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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

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.

Essential oils were traditionally added to foods to improve taste and aroma. It was only later realized that many had the potential to confer antimicrobial protection from a wide variety of microbial strains, such as Staphylococcus, Lactobacillus and Enterobacteriaceae, as well as certain molds like Aspergillus.

The demand for creating safe, organic or even conventional foods without the addition of chemical preservatives is increasing rapidly and has been motivating research on the antimicrobial effects of plant derivatives. Examples of substances with potentially important antimicrobial activity are the essential oils (EOs), shown in studies to confer antibacterial, antifungal, and antioxidant activity. Recent in vitro studies have demonstrated that different EOs confer anti-listerial activity. Other studies have shown that EOs of Chinese cinnamon (Cinnamomum cassia), tea tree (Melaleuca alternifolia) and lemongrass (Cymbopogon flexuosus) were effective against L. monocytogenes.

Building on in vitro studies, researchers reported in a 2013 article published in the Brazilian Journal of Microbiology on the effect of using essential oils from two well-known herbs — thyme and rosemary — as preservatives in the control of Listeria monocytogenes in raw beef. In this study, two methods of preserving meat were tested. One used an edible gelatin that included EOs from thyme or rosemary as a coating for chunks of raw meat; the other subjected the meat to a vapor that contained EOs from both herbs. In both instances, the raw bovine meat had been inoculated with L. monocytogenes.

In first experiment, using edible coatings containing EOs, the greatest antibacterial activity occurred at 48 hours of storage. In the vapor effect experiment, the maximum reduction in the population of inoculated bacteria occurred after 96 hours of storage using the EOs of thyme. In both experiments EOs from thyme and rosemary were considered “promising alternatives” as preservatives for the meat industry.

There are several mechanisms proposed to explain the actions of essential oils against microbial growth. For example, components of essential oils could inhibit enzymes that are important to microbial energy production. Essential oil components may alter the permeability of the cell membrane or otherwise deform the structure of microorganism. Other components may damage proteins critical to microbial cell function. Confirmation of these mechanisms must be confirmed by further research.

The recent study, “Potential application of spice and herb extracts as natural preservatives in cheese,” in the Journal of Medicinal Food, investigated the antibacterial potential of five spice and herb extracts, including cinnamon stick, oregano, clove, pomegranate peel and grape seed, against L. monocytogenes, Staphylococcus aureus, and Salmonella enterica in cheese at 23°C, generally considered room temperature. Cheeses were monitored periodically for signs of lipid oxidation. All five plant extracts proved to be effective against the three foodborne pathogens in cheese, indicating there is a decrease in markers of lipid oxidation along with a decreasing concentration of all test microorganisms.

Of the extracts tested, clove demonstrated the highest antibacterial and antioxidant activity. There were other interesting results from this study, too: The concentration of extracts required to control group of bacteria and oxidation of in this experiment was greater than in previous studies done on colonies of the bacteria never run separate from the food. It has generally been observed that foods high in fat and protein and low in moisture require a greater concentration of natural preservatives.

Spice works

One recent study, “Evaluation of Antimicrobial Activities of Commercial Herb and Spice Extracts Against Selected Food-Borne Bacteria,” published in the Journal of Food Research, evaluated the potential antimicrobial properties of extracts of 30 different herbs and spices used commercially in the production of “ready meals.”

The herbs and spices were extracted via different methods and evaluated for their antimicrobial activities against Escherichia coli, Listeria innocua, Staphylococcus aureus and Pseudomonas fluorescens using a microdilution broth method. Ethanol and hexane extracts of oregano, clove, sage, rosemary and celery demonstrated strong antimicrobial activities against all bacteria tested.

In contrast, water extracts displayed little or no antimicrobial activity. The hexane/ethanol method of extraction has two stages. The first stage is designed to rupture the membranes and free all substances into solution. The second stage separates fat-soluble substances from water-soluble substances. Water extraction can only extract water-soluble products, leaving the fat-soluble products behind. This indicates that the effective extracts in this experiment were fat-soluble components—which perfectly describes essential oils, terpenes and most phenols.

Results also indicated something of the mechanism by which protection was conferred. Bacterial cell membrane structures were damaged by spice and herb active extracts. This caused an intracellular leakage and loss of bacterial ATP. In other words, the cell was most likely depleted of energy due to membrane damage. The most effective extracts were hexane/ethanol extracts of oregano, clove, sage, rosemary and celery.

In general, there appeared to be little additive effect among extracts, though some synergistic effects were observed when oregano was combined with sage or rosemary against L. innocua or S. aureus. This study demonstrated that some commercial spice extracts have antimicrobial activity against food-borne bacterial species and should be considered as potential antibacterial agents for addition to ready meals.

Effective effectiveness

In an effort to meet consumer demands for more naturally preserved foods, many companies have launched food preservation solutions based on a variety of herbal antioxidants. Tapping into the natural antioxidant power of rosemary extract, Kalsec Inc.’s natural Herbalox seasoning is designed to preserve the freshness of products including meats, oils, and beverages.

Duralox, also by Kalsec, Kalamazoo, Mich., is designed for products that are highly susceptible to oxidation, and uses a combination of antioxidants that include herbal extracts along with antioxidant vitamins. This liquid blend is more suited to beverages and edible oils. Edible oils are often rich in omega-6 and omega-3 fatty acids that are susceptible to oxidation.

Nature Seal Inc., Westport, Conn., created its own blend of antioxidant vitamins and minerals that can protect the oxidation of fresh cut fruit and vegetables. Oxidized fruits and vegetables quickly turn brown, which makes them unacceptable to consumers. The Nature Seal product is sodium- and sulfite-free and gives produce handlers the advantage of keeping sliced and chopped produce from oxidizing. One version is for fruits and vegetables, and another is specialized to keep guacamole from turning brown, no doubt taking advantage of fat-soluble antioxidants.

France's Naturex Inc. USA, launched a new line of natural antioxidants derived from acerola cherries that can serve as curing enhancers and shelf life extenders for meat and poultry. Acerola cherries are naturally rich sources of vitamin C, a potent water-soluble antioxidant. Named Acerola Cherry 17, the new product can be used as a curing accelerator for meats. XtraBlend RA combines acerola with rosemary for increased antioxidant effect.

While there can be some cost issues associated with using natural preservatives, it’s clear that the combination of consumer demand, modern ingredient technology and the very versatility of these natural ingredients confer added value to final products that should make up for any reformulation costs or challenges. That most of these ingredients confer marketable health benefits and can even enhance flavor is helping to make them a key choice for today’s processors.