When it comes to ways baked goods spoil, mold growth springs first to mind, followed closely by staling. Both of these deleterious states, visible to the consumer, render baked goods inedible. But there’s a third condition, hidden somewhat behind the scenes yet eventually detectable by nose and mouth, that bakers try to delay as long as possible. It’s the development of objectionable flavors and odors, described as rancid, through the degradation of fats and oils by oxidation.
Rancidity is a natural process with degradation starting the moment the fat or oil comes into being. There’s no way to prevent it, only to slow it, and there’s no recovery.
“Many people think that only bulk oils and high-fat foods have oxidation problems,” said Xin Tian, PhD, lead scientist, Kalsec, Inc., Kalamazoo, MI. “The fact is that low-fat products go rancid fast due to large surfaces exposed to air. In highly seasoned products, oxidation may be masked by strong flavors from the product itself; yet, in mild flavor products such as cereals, crackers and breadings, off-odors and flavors will become distinct once they are developed.”
The desire to enrich baked foods with nutritional but unstable ingredients, most notably omega-3 fatty acids, greatly increases the oxidative challenge. Additional problems are encountered with the use of specialty whole grains because they contain the germ, a source of naturally occurring polyunsaturated fatty acids prone to oxidation. Baked goods with fatty nuts and seeds can also pose an issue.
“Such challenges can be met by using antioxidant systems containing different combinations of natural phenols, vitamins and organic acids,” Dr. Tian said.
The most common approach to retard lipid auto-oxidation is to include antioxidants in the formulation. This is often done at the ingredient level, with suppliers adding antioxidants to the fat or oil to slow the chain reaction from getting past the initiation stage. For extra protection, antioxidants can be added to batters and doughs.
Traditional synthetic antioxidants are very effective, easy to use and low cost. But being chemically derived, which is obvious from their names — ethylene diamine tetra acetate (EDTA), tertiary butyl hydroquinone (TBHQ), butylated hydroxyanisole (BHA) and butylated hydrotoluene (BHT) — consumers can think them undesirable. In response, bakers are embracing clean-label antioxidants that can be discreetly added to product formulations. Common options are classified as tocopherols and high-phenolic plant extracts, such as those sourced from rosemary, green tea and licorice.
Tocopherols, also known as vitamin E, are popular oxygen scavengers. There are a number of forms of vitamin E, each with different physiological activity and functionality. When it comes to retarding development of rancidity, research suggests that the delta and gamma forms are slightly stronger antioxidants in food systems than the alpha and beta forms. However, in the human body, alpha-tocopherols have the highest bioavailability. Thus, mixed tocopherols high in non-alpha or beta tocopherols are typically used to delay lipid oxidation. They are appropriately labeled as “mixed tocopherols.”
“In addition to tocopherols that are extracted from soybeans, we offer rosemary and green tea plant extracts, all of which have both flavor and antioxidant properties, as they break the auto-oxidation chain reaction,” said Courtney Schwartz, marketing communications manager, food technologies, Kemin, Des Moines, IA. “If they are added early enough in the process, they interfere with the initiation or propagation phase by donating hydrogen to the unstable radicals, thereby breaking the cycle.”
Rosemary extract is a concentrated source of phenolic compounds, in particular carnosic acid, which functions as an antioxidant. Advanced technologies are used to remove or reduce the rosemary taste. The ingredient is simply labeled as “rosemary extract” or “natural flavor.”
Kemin is one of the world’s leading growers of rosemary and the only rosemary extract supplier that is SCS Sustainably Grown Certified and 100% grown in the US. “Our level of vertical integration allows us to provide the industry with a traceable rosemary source that will perform consistently each and every time,” Ms. Schwartz said.
Dr. Tian observed that rosemary is one of the most effective herbs to function as an antioxidant used in food systems. However, not one rosemary fits all applications.
“We offer natural rosemary extracts with different solubilities, antioxidant strengths and flavor options, tailored for various applications,” Dr. Tian said. “We also offer unique products combining rosemary with other functional antioxidants such as ascorbic acid, tocopherols and citric acid to provide extra protection for specific products and processing conditions.”
Green tea, licorice effects
Apart from the predominant phenolics — i.e., carnosic acid and carnosol — natural rosemary extracts contain other phenolic compounds that improve their efficiency. “These compounds are either antioxidants themselves, are synergists of the primary compounds or serve as emulsifiers that enhance the partition of active components into the oil or food system,” Dr. Tian said. “As a result, the natural extracts possess much higher antioxidant activities.”
Kalsec’s proprietary extraction and processing techniques allow retention of all the useful phenolic compounds. These retained, active phenolic compounds reinforce the activity of carnosic acid and carnosol, she noted.
Rosemary extract is often used in conjunction with green tea extract, a concentrated source of antioxidants classified as catechins, specifically the highly effective catechin known as epigallocatechin gallate (EGCG). Green tea extract also contains an array of other chemicals that work synergistically with EGCG, including gallic acid, carotenoids, tocopherols, ascorbic acid and minerals such as chromium, manganese, selenium and zinc.
New at Kemin is lipid-soluble green tea. “Green tea has been used in the industry for years, but it’s typically water soluble,” Ms. Schwartz said. “Our patented manufacturing process allows us to provide the industry with a truly lipid-soluble green tea that we have seen effective in matrices high in fat, such as butter cookies, cereal bars and granola.”
Natural antioxidants are typically added at higher levels compared with their synthetic counterparts. “An addition of 0.05 to 0.20% of our rosemary products, on final weight basis, is usually recommended, but dosages vary depending on application and addition method,” Dr. Tian said. “Our products can be added into the oil used in baked foods, incorporated into the dough itself or applied topically onto the surface.”
To determine the best antioxidant, as well as the best addition point and dosage, scientists typically measure the presence of the chemical hexanal, a major marker for rancidity, as well as run formal sensory tests. “We conducted a study on multigrain chips that showed our rosemary extract provided a 75% reduction in the formation of hexanal. A similar reduction was observed in an extruded cereal product containing 5% milled flax seed,” Dr. Tian reported. “Our water-soluble rosemary extract added to a granola bar formulation reduced ‘painty,’ ‘cardboard’ and ‘oxidized’ off-notes by two to three times during storage.”
Another natural ingredient is extracted from the root of the licorice plant. “It is naturally high in phenolic compounds, as much as 24%, making it a very effective free-radical scavenger at low use level (typically <1,000 ppm),” said Jenny Zhou, food technologist, ICL Food Specialties, St. Louis. “It also will not impact finished product color or flavor.” This clean-label ingredient is indicated simply as “licorice,” “licorice extract” or “natural flavoring.”
No matter the antioxidant, bakers are smart to add it early in the processing and with minimum agitation, which incorporates oxygen into the system. Further, modified-atmospheric packaging, with or without desiccant packets, can assist with keeping oxygen away.
Although there’s a trend toward clear packaging to give consumers a view of what’s inside, light accelerates oxidation, as does heat. Metal ions and biological catalysts naturally present in foods can also fuel oxidation; thus, it is helpful to incorporate ingredients that suppress their involvement as early as possible.
“We manufacture ingredients that act as ‘pro-antioxidants,’ ” said Barbara Bufe Heidolph, director, commercial and applications development, Innophos, Inc., Cranbury, NJ. The two primary ingredient categories are polyphosphates, which function as sequestrants, and acidulants, which lower pH.
“Both work synergistically with most antioxidants added to foods,” Ms. Heidolph said. “Sequestrants function by forming chelating complexes with metal ions, such as copper and iron, preventing them from catalyzing the oxidation process. Acidulants, such as phosphoric acid, supply a desired reducing environment of hydrogen ions to regenerate antioxidants.”
Iron, a nutrient added to many baked goods, also happens to be one of the most deleterious metal ions. One of the best sequestrants to manage iron is phosphate such as sodium acid pyrophosphate (SAPP).
“SAPP provides dual functions. As a chemical leavening acid, SAPP gives the finished baked good desired volume and texture; however, other than this well-known property, SAPP also helps in oxidation protection,” Ms. Zhou said. The best part, SAPP is allowed in organic baked goods as a leavening acid.
This material is effective at low doses. “Generally, the level in a chemically leavened baked good of SAPP is 2% or less of the formulation,” Ms. Heidolph said. “Chelation is pH dependent, so at a lower pH, more iron is managed. Thus, acidulants can be used to lower the pH of the environment, increasing iron binding and allowing the antioxidants to regenerate and sustain their functionality over a longer period of time.
“Because both SAPP and phosphoric acid are acidic, the formulator must take this into consideration, in particular, in chemically leavened products,” she continued. “It is important that timing of the release of carbon dioxide be taken into consideration when selecting a SAPP ingredient. There are a number of SAPP options in order to ensure a controlled rate of reaction at the target point in the baking process.”
A study conducted on crackers found that SAPP could also increase product shelf life by as much as three to four months, according to Ms. Zhou.
Bakers must remember that none of these ingredients prevents auto-oxidation. Rather, these ingredients delay and then prolong the initiation stage. The more vulnerable ingredients present in the baked item — omega-3 fatty acids, whole grains, nuts, seeds and similar materials — the more precautions must be taken to delay the inevitable rancidity reactions in fats.