Enzymes as Tools.
Fresh pineapple in a gelatin dessert leaves a puddle: its bromelain cuts the gelatin to pieces. Heat the pineapple first, or use canned, and the jelly sets.
An enzyme speeds one kind of reaction by holding its target in exactly the right position (V.9). Its rate rises with temperature, like any reaction, until the enzyme itself — a folded protein — unfolds and stops working (VI.1). So every enzyme has a working range and a temperature, and a time, at which it is destroyed. Cooks meet this constantly: browning enzymes in cut fruit (VIII.6), the amylase in egg yolk that thins an undercooked pastry cream (XXV.9), the amylase of rye (XXX.4).
Used as tools: papain (papaya) and bromelain (pineapple), and actinidin in kiwi, are proteases that cut proteins; in marinades they tenderise, most rapidly as the meat warms through 50–70 °C, until heat destroys them — and if left too long they turn the surface mushy. The same bromelain cuts gelatin, so fresh pineapple, kiwi or papaya prevent jellies from setting; heating the fruit to the boil first destroys the enzyme. Transglutaminase, made by fermentation, links proteins covalently and is used to bind pieces of meat or fish into one, to make noodles of shrimp, or to firm yoghurt; it has to be labelled and handled with care. Koji, the mould Aspergillus oryzae grown on rice or barley, supplies the amylases and proteases that turn grain and soy into sake, miso and soy sauce (XIV.7), and modern cooks use it to age and season meat. The workshop warms an enzyme.
Below: the work a tenderising enzyme does over the minutes you choose at each temperature — faster with heat until heat destroys it (course enzyme kinetics with inactivation for papain and bromelain) — and its half-life at the temperature you choose.
- Explain how enzymes speed reactions and are destroyed by heat.
- Tenderise with papain and bromelain.
- Keep enzymes from ruining gels.
- Know transglutaminase and koji.
Warm to work, hot to stop
In the course kinetics bromelain does little in an hour at fridge temperature (0.31 on this scale) but a great deal in ten minutes at 55 °C (7.8); at 80 °C its half-life is only about 2 seconds, at 60 °C about 6 minutes. That is why a pineapple marinade works mainly as the meat heats on the grill, why fresh pineapple ruins a cold jelly over hours, and why bringing the fruit or juice briefly to the boil makes it safe for gelatin.
Practical use: for tenderising, a short marinade of grated pineapple, papaya or kiwi (30 minutes to 2 hours) on thin cuts, then cook — longer turns the surface mealy; for jellies with these fruits, boil the fruit or juice first, use canned fruit, or set with agar, which is a carbohydrate the enzymes cannot cut (XXXIII.2); transglutaminase is used at about 0.5–1 % by weight on clean, dry surfaces, pressed together and chilled for hours, wearing a mask when handling the powder; koji is grown at about 30 °C and high humidity on steamed rice, and is the basis of shio-koji, a salty seasoning that tenderises and adds umami.
Set three small gelatin jellies: plain, with fresh pineapple, and with pineapple boiled for a minute. Check them after four hours.
Terms
- Protease
- An enzyme that cuts proteins.
- Bromelain / papain
- Proteases from pineapple and papaya.
- Transglutaminase
- An enzyme that links proteins: "meat glue".
- Koji
- Aspergillus oryzae, the mould behind sake, miso and soy sauce.
Sources
- H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.