starch microscopies

7/17/2019 Starch Microscopies

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Starch

Maize Starch in polarised light

Starch is a ubiquitous material in the plant world and is the means by which plants

store energy. We humans find it extremely useful also, and use it as food, as a food

thickener and for many other purposes. Examples include stiffening clothing, binding

tablet granules together and acting as a disintegrant in tablets. It has unusual

properties. Dry, it is a powder. It readily forms suspensions in cold water, but on

heating it gels and can be used as a thickener or as a type of glue. his ability to gel is

fundamental to its use in cooking. It is stained blue by iodine, although only in the

cold ! if you heat an iodine stained starch gel, there comes a point when the colour

"anishes. #nder the microscope, starch has a characteristic structure, which is best

obser"ed using crossed polarising filters. #nder these conditions, starch grains show a

characteristic $maltese cross$. Starch grains from different plants show different

shapes and si%es and this can be used as the basis for identification of the starch type.



Potato Starch

&ere is a picture of potato starch in polarised light. his image is to the same scale as

the mai%e starch at the top of this page and you can see that the two starches are "ery

different in si%e and shape.



'otato starch at higher magnification

in polarised light.

he drawing of potato starch abo"e is from (abe% &ogg)s book History of

the Microscope *th edition, +*-, and clearly shows the characteristics of potato starch, including features common to all starches the hilum and the

layers around this point that construct the grain. It is at this point that the

cross seen in polarised light has its centre. /elow is an image taken in

circular oblique lighting 01234, almost set to darkground, showing each

hilum as a bright spot.



Aspirin Dispersible tablet in water 5inally, for this section on potato starch, here is an image taken of an 6spirin

Dispersible tablet in water.

his effer"escent tablet used potato starch as a disintegrant. he small

particles are probably talc, which is used as a lubricant during tablet

compression.

Other Starches

&ere is a selection of other starches for comparison



Maize Starch showing polygonal grains and well defned hilum



Oat starch

he grains are "ery small and tend to occur in clumps



Wheat Starch7ounded separate grains



Sarsaparilla Starch(ust look at how it forms little balls of granules8

starch microscopies

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