Freeze Drying Benefits

In preserving sensitive biological materials, the main enemies are water, oxygen, and heat. Water is a powerful solvent, and is required for many chemical reactions, including enzymatic breakdown. Oxygen causes adverse chemical changes through oxidation, which is why anti-oxidant compounds are of such interest. Heat can decompose (break down) ingredients by itself, while at the same time accelerating other chemical changes, including enzymatic breakdown and oxidation.

Freeze drying is a process in which water is removed as vapor directly from ice, without passing through the liquid state. This process is called sublimation, and requires reduced pressure to occur. All other drying methods use evaporation - that is, water is removed as vapor from liquid water with heated air.

The ancient Incas were the first to learn the benefits of sublimation. They discovered that when they dried food at high elevations, the results were better. Even though the food would freeze, it would dry well if left exposed to the sun. The reduced pressure at high elevation, combined with the dry air and energy from the sun, caused sublimation to occur.

As the Incas discovered, freeze drying is well suited to preserving sensitive biological materials. There are three reasons for this. First, freezing slows or stops most chemical reactions. Second, the process occurs under a vacuum, and the absence of oxygen prevents oxidative reactions. And third, the process can be performed at very low temperatures - lower than by any other drying method. Enzymatic or bacterial breakdown cannot occur at such low temperatures, and chemical changes in general are minimized.

Freeze drying is so effective in preserving chemical components that small living organisms can be preserved and kept alive during and after freeze drying. They pass into a dormant state, from which they can be revived by the addition of water. If you eat yogurt or cheese, there is an excellent chance that the starter cultures used to make your favorite products were added in freeze dried form. "Friendly bacteria" that are sold in dry form as supplements for healthy intestinal flora, such as Lactobacillus acidophilus, and Bifidobacteria, are invariably freeze dried. Few of these sensitive organisms will survive any other drying method.

Today, freeze drying is regarded as the "gold standard" of drying methods, where the preservation of biological activity, flavor, aroma, and/or chemistry are important. It is used widely in the pharmaceutical, food, and food supplement industries. One well-known example is coffee. However, freeze drying is a costly process, and few instant coffees today are freeze dried. Most (e.g., Folgers) are spray dried, and then agglomerated into granules. The description of instant coffees as "roasted" refers to the roasting of the coffee beans, not the drying method. Freeze drying is widely used to preserve sensitive pharmaceutical proteins and similar molecules, such as enzymes.

A good example of freeze drying's benefits versus alternatives is the popular blue-green alga, Aphanizomenon flos-aquae. Aphanizomenon is characterized by a high natural enzyme content. After the algae has been harvested, it is critically important to stabilize it as soon as possible so that the enzymes do not break down their other nutritional components in the algae. A serious loss of potency can take place within a few hours or minutes, depending on temperature. However, as the enzymes themselves are valuable, it is important to preserve them as well. Since the enzymes are active only in a liquid environment, prompt freezing, followed by freezing drying, effectively protects the algae from enzymatic degradation while preserving the enzymes. By contrast, other drying methods maintain the algae in a liquid state for longer periods, during which serious nutritional losses can occur.

During freezing, the cell walls of the algae break. This is a normal effect of ice crystal formation during slow freezing, and is not a cause for concern. There is no evidence that this has any significant effect on the nutritional properties of the algae. Some processors prefer to break the cell walls prior to freezing as an aid to purification steps, and to produce specialized algae products from different fractions of the cell.

When you buy supplements that have been freeze dried, you can be sure that the manufacturer has chosen the most gentle and effective method of drying available.

Walter S. Pebley, PE is a noted authority on freeze drying and speaker to conferences on industrial drying methods. James S. Baglien is a physiologist. Both work in the Advanced & Specialty Products division of Oregon Freeze Dry, Inc., Albany Oregon, USA

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