Wheat and Rice – Ancient and Modern Cereals
Raymond Cooper, Jeffrey John Deakin in Natural Products of Silk Road Plants, 2020
White rice has had the bran and germ removed through the process of milling. White rice consists of just the endosperm layer, and it is almost entirely composed of starch. White rice grain consists of about 90% carbohydrate, 8% protein, and 2% fat but is low in fiber. Most of the available carbohydrate in rice grain is starch, which is broken down into glucose by enzymes in the human body to provide energy. There are two types of starch in rice grain: amylose and amylopectin, and they are shown in Figure 10.6. Both amylose and amylopectin are large carbohydrate polymers made of glucose molecules. The difference between them is that amylose has a straight chain, while amylopectin is highly branched. These are very large polymeric molecules, made up of a high number and/or a great variety of monosaccharides, and known as polysaccharides. Polysaccharides are a major source of metabolic energy, both for plants and for those animals, which depend on plants for food. Polysaccharides are a component of the energy transport compound, ATP. Starch is also a homopolysaccharide and only very partially soluble in water. Starch is the substance in which plants store their reserves of carbohydrate and is typically found in bulbs, tubers, and seeds. The main commercial sources of starch are found particularly in rice, and in wheat, maize, and potatoes. Starch is hydrolyzed and broken down in human metabolism to provide glucose.
Starch-Based Nanocarriers of Nutraceuticals: Synthesis and Applications
Raj K. Keservani, Anil K. Sharma, Rajesh K. Kesharwani in Nutraceuticals and Dietary Supplements, 2020
Starch is the main source of energy produced by photosynthesis in plants. It is found in nature as granular structures with dimensions ranging from 1 to 100 µm and with different morphologies. It is mainly composed of linear amylose and branched amylopectin molecules, polymers integrated into anhydrous glucose units (Kim et al., 2015). In the common native starch, amylose percentages vary between 72% and 82%, and amylopectin ranges between 18 and 28%. However, there are mutant starches such as high amylose (up to 70% and more for amilomaize) and low amylose (1% for waxy corn) contents (Bras and Dufresne, 2010). Amylose consists of linear molecules linked mainly by α-(1–4)-D-glycosidic bonds; however, it has now been established that some molecules are slightly branched by α-(1–6) bonds; amylopectin consists of branched chains formed by α-(1–6) bonds and with an average molar mass (Daltons) of up to hundreds of millions (Gul et al., 2016). The upgrowth of the microgranules starts in the hilum such as an onion-like structure with growth rings composed of crystalline and amorphous lamellae densely packed with a certain number of blocklets, with diameters of 20–500 nm (Kim et al., 2015). Concisely, considering a multiscale structure, there are the starch granules (1–100 µm) formed of growth rings (120–500 nm) composed of blocks (20–50 nm) made of amorphous and crystalline lamellae (9 nm) that contain amylopectin and amylose chains (0.1–1 nm) (Bras and Dufresne, 2010).
Dietary Fiber and Coronary Heart Disease
Robert E.C. Wildman, Richard S. Bruno in Handbook of Nutraceuticals and Functional Foods, 2019
Cellulose is known to be the most abundant organic molecule on Earth. The molecular structure is similar to amylose in that it is made up of repeating units of the hexose glucose. However, again, the linkages will be 1–4 in nature. Cellulose is produced as a component of the plant cell wall by an enzyme complex called cellulose synthase. Once cellulose chains are formed, they quickly assemble with other cellulose molecules and form microfibrils that strengthen the cell wall. Cellulose, along with certain other fibers (hemicellulose and pectin) and proteins, is found within the matrix between the cell wall layers. This concept is somewhat similar to connective tissue matrix found within bone, tendons, and ligaments in humans. Hemicellulose is different from cellulose in that its monomers are heterogeneous. Hemicellulose will contain varied amounts of pentose and hexose covalently bound in a 1–4 linkage, as well as some branching side chains. Some of the more common and familiar monosaccharides in hemicelluloses are xylose, mannose, and galactose (Figure 10.2). Other monosaccharide subunits include arabinose and 4-O-methyl glucuronic acids.
Amelioration of ethanol induced apoptotic DNA damage and ulcerative injuries in the mice gastric tissues by starch oral administration
Published in Toxicology Mechanisms and Methods, 2018
Sherin Ramadan Hamad, Hanan Ramadan Hamad Mohamed
Recently, there is a growing awareness that some of the compounds that naturally occur in plants have promising effects in the gastric ulcer treatment (Coşkun et al. 2004; Al-Bayaty et al. 2011; Rtibi et al. 2015; Mard et al. 2016). Starch (amylum) is a white, tasteless and odorless polysaccharide consisting of many glucose units joined by glycosidic bonds and produced by most green plants as energy store. This carbohydrate polymer consists of two molecule types including the linear and helical amylose and the branched amylopectin and represents the most common carbohydrate in human diets and present in large amounts in staple foods such as potatoes, wheat, maize (corn), rice and cassavais (Brown and Poon 2005). Starch has been shown to be a potent antioxidant by significant decreases in plasma thiobarbituric acid (TBA) reactive substances and significant increases in the activities of liver superoxide dismutase (SOD) and catalase (CAT) and the concentrations of serum and liver alpha-tocopherol in rats fed diet rich with starch (Hirao and Igarashi 2003).
Resistant starch, microbiome, and precision modulation
Published in Gut Microbes, 2021
Peter A. Dobranowski, Alain Stintzi
Starch is synthesized in the amyloplast and chloroplast organelles of plants, forming mixtures of amylose and amylopectin. These molecules both consist of chains of glucose subunits linked by α-1,4- and α-1,6-glycosidic bonds, but differ in their chain length (i.e. degree of polymerization; DP) and branching (α-1,6 bonds). Amylose possesses a DP below 6,300 glucose subunits, almost entirely (>99.3%) bonded by α-1,4-glycosidic linkages.16 Conversely, amylopectin forms much larger molecules (DP up to 26,500) with dense networks of short chains (mean DP 15–18) branching from longer chains (mean DP 48 to 60).16 The intra- and intermolecular interactions of amylose and amylopectin impart starch granules with a complex hierarchical structure (Figure 1).
Cassava toxicity, detoxification and its food applications: a review
Published in Toxin Reviews, 2021
Anil Panghal, Claudia Munezero, Paras Sharma, Navnidhi Chhikara
In cassava, majority of the starch is stored within amyloplasts in the thickened root. The starch content in roots varies from 73.7% to 84.9% on dry weight basis (Asaoka et al.1991). Amylose varies from 13.6 to 23.8% and amylopectin is about 83%. The content of soluble amylose (which is thought to be responsible for cohesiveness in cooked starch) of cassava was found in range from 10 to 40% of total amylose. Water absorption capacity and swelling power of starch are essential parameter for its viscosity and textural attributes in finished product. Cassava starch has good potential as food industry base product due to its high viscosity, low tendency for retrogradation, low gelatinization temperature, and also the absence of the undesirable flavors found in many cereal starches (Demiate and Kotovicz 2011). The starch obtained from fresh roots is having more swelling power than the one obtained from dried roots, therefore have better textural and viscosity attributes of finished products (Zhu 2015). Moreno and Gourdji (2015) reported that high rainfall leading to humid conditions results in sprouting causing the translocation of photoassimilates from the roots to the top and thus declining both dry matter and starch content of the roots.
Related Knowledge Centers
- Amylopectin
- Aromatic Compound
- Fatty Acid
- Glucose
- Glycosidic Bond
- Iodine
- Polysaccharide
- Resistant Starch
- Starch
- Nucleic Acid Double Helix