Antimicrobials: Setting Up Additional Hurdles to Ensure Food Safety

At this year’s IFT Annual Meeting & Food Expo, we’ll be seeing a wide range of exciting applications, such as Hispanic cheeses, dishes highlighting Pan-Asian flavors, sushi and vegetarian items, novel frozen desserts, and fortified beverages and foods, to name only a few. These applications frequently illustrate developments in flavor and health, as well as improvements in functionality and appearance. But as exciting as these developments may be, we must never forget—or take for granted—how important food safety is and the role that ingredients play as antimicrobials, substances used to preserve food by preventing growth of microorganisms and subsequent spoilage.

In fact, many of the developments highlighted at the show not only provide a mirror of the hottest trends today, but in a more subtle way, underscore the growing importance of food safety and the continued need for the development of new or additional hurdles to ensure that food safety. The popularity of raw fruits and vegetable products, refrigerated ready-to-eat meat entrees, cheeses with a high moisture content, seafood, and other convenience foods should clearly reinforce the importance of that message.

In addition to popular consumer trends, other factors are emerging, such as the globalization of the food supply, that should be taken into careful consideration when thinking about food safety and the prevention of serious foodborne illnesses.

The global nature of Food Expo—exhibitors and attendees coming from all parts of the world, ranging from Australia to China—tends to give further “food for thought” to the Science, Communications, and Government Relations column that appeared on p. 20 of the April issue of Food Technology.

The column, entitled “The ‘Shrouded Threat’ of Foodborne Parasites,” provided some interesting insight into the possible health impact of such globalization of the food supply. Author E. Spencer Garrett noted that “Within the United States, a single dinner entree can consist of ingredients from many countries. . . . Moreover, cultural habits have shifted toward the consumption of fresh, raw, and undercooked foods that bypass important preparatory measures intended to reduce or prevent infections by pathogens.”

Furthermore, according to Garrett, “Emerging global microbiological and chemical concerns, coupled with the international food trade explosion, including direct retail product sourcing and changing consumer preparation and eating habits, will likely change consumer food safety risk exposure scenarios. This new and generally unrecognized risk of foodborne parasitism can be considered a ‘shrouded hazard.’”

A sobering thought, but it does emphasize the need for continued vigilance when it comes to food safety. This month’s Ingredients section looks at some of the new and different directions that antimicrobials are taking to provide additional hurdles to ensure food safety. Some of these may include combinations of antimicrobials for synergistic effect, special ingredients working with packaging, new processing aids, ingredients combined with novel processing technologies, use of ingredients having antimicrobial components, and a variety of alternative antimicrobial agents.

An examination of these developments makes you realize that, when approaching the issue of food safety, there is no one easy answer. We have to consider not only the ingredients or the ingredient components, but other factors as well—processing, packaging, laboratory, health, and available technical, marketing, and consulting services.

Let’s now look at some of these developments. Several of them will be highlighted at the 2002 IFT Annual Meeting & Food Expo, and you might want to keep a special eye out for them. After presenting this roundup of new developments, I’ll be back to provide a few cautionary words.

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Patent discloses synergistic antimicrobial combinations. Antimicrobial combinations of natamycin, a dialkyl dicarbonate, and a sorbate preservative for treating food and beverage products is the subject of U.S. patent 6,376,005, issued April 23, 2002, assigned to The Procter & Gamble Co., Cincinnati, Ohio.

Inclusion of antimicrobials in dilute juice beverages and other such applications can create certain problems described in the patent. Consequently, it would be desirable to use preservative systems that (1) can be formulated with existing antimicrobials such as potassium sorbate; (2) are stable against microbial growth at ambient temperatures, including yeasts such as Zygosaccharomyces bailii; (3) do not contribute off-flavors to the application; (4) can be fortified with calcium; (5) can include milk or tea solids; and (6) do not require special handling, especially refrigeration, during transportation and storage.

According to the patent, it has been found that combinations of natamycin, a dialkyl dicarbonate, and a sorbate preservative can synergistically prove effective against microbial growth in a variety of food and beverage products susceptible to food spoilage microorganisms, including yeasts such as Zygosaccharomyces bailii. Furthermore, because each of these antimicrobial components are present at levels below their taste threshold, off-flavors are not contributed by their combinations.

Beverages treated with the antimicrobial combinations can be formulated with calcium or other nutrient minerals, as well as milk or tea solids. Also, treated beverages, especially dilute juice products, do not require refrigeration during transportation and storage.

Special delivery system developed. A unique delivery of sensitive ingredients in functional beverages has been developed by BioGaia AB, P.O. Box 3242, Stockholm, Sweden (phone +46 0 8 555 293 00; fax +46 0 8 555 293 01; www.biogaia.com). Called LifeTop, the system makes it possible to effectively use probiotics in shelf-stable beverages, as well as create novel opportunities for antimicrobials.

The system is designed to protect the sensitive ingredient, such as the company’s probiotic Lactobacillus reuteri, during storage and distribution, extending long-term survival of the sensitive ingredient in packages that have a long shelf life. L. reuteri is a probiotic bacterium naturally occurring in the intestinal flora of humans and animals. It can withstand exposure to the acidic gastric juice and bile salts in the upper small intestine, and can adhere to the intestinal mucous membrane and epithelial cells—a vital characteristic for a probiotic bacterium to generate health benefits.

Reuteri is special among probiotic bacteria in its ability to form the antimicrobial substance called reuterin. This substance can reduce or prevent the growth of potentially pathogenic microorganisms of different types, both Gram-positive and Gram-negative bacteria, viruses, funguses, and protozoa. Another more recent discovery is a substance called reuteri-cyclin, which also combats other microorganisms. Supplementation of reuteri promotes equilibrium in the normal intestinal flora.

According to the manufacturer, the functional ingredient is packed in a blister with a protective barrier that is integrated in the cap of the bottle. This barrier protects the ingredient from oxygen, moisture, and other factors. When activated, a special mechanism efficiently releases the ingredient into the beverage where it dissolves quickly and distributes evenly in the liquid.

In addition to the cap, a straw has been developed which delivers the important ingredient into the beverage. Like the cap, the straw is designed to protect sensitive ingredients during storage and distribution. The sensitive ingredients are automatically released and mixed with the liquid when the beverage is drunk through the straw. The straw is attached to the package in the same way as a regular drinking straw and fits virtually any portion-size package.

The system is suitable for a wide range of different ingredients, such as probiotics, vitamins, minerals, colors, and flavors. As already suggested, the use of a particular ingredient—or ingredient combinations—with the novel packaging can create unique opportunities in such areas as antimicrobials.

At Food Expo, the product will be highlighted by the company, a first-time exhibitor.

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A sweet antimicrobial. Honey, in addition to its sweetness, offers a variety of functionality and health benefits. Latest technical studies are now looking at how the incorporation of certain varieties of honey into foods can enhance their safety and shelf life.

Past research has demonstrated strong antimicrobial activity by specific honey samples against Staphylococcus aureus. As a result of those findings, a new study conducted by researchers at Cornell University investigated the spectrum of antimicrobial activity of different types of honey against several food pathogens and food spoilage microorganisms.

According to the researchers, the microorganisms tested were inhibited by both hydrogen peroxide and other antimicrobial agents found in the honey. Tarweed and Montana Buckwheat samples impeded growth of L. monocytogenes at one-quarter and one-eighth dilutions, respectively, as well as Lactobacillus, Bacillus, E. coli, and Salmonella at stronger dilutions. The Chinese Buckwheat sample was effective against E. coli and Salmonella only at full strength. Gram-negative bacteria seem to be inhibited by honey’s high sugar concentration, while Gram-positive bacterial appear to require a threshold inhibitory level of antibacterial activity to prevent growth.

The researchers found that certain varieties of honey were shown to exhibit non-peroxide antimicrobial activity and were capable of inhibiting the growth of food pathogens and food spoilage microorganisms. Consequently, the incorporation of certain varieties of honey into foods could enhance their safety and shelf life without the use of chemical preservatives.

The findings of this study will be provided in Paper 61C-11.

Lactoferrin formulation can enhance meat safety. Activated lactoferrin, discussed in the March 2002 issue of Food Technology (see feature article, “Activated Lactoferrin—A New Approach to Meat Safety,” p. 40, and the Ingredients section, “Beefing Up Innovations for Meat and Poultry Ingredients,” p. 54), can help enhance food safety of meat and poultry products.

The formulation of lactoferrin may be used as a processing aid to provide fresh meat with an added level of protection from pathogenic bacteria, such as Escherichia coli O157:H7, Salmonella, and Campylobacter. Researchers at California State Polytechnic University have shown that applying an activated form of lactoferrin to meat surfaces prevented harmful bacteria from attaching and multiplying.

The product is manufactured and marketed by aLF Ventures, LLC, 299 S. Main St., Salt, Lake City, UT 84111 (phone 801-961-1131; fax 801-961-1135). The company—a joint venture between Farmland National Beef Packing Co. L.P. and DMV International—will open a new state-of-the-art research and development laboratory in Pomona, Calif., to pursue additional uses for the food safety technology, including chicken, pork, fish, and fresh produce.

On January 10, 2002, the U.S. Dept. of Agriculture approved the use of activated lactoferrin.

Ultrasound can improve the activity of antimicrobials. Novel processing technologies, such as high-intensity ultrasound, are being explored as a way to yield antimicrobials with improved activity. The resulting enhanced antimicrobials would enable food manufacturers to develop new products that are stable at room temperature and have a prolonged shelf life.

A recent study conducted by University of Tennessee focused on altering antimicrobial efficiency of lysozyme against Listeria monocytogenes using high-intensity ultrasound. The antimicrobial activity of lysozyme may be influenced by its physicochemical properties (such as molecular structure and interfacial activity). Manipulation of these properties by high-intensity ultrasound could improve the antimicrobial activity of lysozyme.

The results of the study, which will be reported in Paper 61C-20, suggest that partial denaturation of lysozyme may be used to enhance activity against L. monocytogenes strains. The results also suggested that ultrasonicated lysozyme retained some activity compared to heat-treated lysozyme.

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Identifying and isolating antimicrobial components. Researchers from different food areas are pursuing the identification and isolation of certain health-promoting components within foods and food ingredients. Some of these components have antimicrobial properties and may play an increasingly important role in providing another hurdle to ensure food safety.

Here are just a few emerging developments:
• Anthocyanin extracts from black carrots and red grapes, along with flavonoid extracts from rosemary and sage, were studied for their antimicrobial properties. A study conducted by researchers from Monterrey Institute of Technology–Campus Monterey, Mexico, and the University of Florida evaluated these antimicrobial properties and their interaction within an optimized range of antimicrobial activity. Favorable antimicrobial interactions between polyphenolics isolated from these various sources were found, demonstrating potential value. Paper 61C-38, “Determination of Antimicrobial Properties of Anthocyanins Naturally Stabilized by Flavonoids,” will discuss these results.

• The effect of natural extracts on growth of foodborne pathogens in cooked beef were studied by researchers from the University of Missouri. Results, which will be presented in Paper 76B-10, showed that the use of such products as grape seed extract, pine bark extract, and rosemary can provide multiple benefits, including antimicrobial effects, in refrigerated pre-cooked beef.

• A dried plum ingredient offering a variety of benefits, including antimicrobial properties, will be highlighted at IFT Food Expo by the California Dried Plum Board, 3841 N. Freeway Blvd., Ste. 120, Sacramento, CA 95834 (phone 916-565-6232; fax 916-565-6237; www.CaliforniaDriedPlums.org). Called Plum Juicy, the ingredient will be showcased in a variety of meat and poultry applications, such as hamburgers, turkey burgers, hot dogs, and pork sausage, which will all be available for sampling.

Researchers at Kansas State University have studied the effectiveness of dried plum puree as a microbe inhibitor in ground meat products. A use of 3% by weight level of dried plum puree has reportedly registered up to a 99% kill rate against virulent pathogens such as E. coli and Salmonella in ground meats.

• Whey products contain a cluster of components that are reported to have physiological functionality. For example, lactoferrin (discussed earlier in this article) has potential antimicrobial properties, as well as anticancer and antiviral value.

Use of gaseous or vaporized antimicrobial agents. In recent years, microbial reduction strategies using gaseous or vaporized antimicrobial agents for potential application in food manufacturing has been studied. Gaseous chlorine dioxide, ozone, ethylene oxide, and vaporized hydrogen peroxide or acetic acid are some examples of treatments that have been evaluated for their ability to reduce microbial levels in produce. Chlorine dioxide gas and ozone gas, or bubbling of ozone gas in water, are examples of promising techniques leading to high microbial reductions.

Some studies have reported a greater than 5-log reduction for selected pathogens on produce surfaces using chlorine dioxide gas or ozone gas. Some studies have also shown that processing parameters, such as gas concentration, treatment time, relative humidity, and temperature, play an important role.

Paper 19-5, presented by Purdue University, will highlight some of the research and potential use of these and other nonthermal technologies. Understanding alternative methods for nonthermal processing will aid in the production of safer and higher quality fruit and vegetable foods.

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Inhibiting C. perfringens in roast beef system. Inhibition of Clostridium perfringens outgrowth during chilling of roast beef was the subject of a recent study conducted by researchers at Kansas State University. The study found that incorporation of antimicrobials sodium lactate and buffered sodium citrate in a roast beef system can provide an additional measure of safety in controlling germination and outgrowth of C. perfringens spores.

C. perfringens spores are common contaminants of meat, poultry, lentils, and many other foods, and has been implicated in a number of foodborne disease outbreaks in the U.S. Proper cooking reduces pathogenic vegetative cells of C. perfringens; however, heat-resistant spores may survive and receive sufficient heat inactivation to germinate and multiply in cooked beef and poultry if the rate and extent of cooking are not sufficient.

According to the researchers, previous studies have shown that antimicrobials such as nitrite and potassium sorbate have been effective in inhibiting C. perfringens spores.

Encapsulated acidulants provide higher microbiological safety. Encapsulated acidulants called Meatshure DA, can control the pH in fermented meat upon cooking, resulting in products with reportedly a higher margin of microbiological safety. Made using a proprietary technology, the encapsulated acidulants are available from Balchem Encapsulates, P.O. Box 175, Slate Hill, NY 10973 (phone 877-222-8811; fax 845-355-4204; www.balchem.com).

The encapulated acidulants can be mixed into the meat without protein reactions, and the acids released through a choice of heat, moisture, and time. Typical applications include traditional dry and semi-dry sausage, deli meats, other processed meat emulsions, meat-containing sauces and pasta products, and pizza toppings.

According to the manufacturer, the acidulants produce end results that are said to be 30–40% faster than other processing methods. The major benefit of this process is the elimination of the incubation step: the need for adding acid slowly to meat, as occurs in natural fermentation, is accomplished using acid that is encapsulated in an edible food coating.

New lactic acid developments highlighted. The versatility of lactic acid and derivatives will be highlighted at Food Expo by Purac America, Inc., 111 Barclay Blvd., Lincolnshire, IL 60069 (phone 847-634-6330; fax 847-634-1992; www.purac.com). The company will focus on safety enhancement for meat and poultry products.

An antimicrobial product—called Purasal Optiform—combines potassium or sodium lactate and sodium diacetate for use by the meat industry. In March 2000, the allowed use level of sodium and potassium lactates was increased from 2.0% to 4.8%, while the allowed use level for sodium diacetate was increased from 0.1% to 0.25%. With the combination of these two ingredients, it is possible to fully inhibit or control the growth of L. monocytogenes, resulting in safer meat products. The product reportedly offers a special balance in flavor and antimicrobial effectiveness.

Another recent development is the OptiForm Listeria Control Model, a tool to calculate appropriate levels of potassium or sodium lactate and sodium diacetate to control or retard the growth of Listeria in cured meat and poultry products. In appropriate formulations, it can help make a broad range of cured products—from hot dogs to hams—safer. The tool works by having the processor enter in the amount of salt, product moisture, sodium or potassium lactate, and sodium diacetate in a cured product. The resulting calculations would predict how L. monocytogenes would grow during storage at 4ºC.

Also, new at Food Expo will be the self-affirmed GRAS status for magnesium lactate and potassium lactate as nutrients in foods and dietary supplements.

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Future antimicrobials? Researchers continue to look for alternative microbial agents, and based on the number of papers on food safety and the use of antimicrobial agents that will be presented at the IFT Annual Meeting this year, there is a wide range of potential sources to further investigate.

Essential oils of South American plants—molle, muna, cedronicillo, and arrayan—have been studied for their antimicrobial properties by researchers from Texas A&M University. The antibacterial activity of these essential oils against E. coli O157:H7, L. monocytogenes, Salmonella enteritidis, and Staphylococcus aureus was tested using different methods for quantitative evaluation. The study found that the essential oils of these South American plants have a strong antimicrobial activity and could serve as potential antibacterial agents to inhibit the growth of pathogens of public health significance in foods. Paper 100C-33 will further describe these findings.

Natural antimicrobial peptides have potential application in food preservation as they kill microbial cells by destroying their membranes. Pleurocidin, an antimicrobial peptide isolated from the edible winter flounder, has been found to be active against Gram-positive and Gram-negative bacteria and is heat and salt tolerant. A study was conducted by Rutgers University to investigate the potential use of pleurocidin as a food preservative by testing its efficacy against foodborne microorganisms. Results indicated that it has broad spectrum antimicrobial activity against foodborne microorganisms at levels well below the legal limit for nisin—the only antimicrobial peptide approved for use in food. Paper 76B-23 will present these findings.

Acidified sodium chlorite (ASC) solution at concentrations between 40 and 50 ppm of sodium chlorite was recently approved by the Food and Drug Administration for use as an antimicrobial agent in water and ice to rinse, wash, or store seafood. Application of ASC to raw salmon may reduce microbial contamination and improve shelf life and safety of cold-smoked salmon products. Oregon State University conducted a study to evaluate the effects of ASC on reducing L. monocytogenes and overall bacteria populations in contaminated raw salmon. The researchers found that washing salmon with ASC reduced initial bacterial and Listeria contamination. The antimicrobial activity of ASC was enhanced when salmon was washed with ASC solution and stored in ASC ice. Findings of this study will be reported in Paper 76B-5.

The effect of selected combinations of vanillin and citral on Aspergillus flavus growth were evaluated by Mexico-based Universidad de las Americas–Puebla and Argentina-based Universidad de Buenos Aires. Synergistic effects on mold inhibition were demonstrated when vanillin and citral were applied in combination. Furthermore, mixtures of these natural antimicrobials show less pH dependence in its activity than other common antimicrobial agents, which encourages further research on applications of natural antimycotic agents. Paper 61C-4 will discuss the antimycotic activity of vanillin and citral combinations.

While many of these developments show promise and may find increasing application, it should be noted that food safety can be a complicated affair, dealing with a variety of issues, including regularity, packaging, international considerations, and consumer perceptions.

Take regulatory, for instance. Paper 24-5, which will be presented by FDA’s Center for Food Safety & Applied Nutrition, provides a regulatory perspective on antimicrobials in packaging. According to the paper, “the use of antimicrobial systems can have less obvious, but nevertheless important and unforseen effects on the safety of foods. For example, the combination of antimicrobial agents together with novel packaging materials may appear promising by reducing spoilage, resulting in an extended shelf life. However, the extended shelf life and inhibition of competitive spoilage microorganisms could also allow for pathogenic microorganims which may not have grown if the antimicrobial packaging had not been used.”

Also, there has been a tendency over the years to develop natural antimicrobial agents in reaction to consumer perception over synthetic antimicrobial chemicals—another thorny issue. While many of the new developments discussed in this article show potential, more research still needs to be done to determine their effectiveness. Consequently, caution needs to be exercised. Also, the focus of this month’s ingredients section was on emerging antimicrobials, but this should in no way negatively reflect on more traditional antimicrobials or combinations of them.

And, of course, there is no one answer when it comes to food safety. The new developments discussed here—combinations of ingredients, processing, packaging, and numerous factors—are designed to provide additional hurdles to ensure food safety.

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Some of the antimicrobials that will be highlighted at FOOD EXPO®

The following are some of the antimicrobial products that exhibitors will be highlighting at Food Expo.

• Antimicrobials, antioxidants, and other products will be featured by Eastman Chemical Co., P.O. Box 431, Kingsport, TN 37662 (phone 423-229-1388; fax 423-229-1525; www.eastman.com). Booth 2310

• A natural antimicrobial—called Inovapure—will be highlighted by Inovatech, 3911 Mt. Lehman Rd., Abbotsford, British Columbia, V4X 2N1 Canada (phone 604-857-9080; fax 604-857-0843; www.inovatech.com). The natural bioprotectant is said to be effective against a wide range of food spoilage organisms. It can be successfully used to extend the shelf life of various food products, including raw and processed meats, wine, cheeses, and other dairy products. Booth 2910

• Dust-free antimicrobial agents for use in food, animal feed, and pharmaceutical industries will be available from Macco Organiques, Inc., 100 McArthur, Valleyfield, Quebec J6S 4M5, Canada (phone 450-371-1066; fax 450-371-5519; www.macco.ca). The company manufactures organic acid salts of propionates, benzoates and acetates, as well as calcium chloride USP for pharmaceutical applications. Booth 3032

• Custom-formulated antimicrobial systems for controlling the growth of yeast, mold, and bacteria will be featured by H&A Chemicals, 1160 Tapscott Rd., Toronto, Ontario M1X1E9, Canada (phone 416-412-9518; fax 416-293-9066).

Also available are multifunctional systems, including antimicrobial, antioxidant, and antistaling agents. Applications for these products include meat and poultry, baked goods, and dairy products. Booth 8142

• A natural antimicrobial food ingredient will be offered by Rhodia, Inc., Prospect Plains Rd., Cranbury, NJ 08512 (phone 609-860-4000; fax 609-860-0245 (phone www.us.rhodia.com). Called MicroGard® MG300, the ingredient may be used in cheese and other applications to reduce the risk of L. monocytogenes contamination and improve shelf stability. Also included in the company’s portfolio is an antimicrobial rinse (Assur-Rinse) for poultry and beef slaughter, phosphoric acid, sodium phosphates, and probiotic cultures. Booth 5715

• Preservatives and fresh keeping agents will be highlighted by Anhui Chemical Importing and Exporting Co., Ltd., Jinan Mansion, 306 Tunxi Rd., Hefei, Anhui, 230001 China. Other products featured include citric acid for solution, antioxidants, flavors and fragrances, sweeteners, and colorants. Booth 2101

by DONALD E. PSZCZOLA
Associate Editor