**2. Corn starch**

Corn is one of the staple foods and is used as an industrial by-product. The corn grain comes from the independent fruit called caryopsis that is inserted in the cylindrical rachis "ear", each grain or seed is limited by the number of grains per row and rows per ear. The pericarp (wall of the ovary) and testa (seed coat) join to form the wall of the ear. The corn kernel is made up of 3 main parts: "embryo", "endosperm" and "wall of the fruit". The amount of kernels produced on each ear and the number of ears that grow is generally confirmed when pollinating [3, 4]. In addition to the different derivatives of corn such as corn oil, gluten, syrup, dextrose, ethanol among others. Corn starch provides ideal characteristics for various industrial applications in the textile, food, pharmaceutical, construction fields, among others. It is composed mainly of amylose/amylopectin in different proportions and polymeric organizations. These two components of starch represent approximately ≥99% of starch by dry weight. Commonly the conformation is 75% amylopectin and 25% amylose. The polymeric structure of amylopectin provides the morphology of the granule. Amylopectin is made up of -D-glucopyranosyl chains, which are highly branched and the chains are connected to each other by 1,4 bonds, with almost 6% of 1,6 bonds forming branch points. Amylose is found in small amounts compared to amylopectin. It is an unbranched unit with 1,4-linked glucopyranosyl units, although it does not have branches, but there are some molecules that are slightly branched with 1,6-linkages. Amylopectin is the main molecule that causes the various changes on the physicochemical properties of the starch granule, changing the rheological, hygroscopic, retrogradation and leaching properties of amylose, generating new structural conformations, glass transition and maximum viscosity. On the other hand, amylose (leaching) also has a directly proportional effect on the changes that amylopectin presents, due to the response factors applied to starch [5].

Starch in the native state (without amylose/amylopectin structural modification) is available as a reserve carbohydrate in many parts of plants, including roots, tubers, cereals, and seeds. **Figure 1** presents a proposed scheme on the biosynthesis of corn starch. In general, the main enzymes for starch biosynthesis include mainly ADP-glucose pyrophosphorylases (AGPases), granule-bound starch synthases (GBSS), soluble starch synthases (SS), starch branching enzymes (BE) and starch debranching enzymes (DBE). AGPase catalyzes the first step reaction of starch biosynthesis by converting glucose 1-phosphate (Glc-1-P) and ATP to ADP-Glc and inorganic pyrophosphate (PPi) in amyloplasts. GBSS and SSS are responsible for synthesizing amylose and amylopectin, respectively. SBE introduces a branched structure by cleaving the internal chains of α-1,4-glucan and transferring the chain

*Advances and Trends in the Physicochemical Properties of Corn Starch Blends DOI: http://dx.doi.org/10.5772/intechopen.101041*

**Figure 1.** *Corn starch biosynthesis scheme.*

segment of six or more glucose units to the C6 position of a glucosyl residue of another glucan chain. DBEs, through their α-1,6-hydrolytic activity, act on highly branched pre-amylopectin, generating polymodal distributed end chains of amylopectin. However, recent research has shown that by modifying the plant gene, variations in the content, distribution, size and polymeric organization of amylose and amylopectin are obtained [6–8]. AGPase catalyzes the first key regulatory step in the starch biosynthetic pathways present in all higher plants that produce ADP-Glc and pyrophosphate (PPi) from Glc-1-P and ATP. Plant AGPases exist as a heterotetramer (α2β2) composed of two large (LSU) and two small (SSU) subunits with slightly different molecular masses [9, 10]. SSUs are responsible for the catalytic activity of the enzyme complex, while LSU is believed to modulate enzymatic regulatory properties that increase the allosteric response of SSU to 3-phosphoglyceric acid (3-PGA) and inorganic phosphate (Pi) [9, 11]. AGPase activity is localized to both plastids and the endosperm cytosol of cereals, in contrast to other plant species where it has been reported to occur only in plastids [12]. In a previously reported subcellular fractionation experiment using corn endosperm, the highest AGPase activity was detected in the cytosol [13]. Furthermore, the genes responsible for the shrunk2 and brittle2 starch-deficient maize kernel phenotypes encode the endospermspecific cytosolic LSU and SSU isoforms, respectively [14, 15]. This information is an indicator that plastid AGPase, by itself, is not sufficient to support normal starch biosynthesis processes in cereal endosperm, therefore, some researchers suggest that it is possible that plastid starch phosphorylase (Pho1) play an important role in the formation of primers to complete starch biosynthesis in the endosperm. Recent advances still trying to understand the functions of individual enzyme isoforms have provided new insights into how linear polymer chains (amylose) and branched bonds (amylopectin) are synthesized in cereals. Let us remember that both polysaccharides are made up of D-glucose chains linked by α (1–4) bonds. Amylose is essentially linear with α (1–4) bonds, while amylopectin is highly branched through α (1–6) bonds. Amylopectin forms type A and B polymorphic crystals that influence the arrangement of its double helices. Type A crystals produce relatively compact helices with a lower proportion of water, while type B crystals give rise to a more open structure containing a hydrated helical nucleus. X-ray diffraction studies allow us to know this type of crystal arrangements [16]. These conformations will always be different depending on the type of botanical source (TFB), as well as the enzymes involved in the formation of amylose and amylopectin.

The functional and physicochemical properties of corn starch are influenced by the amylose/amylopectin ratio, its chain length distribution and the presence of complexes in lower proportions with lipids/proteins. In its native form, corn starch has limited applications due to its low resistance to extreme processing conditions, shear, insolubility to water at room temperature, hygroscopicity among others, which are frequently found in the industry. Therefore, at present various modification techniques have been implemented that can be achieved by enzymatic, genetic, chemical, physical methods or a combination of some of these methods, which will allow a modification, mainly on the structure of amylopectin to obtain a functional starch that can overcome deficiencies and increase its usefulness for various industrial applications [17].

### **3. Starch blends**

The use of different techniques to modify the polymeric structure of starch unfortunately have disadvantages, it can have high costs due to the use of reagents, some processes take long periods of time, low yields can generate residues that

could affect the environment. Therefore, the proposals to use starch blends that promote new physicochemical characteristics that can replace conventional methods, trends that are diversifying unique properties by combining starches from different botanical sources [18]. Physical treatments are considered ecological friendly to the environment due to the absence of chemical agents and/or concentrated alkaline/acid solutions. It's essential to know the physicochemical properties of each starch to obtain the best combination in order to focus on the application, innovation or continuous improvement of some industrial type product.
