Dried Pig Bile Powder: The ChP Specification Explained
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Dried pig bile powder is monographed in the Chinese Pharmacopoeia, and its assay rests on a single number: not less than 2.0% taurohyodeoxycholic acid, calculated on the dried substance. That marker choice is the detail most often missed, because older references to pig bile measure a different substance and quote a much larger figure.
This article sets out what the ChP specification requires, which checks exist only because the material comes from an animal, and what a buyer should be able to verify about source and traceability. It covers identity, quality parameters and documentation only — it makes no statement about physiological or traditional use.
What dried pig bile powder is
Dried pig bile powder is prepared from the bile of the pig, Sus scrofa domestica Brisson. The bile is filtered, dried and milled to a powder. It is a raw material rather than a purified substance: the powder contains the bile-acid conjugates of pig bile together with the other constituents that survive drying.
That distinction matters commercially. A buyer who needs a single defined molecule will buy the purified substance — hyodeoxycholic acid, or one of the other bile acids isolated from the same source. A buyer who needs the whole powder buys it against the pharmacopoeial monograph. The two are different products with different specifications, and a quotation that does not say which one is being offered has not answered the first question.
The ChP 2020 specification in one table
The Chinese Pharmacopoeia (2020 edition, part one) describes pig bile powder as follows. Where a value is deliberately not restated here, it is flagged rather than filled in.
| Item | Requirement |
|---|---|
| Source | Bile of Sus scrofa domestica Brisson, filtered, dried, milled |
| Appearance | Yellow to grey-yellow powder; faintly rank odour; bitter taste; readily absorbs moisture |
| Identification | Thin-layer chromatography against a hyodeoxycholic acid reference |
| Foreign organic matter | No plant tissue, animal tissue or starch visible under the microscope |
| Cattle bile / sheep bile | No spot corresponding to cattle or sheep bile reference material |
| Water | Not more than 10.0% |
| Assay marker | Taurohyodeoxycholic acid (C26H45NO6S) |
| Assay limit | Not less than 2.0%, calculated on the dried substance |
| Assay method | HPLC, UV detection at 200 nm; column 250 mm × 4.6 mm, octadecylsilyl silica gel |
| System suitability | Not fewer than 3,000 theoretical plates, calculated on the taurohyodeoxycholic acid peak |
| Storage | Sealed, protected from light, in a cool dry place |
Two of those lines are unusual among the materials a pharmaceutical buyer normally handles, and both are worth pausing on: the foreign-matter microscopic check, and the cattle-and-sheep-bile check. Both exist because the material is animal-derived and unrefined.
The assay, and why the marker is a conjugate
Pig bile powder is assayed on taurohyodeoxycholic acid — the taurine conjugate of hyodeoxycholic acid — and the limit is not less than 2.0% on the dried substance.
Some older or alternative references for pig bile measure hyodeoxycholic acid itself, and quote a figure nearer 16%. Those two numbers are not a disagreement about quality; they are an assay against a different marker. One counts the conjugated form of one bile acid, the other counts the free acid after hydrolysis. A certificate quoting a percentage for pig bile powder without naming the marker is therefore not comparable with any other certificate.
The first thing to check on a certificate
Not the number — the marker. A “2.0%” and a “16%” can both be correct for the same material, stated against different markers and different sample-preparation routes. Naming the marker resolves the apparent conflict in one word.
The method itself carries a detail worth knowing. Detection is at 200 nm, in the far ultraviolet, because taurohyodeoxycholic acid has no strong chromophore. The mobile phase is methanol and 0.03 mol/L sodium dihydrogen phosphate (70:30), adjusted to pH 4.4 with phosphoric acid. A method quoted without its wavelength and mobile phase is not reproducible, and a certificate that reports the result without the method cannot be checked.
Two checks that exist only because the material is animal-derived
Most pharmacopoeial specifications test a purified substance. This one tests a powdered animal material, and two of its checks only make sense in that context.
Foreign organic matter. The powder is dissolved in water, the insoluble residue is collected, and it is examined under the microscope. No plant tissue, animal tissue or starch may be present. The check exists because an unrefined animal material can carry plant or other tissue contamination through handling or adulteration, and because a powder's appearance alone will not reveal it.
Cattle bile and sheep bile. A thin-layer chromatography check compares the sample against cattle and sheep bile reference materials. No matching spot is permitted. This is an identity-and-purity check aimed at species substitution — the risk that bile from another species is blended with, or passed off as, pig bile. It is the pharmacopoeial expression of a question a buyer should be asking anyway: whose bile is this?
Neither check can be inferred from an assay result. A powder can meet the 2.0% marker and still fail either one, which is why both belong on the certificate and not only in the monograph.
Water content, and why the ceiling is 10.0%
Water is limited to not more than 10.0%, determined by the third method of the general water-determination procedure.
A 10.0% ceiling is high by the standards of a purified bile acid, where loss on drying is commonly held to 1% or 1.5%. The difference is not laxity; it reflects the material. Dried bile powder is hygroscopic and is not a single crystalline substance, so it holds water that a purified acid does not.
The practical consequence is a handling question. A powder specified at up to 10.0% water will gain moisture if it is opened in humid air, and the assay is calculated on the dried substance — so the reported figure and the delivered mass move in opposite directions as the material takes on water. Storage sealed and protected from light is not a formality here.
Source and traceability: the documents a compliant chain should produce
For any animal-derived material, the specification covers the substance and the source documentation covers the supply chain. The two are separate, and a compliant supplier should be able to produce both.
The framework below is what a buyer should be able to obtain. It is stated as a checklist rather than a description of any particular supplier, so it can be used to evaluate any source:
| Document or statement | What it should address |
|---|---|
| Species and material of origin | That the material is porcine bile, and where the animals were raised and slaughtered |
| Veterinary / quarantine documentation | Evidence the source animals passed the applicable inspection regime |
| TSE / BSE statement | A position on transmissible spongiform encephalopathy risk, appropriate to a porcine (non-ruminant) source |
| Traceability record | Batch-level link from the delivered lot back to the source material |
| Manufacturing and storage controls | How drying, milling and packaging are controlled to hold the 10.0% water limit |
| Certificate of analysis | The monograph items above, with methods stated |
Because these documents are specific to a supplier's chain, they should be requested as documents — not accepted as assurances. A supplier that cannot produce a batch-level traceability record is not describing the same product as one that can, whatever the certificate says about the powder itself.
Hyodeoxycholic acid: the purified substance from the same source
The pig bile acids that make up the powder are also supplied as purified substances. The one most closely associated with this source is hyodeoxycholic acid, a 3α,6α-dihydroxy bile acid that is characteristic of pig bile.
The 6α-hydroxyl is the structural marker of this molecule, and it is unusual: the more familiar bile acids carry their hydroxyls at 3, 7 and 12. That difference is what allows hyodeoxycholic acid to be distinguished from the human-type bile acids, and it is the reason the compound appears in the pharmacopoeia as a substance in its own right rather than only as a marker in a powder.
The distinction between the powder and the purified acid is the same distinction as between a raw material and a refined one: the powder is judged by the monograph above, the purified acid by its own specification, and a specification sheet should make clear which is being quoted. The general discipline of matching a certificate against the product it claims to describe is set out in how to verify a bile-acid supplier.
Questions buyers ask
What is the assay specification for dried pig bile powder?
Not less than 2.0% taurohyodeoxycholic acid, calculated on the dried substance, by HPLC under the Chinese Pharmacopoeia.
Why do some references quote about 16% for pig bile?
Because they measure a different marker — hyodeoxycholic acid itself, typically after hydrolysis — rather than the taurohyodeoxycholic acid the ChP 2020 assay uses. The two figures are not comparable.
What is the water limit?
Not more than 10.0%, which is high compared with a purified bile acid because the powder is hygroscopic and not crystalline.
Why does the monograph check for cattle and sheep bile?
To guard against species substitution. It is a thin-layer chromatography check that no cattle or sheep bile reference spot appears in the sample.
What is checked for foreign organic matter?
The water-insoluble residue is examined microscopically. No plant tissue, animal tissue or starch may be visible.
What is the difference between pig bile powder and hyodeoxycholic acid?
The powder is the dried raw material, assayed on a conjugate marker; hyodeoxycholic acid is the purified 3α,6α-dihydroxy bile acid isolated from the same source, with its own specification.
What to ask a supplier
Because the powder is a raw material, the questions that matter are about the source as much as the substance.
Ask which marker the assay figure is stated against, since the 2.0% and 16% figures circulating for pig bile describe different things. Ask for the foreign-matter and species checks as results, not as statements of compliance. Ask for the water result, and for how storage holds it. And ask for the source and traceability documents as documents, since those are what a certificate alone cannot evidence.
The wider context for animal-derived bile materials and their documentation sits alongside the CDCA specification and the framework for supplier verification. Our bile-acid range is described with the parameters buyers ask about most, and you can request a quotation against your own acceptance criteria.
The specification above is drawn from the Chinese Pharmacopoeia, published by the Chinese Pharmacopoeia Commission and enforced through the National Medical Products Administration. Neither register is linked here: both sit on Chinese government infrastructure and are frequently slow or unreachable from outside the country. For comparison, the European Pharmacopoeia handles animal-derived materials through its general monograph on substances for pharmaceutical use and the accompanying TSE risk statements, while the EMA TSE risk assessment framework and the World Organisation for Animal Health set out how source animals and tissues are classified.
This article describes pharmacopoeial requirements, identity and documentation practice only. It makes no statement about traditional use, physiological effect or therapeutic purpose, and it does not set out commercial guarantees. Always work from the pharmacopoeia edition in force at the time of your release.
Frequently asked questions
What framework does dried pig bile powder sit in?
In China, the pharmacopoeia monograph defines identity tests, an assay on characteristic bile acids, and physical limits such as loss on drying. Other markets may treat the same powder under feed or supplement rules. The specification should be written for the destination framework, because the same material answers to different documents in different markets.
How does bile powder differ from a single purified bile acid?
It is a mixture, so its assay is on marker acids rather than a single purity figure. Everything that follows from that difference matters: the identity tests must distinguish species, the limits must cover the accompanying substances, and the COA has more lines, not fewer, than a purified acid.
Why does origin traceability weigh more for animal-derived powder?
Because the regulatory story starts upstream of the factory: the species, the veterinary controls, and the health status of the source. Traceability documents connect a batch to that chain. For a purified synthetic acid, origin is one line; for an animal-derived powder, it is the spine of the file.
What should be checked on a powder COA beyond the assay?
Loss on drying, ash, microbial limits, and the identity tests that actually separate pig bile from other species. An assay on a marker acid proves nothing about species identity on its own. The identity section is where a powder COA earns or loses credibility.
Is the powder used directly, or purified first?
Both happen: feed and some traditional applications use the powder, while pharmaceutical use generally takes purified individual acids from it. The specification has to match the application. A powder specification will not satisfy a purified-acid buyer, and the reverse is also true.
Why do marker-acid assays differ between suppliers?
Different markers, different methods, different expressions of the result. Two certificates can quote 90% and 16% for the same powder and both be correct. The question that resolves it is which acid the assay quantifies, by which method, and expressed on what basis.