Fry with stability
Oct. 29, 2013
by Laurie Gorton
A steady move away from partial hydrogenation tells the story of the past decade in bakery shortenings and frying oils. Concerted efforts to change the programming of the oilseeds themselves are now paying off in rising availability of new high-oleic, low-linolenic oils. Moved into commercial production during the past decade, they address the problem of oxidative stability by turning on the plant’s genetic machinery to skew production of fats toward more stable oleic forms and away from less stable linolenic ones.
“There are increasingly more options for high-stability oils for use in frying, spraying and shortening applications,” said Michelle Pietz, technical sales representative, ADM Oils, Decatur, IL. “These high-stability oils from multiple seed sources — soy, canola and sunflower — can be used as-is in blends or with the addition of oxidants to satisfy the needs of almost any end application.”
It’s not just the trans fats that matter in today’s debate of the nutrition of fat, it’s also the saturated fatty acids. But the discussion doesn’t stop there. “Lowering the saturated fat content makes sense for health and wellness, but you also have to have good functionality and good stability,” said Lynne Morehart, oils and shortenings technical service manager, Cargill, Sidney, OH.
Success in the switch
To date, a good many baked foods and snacks have made the switch out of partially hydrogenated oils. “Donuts, pizza crusts and biscuits are a few bakery products that have been successful in making the switch to trans-free fats,” said Jackie Steffey, product development scientist, customer innovations, AAK USA, Louisville, KY. “In frying applications, replacing partially hydrogenated oils with more stable liquid oils such as the high-oleic varieties gives the stability required for frying oils.”
The applications that adapt best to the switch are the ones that don’t require the structuring aspect of solid fats. “In general, the snack food industry has been successful in converting from partially hydrogenated oils to low-trans-fat oils that offer similar performance and flavor characteristics,” Ms. Pietz said.
In addition to transforming the frying media for potato and tortilla chips, the high-oleic oils adapted well to spray oils for crackers and similar products, according to Mary LaGuardia, Omega-9 Oils market manager, Dow AgroSciences, Indianapolis. So did microwave popcorn. “The popcorn application was tricky but has gone through the transition very well,” she noted.
About a dozen years ago, Dow commercialized its high-oleic, low-linolenic oils to replace partially hydrogenated oils for foodservice frying. Fast food outlets, in particular, comprise a large market using billions of pounds of frying fats annually. “The oils are very robust,” Ms. LaGuardia reported, “and can withstand frying temperatures longer. This means less frequent oil changes for operational and financial efficiences.”
Stability, structure hurdles
The job of a frying shortening is to transfer heat. This dehydrates the dough or batter of the fried food and drives out excess water from potato, corn and tortilla chips. Because it is absorbed by the food, it also provides mouthfeel and flavor. And that’s where stability comes into the picture.
The high-oleic, high-monounsaturated fats were designed to be stable. “These trans-free frying shortenings can give stability comparable to partially hydrogenated shortenings,” Ms. Steffey said.
Stability is required because, “first, these oils have to be robust enough to stand up to a high-heat process,” Ms. LaGuardia said. “Second, the oil is absorbed into the product, sometimes at rates as high as 20% by weight. So you need stability to support the shelf life of the product.” Hydrogenation also provided crystal structure, but in frying, stability is the most important factor.
“In frying, you also need some breakdown products to ‘condition’ the oil and produce the desirable fried flavor notes,” Ms. LaGuardia added. While that’s an important sensory aspect to the oil, an overabundance of such breakdown compounds will negatively affect flavor. “The finished food has to taste good. So, you are balancing stability with flavor development, and for that, you need the right balance of fatty acids,” she said.
Users of palm oil have stability on their side, according to Gerald McNeill, PhD, vice-president of R&D, IOI Loders Croklaan Americas, Channahon, IL. “It is naturally stable at room temperature, with the texture of butter. As a natural solid, it is an excellent candidate for products like donuts that require a non-oily texture.”
Donuts and beyond
Fried bakery applications need the additional functionality provided by solid fats. Specifically, donuts require a solid frying shortening, explained Bob Johnson, director of R&D, Bunge Oils, Bradley, IL, to achieve desired sugar and coating adhesion and avoid oil wicking onto packaging material.
“Some fried products, donuts especially, need some solid fat for structure and mouthfeel,” Ms. LaGuardia observed. “Liquid oils won’t do that on their own. Rather than use a highly saturated fat alone — the traditional choice — many oil processors are now blending naturally stable liquid oils with hard fat to achieve an overall lower saturated fat level. The combination takes advantage of the natural stability and structure of the blend.
Icings and laminating fats present other concerns, according to Mr. Johnson. These uses, he said, “require the greatest structuring and most challenging consistency in crystal structure over time.”
Frying shortenings must be able to retain acceptable flavors over the course of their fry life, according to Roger Daniels, vice-president, R&D and innovation, Stratas Foods, Memphis, TN. “In addition, if a fried product application is a donut, care must be exercised to achieve a saturated fat level that will minimize wicking or leaching out of the liquid oil component and not too high to impart a waxy mouthfeel.”
Water and oxygen are the enemies of frying fats. If present in an uncontrolled fashion, they will negatively affect the taste and quality of the finished product, Mr. Daniels explained. They degrade lipids and drive autoxidation reactions, characterized by off-odors and flavors ranging from “grassy” to “painty.” What hydrogenation did to stabilize oils against oxidation is today accomplished by advances in crop science as well as selective blending and enzymatic interesterification.
“From a formulation perspective, several alternative oils have emerged to replace partially hydrogenated vegetable oils,” Dr. McNeill observed. “All these oils have one thing in common — a very low content of polyunsaturated fat without the need for hydrogenation.”
The polyunsaturated problem
Polyunsaturated fats require some form of stabilization, one of the reasons that hydrogenation was invented. “The combination of heat and air in fryers causes polyunsaturated fat to break down quickly, causing rancid flavors to develop,” Dr. McNeill said. Additionally, frying oils containing a lot of polyunsaturated fats must be replaced frequently, thus adding to the costs of fried foods.
Omega-9 canola oils first went commercial for foodservice. “Some-thing we learned from foodservice frying is that commodity oils can polymerize and gum up fryers,” Ms. LaGuardia said. “That’s a big clean-up job. The new, more stable oils resist polymerization, and that’s important to food manufacturers as well as foodservice operators.”
Polymerization is a big problem, according to Dr. McNeill as well. He described the results as a thick “gunk” that accumulates in the bottom of the fryer. “This requires difficult, time-consuming cleanouts and loss of oil,” he said.
From bench to line
All of today’s food oils contain some saturated fats, but levels are much lower than previous oils. John Sandbakken, executive director, National Sunflower Association, noted mid- and high-oleic sunflower oils as among the lowest. “In addition, both oils have a very neutral taste and provide excellent stability without hydrogenation,” he noted.
Commodity soy oil contains 15% saturates, and partially hydrogenated soy comes in at 30% saturates plus 40% trans fats. High-oleic soybean oil, however, is 6% saturates and mid-oleic sunflower 9%. The saturateds in both high-oleic canola and commodity canola stand at 7%.
But it’s the oleic content that makes the difference on the health-and-wellness scale. High-oleic soy is 75% oleic and high-oleic canola 74%. Commodity soy is 22% oleic and conventional canola 62%.
These ratios make a difference to formulations in terms of flavor and stability. They also affect handling in the bakery and snack food plant. “It is important to look at all parameters that could affect the end product and understand how changing the oil source will impact the final product,” Ms. Pietz said. “Considering the differences in stability from the trans-fat-containing product to the low-trans-fat options is important to the oil handling and finished product shelf life.”
High-oleic oils contain natural antioxidants, but these can be destroyed by heat at frying temperatures. “You may have to look at replenishing antioxidant activity,” Ms. Morehart cautioned.
Such radical changes in fatty acid ratios will also drive changes in the production environment. “Some adjustments to the production process may need to be made to account for the alternate shortening composition of trans-free frying oils,” Ms. Steffey observed. “Users will need to test the trans-free fats in their specific application to verify if changes in production plants are needed. Even so, most have not had any difficulty in adapting to the trans-free frying shortenings.”
Turnover rates for frying oils with higher levels of polyunsaturated will need closer monitoring, Mr. Johnson stressed, “to ensure that breakdown is not outpacing carry-out.” Filtering frequency may need to increase to remove particulates that accelerate breakdown, and frying temperatures will need closer attention.
A big benefit of these liquid-at-room-temperature frying shortenings is that they can be pumped around the plant. “This is a major improvement over handling the weighty cubes of plastic and solid shortenings,” Ms. LaGuardia noted. No melting is required.
Some changes in handling actually benefit the bakery. It’s possible, Ms. Pietz observed, to save the energy once needed to melt shortening and keep a melted product in storage. “It is important to confirm with your oil supplier the optimum storage temperature for such oils,” she added. “Storing at too high a temperature can cause an increase in breakdown reactions and energy use.”
Liquid oils, such as the high-monounsaturated oils, don’t need to be held at high temperatures. “But you may need to increase their temperature to a greater degree when adding them to the fryer,” Ms. Morehart noted. “For example, if you hold oils at 80°F and take them into the fryer running at 350°F, they need more pre-heating than an oil held at 120°F going into that same fryer.” More time may also be required for preheating. She advised holding oils at no more than 10 F° above the high end of their melting point.
Still, care in managing these oils will pay off for the user. “In most instances, it is necessary to review or audit the bulk handling and storage system to ensure optimal handling within the constraints of the system or, in some cases, to identify capital needs for protection of the oils,” Mr. Johnson emphasized.
What’s to come?
Oil scientists are not done improving the functionality of fats and oils. Nor are product developers and formulators. “People continue to strategize to find the optimum lower-saturated fat for their applications,” Ms. Morehart said. “The main concerns continue to be how to keep frying fats and liquid oils in good stable condition for the best shelf life and flavor of the finished products.”
And looking at applications for these oils, Ms. LaGuardia said, “The snack category is ripe for reinvention with more healthful products. Now is the time for snack marketers to take advantage of the nutritional benefits of the new generation oils and fats.”
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