# Fermented palm oil alternatives

What palm oil is functionally: chain length set by thioesterase specificity, solid fat content and the crystal behaviour it gives, and why the sugar-to-lipid carbon yield decides whether fermentation genuinely saves land.

Palm is the highest-yielding oil crop there is — so any replacement has to beat it on land, not merely avoid it.

Source: https://en.bioecon.ru/docs/biochem-industrial/specialty-fine-chem/biosynthetic-palm-fat/
Updated: 2026-08-25



Palm oil is replaced for deforestation reasons, not performance ones. Understanding the substitution problem means being clear about what palm actually supplies and about the comparison being made.

## What palm oil is, functionally

Palm oil is roughly half saturated — dominated by palmitic acid, C16:0 — and roughly forty percent oleic acid, C18:1. That composition places it in an unusual and useful position: **semi-solid at ambient temperature**, with a gradual melting profile rather than a sharp one.

That gradual profile is the property being bought. A fat's **solid fat content** curve — the fraction still crystalline at each temperature — determines whether a margarine spreads, whether a pastry laminates, whether a filling holds shape at room temperature and melts in the mouth. Palm delivers a workable curve without hydrogenation, which is precisely why it displaced partially hydrogenated fats when trans fats were removed from the food supply.

Palm kernel oil, from the seed rather than the flesh, is different again: dominated by lauric acid, C12:0, with a sharp melting point, used where a fast melt matters.

Any replacement must reproduce a curve, not a fatty-acid list.

## How chain length is actually controlled

Fatty acid synthase builds a chain two carbons at a time and would keep extending it. What stops it is a **thioesterase**, which hydrolyses the growing chain off the carrier protein and releases it. The chain length of the product is therefore set by the chain length at which the thioesterase acts.

This is the single most useful lever in engineering a designer oil. Expressing a thioesterase with a different specificity — plants provide a range of them, including the medium-chain thioesterases responsible for lauric acid in coconut and palm kernel — changes the product distribution directly. Desaturases then set unsaturation, and, as with cocoa butter, acyltransferase specificity determines which position on the glycerol each acid occupies, which is what actually governs crystal packing and the melting curve.

## The comparison that decides everything

Oil palm yields several times more oil per hectare than any other oil crop — a fact that is central rather than incidental. It is the reason palm displaced other oils, and it means that substituting palm with soy, rapeseed or coconut requires substantially *more* land for the same oil, potentially making the deforestation problem worse rather than better.

For fermentation the comparison runs through the feedstock. An oleaginous yeast converts sugar to lipid at a carbon yield bounded by stoichiometry: converting carbohydrate into a much more reduced fatty acid costs reducing equivalents, and burning carbon to supply them, so the theoretical maximum sits near a third of a gram of lipid per gram of sugar, with practical yields lower.

**That sugar comes from land too.** The honest accounting is therefore hectares of cane or beet needed to supply the sugar for a tonne of microbial fat, against hectares of oil palm for a tonne of palm oil — not fermentation against deforestation. On that comparison the case rests on using non-food or waste carbon sources, on the fat being compositionally superior rather than merely equivalent, or on siting production where land is not the constraint.

Routes using lignocellulosic sugars, food-industry side streams or gas fermentation change the arithmetic materially, and are where the argument is strongest.