FST 1800 Fundamentals of Food and Sensory Science
Report 2: Starch
Introduction:
Starch is the primary source of energy which is important to humans. It is essential for daily
diet and can be found in many different foods from green plants, fruits, seeds, roots and
tubers.
Starch granules are composed of two types of polysaccharides which are amylose and
amylopectin that are made up of monomer, glucose. Amylose is a linear fraction whereas
amylopectin is a branched-out fraction. Both polysaccharides contain 1,4-α-glycosidic
linkages, whereas amylopectin has an extra linkage which is 1,6-α-glycosidic linkages which
results in the branching of molecule. Starch granules are hydrophilic in nature and consist of
strong intermolecular interaction due to hydrogen bonding formed by the –OH group on the
granule surface (Pokhrel, 2015)
When uncooked starch granules are in the presence of water, it is not soluble. When starch is
in an uncooked state, any uptake of water is reversible by drying the starch granules. Before
cooking, starch granules are not vulnerable to shear damage in their raw, unswollen form.
Moreover, under a polarised light, Maltese cross formation, and birefringence will be
presence in the starch granules. However, when starch granules are heated in the presence of
water, it will undergo a process called gelatinization. As heating is continued, the starch
granules take up more water known as water imbibition, however it is irreversible, and swells
and some short chain of amylose is leached out of the granules (Vaclavik & Christian, 2018).
When overheated, the granules will rupture which causes spilling of the contents into the
solution. This causes the liquid to be thickened and act as a good thickening agent. Upon
cooling, the gelatinized starch attempts to reorganise itself by creating new bonds to retain
the water absorbed during swelling. The starch crystalline structure is disrupted in a
amorphous state and thicken up the starch solution.
The water that was coating the starch molecule which will then weep out of the Gel is known
as Retrogradation. It is linear and is stacked closely together to make many starch-starch
hydrogen bonds. Amylose is very prone to retrogradation compared to amylopectin. The
shear refers to the breakdown of swollen starch granules. The starch shear is caused by shear
tension that accumulated during the retrogradation process and the gel drying process of
gelatinized starch. (Omeregie, 2019). Furthermore, syneresis is the discharge of water during
retrogradation. Syneresis occurs when water is leached out of the starch and starch gel starts
to shrink. When gels are exposed to protein, they become more susceptible to syneresis (Mu,
Sun, Chang & Wang, 2017).
The aim of this experiment was to investigate starch in different types of food and to
investigate the microscopic appearances of raw and cooked starch.
Materials:
Part A: Identify starch in food
