Oils & fats processing biotech

Two enzymatic operations dominate industrial fats processing, and both replaced chemical steps that had specific drawbacks.

Degumming: converting the problem into a product

Crude vegetable oil carries phospholipids — “gums” — which must be removed because they hydrate, form emulsions, foul equipment and darken oil on heating. Water degumming removes the hydratable ones; the non-hydratable phospholipids, calcium and magnesium salts of phosphatidic acid, require acid and caustic treatment that also saponifies neutral oil, so yield is lost with the gums.

Enzymatic degumming attacks the molecule instead. Phospholipase A1 hydrolyses one fatty acid from the phospholipid, and phospholipase C cleaves the phosphate head group.

The consequence differs between the two, and it is not merely tidier chemistry. Phospholipase A1 converts the phospholipid to a lysophospholipid, which is far more water-soluble and separates cleanly, and releases a free fatty acid. Phospholipase C releases a diglyceride — which stays in the oil and counts as yield. So the enzymatic route recovers oil that the chemical route discarded, uses milder conditions, and generates far less effluent. This is one of the clearest cases in food processing of an enzyme paying for itself in yield rather than in quality.

Interesterification, and the trans fat story

The functional problem in fats is melting behaviour. Liquid oils are too soft for margarine, shortening or confectionery fat, and hardening them was historically done by partial hydrogenation — adding hydrogen across some of the double bonds in unsaturated fatty acids.

The defect was mechanistic. Hydrogenation catalysts do not only add hydrogen; they also isomerise remaining cis double bonds to the trans configuration. A trans double bond leaves the chain nearly straight, like a saturated fatty acid, so it packs and melts like one — which is precisely why partial hydrogenation hardened the fat. The hardening and the trans isomers were the same phenomenon, which is why the process could not simply be adjusted to avoid them.

Interesterification takes a different route entirely. It leaves every fatty acid and every double bond untouched, and instead rearranges which fatty acids are attached to which positions on which glycerol backbones. Because melting behaviour depends on triglyceride structure and crystal packing — not only on fatty-acid composition — blending a liquid oil with a hard fat and redistributing the acyl groups produces an intermediate melting profile with no trans fat generated.

Chemical interesterification with sodium methoxide randomises the positions completely. The enzymatic version uses an sn-1,3-specific lipase, which exchanges fatty acids only at the outer two positions and leaves the middle position intact. That selectivity is the point: it allows a defined structure rather than a random one, and it is how cocoa butter equivalents and structured lipids are built — including infant formula fats designed to place palmitic acid at sn-2, as it is in human milk, because the position determines whether it is absorbed as a monoglyceride or released as a poorly absorbed free fatty acid soap.