German University Bangladesh

Abstract

Starch, a polymer of sugars in plants, is widely used in various industries due to its properties. It is synthesized through ADP-glucose formation and enzyme-mediated processes. Starch is formed during the day and broken down into sugars at night, which are then transported and converted back to starch in storage tissues. This review explores starch metabolism pathways and its role in the food industry, providing valuable insights on energy storage in plants.

Keywords

Starch Metabolism, Gelatinization, Retrogradation, Starch Biosynthesis, Starch Degradation

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1. Introduction

Starch has been many years commonly employed in human day-to-day life. Egyptians cooked wheat flour paste with diluted vinegar to strengthen strips of papyrus, whereas in prehistoric Chinese booklets were first layered with a high fluidity starch to deliver resistance to ink penetration, then engulfed with pulverized starch to offer weight and thickness [1] [2] . Starch is a white soft formless powder, tasteless, and odorless, it is insoluble in water, ether and alcohol and it is a non-reducing carbohydrate [3] [4] . From a labelling perspective, starches is mainly classified into two clusters, such as native and modified. Native starches are manufactured via the extraction of naturally occurring starch from grain or root crops (including corn, potato, rice, cassava, and tapioca) and can be employed directly in making specific foods, including noodles; while modified starch is made from the native starch through either chemical or physical modifications [5] .

The modification of starch is done to increase its functionality (e.g. its capacity to tolerate low pH environments and high temperatures during processing); starch modification is an important process as native starches are habitually not process friendly [1] [5] - [10] . Native starches are regarded clean label constituents, while chemically altered starches have an E number title and are not recognized as natural [5] . The physical modification of native starches is used to make them as useful as their chemically altered equivalents, thus maintaining the label affirmation native which gives them a lucrative benefit. Apart from its carbohydrates content, starch granules normally hold 10% - 20% moisture and minorquantities of proteins, lipids and traces of inorganic materials [5] .

The moisture content of starch foodstuffs depends on the relative humidity (RH) of the atmosphere in which they have been stored. At RH zero, the moisture content of starches is near zero while at RH 20 %, the moisture content of all starches is about 5% - 6% (w/w). Standard water of hydration in starch granules is positioned on carbon 6 of the glucose units. Starches of potato tuber and tapioca root contain a very small amounts of lipids of nearly 0.1%contrast to the cereal starches of maize, wheat, rice, and sorghum, which hold 0.8% - 1.0% lipids. The increase of fatty substances in cereal starches reduces their suitability for use in food products due to the tendency to increase the rancidity upon storage [5] [11] . The increased amounts of lipids in starch granules do not only cause rancidity upon storage but also can reduce the swelling power of starch paste [12] .

Starch has found to have different properties, most of which are associated to the temperature-dependent interactions of starch with water in the processes recognized as gelatinization, pasting, and retrogradation [13] . Starch gelatinization is linked with the interruption of granular structure making starch molecules to scatter in water and highly influences thickening and gelling of sauces and pastry fillings processes [14] [15] . Pasting properties refer to the variations in viscosity before, during, and after the process of gelatinization and during retrogradation [13] . Starch retrogradation on the other hand refers to the reassociation and recrystallization of amylose and amylopectin molecules upon cooling [13] [16] [17] [18] . Being renewable natural synthetic polymer, starch has been used in many industrial applications where it can be used in food industry, tissue engineering, drug delivery systems, and agriculture [4] .