IJsbrand Velzeboer: Enzymes: hidden flavour killers

Freezing temperatures can ensure a long shelf life. And by long, I really do mean long. Just think of the Italian ice mummy Ötzi, who died more than five thousand years ago and wasn’t discovered until 1991. Dry conditions, wind, and a prolonged freezing process preserved him remarkably well. And dried him out, too.

Now imagine the mummy had been defrosted: would he have been appetizing to a passing wolf? I don’t think so; it must have become completely inedible due to the fats in the body being heavily oxidized. That’s what makes meat go rancid. Wild animals would have definitely left him well alone. For archaeologists and other scientists, of course, it was a different story; they were eager to examine the body in detail. Ötzi is now kept in a specially designed freezer at a constant temperature of -6 degrees Celsius (and a humidity level of 99% to prevent dehydration).

In a standard freezer, the ideal conditions are -18 degrees Celsius and dry. At that temperature and low humidity, not much happens in terms of enzymatic activity in the products you store. Still, spoilage can occur unnoticed. Fat oxidation doesn’t stop in the freezer; the chemical oxidation process continues, albeit very slowly. And while microorganisms no longer grow at temperatures below -4 degrees Celsius, they can rebound quite effectively once defrosted. The interaction between bacteria, molds, and yeasts, combined with enzymatic reactions, can cause food to become not only unpalatable but also unsafe.

Fresh meat can easily be stored in the freezer for several months, but seasoned products can turn rancid within just a few weeks. Making vegetarian burgers with still-frozen peas is asking for trouble; the peas are only just defrosted during the pre-cooking of the burger and can then start doing their unpleasant work. In many vegetarian and hybrid products, the necessary inactivation of enzymes is unfortunately overlooked. Tip: when processing plant-based materials, always check the purchasing specification. It must state that the raw material has been enzymatically stabilized.

IJsbrand Velzeboer
Curative food technologist