Starch granules: structure and biosynthesis.

Starch-composition, fine structure and architecture

Recent developments in methods and instrumentation have contributed to major advances in our understanding of the fine structure of amylose and amylopectin. The structure of the starch granule slowly unravels with new insight into key structural features. Following a brief presentation of the structural features common to all starches, the most recent findings for the structure of amylose and amylopectin are reported. The organization of different types of chains in amylopectin is discussed with a critical review of the 'cluster' model leading to the presentation of alternative models. The locations of molecular components in the starch granule are described according to a progress structural order. The description of the crystalline components is followed by a presentation of their supramolecular arrangements. The crystalline components comprise platelet nanocrystals which have already been identified and characterized, and other less well characterized 'blocklet components'. The location and state of amylose within the granule is also presented. This comprehensive review aims at distinguishing between those structural features that have received widespread acceptance and those that are still under debate, with the ambition of being educational and to provide stimulation for further fundamental investigation into the starch granule as a macromolecular assembly.

The molecular structures of starch components and their contribution to the architecture of starch granules: 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.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12143

Starch retrogradation: a comprehensive review

Epidemiological studies have clearly shown that whole-grain cereals can protect against obesity, diabetes, CVD and cancers. The specific effects of food structure (increased satiety, reduced transit time and glycaemic response), fibre (improved faecal bulking and satiety, viscosity and SCFA production, and/or reduced glycaemic response) and Mg (better glycaemic homeostasis through increased insulin secretion), together with the antioxidant and anti-carcinogenic properties of numerous bioactive compounds, especially those in the bran and germ (minerals, trace elements, vitamins, carotenoids, polyphenols and alkylresorcinols), are today well-recognised mechanisms in this protection. Recent findings, the exhaustive listing of bioactive compounds found in whole-grain wheat, their content in whole-grain, bran and germ fractions and their estimated bioavailability, have led to new hypotheses. The involvement of polyphenols in cell signalling and gene regulation, and of sulfur compounds, lignin and phytic acid should be considered in antioxidant protection. Whole-grain wheat is also a rich source of methyl donors and lipotropes (methionine, betaine, choline, inositol and folates) that may be involved in cardiovascular and/or hepatic protection, lipid metabolism and DNA methylation. Potential protective effects of bound phenolic acids within the colon, of the B-complex vitamins on the nervous system and mental health, of oligosaccharides as prebiotics, of compounds associated with skeleton health, and of other compounds such as alpha-linolenic acid, policosanol, melatonin, phytosterols and para-aminobenzoic acid also deserve to be studied in more depth. Finally, benefits of nutrigenomics to study complex physiological effects of the 'whole-grain package', and the most promising ways for improving the nutritional quality of cereal products are discussed.

/pdf/new-hypotheses-for-the-health-protective-mechanisms-of-whole-1j7sw6pesk.pdf

New hypotheses for the health-protective mechanisms of whole-grain cereals: what is beyond fibre?

Microscopy of starch : evidence of a new level of granule organization

Publisher Summary
The amylose and amylopectin molecules, the granule structure, and the natures and amounts of the lipid and protein molecules present in granules vary with the botanical source of the starch. Starch granules are mainly found in seeds, roots, and tubers, but are also found in stems, leaves, fruits, and even pollen. They occur in all shapes and sizes (spheres, ellipsoids, polygons, platelets, irregular tubules) and are long dimensioned. Differences in external granule morphology are generally sufficient to provide unambiguous characterization of the botanical source via optical microscopy. The starch granule is nature's chief way of storing energy over long periods in green plants. The granule is well suited to this role, being insoluble in water and densely packed, but still accessible to the plant's catabolic enzymes. Native starch granules have a crystallinity varying from 15% to 45%, thus, most native starch granules exhibit a Maltese cross when observed under polarized light. Most starch granules are made up of alternating amorphous and crystalline shells, which are between 100 and 400 nm thick. These structures are termed “growth rings.” Birefringence remains unchanged on both polar and equatorial sections of elongated starch granules. Most starch polymers in the granule are in an amorphous state. Most cereal starches give the so called A-type pattern; some tuber starches (e.g. potato) and cereal starches rich in amylose yield the B-type pattern, while legume starches generally give a C-type pattern. The two major macromolecular components of starch are amylose and amylopectin.

Chapter 5 – Structural Features of Starch Granules I

Involvement of the protein network in the in vitro degradation of starch from spaghetti and lasagne: a microscopic and enzymic study.

Influence of technological modifications of the protein network from pasta on in vitro starch degradation

The structure of pasta is largely governed by the presence of a structured protein network. This work analyzed the protein network textures of various cooked pasta products through textural image analysis. Six different pasta types were investigated: reference pasta made from durum semolina; pasta enriched with gluten proteins from soft wheat flour at 10 and 20%; autoclaved pasta; soft wheat flour pasta; and pasta made from reconstituted flour fractions. Pasta samples were sectioned, and each crosssection consisted of three distinct zones (central, intermediate, and external) based on the state of swelling of starch granules for each pasta product. Digital images of the protein network in each zone were acquired using confocal laser scanning microscopy. Textural image analysis was then performed. Similarities and differences in protein network texture were assessed by principal component, stepwise discriminant, and variance analyses. With the exception of autoclaved pasta, protein network structu...

Paul M. Baldwin

Papers

Microscopy of starch : evidence of a new level of granule organization

Chapter 5 – Structural Features of Starch Granules I

Involvement of the protein network in the in vitro degradation of starch from spaghetti and lasagne: a microscopic and enzymic study.

Influence of technological modifications of the protein network from pasta on in vitro starch degradation

Textural Images Analysis of Pasta Protein Networks to Determine Influence of Technological Processes