devising more efficient methods of cultivar identification or discrimination. Australian wheats (Halberd, Cranbrook, CD87 and Katepwa) were used as the basis of this study. These cultivars were selected on the basis of differences in the quality types represented, in terms of dough‐processing attributes that can suit one cultivar better than another for specific types of industrial utilisation. Total wheat endosperm (flour) protein extracts were prepared from mature wheat for two‐dimensional electrophoresis, across both acidic (pH 4–7) and basic (pH 6–11) pH ranges. Three particular regions of the proteome maps were chosen for close comparison, involving two sets of gluten proteins and a nongluten protein region (involving small heat shock proteins), based on previous protein characterisation. Differences in the nongluten protein regions (heat shock proteins and other unidentified polypeptides) are of particular interest as being possible targets for use in developing new approaches to cultivar discrimination, such as the development of simple immunoassays.

Genotype and Environmental Influences on Pasting Properties of Rice Flour

ABSTRACT The pasting behavior of flour from several Australian rice (Oryza sativa L.) cultivars, differing in amylose content and grown in three different locations and three seasons, were determined using the Rapid Visco Analyser. Genotype, growth season, and growth location all affected the pasting behavior of rice flour. The amylose content of the same cultivar was significantly higher in the coolest growing season, resulting in RVA traces with lower peak viscosity and higher setback than samples with lower amylose content. When the same cultivar of rice was grown in different locations in the same season, there were no significant differences in the total starch, protein, lipid, and amylose content of the flour, but there were significant differences in the pasting behavior. This indicates that environmental as well as genetic factors influence the pasting behavior of rice flour. Flour from parboiled and quick-cooking rice did not paste and had low viscosities compared with unprocessed rice. Results f...

Role of malonate in chickpeas

Analysis of the content and distribution of organic acids in chickpea plants (Cicer arietinum L.) showed that malonate was the most abundant acid in roots and nodules, whereas malate was the main acid in leaves and stems. The highest concentration of malonate in roots was in the apices. Malonate metabolism did not appear to be directly related to abiotic stress. We suggest that malonate has a role as a defensive chemical in roots and nodules of chickpeas.

Effect of alkali treatment on structure and function of pea starch granules

The effect of alkaline treatment on the structural and functional properties of pea starch granules was studied using a range of characterization methods including amylose content, scanning electron microscopy (SEM), X-ray diffraction (XRD), (13)C nuclear magnetic resonance (NMR), swelling power, differential scanning calorimetry (DSC), the Rapid Visco Analyser (RVA) and in vitro digestibility. The amylose content decreased by about 20-25% after 15days of alkaline treatment and there were small decreases in relative crystallinity and double helix content. Deformations were observed on the surface of alkali-treated granules, and there was evidence of adhesion between some of the granules. There was a 25-30% reduction in peak and final RVA pasting viscosities, but only a small reduction in swelling power. The endothermic transition of alkali-treated starch was broadened with a shift of the endothermic peak to higher temperature. However, the endothermic enthalpy remained largely unaffected. Alkali-treatment greatly increased the rate of in vitro enzymatic breakdown of the pea starch. More prolonged alkaline treatment for 30days did not cause further significant changes to the structural and functional properties of the starch granules. The effects of alkali on structure and function of pea starch are explained on the basis of limited gelatinization of the granules.