Heteropolymers may contain sugar acids, amino sugars, or noncarbohydrate substances in addition to monosaccharides. Heteropolymers are common in nature gums, pectins, and other substances but will not be discussed further in this textbook. The polysaccharides are nonreducing carbohydrates, are not sweet tasting, and do not undergo mutarotation.
It occurs in plants in the form of granules, and these are particularly abundant in seeds especially the cereal grains and tubers, where they serve as a storage form of carbohydrates. The breakdown of starch to glucose nourishes the plant during periods of reduced photosynthetic activity.
Commercial starch is a white powder. Starch is a mixture of two polymers: amylose and amylopectin. When coiled in this fashion, amylose has just enough room in its core to accommodate an iodine molecule. The characteristic blue-violet color that appears when starch is treated with iodine is due to the formation of the amylose-iodine complex.
This color test is sensitive enough to detect even minute amounts of starch in solution. The helical structure of amylopectin is disrupted by the branching of the chain, so instead of the deep blue-violet color amylose gives with iodine, amylopectin produces a less intense reddish brown. Dextrins are glucose polysaccharides of intermediate size.
The shine and stiffness imparted to clothing by starch are due to the presence of dextrins formed when clothing is ironed. Because of their characteristic stickiness with wetting, dextrins are used as adhesives on stamps, envelopes, and labels; as binders to hold pills and tablets together; and as pastes. Dextrins are more easily digested than starch and are therefore used extensively in the commercial preparation of infant foods. In the human body, several enzymes known collectively as amylases degrade starch sequentially into usable glucose units.
Glycogen is the energy reserve carbohydrate of animals. Like starch in plants, glycogen is found as granules in liver and muscle cells. When fasting, animals draw on these glycogen reserves during the first day without food to obtain the glucose needed to maintain metabolic balance. Glycogen is structurally quite similar to amylopectin, although glycogen is more highly branched 8—12 glucose units between branches and the branches are shorter.
When treated with iodine, glycogen gives a reddish brown color. Cassava bagasse is generally disposed in the surrounding environment of the processing units. Starch is a polymer of glucose and contains amylose and amylopectin as building blocks. The hydrolysis of the starch present in cassava bagasse produces a broth with available reducing sugars, chiefly glucose, which could be directly fermented by microrganisms Bobbio and Bobbio, Due to richness in organic matter, basically starch, cassava bagasse could be in ideal substrate for biotechnological processes where the objective could be to produce metabolites with commercial value.
Cassava bagasse can be used directly in solid-state fermentation, or in submerged fermentation after hydrolysis. Table 1 shows the range of variation of its physico-chemical contents. Another approach to utilize cassava bagasse involves its hydrolyze to convert starch present in it into reducing sugars mainly glucose , and then uses it in submerged fermentation to produce metabolites. To obtain reducing sugars from cassava bagasse, it must have a thermal hydrolytic treatment with acid or enzyme.
The acid or enzymatic hydrolysis of cassava bagasse produces two fractions: one liquid composed of soluble sugars from the starch hydrolysis basically glucose , and one solid fraction composed of insoluble cellulose and fibers. The objective of this work was to compare the recovery of reducing sugars from cassava bagasse using two different hydrolysis methods, and also to compare the cost economics of both the methods of hydrolysis.
The physical conditions for acid and enzymatic hydrolysis were optimized using an experimental factorial design, where the response variable was the reducing sugars concentration.
The response data were analyzed using the statistical program " Statistica " based on the response surface. Acid Hydrolysis: Acid hydrolysis was performed using hydrochloric acid at 0. The tests were made in mL flasks, using 5 g of cassava bagasse and 50 mL of the acid solution. The enzymatic hydrolysis was performed in two steps. The optimal pH, reaction time, temperature and the enzyme concentration of both the steps were determined using the experimental factorial design.
The tests were made in mL flasks, using 6 g of cassava bagasse, and 50 mL of water with the appropriate enzyme Carta, Reducing Sugar Analysis: The reducing sugars recovered from the cassava bagasse was analyzed by Somogyi-Nelson method Nelson, ; Somogyi, ; Somogyi, Energy Costs: The energy costs of both the processes, viz.
The hydrolysis costs were calculated considering the energy and the chemicals necessary for both the processes. Reactor: A cylindrical stainless steel reactor L with thermal insulation and jacket heated was used. Its diameter was 1. Heat Needed for the Processes: In order to compare the heat necessary by both the methods of hydrolysis, the heat necessary to increase the temperature and the heat necessary to maintain it during each step of the both processes was calculated as described by Holman Heat to increase the temperature of the aqueous medium with cassava bagasse :.
The global coefficient of thermal exchange for the cylindrical wall was calculated using the following expression:. The first term was related to the convection inside the reactor. To determine the medium parameters, water was considered. The global coefficient of thermal exchange for top and bottom flat walls was calculated using the following expression:. As the probability of new buds increases with an increasing radius, the competition for space between the buds would increase, possibly resulting in impeded bud formation, whereby a bud is unable to reach maximum density.
As the size of the molecule increases, the chance of impeded and incomplete buds also increases, resulting in a decrease of the density. While the nature of the linkage between particles in particles in glycogen is unclear, the results obtained here and those described elsewhere are consistent with this being a covalent or strong non-covalent linkage involving a protein.
Some candidates are glycogenin or a lectin. Glycogenin is relatively abundant in rat and mouse livers and it has been theorized that it is possibly present on the surface of glycogen particles [ 8 ]. However, there is little effect of protease which hydrolyses amide linkages in protein on the distributions of either phytoglycogen or liver glycogen [ 14 ], which is ascribed to the large protease molecule being hindered from diffusing within the liver glycogen molecules and thus unable to digest internally-located proteins [ 14 ] see S2 Text and S4 Fig.
Curves have been normalized to the distribution peak. As can be observed, using the data obtained from liver glycogen for this model, the distribution maintains its bimodality over the course of hydrolysis. If band-broadening were qualitatively affecting the distribution, it would be expected that the peak at higher hydrodynamic size would turn into an extended tail. This is qualitatively different from what is seen experimentally, suggesting that band broadening does not affect the conclusions drawn from fitting to the model.
The actual red and fitted dimensionless blue times are shown. Curves have been normalized to the population peak of interest. The full-bud model reflects the protein mediated binding-assembly model where the structure of the molecule is most likely to be loosely randomized resulting in a decreased density. The semi-bud model represents the crowding-budding model where new buds are incomplete decreasing the density of the molecules as the buds are unable to reach maximum density.
Molecular weight and radius of gyration R gz results were taken from the literature [ 44 ]. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Abstract Phytoglycogen from certain mutant plants and animal glycogen are highly branched glucose polymers with similarities in structural features and molecular size range. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited Data Availability: All relevant data are within the paper and its Supporting Information files.
Introduction Phytoglycogen is a highly branched glucan found in certain mutant plants that arises as a consequence of a variety of mutations that result in disruptions in the gene encoding the isoamylase debranching enzyme. Materials and Methods Materials Grain from sugary-1 mutant maize plants was obtained from Prof. Model for the Uniform Degradation of Glucans during Acid Hydrolysis over Time Data interpretation was aided by the following mathematical model describing the time evolution of the size distribution for the ideal case where acid hydrolysis of phyto glycogen occurs uniformly and randomly throughout the molecule.
Under the assumption of unit local dispersity [ 23 ], one has: 1 Here. By a straightforward change in the derivation of the time evolution of the particle size distribution of the growth of synthetic polymer colloids [ 24 ], one then has the following evolution equation for the number distribution under uniform degradation: 2 Here K V is the rate of degradation.
Download: PPT. Fig 1. Aqueous SEC weight distributions of acid hydrolyzed glucans. Acid Hydrolysis Fig. Fig 3. Aqueous SEC weight distributions of water-hydrolyzed glucans. Modeling Glucan Hydrolysis The mathematical model for the uniform degradation where non-preferential bond cleavage of glucans occurs over time was fitted to the observed time evolution see S1 Text of the size distribution during hydrolysis Fig.
Fig 4. Fittings of phytoglycogen acid hydrolysis experimental data to the model of uniform degradation. Fig 5. Fittings of liver glycogen acid hydrolysis data to the model of uniform degradation. Fig 6. Aqueous SEC weight and molecular density distributions of glucans.
Discussion There are many enzymes that both starch and hence phytoglycogen and glycogen utilize during their biosynthesis. Supporting Information.
S1 Fig. The model of uniform degradation over an extended time period. S2 Fig. Comparison of fittings generated from the uniform model of hydrolysis. S3 Fig. Modified crowding budding models. S4 Fig. Aqueous SEC weight distributions of glucans subjected to protease treatment.
S1 Table. Densities of phytoglycogen and starch samples. S1 Text. Derivation, numerical solution and data fitting of evolution equation for size distribution during acid hydrolysis. S2 Text. Effects of proteases on glucan structure. References 1. Structure, physical, and digestive properties of starch from wx ae double-mutant rice.
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