How 'Natural' Food Preservation Works

A garden of natural ingredients can increase shelf lives while also cleaning up food labels.

By Mark Anthony, Ph.D., Technical Editor

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Cell structureThe label “No artificial preservatives” has practically become an icon in natural foods. But it doesn’t mean reduced shelf life is acceptable, only that a growing number of food processors prefer to extend the shelf life of their products with natural techniques and ingredients, often using the very herbs and spices that provide flavor to foods.

The tradition of natural food preservation predates even the cultivation of foods. The wind and sun allowed for drying of meats, fruits, and vegetables in the Middle East as early as 12,000 BC. And salt has been used as a natural preservative for at least as long. The only question is whether these natural techniques of spoilage prevention can keep pace with synthetic preservatives while appealing to consumers.

Oxidization is a primary cause of spoilage. The oxygen in the air causes chemical reactions that alter the molecular structure of a substance and cause its various components to break down. This is why so many preservatives function as antioxidants. Numerous wild and cultivated plants have been investigated for their natural antioxidant potential.

Antioxidant protection is only one factor capable of extending the shelf life of foods. For most products, contamination with microorganisms poses the greatest threat to shelf life. Numerous natural methods can prevent contamination from microorganisms. These include refrigeration, freezing and water-activity reduction. Also successfully employed are restriction of nutrients, acidification, modified atmosphere packaging (MAP), fermentation, high pressure, electric pulses, nanotechnology, irradiation and the addition of antimicrobial compounds. Most of these methods work by creating an unfriendly environment for the growth of bacteria and other microorganisms.

The potential toll on the food is extensive, resulting in a significant loss of nutritional value due to a destruction of fat-soluble vitamins and reduction of essential fatty acid activity. Lipid oxidation further shortens shelf life by altering the organoleptic qualities of the final product, changing the color, texture and taste.

In with the new

To prevent spoilage and lengthen shelf life, the food industry often employs synthetic antioxidants, including butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and propyl gallate (PG). Consumer apprehension regarding the safety of these and other preservatives has driven the search for more natural antioxidants. In fact, several large food companies, such as General Mills, recently declared they are removing BHT from key product formulations.

The distinction between herbs and spices is generally pretty simple. The leafy parts of the plant are generally considered an herb. All other components of the plant -- flowers, grains, seeds, roots, etc. -- are considered spices.

The mechanisms by which the antioxidant activity occurs in many herbs and spices can vary substantially. In fact, the breadth of a single plant’s antioxidant activity is not always clearly understood because there are so many different compounds involved. However, oxygen free-radical scavenging, chelation of minerals that can cause oxidation and inhibition of enzyme systems that can catalyze damaging reactions are key parts.

Chief among natural antioxidant sources are spices, many of which traditionally have been used to retard spoilage by slowing the process of lipid oxidation. Oxidation of lipids can occur anytime during the storage and processing of raw materials. It is a constant threat, up to and including the final stage of production and during shelf life of the final product.

Among the potent complexes responsible for the beneficial action of herbs and spices are phenolic compounds. These exist in many forms including simple phenols, flavones, flavanones, flavanols, anthocyanins and flavonoids. Several studies have demonstrated the potential functional properties of these compounds.

In addition to their antioxidant activity, many display antibacterial, antiviral and anti-inflammatory capacity. As a result of these abilities, most of these compounds also are believed to be cardioprotective, acting to inhibit platelet aggregation, and anticarcinogenic, by inhibiting the growth of cancer cells, at least as shown in vitro.

Hundreds of studies have demonstrated the effectiveness of herbal antioxidants as food preservatives where the measure of effectiveness was a reduction in markers of oxidative damage. Rosemary extracts have been tested extensively for their ability to protect beef, pork, chicken, bison and lamb. Sage has been used to protect turkey, chicken, pork and fish.

Oregano oil has been tested on beef, fish, fish oil and mackerel oil. Tea catechins are powerful antioxidants and have been tested using pork patties. Thyme and oregano essential oils were tested using 0.2 percent added volume with sausage. Thyme, rosemary, sage, marjoram and cumin also are known for their ability to reduce signs of oxidation salad oils and baked goods.

Food safety first

Most antimicrobial compounds are synthetic. However, the food industry is under great pressure from health-conscious consumers to find natural substitutes for synthetic preservatives. Some of the best candidates for natural antimicrobials are spices and their derivatives, referred to as essential oils (EOs). The term essential oils simply refers to the oil portion that confers an aroma.

They are attractive candidates because they are classified as GRAS (generally recognized as safe). A disadvantage of using essential oils as antimicrobial agents lies in the fact that their maximum efficiency may be at concentrations that could stimulate significant changes in the organoleptic properties of the foods to which they are added.

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