= Solution
\b[<Starch granules> can often be distinguished by their shape, size distribution, hilum and lamellae; <dextrin> and <inulin> are distinguished chiefly by their molecular constitution, solubility and chemical reactions.] An isolated particle of uncertain origin cannot always be identified uniquely by one feature.
In a <water>-mounted preparation of unheated <starch>, potato granules are usually relatively large, oval or pear-shaped, often with an eccentric hilum near the narrower end and conspicuous curved growth markings. Wheat gives a characteristic mixture of larger flattened lenticular granules and small rounded granules; the hilum and rings are less conspicuous. Rice <starch> consists of very small angular or polyhedral granules, often still associated into compound groups. These are distributions rather than a guarantee that every potato granule is larger than every wheat granule.<Starches in The International Pharmacopoeia>[Microscopic identification: potato, wheat and rice granule shape, hilum and striations]{ref}
Maize commonly gives polygonal or rounded granules with a central point or fissured hilum; oats characteristically include aggregates of small angular granules. Arrowroot commonly has oval or elongated granules, sometimes with a transverse fissure towards one end. Preparation, variety and processing change the apparent population. Rotation between crossed polarizers shows the organized granule structure through a characteristic extinction cross in many intact granules. Swelling and loss of birefringence on heating with sufficient <water> help demonstrate <starch gelatinization>, although the precise <temperature> depends on the <starch> source.
Cold <water> normally leaves native <starch granules> as a suspension rather than a clear molecular solution. On heating, granules swell and a paste develops. With <iodine> in iodide solution, ordinary <starch> rich in sufficiently long <amylose> helices produces an intense blue or blue-black complex. Its intensity depends on chain structure and conditions; the response can weaken on heating and return on cooling if the chains remain suitable. Continued acid or enzymatic <hydrolysis> shortens chains and eventually destroys this characteristic blue response.
<Dextrin> denotes a range of shorter or modified <glucose> polymers derived from <starch>, rather than one pure substance. Many preparations dissolve or disperse in <water> more readily and no longer show intact native granules. Their <iodine> reactions vary with chain length: some give violet or reddish-brown colours, while extensively shortened material gives no characteristic colour. It is therefore too absolute to say that every <dextrin> is chemically identical or that no <dextrin> can react with <iodine>. The modern international specifications themselves distinguish <starch> modifications and their variable <iodine> colours.<Dextrins in MeSH>[Definition: mixtures of glucose polymers produced by starch or glycogen hydrolysis]{ref}<Modified Starches: Specifications by the Joint FAO and WHO Expert Committee on Food Additives>[Identification; iodine colours and hydrolysis test in the specifications summary]{ref}
<Inulin> is principally a <fructose>-based <fructan>, with a different linkage pattern from <glucose>-based <starch>. It occurs, for example, in chicory and related storage organs. It does not give <starch>'s blue <iodine> complex. It dissolves more readily in hot <water>, and may separate as deposits on cooling or precipitation, but such deposits are not the characteristic native <starch granules>. <Hydrolysis> yields mainly <fructose>, whereas complete <starch> or <dextrin> <hydrolysis> yields <glucose>. A copper-reduction test after <hydrolysis> detects reducing products in both cases and is therefore insufficient by itself to distinguish them. Their different <hydrolysis> products, interpreted with <iodine> reaction and <microscopy>, give a more specific comparison.<Inulin in ChEBI>[CHEBI:15443: beta-(2→1)-fructan identity]{ref}
A sound comparison uses separately labelled reference preparations, equal <iodine> conditions and separate unheated and heated mounts. Inspecting an unknown mixture only after boiling destroys much of the morphological evidence. The combined observations distinguish source-related morphology from the effects of processing.
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