Abstract
Indonesia has many local starch sources, including rice, taro, arrowroot, sago, corn, konjac, cassava, and elephant foot yam (suweg). Several uses of natural starch have been widely used as the primary raw material or as a food additive. Natural starch generally has some drawbacks limiting its use, such as color, solubility index, retrogradation, and paste stability. Starch modification is needed to improve these limitations. Starch modification is carried out physically and chemically. In this chapter, the authors will discuss the physical and chemical characteristics of several local Indonesian starches, both natural and modified, and their potential to be developed as food ingredients.
TopIntroduction
Starch is a carbohydrate polymer used as the primary source of calories for consumption. Apart from being used as a food ingredient, starch may act as a gelling agent, thickener, foam and emulsion stabilizer, battered and breaded, binder, crispy texture maker, clouding stabilizer, and flavor encapsulant. Starch could also be employed in the paper, textile, and pharmaceutical industries. Various plant sources of starch, such as rice, taro, arrowroot, sago, corn, konjac, cassava, and elephant foot yam (suweg), are growing a lot in Indonesia. They respectively produce starch with different properties. This chapter reviews the physicochemical characterization of several Indonesian starch plants and their roles in controlling food processing. The scientific information from this chapter is expected to enrich the study of starch sources worldwide.
Rice (Oryza sativa)
Rice is a carbohydrate source and a staple food for most Indonesians. Rice is mainly consumed as cooked polished grains, whereas rice flour is used as an ingredient in many Indonesian cuisines. Starch is the most significant component in rice grains and determines the quality of rice products. The starch content in rice is in the range of 80% (Hasjim et al., 2013).
Gelatinization characteristic is considered one of the essential properties in evaluating rice starch properties. In particular, gelatinization is the most crucial rheological indicator of the quality characteristics of rice cooking and processing. Amylose content and branch chain length distribution have also been found to impact rice starch's swelling and pasting properties substantially. Rice starch granules with high amylose content act as swelling inhibitors. Amylopectin contributes to swelling, while amylose and amylose-lipid complex inhibit swelling. In addition, low swelling levels and solubility tend to increase with the increasing temperature of amylose molecules in rice. Studies show that a higher level of long chain amylopectin in rice starch is associated with firmer rice after cooking. Retrogradation was also found higher in rice starch with a longer amylopectin chain (Yoon et al., 2012).
Taro (Colocasia esculenta)
Taro has a starch content of about 80%. The characteristics of taro starch have been evaluated based on swelling power and solubility index. The swelling behavior of starch can be influenced by amylose and amylopectin compositions. According to Aboubakar et al. (2008), the swelling power of taro starch will increase along with starch cooking level, indicated by an increase in Water Absorption Capacity (WAC). Temperature increase led to a significant increase in WAC to a maximum of 60–70 ºC, from which they decreased.
At 20°C, taro starch shows lower solubility and forms only a temporary suspension when stirred in water. Minimal solubility of starch at low temperatures is associated with starch semi-crystalline structure due to the hydrogen bonds formed between hydroxyl groups of starch molecules. At higher heating temperatures, taro starch solubility will increase and make it highly digestible, which is used to prepare various foods. The concept of increasing solubility while the starch granule breakdown causes heating starch in water, exposure to hydrophilic groups, and leaching of amylose (Himeda et al., 2012).
Key Terms in this Chapter
Gelatinization: A process of breaking down the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites to engage more water.
Amylopectin: A polymer of alpha-glucose units and linked linearly with a-l,4 glycosidic linkages, as well as a-l,6 glycosidic linkages occurring at intervals of 24 to 30 glucose subunits.
Starch viscosity: The thickness, or resistance to shear, agitation or flow of starch. Measuring the viscosity of starches gives a direct assessment of their processability in terms of pumping and mixing.
Swelling power: The ability of starch granule to inflate due to weakened hydrogen bond during the heating process causes water hydration.
Pregelatinized: Physical modification of starches which are accomplished by heating and by mechanical shearing resulting in cold-water-swelling capacity.
Amylose: A straight linear chain of glucose molecules linked by a-l,4 glycosidic linkages.
Solubility: The ability of a substance, the solute, to form a solution with another substance, the solvent.
Starch: A carbohydrate polymer consisting of two types of polysaccharides: amylose and amylopectin
Retrogradation: A process in which disaggregated amylose and amylopectin chains in a gelatinized starch paste reassociate to form more ordered structures.