Abstract
Scope. The four previous volumes went from the molecule into the nose and the brain. This volume turns to the chemistry of odorants itself: why one functional group, one carbon chain or one spatial arrangement gives this odour rather than another; and what essential oils — the core product of muihuong.vn — actually consist of, how they vary, and against which standards they are tested.
Method. Four independent collection strands: terpenoids and phenylpropanoids; odorant families outside the terpenoids; the composition and chemotypes of 12 groups of international essential oils, cross-checked against 19 ISO standards (24 editions); and essential oils sampled in Vietnam. Equivalent TCVN standards are noted where they exist. In total 718 facts, each recorded with its source, sample origin, analytical method and level of access.
Main findings. (1) The percentage on a certificate of analysis is not the percentage of the odour. β-damascenone makes up 0.14% of rose oil but carries about 70% of the “odour units”; limonene makes up about 80% of mandarin peel oil but serves only as a background. (2) Structure–odour rules are tendencies, not laws: cyclising linalool to α-terpineol weakens the odour about 50-fold, yet some hydrocarbons are stronger than alcohols. In the C3–C9 aldehyde series measured in air, the threshold is lowest at 8 carbons. (3) ISO standards do not prove naturalness: only 3/64 batches of Romanian lavender and 18% of batches of Spanish lavandin fully met ISO, whereas for an oil adulterated with 27% synthetic material the percentage profile can still fall within ISO — only chiral analysis could detect it. (4) Vietnamese essential oils have their own profiles: cassia bark oil contains 93–96% cinnamaldehyde, above the 88% ceiling of ISO 3216 (the standard could be read only in part); cajuput is not uniformly a cineole type (0–47% depending on the region); lemongrass is often at or below the citral threshold of ISO 3217. (5) The substances requiring control — methyl eugenol, safrole, estragole, nitro musks, bergapten — all already have specific quantitative limits.
Conclusion. For a batch-based essential oil distributor, the value of chemistry lies not in memorising constituent names but in reading the certificate of analysis correctly: knowing which constituent determines the odour despite being minor, knowing which standard range applies to which origin, knowing when “meets ISO” is not enough, and knowing where and why Vietnamese essential oils deviate from international standards.
Keywords: structure–odour relationship · odour activity value · character-impact compound · terpenoid · phenylpropanoid · musk · chemotype · ISO standard · chiral analysis · Vietnamese essential oils
Contents
- Part I. From biosynthesis to odour profileThe two isoprene pathways, the methylation step in phenylpropanoids, and why a percentage in an oil is not a smell: odour activity values.
- Part II. Structure–odour relationships in terpenoidsFunctional groups, double-bond position, E/Z isomers and enantiomers, sesquiterpenes and woody notes: strong trends and where they break down.
- Part III. Non-terpenoid odorant familiesStraight-chain aldehydes, esters, lactones and coumarin, musks, ionones and damascones, thiols and pyrazines, nitrogen heterocycles in flowers.
- Part IV. The chemistry of deteriorationAutoxidation turns non-allergens into allergens; citral in acid; isomerisation and resinification; ageing markers measurable by GC.
- Part V. International essential oils: composition, chemotypes and ISOWhat a chemotype is, a reference card of key marker compounds, three special cases, the limits of “ISO-compliant” and chiral checks for authenticity.
- Part VI. Vietnamese essential oils: composition and chemotypesComposition of oils grown in Vietnam against international standards, notable chemotypes, agarwood, safrole-rich oils and data gaps.
- Part VII. Synthesis and practical implicationsFive main conclusions, a protocol for reading a lot GC-MS report, a quick-reference table of restricted constituents and key references.
- Appendix A1. Facts on terpenoids, phenylpropanoids and other families267 sourced facts on biosynthesis, structure–odour relationships, detection thresholds and non-terpenoid odorant families.
- Appendix A2. Facts on international essential oils and ISO standards361 sourced facts on the composition of international essential oils, chemotypes and the reference ranges in ISO standards.
- Appendix A3. Facts on Vietnamese essential oils90 sourced facts on the composition and yield of essential oils grown in Vietnam, compared with standards.
- Appendices B and C. Glossary, sources and access limitsA Vietnamese–English glossary of aroma chemistry and a note on the four data-collection strands, levels of access and the limits of this monograph.
A monograph compiled from 718 sourced facts collected under a common protocol and cross-checked independently. Items labelled Inference are the compilers’ own judgements. Diagrams are newly drawn from published data. Scientific reference material — not legal or medical advice, and no substitute for the text of the standards.