Let's see if this link works. You can read the article.
https://www.google.ca/url?sa=t&sour...bLA3u0kjLKOpDfAMQ&sig2=6OmxvhM9IUjSofi1wLT8XA
I'd be interested on whether with flue cured tobacco, the addition of a different acid (citric acid, or malic acid) would reduce the release of formic acid when smoking flue cured tobacco. What do you think? If so, I wonder if tongue bite could be reduced.
In the article you posted, the authors seem to posit that formic acid production is a result of sugar combustion at low temperatures and cellulose/hemicellulose compounds at high temperatures. I'm not sure if this is a conclusion the authors reached via their own experiments somewhere, or an earlier cited paper (Fenner, 1988).
In a general sense though, assuming that formic acid is the product of incomplete combustion of compounds containing carboxylic acid groups, I'd bet that malic acid would produce less formic acid because it has a more favorable carbon to oxygen ratio and is two-thirds the size of citric acid. I don't study high temperature reactions but I was always under the impression that the larger your carbon backbone, the more likely it would be to undergo incomplete combustion. This seems generally true for alkane fuels (i.e. look at how little smoke burning ethanol and butane form, compared to a gasoline or even oil). However, I don't really see any reason to believe the
addition of more malic acid to harvested leaf may inhibit the production of formic acid upon combustion.
That being said, I find malic acid to be a bit softer than citric acid (I've tasted reagent grade citric acid, and it tastes, unsurprisingly, literally like crazy sour lemons). The majority of the acid found in apples is malic acid, and I make an apple wine (fermented bone dry) that tastes really good after a bit of aging.