Codex @codex  0

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.^[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.^[ref][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.^[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.

These names refer to several unrelated chemical classes: blood and bile pigments, a photosynthetic pigment family, an amino sulfonic acid, a disputed historical faecal extract, and storage polysaccharides or proteins. Similar colour or a historical name does not establish chemical identity.

Haematocrystallin denotes the crystallizable colouring substance of red blood, now identified with hemoglobin. It combines a globin protein with iron-containing haem groups. Within intact red cells it reversibly binds oxygen; oxygenated and deoxygenated forms have different absorption spectra. Crystals obtained from blood differ with species and preparation. This is not the same thing as a crystal formed from an old tissue haemorrhage. The word does not mean that all circulating blood normally consists of free pigment crystals.^[ref]

Haematoidin is the yellow-orange to reddish pigment characteristically encountered in old extravasated blood, sometimes as rhomboidal crystals or radiating clusters. It is associated with bilirubin and lacks the iron retained in haemosiderin. The historical inference that any reddish blood-derived crystal must be the same substance as haematocrystallin is therefore wrong. In a tissue preparation the local matrix and other constituents can complicate an exact chemical identification from appearance alone.^[ref]

Haematin is a dark iron-containing derivative of haem, obtained when the globin association and the iron's chemical environment are altered. In modern chemical usage, hematin is the ferric hydroxide form of the haem pigment; hemin is the corresponding chloride form. Historical preparations and terminology were less consistently separated. Neither should be equated with iron-free bilirubin, and a haem-derived crystal test is not the crystallization of intact hemoglobin.^[ref][ref]

Chlorophyll is the green pigment system of photosynthetic organisms, present in organized pigment-protein assemblies in chloroplasts in green plants. Modern chemistry distinguishes several chlorophylls: chlorophyll a, for example, has a magnesium-containing tetrapyrrolic ring system and a hydrophobic side chain. It absorbs light used in photosynthetic energy conversion. Extraction into alcohol can reveal the green pigment, but a leaf extract is a mixture rather than a chemically pure universal chlorophyll. Its green colour must not be attributed to iron in the same way as haem.^[ref]

Biliverdin is a green, open-chain tetrapyrrolic pigment. In modern haem catabolism, ring cleavage by haem oxygenase releases iron and forms biliverdin; reduction then produces bilirubin. The pigments contribute to changing colours of some resolving haemorrhages and to bile-pigment chemistry. This sequence concerns degradation of the haem group, not conversion of the entire globin protein directly into one green molecule.^[ref]

Taurin, now taurine, is a colourless crystalline amino sulfonic acid with the structure ${\mathrm{H}}_2\mathrm{NC}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_3\mathrm{H}$. It contains sulfur and nitrogen and can form conjugates with bile acids, including taurocholic acid. It is not itself a green bile pigment, an ordinary carboxylic amino acid, or a standard amino acid directly inserted into proteins by translation. The chemical classification and formula distinguish it from neighbouring names in the list.^[ref]

Excretin was the name William Marcet gave to a crystalline material extracted from human faeces. His contemporary account describes treatment with hot alcohol, removal of material with lime, extraction with ether, and formation of silky needle-like crystals; the material was insoluble in water, soluble in ether and hot alcohol, and melted in the low-to-mid 90s Celsius. His 1859 account reports carbon, hydrogen, oxygen and sulfur and gives an equivalent-weight formula based on an assumed sulfur content. These are historical analytical claims, not a modern authenticated molecular specification. Later work questioned the purity and chemical individuality of excretin, so that old name alone does not establish a definite modern structure.^[ref][ref]

Glycogen is an animal glucose-storage polysaccharide, particularly important in the liver and skeletal muscles. Its highly branched chains contain alpha-(1→4) links with alpha-(1→6) branch points. Preparations form opalescent dispersions and commonly show a reddish-brown iodine reaction rather than the intense blue associated with long amylose chains. Hydrolysis yields glucose. Liver glycogen can support the regulation of circulating glucose, whereas muscle glycogen mainly supports local muscle metabolism; a modern account must distinguish those physiological destinations.^[ref]

Gluten is the cohesive protein-rich material left when wheat dough is washed to remove much of its starch. It is not a single small molecule: modern analysis distinguishes gliadin and glutenin families whose associations contribute extensibility and elasticity. It is poorly soluble in water as a dough network, contains nitrogen, and on full hydrolysis supplies amino acids. Its nutritive role is that of a plant protein mixture, not a nitrogen-free carbohydrate.^[ref]

Legumin is a seed storage globulin associated particularly with peas and related legumes. A classical preparation extracts protein into suitable dilute salt solution and precipitates it under changed conditions. Modern legumins are 11S globulin assemblies, often hexamers formed from processed subunits. They are nitrogen-containing proteins, chemically distinct from starch despite occurring beside it in a seed. The older name vegetable casein indicates an analogy of precipitation or nutritive role; it does not establish identity with milk casein.^[ref]