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Starch in Food Applications

Amit Paul1, Victor Roychowdhury1, and Santanu Ghosh2

1JIS University, Department of Pharmaceutical Technology, 81, Nilganj Road, Agarpara, Kolkata 700109, West Bengal, India

2Department of Pharmaceutical Sciences & Technology, Birla Institute of Technology, Mesra, Ranchi 835215, Jharkhand, India

1.1 Introduction

Starch is a branched homopolysaccharide consisting of D-glucose units as its building blocks. Moreover, starch consists of two polyglucans: amylose and amylopectin. In amylose, D-glucose units are connected to each other by a-1, 4 glycosidic linkages, while amylopectin is a highly branched polymer of D-glucose comprising a-1, 4 glycosidic linkages at the linear chains and a-1, 6 glycosidic linkages at the branching points [1, p. 7011]. Generally, starches constitute 20-30% amylose and 70-80% amylopectin in their structure. The branched chain length varies depending on the type of starch. The structural components of starch, i.e. amylose and amylopectin, are deposited in distinct granules in amyloplasts of plants' storage organs. These granules could be of various sizes and forms, like it could be disk or spherical, as in case of Triticeae family's starch granules [2, pp. 1003-1017]. According to their size, starch granules are categorized as A, B, and C type.

Starch-based foods are an abundant source of energy and are frequently used as the main diet by people all over the communities due to their widespread availability and low cost [3, pp. 513-523]. Starch is widely used in food industries not only due to its nutritional values [4, p. e0228624] but also to manage the homogeneity, stability, and texture of foods. Moreover, it is used to prevent gel disintegration during processing and to enhance the shelf life of foods [5, pp. 1-26]. Despite of its wide use in food-manufacturing sectors, it showed its promise in diverse fields like health and medicine, textiles, paper, fine chemicals, petroleum engineering, agriculture, and construction engineering [6, p. 13]. Pure starch is a white, tasteless, and odorless powder that is insoluble in cold water or alcohol. Starch can be obtained from various sources like roots, tubers, and seeds of plant. Most readily available starches are now derived from tapioca, potatoes, maize, rice, wheat, and other sources [7]. It is estimated that by 2026, the global starch market will reach 160.3 million metric tons. It is due to the rapid development of the food processing industries, along with the increasing demand for starch-based adhesives in commercial settings.

Native form of starch is rarely used in food industries due to its poor cold-water solubility, susceptibility to freeze-thawing, shear pressure, pH change, and proneness to retrogradation, demanding structural modification to overcome these limitations. Modification techniques can significantly improve the properties of native starch by improving its physicochemical attributes and structural aspects, as well as increasing its technical value [8]. Such modifications are generally done by enzymatic, physical, or chemical means. Physical modifications (ultra-high-pressure treatment, heat-moisture treatment [HMT], and freezing) are comparably simple and cost-effective than chemical modifications (esterification, acid treatment, etherification, and cross-linking) used to introduce desired functional groups into the native structure of starch molecules [9, pp. 299-312]. Nowadays, considering more greener approach, enzymatic modification techniques have been employed as an alternative to physical and chemical approaches as they are more eco-friendly and healthier than other techniques [10, pp. 278-321]. In the baking sector of food industries, enzymatic modification has a significant impact, as enzymes could react with carbohydrates to render more desirable derivatives [9, pp. 299-312]. Oxidoreductases, like lipoxygenase and glucose oxidase, and hydrolases like, amylases and proteases, are the most common enzymes employed in bakeries. Therefore, in the present chapter, we discussed about the native starch, different modifications of starches, and their applications in the food industries.

1.2 Natural Starch

Being a calorie-rich food component, starch is used around the globe. Moreover, it offers organoleptic properties by aiding the crispness when used as an ingredient in food products. Broadly starch could be used in its two forms i.e. native and modified form. Native starch could be obtained from abundant natural resources, while modified form is achieved through different modification techniques to meet industrial requirements, which are discussed later in this chapter. The characteristics of the native starch largely depend on the source from where it is extracted. The demand for native starch obtained from natural sources is high due to its easy availability and low production cost. Here, we discussed about some commonly used natural starches, i.e. corn, potato, wheat, and tapioca starch [11, pp. 103-165].

1.2.1 Corn Starch

Corn starch is also commonly known as maize starch. It is observed that around 80% of the world's commercial production of starch is corn or maize starch. This is the most abundantly used starch. Corn or maize starch is isolated from corn kernels. The kernel itself contains about 64% to 80% starch. The isolation of starch from the kernels is done by the wet-milling process. Corn starches are used in various products and have a wide range of applications not only in food industries but also in several other sectors. In corn starch, the protein content is about 0.35%, lipid content is about 0.8%, very less little of ash is present, and two polysaccharides: amylose and amylopectin are present in large amounts (about >98%). All natural starches are found in the form of granules that are insoluble in water at room temperature. It is also observed that natural starch granules obtained vary in size and shape. The size of the starch granules varies from 2 to 30 µm [12, pp. 537-549]. Corn starch is commonly found as a white, tasteless, and odorless powder. Corn starch finds its application in papermaking, food processing, manufacturing of industrial adhesives, and as a lubricant in surgical gloves. It is also used as a component in many cosmetics and oral pharmaceutical products [13, pp. 11-14].

The granular nature of corn starch and the partially crystalline nature of their granules are important. These nature of the corn starch helps in many ways. This nature of the starch granules makes them useful for physical and chemical modifications. It is seen that when corn starch granules are added to aqueous systems, they readily absorb water and become hydrated. If the temperature of the aqueous system, in which the hydrated granules are immersed is increased, significant changes could be observed. The water of hydration first disrupts the hydrogen bonds in the amorphous regions of the granules. This results in swelling of the granules, which ultimately changes their shape and makes them more of a spherical one. If the temperature is continuously increased, it will lead to increased hydration and swelling in the amorphous regions [12, pp. 537-549]. The irreversible disruption of amorphous and crystalline structures in the starch granules is called gelatinization. Some dissolved starch polysaccharide molecules, primarily amylase, leaches from the swollen granules during gelatinization.

A process called pasting is achieved by heating starch granules with some shear in excess water. This process leads to further granule swelling, leaching of polymer molecules (mainly amylose), and granule disruption (since swollen granules are fragile). This results in a hot starch paste. Again, cooling the hot paste results in the formation of a gel [12, pp. 537-549]. It should be noted that inhalation of corn starch can cause lung damage [14, pp. 767-769]. A substitute for talcum powder that contains corn starch powder was found to result in severe pneumonitis among infants [15, pp. 108-110].

1.2.2 Potato Starch

Potato starch comprises 70-85% of the dry matter, providing food and energy for a considerable portion of the world's population. However, potato starch also has a number of useful applications outside of food and nutrition [16, pp. 2588-2612]. Essentially, potato starch is made up of two a-(1,4)-D-glucose monomers: amylose, a polymer with an extremely shallow branching, and amylopectin, a polymer with a very steep branching. Along with polysaccharides, proteins, lipids, and minerals are the other components of potato starch [17, pp. 979-988].

Potato starch and its derivatives have properties, such as low temperature of gelatinization and a high sticky consistency. Potato starch is commonly used in the food industries because of its excellent clarity and neutral flavor. Potato starch also finds its importance in the paper and textile industries. The large granule size of potato starch is preferred as a precoat on filters [18, pp. 511-539]. Potato starch is effectively used in puddings. When cold milk is added to the starch, it quickly dissolves and forms a gel. Potato starch is also used as a thickening agent...