Uses of Waste Starch - The Economic Utilisation of Food Co-Products - page 68

defective blocklets. These are also postulated to occur where there are
surface pores.
Growth rings can be seen in large starch granules with a light microscope.
The blocklets can also be seen using the same technique after partial hydrolyses.
From the growth ring pattern it is thought that the initial growth of the granule
starts at the hilum (centre of granule), which contains the reducing ends of the
amylose and amylopectin, and is packed in a less-organised manner than the
rest of the granule. The continuing growth of the granule occurs with amylose
and amylopectin chains radiating outwards to the surface, allowing further
glucose residues to be deposited, leading to the continued growth of the starch
molecules. The formation of growth rings in the development of the granule
suggests that the starch material is deposited in a diurnal rhythm, as the granule
increases in size.
The interaction between amylose and amylopectin in the granule is an area of
great debate, as there are many aspects that are not fully understood.
Generally, it is thought that the majority of amylose within the granule acts as a
separate entity to the rest of the molecules. This is especially the case for shorter
amylose molecules near the periphery of the granule that can leach out of the
granule during the gelatinisation process. However, long-chain amylose present
can form amylose-lipid inclusion complexes, double-helical structures with
other amylose molecules or with amylopectin chains, or even single-helical-type
structures. 6 This interaction with the amylopectin clusters increases the size of
the crystalline regions but, by doing so it affects the packing eciency of the
amylopectin chains. 17 Two mechanisms have been proposed to explain this
occurrence. 1.) The crystallisation of amylose and amylopectin (see Figure 5.3),
suggests that increasing amylose content in A-type crystallinity may result in
interference of the packing of the mesogens. 26 2.) The interaction of the
amylopectin branch points in the amorphous regions of the cluster with
amylose. This will strain the main amylopectin C chain disrupting the
crystalline packing of the A chains.

d n 9 r 3 n g | 0

3 .

5.3 Applications of Starch

5.3.1 Starch Adhesives
5.3.1.1 Background
The earliest known records of starch adhesives being used was for bonding
papyrus strips by Egyptians nearly 6000 years ago. Starch is still currently used,
but to a lesser extent than dextrins. These were supposedly serendipitously
discovered in a fire in Dublin where the partially burned starch, ''pyrodextrin''
was discovered. This brown sticky compound, with lower molecular weight
compared to that of starch, can be pasted at higher concentrations, and hence
dries more quickly, gives faster tack (resistance to separation of two materials
brought momentarily into contact), and consequently increased production
rates when used for attaching bottle labels, etc. 27,28