By Amy Schauwecker
As product developers, sometimes we tend to select tried-and-true preserving techniques as opposed to branching out to new designs that we have no prior experience with. Between antimicrobials and antioxidants derived from chemical synthesis, microbial fermentation or even recycled pulverized shrimp shells, the vast food-preservative options to choose from can overwhelm a formulator.
Formulating differently with preservatives might provide the answer to higher product quality and more opportunities for a food or beverage company. The aim of manufacturer investment in food preservatives is to offset losses due to food safety and shelf life. Preservatives allow for exponential product savings through broader distribution worldwide, more production flexibility and efficiency, increased product consistency and reduced product returns. Preservation depends on many factors, including the product pH, water activity (aw), nutrient content, oxidation-reduction potential, processing conditions, packaging and formulation. Of course, the products themselves must begin with quality materials.
Food preservation is one of the oldest technologies employed by humans. Ancient antimicrobial techniques, such as, drying, smoking, pickling, salting and candying, alter the food environment and create harsh living conditions for microbes.
Smoking preserves by drying the food and reducing aw. In addition, the incomplete combustion process synthesizes formaldehyde and phenol preservatives. Many formulators eliminate the physical smoking step in their process by using liquid or dry smoke flavors readily available in the industry. The flavors also exhibit antimicrobial properties that enhance taste and mask off-flavors caused by oxidation.
Salt is ubiquitous and inexpensive. When the salt concentration outside a microbial cell is higher than inside it, it draws water out of the cell in an attempt to equilibrate the salt concentration with the outside. This process of osmosis dehydrates the cell and eventually destroys it. Salting is commonly used in meat and fish. Sugar, sweetener syrups and honey also act on the same principle as salt by tying up the available water necessary for microbial growth as in fruit preserves and syrups. Researchers at Clemson University, SC, also concluded that the sugar and hydrogen peroxide found naturally in honey protects food from oxidation and can extend shelf life by several weeks to a month in some types of food.
Traditionally, lowering a food's pH is often achieved by acetic acid. However, balancing sourness and stability can be a challenge depending on the food substrate a developer has to work with.
"With regard to microbial control, all acids are not created equal. Often, formulators look at acidified foods strictly as a pH game when in fact it is typically the undissociated form of the acid that is the more-effective antimicrobial. Therefore, it can be useful to know an acid's pKa value," explains John Fenstermacher, senior market development specialist, PURAC America, Lincolnshire, IL.
The pKa is the point where 50% of the acid is undissociated and able to react. Acids are more-effective antimicrobial agents in the undissociated state. Depending upon the substrate, use an acid with a pKa value in the same range as the targeted pH of the product. For example, acidified products are optimal in a pH range between 3 and 4. Acetic, sorbic, benzoic, lactic and gluconic acid have a pKa between 3.70 and 4.75. Every acidified formula is different and requires some level of modification in the initial stages of development to effectively preserve and minimize sourness perception.
When a formulator can synergistically preserve the product with a combination of acids and their salts, they can most-effectively balance sourness. Fenstermacher suggests, "It would require an acetic-acid combination of 2% or lactic-acid concentration of 2.5% to realize the same inhibitory effect against Lactobacillus plantarum as a 1.5% of a lactic-acetic combination." The combination has a greater effect than the ingredients alone.
Common synthetic preservative chemicals with current regulatory limits established are: acid salts, nitrites, BHA, BHT, sulfites and EDTA. These agents might prevent the growth of molds and bacteria and also help to keep foods from becoming rancid.
Sodium benzoate salt forms benzoic acid -- the antimicrobial agent found naturally in cranberries, plums, cinnamon, cloves and apples -- once dissolved in water. Product designers prefer sodium benzoate to benzoic acid in many food applications because of its greater water solubility. Sodium benzoate provides the most-effective protection against yeast, molds and some bacteria in food products with a pH below 4.5, such as jams and dressings. The maximum allowable level of sodium benzoate by U.S. law is 0.1%, with an explanation of intended use on the label. Sodium benzoate is under investigation by researchers at Southampton University, England, for increasing hyperactive behavior in children.
In many food products, combining sorbate and benzoate together provides greater protection against a wider variety of microorganisms. Potassium sorbate salt forms sorbic acid in water, and is also much more soluble than the acid by itself. It's most effective against yeast, molds and some bacteria in products below pH 6.5.
Nitrates and nitrites can inhibit the growth of bacterial spores that cause botulism in meats such as ham and bacon. The compounds also enhance the meat color. Nitrates can react with secondary amines to form cargenogenic nitrosamines. The use of nitrites in cured meats is justified, because the risk of botulism is much greater than the risk of developing cancer. Nitrates are not to exceed 120 ppm in cured meat, and the food manufacturer must prove that nitrosamines will not form in hazardous levels.
Glucono delta lactone (GDL), another acidifying tool, provides less astringent sourness. GDL hydrolyzes in water to form gluconic acid. It is sweet at GMP usage levels, but can taste bitter when added excessively. Additionally, formulators must be patient when measuring analyticals for a formula using GDL. It takes several hours for GDL to equilibrate and give an accurate pH reading.
Sulfites are common antioxidants added to prevent the browning of fruits. In winemaking, they inhibit bacterial growth and do not interfere with the desired function of yeast. FDA prohibits the use of sulfites in raw foods and in important sources of thiamin, such as meats, because they destroy the nutrient. In all food products containing at least 10 ppm, sulfite must be declared and cannot exceed 200 to 300 ppm, depending on the food substrate.
Common mold inhibitors in breads, calcium and sodium propionate convert to proprionic acid. The undissociated form of the acid is lipophilic and necessary for microbial inactivation. GMPs in the United States typically dictate use of this preservative in bread, cheese and other bakery products at a maximum of 0.32%. It is an inexpensive ingredient that can yield an extra week or two of shelf life.
BHA and BHT are phenolic antioxidants, which prevent rancidity of fats and oils. GRAS regulations limit BHA and BHT to 0.02% of the fat content of the food product.
EDTA, polyphosphates, citric, phosphoric acids and other chelating agents remove and form complexes with metallic ions that catalyze oxidation in food. With EDTA, it is easy to minimize rancidity in dressing, fruits and vegetables, and canned seafood at a usage level of 0.07%.
Scaling-up all natural
Although consumers are demanding more safety and longer-lived foods, there are also increasing trends in fresh foods that are minimally processed and without chemical additives. Chemical additives may also complicate label declarations depending on country regulations. Some natural products on the market include fermentates, live cultures, animal and plant extracts, acids, metabolites, and enzymes. "There is a growing trend towards natural and organic. A bioconversion, if you will, away from chemical preservatives. Whether there is a need for antimicrobials or antioxidants, it is clear that consumers want more natural-type products from which to choose. These products taste better and seem more like homemade," observes David Charest, senior business manager, food protection North America, Danisco, New Century, KS.
Botanical extracts with antioxidant activity generally quench free-radical oxygen with phenolic GRAS compounds. Connie Sandusky, Ph.D., director of marketing Kalsec Inc., Kalamazoo, MI, reports successful antioxidant results when Herbalox® Seasoning, a concentrated herbal extract, is added at approximately 0.05% to 0.20% usage level in fresh and precooked/processed meat and poultry. Plant and botanical extracts do not compromise product flavors. "Extracts used for antioxidant activity have a portion of the volatile oil removed, so that you can use them for this purpose without causing flavor problems," she explains.
Rosemary, oregano, clove and sage are common antioxidative spices. Clove contains active eugenol and gallic acid, while oregano contains rosmarinic acid. Danisco's rosemary-extract blend added at 500 to 1000 ppm in precooked and frozen chicken patties can significantly reduce any "warmed-over" flavor after several months of storage, explains Charest.
Frutarom USA Inc., North Bergen, NJ, supplies Originox, an antioxidant derived from Origanum vulgare, or oregano. It is particularly high in rosmarinic acid and works in various applications, including fruits, vegetables, meat and dressings.
Active ingredients galangal root, lemongrass and kaffir leaves in Thai tom-yum soup mixtures are considered natural preservatives when marinated with fish as noted in a recent report by S. Siripongvutikorn at Prince of Songkla University, Thailand. Their results indicate that the mixture reduced Pseudomonas fluorescens, E. coli and Staphylococcus aureus by a 4 to 5 log cycle in the fish; however, Listeria monocytogenes was reduced by only a 1 to 2 log cycle. Siripongvutikorn suggested that adding more garlic to the mixture could deliver more lethality.
In a recent study at the Kansas Academy of Science, Topeka, KS, Salmonella and E. coli were reduced by 90% between five and 15 days at refrigerated temperatures when marinating chicken in garlic extract for 10 minutes.
Tea and fruit are promoted for more than their health and diet benefits. Several studies found significant antioxidant effects from green-tea-catechin extracts added to raw and cooked meats. Fruit even contains organic acids that act as natural preservatives. Researchers at the University of Massachusetts, Amherst, found significant reductions of L. monocytogenes in beef and fish with an oregano-cranberry-extract mixture. Cherry tissue mixed with ground beef reduced oxidation by 80%. Researchers at the California Raisin Board, Fresno, report that adding raisin paste to baked products, at levels ranging from 1% to 5%, extends shelf life without imparting noticeable raisin flavor to products. A naturally occurring organic acid in the grape, tartaric acid, can also enhance flavor and freshness perception. Moisture in the raisins can also slow staling of breads. Grape byproducts from wine manufacturing, such as grape seed extract, pomace and skin, have great promise as effective antioxidants due to their proanthocyanidins. Kikkoman International, Inc., San Francisco, recently introduced Gravinol®, a grape seed extract antioxidant formulated for use in functional bars, cereals, beverages and pasta products.
Chitosan, derived from chitin found in the exoskeleton of shellfish, is used for many purposes, including a dietary supplement and food preservative. Scientists at Southbank University in London found that microbial growth in a chitosan-glutamate-coated shrimp mayonnaise salad was inhibited by a 4 log reduction after four weeks at standard refrigerated temperatures.
Proteins attacking proteins
Some proteins provide antimicrobial properties. Microbial fermentation, which interrupts and kills other microorganisms, produces antibiotics and bacteriocins, natural occurring chemical proteins. Common antibiotics used in food disrupt permeability in microorganisms by creating pores in their cell walls.
Natamycin acts as a protein fungistat to prevent formation of yeast and mold in dried sausages, fruit juice and cheese products. Some functional limitations of natamycin are insolubility in water and degradation with exposure to Ultraviolet light. In effort to enhance the agent's effectiveness, researchers at Danisco recently discovered that forming molecular inclusion complexes of natamycin with cyclodextrins increased its solubility and chemical stability.
Nisin is a natural antimicrobial agent primarily effective against gram-positive organisms and used as a preservative in cheese, fruits, vegetables, meats, liquid egg products, dressings and sauces. Danisco found that processed-Cheddar-cheese spread with ham showed a shelf-life extension of six weeks when incorporating nisaplin at 250 ppm to control Clostridia species. Danisco's antimicrobial blend of nisin and rosemary extract was approved for use in cooked sausages to kill and control the outgrowth of L. monocytogenes. However, non-GMO label claims require certifications on the antimicrobial proteins from the suppliers.
New pathways for engineering different antibiotic variations are a credit to chemists at the University of Illinois, Urbana-Champaign. These chemists reported that antiresistant antibiotics might now be synthesized after discovering the key enzyme, Lacticin 481, responsible for the catalysis of some antibiotics.
Eggs and shellfish preserve themselves with external biostructures to protect against microbial penetration. These organisms also have preservatives to share with the food industry. Lysozyme, a protein extracted from egg whites, is a known antimicrobial against gram-positive bacteria.
Snug as a bug
Packaging atmosphere can select for aerobic and anaerobic organisms. A number of food processors use "smart" packaging and coatings to preserve food and extend shelf life. Smart packaging may include vacuum, modified-atmosphere packaging (MAP), variable-permeability packaging, oxygen scavengers and preservatives incorporated into the films and coatings.
New research is directed toward antimicrobial substances placed directly into the polymer. Dawson and his colleagues at Clemson University are adding antimicrobials to polymers. In one study involving deli lunch meat laced with Listeria and vacuum-packed in soy-based polymer containing nisin or a nisin-lauric-acid combo, the bacteria level dropped to 10% of the starting count after three weeks. Research is ongoing to improve the film structures because they did not flex or seal as well as conventional plastics.
MAP involves replacing the air in packaging with a specific gas or mixture of gasses, usually argon/nitrogen, carbon dioxide and oxygen. MAP can decrease oxidation reactions, bacterial and mold growth, and enzymatic activities. Gas ratios are established for a product in consideration of aw, ingredients, processing, water vapor and gas permeability, mechanical strength, and seal strength. Carbon dioxide inhibits bacterial, yeast and mold growth in bakery products and refrigerated-vending-machine sandwiches. Oxygen is not always the enemy responsible for the deterioration of products. Ratios of oxygen and carbon dioxide that match the respiration rates of products are widely used to maintain redness of meats and freshness of produce. Permeability is different for each gas and film combination, so product designers must calculate the rate of gas transfer across the film.
Raw or fresh foods, such as fruits and vegetables, commonly get an antimicrobial rinse or wash with organic acids, chlorine, dioxides, ozone, or electrolyzed-oxidizing water in manufacturing plants. However, Mantrose-Haeuser Co., Inc., Westport, CT, recently patented a customer do-it-yourself version of a coating preservative containing calcium and ascorbate ion to maintain the texture, flavor, crispness and color of fresh-cut produce. NatureSeal promises to arrest browning in apples for five days.
Amy Schauwecker specializes in international sauce and dressing product development as a senior food scientist at Unilever Foodsolutions in Lisle, IL. She may be contacted at firstname.lastname@example.org
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