No, free radicals don’t have anything to do with student activists still on the loose since the 1960s. Instead, as fats and oils users know, free radicals are the charged molecules responsible for oxidative rancidity. Antioxidants, a specialized class of functional additives, form the only line of defense against agitators of this sort.
“Antioxidants keep foods from becoming rancid, brown or developing black spots,” explained Mary O’Brien, product manager, Batory Foods, Inc., Des Plaines, IL. “Rancid foods may not make us sick, but they are sensually unappealing.”
Most consumers, however, think of antioxidants in a radically different way. The ones that matter most to them are the phytochemicals popularly credited with disease-fighting properties. They include the mineral selenium and vitamins A, C and E. Many claim that phenolic compounds found in so-called superfoods and superfruits protect cells in the body from the damaging effects of free radicals.
Although science has yet to confirm these claims through clinical studies, such antioxidants appeal powerfully to seekers of health and wellness. These compounds continue to attract attention. For example, blueberries qualify as a superfruit, and the Wild Blueberry Association of North America holds an annual conference on health benefits.
“These are interesting times for anybody working in this area,” said Mary Ellen Camire, PhD, professor, food science and human nutrition, University of Maine, Orono, ME. “There’s so much we don’t know yet.”
Long before nutritional antioxidants grabbed the spotlight, food-grade additive antioxidants protected fats and oils against rancidity. At very low levels, these compounds interrupt the autoxidation cycle in fats and oils. They can also sequester troublesome metal ions at fault in discoloration.
Oxidative rancidity causes sharp, offensive odors and tastes in foods. Oxygen in the air reacts with the unsaturated part of fatty acids to form peroxides, hydroperoxides and, finally, carbonyl compounds. “Reaction products such as aldehydes, acids, ketones and alcohols impart the harsh flavors and odors that render foods useless and actually unfit for consumption,” explained Laxman Singh, senior vice-president of R&D, Vitamins Inc., Michigan City, IN.
Added to fats and oils, antioxidants slow the deterioration of flavor and color and minimize nutritional loss, thus extending shelf life. “Antioxidants will delay or inhibit oxidation by either scavenging free radicals or chelating metals that can act as catalysts of oxidation,” said Cathy Dorko, industry manager, bakery fats and oils, Danisco USA, Inc., New Century, KS. The company produces Grindox food-grade antioxidants and Guardian natural extracts, including TOCO 70 mixed tocopherols.
The most commonly used food-grade antioxidants are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ) and propyl gallate (PG). “BHA and BHT bind up free radicals that can attack fatty acids,” said Brandon Olson, director of R&D, Prinova USA, Carol Stream, IL. The company’s antioxidant roster includes BHA, BHT and PG as well as ascorbic acid.
These materials are often used in combination with chelating agents and synergists such as ascorbic, citric, phosphoric and tartaric acid and ethylenediaminetetraacetate (EDTA), which eliminate trace metals that cause discoloration.
“But [the chemical antioxidants] are controversial,” Ms. O’Brien cautioned. Batory Foods markets acidulants (ascorbic, citric and phosphoric acid) as well as a variety of oils and bakery shortenings.
Natural ingredients such as vitamin E (or tocopherol) also figure into the antioxidant equation, but they require higher usage levels. A number of plant materials carry antioxidant activities, including extracts of rosemary, green tea and oregano, among others.
“Natural extracts and plant-derived antioxidants quench free radicals, thus terminating autoxidation reactions,” explained Kristen Robbins, assistant R&D manager, Kemin Food Ingredients, Des Moines, IA. The company’s Fortium natural extracts and plant-derived antioxidants include an extensive line of TBHQ, mixed tocopherols, and rosemary and green tea extracts.
“A decrease in the snack food seasoning intensity is often the first sign of oxidation,” Ms. Robbins observed. “Depending on the freshness of the raw materials, extract usage level and packaging, natural extracts can increase shelf life by several weeks, if not months.”
Several variables affect oxidation and, thus, the selection of antioxidants. One factor is the type of fat or oil used in the application. “The extent of inhibition and/or delay will depend on the number and position of double bonds in the lipid, its amount of unsaturation,” Ms. Dorko said.
Processing conditions come into play as well. Ms. Dorko noted that BHA, BHT and PG are not suitable for frying. Is the food being produced governed by a federal Standard of Identity that permits or precludes use of antioxidants? Shelf life requirements and packaging type also figure into the choice of antioxidant.
Formulators can achieve performance synergies with the right selection, according to Jill McKeague, senior scientist, Kalsec, Inc., Kalamazoo, MI. The company offers Herbalox and Duralox natural antioxidants and oxidation management systems.
“Our strategy focuses on multifunctional formulations in which each element delivers a different type of antioxidant functionality,” Ms. McKeague explained. Radical scavengers slow down the rate of free radical formation and, therefore, limit and delay oxidative damage. Chelators sequester and deactivate metals that initiate oxidation. Oxygen scavengers react with and remove oxygen from the food system, and secondary antioxidants reduce and regenerate primary antioxidants. Combining natural antioxidants results in synergistic effects, she observed.
Because antioxidants improve the stability of mono- and polyunsaturated oils, they reduce the need for saturated and trans fats, which are less prone to oxidation. Many of these protective ingredients can be added directly to dough. “We have seen improved shelf life in a variety of food matrices including pretzels, shortbread and crackers,” Ms. McKeague reported.
Betsy Blades, technical marketing manager, Kemin Food Ingredients, credited the company’s Fortium line of natural extracts and plant-derived antioxidants, mixed tocopherols and TBHQ with conserving the appearance, taste and nutritional value of many bakery and snack applications without changing their flavor, color or odor profiles. “These antioxidants and natural plant extracts can be added to oil used for frying bakery and snack food items, as an ingredient in the product formulation or included in a seasoning packet,” she said, describing a variety of applications including cereals, nuts, bread, whole-grain products and chips.
Rosemary enjoys a high profile as a natural antioxidant and now comes in odor- and flavor-free forms that add nothing to foods but antioxidant protection. Rodger Jonas, director of national sales, P.L. Thomas, Morristown, NJ, reported a prime opportunity for the company’s Vitiva rosemary extract and SyneROX product blends in foods made with omega-3s and other short-chain fats. “We have found marked improvement in shelf life by employing both fat-soluble and water-soluble products,” he said. “Nuts and seeds have a similar issue that can be slowed dramatically by the use of these antioxidants.”
Natural extracts, mixed tocopherols and ascorbyl palmitate can usually be added at rates consistent with Good Manufacturing Practices (GMPs) unless a food has a Standard of Identity, Ms. Dorko explained. “There is generally no maximum allowable levels for these ingredients; however, cost and flavor may limit the amount that is practical,” she said.
Ms. McKeague noted that Kalsec’s antioxidants are generally recognized as safe (GRAS) and not typically restricted in usage levels.
BHA, BHT, TBHQ and PG have established maximum allowable levels, generally 200 ppm singly or in combination based on weight of fat or oil in a product. “They must be labeled as BHA, BHT or their drawn-out chemical name, often followed by the phrase in parentheses ‘(to preserve freshness),’” Mr. Olson explained.
In the US, natural extracts can be labeled as “natural flavor” or “natural extract,” according to Ms. Blades.
Mixed tocopherols, ascorbyl palmitate, BHA, BHT, TBHQ and PG are listed by the common or usual names with a parenthetical description of their function, “(to protect flavor, color, etc.),” Ms. Dorko observed. Mixed tocopherols can be indicated with a parenthetical description of “(natural antioxidant),” she added.
In Europe, certain rosemary extracts meeting defined processing and purity criteria have been assigned an E number and may be labeled as antioxidants. Ms. McKeague said, “The labeling varies depending on the country and type of rosemary extract but can also include natural flavor, rosemary extract, and rosemary extract flavoring.”
“Alternately, on the nutritional side, natural antioxidants and foods rich in natural antioxidants have received attention for being beneficial in protecting our bodies from the effects of free radicals,” Ms. O’Brien said. These free radicals differ from those involved in rancidity of fats and oils. In this context, free radicals form when the body breaks down foods or are generated by environmental exposure to tobacco smoke and radiation. Many people suspect such free radicals of damaging cells and playing a role in heart disease, cancer and other conditions.
The compounds of interest, those popularized as beneficial, include beta-carotene, lutein, lycopene, selenium and vitamins A, C and E.
“It isn’t just the oxidant power but the polyphenol content as well that is important,” Mr. Jonas said. For example, P.L. Thomas offers an apple extract with 75% minimum polyphenol content. “It is water-soluble and a good means to boost polyphenol content.”
Extracts of interest come from diverse sources and offer a variety of beneficial compounds. Mr. Jonas described pomegranate extract, acai and acerola as providing oxygen radical absorbance capacity (ORAC) impact as well as flavor and vitamin C content. Another is Hytolive, a natural extract from olives for which the European Food Safety Authority just approved the claim that it prevents the oxidation of low-density lipoprotein (LDL, the “bad” cholesterol) and free radical formation.
Certain fruits have been dubbed “superfruits” because of their comparatively high natural content of antioxidant compounds. Blueberries provide a good example. Dr. Camire, a food scientist who researches this subject, explained that these berries contain a variety of phytochemicals, including phenolic compounds, anthocyanins, chlorogenic acid, resveratrol and proanthocyanidins. Wild blueberries have acetylated anthocyanins, which are more stable than other anthocyanins but not common in foods.
Wild blueberries have a natural advantage over the cultivated variety thanks to their smaller size. “Because the anthocyanins are found primarily in the skin of the berry, the smaller size of the wild berry means these compounds are more concentrated on an equal weight basis,” Dr. Camire said.
Much speculation surrounds the effects in the human body of Mother Nature’s antioxidants. Among findings of the scientific research reported at the 2011 Wild Blueberry Health Research Summit were indications that blueberries improve memory tasks and aid in growth of new brain cells, decrease inflammation and exert a positive effect on insulin sensitivity.
Dr. Camire noted that blueberries can act as a conventional antioxidant in food systems, specifically processed meats. “But most people are more interested in the health aspects of blueberries,” she said.