I spent the afternoon teaching a class on cheesemaking for the Douglas County Master Food Preservers. It went quite well; they are a group that knows about food, fermentation, some biology and food chemistry, and yet for most of them dairy products were
terra incognita. This made them ideal students, engaged, intelligent, and naive.
An essential part of making most cheeeses involves rennet. One can use animal rennet, which is a crude extract of the stomach lining of a young ruminant. One can use (as I do) a microbial rennet, which is a single enzyme extracted from the fungus Mucor miehi. One can use an extract from the flower of the cardoon thistle, which doesn't work as well as normal rennet and is only used in a handful of unusual cheeses. Or, these days, one can use recombinant rennet, which is an enzyme extracted from bacteria that have been given the genes that are expressed in the stomach lining of a young ruminant. In all cases, the active ingredient in rennet is a specific protease. This enzyme cuts proteins between two specific amino acids, and in a specific amino acid context (to make an analogy to language, it would be like a text editor that only cuts between the letters "x" and "t" but only if they occur at the end of a word--not very common). Almost all the protein in milk is casein, which happens to have the target for rennet; and when rennet cuts casein at that spot, the casein sticks together so that cheese can be made. No rennet, no fromage. All praise to rennet!
This set me to thinking. Are there other examples where a specific enzyme, with a specific target, is absolutely essential for making a food? Here's all the others that I can think of, after mulling on and off for a day.
1. Candy with syrupy centers. How do they put liquid in a chocolate shell? They don't. They put a solid disaccharide sugar and an enzyme, invertase. Invertase cuts the disaccharide into two monosaccharides and a molecule of water; the sugars dissolve into the water, and there you are. The ingredients on the package will say "invert sugar."
2. Chicha. This is a maize-based beer like product from the Inca empire. Beer requires some sugar to ferment, but corn, which the Inca grew, only has starch. Fortunately, starch can be hydrolyzed to glucose by the very specific enzyme amylase. Where would an Inca find amylase? In spit. There were people whose job it was to chew corn; the amylase in their saliva would act upon the starch in the corn, and they would spit the pulp into a jar. The pulp of chewed-up corn, spit, and glucose liberated from the starch by saliva amylase would then ferment into a beer, which the Inca would drink. Yum! (You can do the same trick; put a little bit of raw potato in your mouth, and eventually it will start to taste sweet.)
3. Not essential, but interesting--papain and bromelain for a tender steak. There's a couple of enzymes, derived from papayas and bromeliads (pineapples), that like rennet, are proteases. However, their specificity differs from that of rennet, and it turns out that they are really good at breaking some of the tougher fibers in muscle proteins. It's not essential for preparing meat, but if you buy meat tenderizer, most likely you'll be getting one of these two plant enzymes.
I would love to hear of other examples of specific enzymes, independent of an organism, being essential for the production of a particular food. There's zillions of examples of specific species being required for a food, but a single cell brings hundreds of enzymes to bear. A single, purifyable enzyme? That's much rarer.
