On the Structure of Native Starch — An Analogue to the Quartz Structure

Characterization of amylose and amylopectin fractions separated from potato, banana, corn, and cassava starches

Analytical techniques such HPSEC, DSC, and TGA have been employed for amylose determination in starch samples, though spectrophotometry by iodine binding is most commonly used. The vast majority of these techniques require an analytical curve, using amylose and amylopectin standards with physicochemical properties similar to those found in the original starch. The current study aimed to obtain the amylose and amylopectin fractions from potato, banana, corn, and cassava starches, characterize them, and evaluate their behavior via thermogravimetric curves. Blue amylose iodine complex and HPSEC-DRI methods have obtained high purity amylose and amylopectin fractions. All molecular weights of the obtained amylose and amylopectin fractions were similar to those presented in other reports. Different results were obtained by deconvolution of the amylopectin polymodal distribution. All amyloses presented as semi-crystalline V-type polymorphs, while all amylopectin fractions were amorphous. The T_g of all V_amyloses presented were directly proportional to their respective crystalline index. TGA evaluations have shown that selective precipitation of amylose with 1-butanol strongly changes its thermal behavior. Therefore, the separation procedure used was an ineffective pathway for obtaining standards for thermal studies.

Thermal behavior of resistant starches RS 2, RS 3, and RS 4

The thermal behaviors of 3 resistant starch types-RS 2, RS 3, and RS 4-were investigated. Samples were heated in excess water to specific temperatures, from 35 to 85 degrees C at 5 degrees C intervals, and freeze-dried. The treated samples were analyzed using SEM, DSC, XRD, and HPSEC to determine the structural changes at granular and molecular levels. Light microscopy was used to determine real-time thermal behavior of the starches. Although the resistant starches did not show significant morphological changes, as revealed by microscopy, they underwent internal structural changes at low temperatures before complete phase transitions occurred. The structural changes were less in RS 2 compared to the other 2 starches studied. The nongranular material of RS 3's crystallinity decreased gradually from 35 to 85 degrees C and showed microscopically visible changes at >80 degrees C. Cross-linking might have prevented RS 4 from becoming completely amorphous within the temperature range (35 to 85 degrees C) tested. The study indicated that the extent of structural changes depended on the treatment temperature and RS type.

Characterization of Amylose-lipid Complexes Derived from Different Wheat Varieties and their Susceptibility to Enzymatic Hydrolysis

Starches from eight wheat varieties were analyzed for contents of dry matter, protein, pentosans, apparent and total amylose, total lipids, starch lipids, phosphorus, lysophospholipids and amylose-lipid complex (AML). Processes of starch gelatinization, reversible dissociation of AMLs and its susceptibility to degradation by α-amylase were monitored by differential scanning calorimetry (DSC). Degree of crystallinity of starches were evaluated based on X-ray diffraction pattern. Starches from different wheat varieties show some slight differences in terms of chemical composition, thermal properties and susceptibility to enzymatic hydrolysis. Endotherms and exotherms of most starch samples obtained by DSC contained single peaks, which indicated that AML complexes existed in one polymorphic form. Only AMLs formed by amylose from Symfonia cultivar was reflected by the double-peak exotherm on cooling of starch gel. Our studies showed that there was no correlation between AML content and enthalpy of its degradation in native starch. During enzymatic hydrolysis of starch AML complex in all examined starches underwent considerable degradation. Enthalpies of dissociation of AMLs, which remained after amylolysis were significantly lowered (80—90%) as compared to that of undigested starch. The susceptibility of AMLs to degradation by α-amylase did not depend on its amount (based on calculation from LPLs), but probably on its structure.

Starch gelatinization

Starch occurs as highly organized structures, known as starch granules. Starch has unique thermal properties and functionality that have permitted its wide use in food products and industrial applications. When heated in water, starch undergoes a transition process, during which the granules break down into a mixture of polymers-in-solution, known as gelatinization. The sequence of structural transformations that the starch granule undergoes during this order-to-disorder transition has been extensively researched. None of the published starch gelatinization theories can fully and adequately explain the exact mechanism of sequential structural changes that starch granules undergo during gelatinization. This chapter analyzes several published theories and summarizes our current understanding of the starch gelatinization process.

Food-derived carbohydrates--structural complexity and functional diversity

Carbohydrates are biomolecules abundantly available in nature. They are found in bewildering types ranging from simple sugars through oligo- and polysaccharides to glycoconjugates and saccharide complexes, each exhibiting characteristic bio-physiological and/or nutritional functions both in in vivo and in vitro systems. For example, their presence or inclusion in food dictates the texture (body) and gives desirable customer appeal (satisfaction), or their inclusion in the diet offers beneficial effects of great therapeutic value. Thus, carbohydrates are integrally involved in a multitude of biological functions such as regulation of the immune system, cellular signaling (communication), cell malignancy, antiinfection responses, host-pathogen interactions, etc. If starch is considered the major energy storage carbohydrate, the gums/mucilages and other non-starch carbohydrates are of structural significance. The most investigated properties of starch are its gelatinization and melting behavior, especially during food processing. This has led to the development of the food polymer science approach, which has enabled a new interpretive and experimental frame work for the study of the plasticizing influence of simple molecules such as water, sugars, etc. on food systems that are kinetically constrained. Starch, although considered fully digestible, has been challenged, and starch is found to be partly indigestible in the GI tract of humans. This fraction of starch-resisting digestion in vivo is known as resistant starch (RS). The latter, due to its excellent fermentative capacity in the gut, especially yielding butyric acid is considered a new tool for the creation of fiber-rich foods, which are of nutraceutical importance. By a careful control of the processing conditions the content of RS, a man-made fiber, can be increased to as high as 30%. Arabinoxylans are the major endospermic cell wall polysaccharides of cereals. In wheat they are found complexed with ferulic acid esters, which after oxidative coupling in vivo mediated by H2O2 and peroxidases or even by photochemical means give cross linked diferuloyl derivatives. The latter confer strength and extensibility to the cell wall and offer resistance for digestibility by ruminants. They also help blocking of the ingress of pathogens. The ester bound ferulic acid after oxidation in vivo generates reactive oxygen species that contribute to the fragmentation of non-starch polysaccharides (hemicelluloses), and thereby reduces the product viscosity, a property seen during long-term storage of rice. In plant tissues, the arabinogalactans are implicated in such diverse functions as cell-cell adhesion, nutrition of growing pollen tubes, response to microbial infections, and also as markers of identity expressed in the terminal sequences of saccharide chains.

Chemistry and properties of starch based desiccants

Desiccants currently used in industry include molecular sieves, lithium chloride, silica gel, and corn grits. Of these, only corn grits (a form of ground corn) are biodegradable and derived from a renewable resource. A major component of the corn grits, starch, is the primary adsorptive material in the corn grits. Other polysaccharides, including cellulose and hemicellulose also have adsorptive properties. The use of alpha-amylase (EC 3.2.1.1) to modify porosity and surface properties of starch resulted in materials with enhanced water sorption properties compared to the native material. This paper reviews the chemical and structural properties of starch, corn grits, and cellulose-based scaffolds on which starch can be affixed, in order to attain structures that might someday find uses in a range of desiccant applications for industrial, commercial, and residential processes.

Deep-freezing of potato starch

Samples of oven-dried, air-dried, and moisturised potato starch (5, 13, and 24% w/w moisture content, respectively) were frozen in liquid nitrogen. Samples after thawing were studied by means of cross-polarised light beam microscope (CLBM), Fourier Transformation Infrared Spectroscope (FT-IR), powder X-ray diffractometer, and non-contact Atomic Force Microscope (nc-AFM). Rapid deep-freezing followed by thawing produced changes on the granule surface. They were accompanied by internal alteration manifested by FT-IR spectra and powder X-ray diffractograms. The results depended on the water content in the sample. Deep-freezing of moistened starch resulted in increased crystallinity of granules. It had minor effect on the granule aqueous solubility and characteristics of gelation.

Amylolytic enzymes and products derived from starch: a review

This review provides current information on starch and its molecular composition, common and potential sources, and manufacturing processes. It also deals with the five groups of enzymes involved in the hydrolysis of starch: the endo- and exoamylases, which act primarily on the alpha-1,4 linkages; the debranching enzymes, which act on the alpha-1,6 linkages; the isomerases which convert glucose to fructose; and the cyclodextrin glycosyltransferases which degrade starch by catalyzing cyclization and disproportionation reactions. This work mainly discusses the enzymatic processes for the manufacture of maltodextrins and corn syrup solids, including the production, both batch and continuous, of glucose syrup, and the processes to obtain sweeteners, such as maltose and 42, 55, and 90% high-fructose corn syrups. It highlights the novel production of Schardinger's dextrins: the alpha-, beta-, and gamma-cyclodextrins, consisting of six, seven, and eight glucose monomers, respectively. New products are emerging on the market that can serve as fat and oil substitutes, moisture-retention compounds, crystal-formation controllers, stabilizers for volatile materials like flavors and spices, or products for the pharmaceutical industry. As a result, particular attention is given to functional properties and applications of the above-cited compounds.