Unsaponified fatty acids

[Kcryss]

I came across an article while jumping down another rabbit hole and although I don't do cold process, I can't find anything similar for hot process.
It seems that with cold process, the majority of unsaturated fatty acids remain unsaponified in the final product. If that's the case, do the lye calculators and the fatty acid compositions shown take that into account? According to this article, the number of unsaturated fatty acids (due the unsaponifiable molecules) attribute to faster oxidation which sounds to me like DOS.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6225244/
It's a great deal of information, especially for someone like me without a chemistry-based degree. I just wonder if the same is true of hot process, although I've never really had a problem with DOS, but also wondering if maybe in addition to the fatty acid profiles on the lye calculators, if other factors should be taken into consideration based on HP or CP?

Does anyone with a chemistry degree or @DeeAnna have any ideas or thoughts?

 

[Mobjack Bay]

There was a short thread about this paper back in 2019. A subsequent related article published by the same researchers repeated the conclusion you highlighted from the first article: "Most of the unsaturated lipids remained unsaponified after soap production via cold saponification." Based on my limited understanding of the chemistry of saponification, it seems plausible to me that the unsaponified fraction of cold-process soap could end up enriched in unsaturated fats relative to the saponified fraction, but not that the majority of unsaturated fats going into the soap pot do not saponify. Past that, I'm no help at all.

 

[DeeAnna]

You aren't the only one to find this paper confusing. This paper is hard to understand even when I read it more carefully some years ago, and I'm a trained researcher. If I had been the major professor advising these authors, I would have asked them to divide this into about 3 separate papers, each with a specific subject. For example, they studied the fatty acid content of the superfat. That's one paper. Then they change to evaluating the sensory qualities of the finished soap -- color, fragrance, etc. That's another paper. Then they tried to relate the sensory qualties to the fatty acids in the superfat (with not much success if I remember correctly). There's a third paper. Taken in one big lump, It's too much info for the authors to cover with care and too much for the reader to digest.

I also I question whether this paper was thoroughly and carefully peer-reviewed and edited. When I was writing academic papers and reviewing others' papers, the review and editing process normally took months to even a year or two. This paper was published barely 3 weeks after it was received. That's not a lot of time for a thoughtful review and edit process, especially for a paper as complicated and rather rambling as this one is.

***

Anyways, Kevin Dunn did a study comparing the fatty acids (FAs) in the superfat with the FAs before saponification. He also found the superfat contained a higher proportion of unsaturated fatty acids (FAs) compared to the starting FA blend. I think Dunn's findings makes sense.

Essentially straight-chain fatty acids (lauric, myristic, palmitic, stearic) saponify more easily than the not-straight fatty acids (oleic, linoleic, linolenic) due to their physical shape. So when saponification is over, there will be fewer straight-chain fatty acids left unsaponified in the soap.

I don't know why hot process (or boiled process) should produce a different outcome than cold process. The only difference between HP and CP is the use of heat to accelerate saponification. The nature of the chemical reaction between the fats, the fatty acids, and the alkali isn't any different.

***

One aspect that this study don't cover well is that NaOH (lye) doesn't entirely deconstruct one fat molecule, turn all those free FAs into soap, and then deconstruct the next fat molecule and so on. That's normally how saponification is explained, but it's a simplified version of what actually happens.

NaOH will deconstruct fat molecules to varying degrees depending somewhat on simple probabilities and somewhat on physical structure. That means the superfat is not just a blend of the original intact fats. Instead the superfat will be a mixture of original fats plus some partly deconstructed fat (aka mono- and di-glycerides) and some free fatty acids. This will be true for soap made with any type of soap making method.

@Mobjack Bay shared some research awhile back that showed the fatty acids locations within a fat molecule will depend on the particular fat being studied. Lard is an example of a fat that saponifies differently than similar fats such as palm and tallow because the FAs in lard are distributed differently than in the other fats. If the authors of the study in OP's first post had studied lard-based soap recipes rather than all veg oil recipes, they might have had different results.

Even if you add superfat to a hot process soap after the cook is complete, there will still be some gradual deconstruction and rearrangement of the superfat. This is due to the alkaline nature and chemical structure of soap. That means the fat originally added to HP soap after the cook might stay mostly intact at first, but it is not likely to remain fully intact as time goes on.

 

[paradisi]

You aren't the only one to find this paper confusing. This paper is hard to understand even when I read it more carefully some years ago, and I'm a trained researcher. If I had been the major professor advising these authors, I would have asked them to divide this into about 3 separate papers, each with a specific subject. For example, they studied the fatty acid content of the superfat. That's one paper. Then they change to evaluating the sensory qualities of the finished soap -- color, fragrance, etc. That's another paper. Then they tried to relate the sensory qualties to the fatty acids in the superfat (with not much success if I remember correctly). There's a third paper. Taken in one big lump, It's too much info for the authors to cover with care and too much for the reader to digest.

I also I question whether this paper was thoroughly and carefully peer-reviewed and edited. When I was writing academic papers and reviewing others' papers, the review and editing process normally took months to even a year or two. This paper was published barely 3 weeks after it was received. That's not a lot of time for a thoughtful review and edit process, especially for a paper as complicated and rather rambling as this one is.

***

Anyways, Kevin Dunn did a study comparing the fatty acids (FAs) in the superfat with the FAs before saponification. He also found the superfat contained a higher proportion of unsaturated fatty acids (FAs) compared to the starting FA blend. I think Dunn's findings makes sense.

Essentially straight-chain fatty acids (lauric, myristic, palmitic, stearic) saponify more easily than the not-straight fatty acids (oleic, linoleic, linolenic) due to their physical shape. So when saponification is over, there will be fewer straight-chain fatty acids left unsaponified in the soap.

I don't know why hot process (or boiled process) should produce a different outcome than cold process. The only difference between HP and CP is the use of heat to accelerate saponification. The nature of the chemical reaction between the fats, the fatty acids, and the alkali isn't any different.

***

One aspect that this study don't cover well is that NaOH (lye) doesn't entirely deconstruct one fat molecule, turn all those free FAs into soap, and then deconstruct the next fat molecule and so on. That's normally how saponification is explained, but it's a simplified version of what actually happens.

NaOH will deconstruct fat molecules to varying degrees depending somewhat on simple probabilities and somewhat on physical structure. That means the superfat is not just a blend of the original intact fats. Instead the superfat will be a mixture of original fats plus some partly deconstructed fat (aka mono- and di-glycerides) and some free fatty acids. This will be true for soap made with any type of soap making method.

@Mobjack Bay shared some research awhile back that showed the fatty acids locations within a fat molecule will depend on the particular fat being studied. Lard is an example of a fat that saponifies differently than similar fats such as palm and tallow because the FAs in lard are distributed differently than in the other fats. If the authors of the study in OP's first post had studied lard-based soap recipes rather than all veg oil recipes, they might have had different results.

Even if you add superfat to a hot process soap after the cook is complete, there will still be some gradual deconstruction and rearrangement of the superfat. This is due to the alkaline nature and chemical structure of soap. That means the fat originally added to HP soap after the cook might stay mostly intact at first, but it is not likely to remain fully intact as time goes on.

It's almost unreadable. And it makes several obvious nonsense claims, including that fruit and vegetable purees are commonly added to scent soap and act as anti oxidants, at 1-8%.

Agree re: fatty acids.

This feels like a panic paper where they knew they didn't have any big conclusion and tried to build one Frankenstein's monster-wise.

 

[AliOop]

panic paper

Not heard that expression before but I do remember friends in college who submitted some such thing at the end of semester.