Week 5: Practical (Starch)

For our second practical, we did an experiment on the functions of starch as thickening agents and gelling agents in food. 

Starch is the major storage polysaccharide found in plants. Starches are found widely applied across the food and beverage industry. Starch selection will depend on its use and the specific requirements of the product including sensory properties, methods of manufacture, co-ingredient and shelf-life expectations (Murphy et al., 2009).

Starches consist of two types of molecules:

i) amylose (linear α-D-glucose) 

ii)amylopectin (branched α-D-glucose) 

Their compositions vary and are depending on the botanic origin (Kurakeke et al., 2009; Garcia-Alonso et al., 1999). 

Starches have the capacity to undergo the process of:

• gelatinization
• gel formation
• retrogradation
• dextrinization. 

The concentration and ratio of amylose and amylopectin in starch determines the degree to which these processes take place and determine the physicochemical properties of starch, such as pasting, gelatinization and retrogradation (Kurakake, et al., 2009; Thitipraphunkul, 2003). These physicochemical properties are important in improving quality of end product in term of firmer texture, freeze-thaw stability, and mouth feel.

The main function of starch in pudding is to work as gelling agents, maintain texture consistency (from loose and watery to creamy or form gel). They work by absorbing water (or other cooking liquid) into individual starch grains and the cross-bonding between the starch molecules to form a gel structure. The water holding ability is greatly related to the ratio of amylose-amylopectin in starch granules while amylose starch exhibits much cross-bonding.

Starch is used as thickening agents in sauce making. Chili sauce is a homogenously blend of chili pulp, seeds and other ingredients intended for use as a seasoning or condiment. The process of swelling is essential to achieve the correct viscosity and desired characteristic of chili sauce. Different starches will contribute varying degree of thickening power and translucency to starch pastes. To use the various starches to best advantage, it is necessary to be familiar with the characteristics of each type.