Ensuring the Safety and Quality of Fried Foods
By Richard F. Stier
On April 30, 2007, Yum! Brands announced that its subsidiaries KFC and Taco Bell restaurants have converted to using trans fatty acid free frying oils after two years of consumer testing showed no adverse effects on product quality. In October 2006, KFC was one of the first quick service restaurants to announce the move to a zero grams trans fat cooking oil. At KFC, the six-month transition to a zero grams trans fat cooking oil resulted in a switch to a low linolenic soybean oil in place of the partially hydrogenated soybean oil previously used in its U.S. locations. All, 4,200 standalone Taco Bell restaurants have converted to a trans fat-free canola oil and about 1,400 locations with multiple Yum! Brands have been converted to soybean oil.
With the U.S. Food and Drug Administration and the American Heart Association establishing recommendations that consumers limit trans fat intake in the fight against obesity, and cities such as Philadelphia and New York passing laws requiring restaurants to phase out trans fat from foods on their menus by next year, the trend to purge restaurants of ingredients containing trans fatty acids is set to continue. News media has reported that foodservice companies such as Burger King Corp., McDonald’s Corp., Starbucks and Wendy’s have also indicated their intentions to phase trans fats out of their menus. Food processors are also on the bandwagon, including Unilever, Kelloggs and Nestlé, which have reformulated products to remove or lower trans fat and hydrogenated fat from their product lines in response to the implementation of the trans fat labeling law.
This is the second frying fat purge in the past two decades, both of which occurred in response to consumer health issues. In the late 1980s, restaurants removed animal fats and animal-vegetable oil blends from their fryers when consumers and public health scientists pushed for the reduction of high saturated fats in foods. Today, statistics show that people, especially children, in the U.S. and other developed nations are simply carrying too much weight. Frying foods in oils and fats and over-consumption of those fried foods are cited as a cause of this problem, yet cooking by frying doesn’t seem to be going away. Why? Fried foods taste great. They are crisp, have wonderful flavors and aromas and fulfill a basic need: enjoyment of your food. There is an old saying, “We must eat to live;” and its corollary, “We should live to eat.” Ultimately, life and diet would be awfully dull without foods that taste good, satisfy the soul and can be a trifle indulgent.
There is another reason, however, that foods will continue to be fried. The frying process is a very efficient means of transferring heat and cooking foods. The frozen potatoes that may accompany an evening meal take 15 minutes in a pre-heated oven at 375F to fully cook, yet are done in a few minutes in hot oil. Restaurants and fast food operations can served more people by using a fryer than by baking or microwaving products. In the food industry, whether it is at the industrial level or in foodservice, efficiency means money. What so many people forget is that we are in the food business. If the business is not successful, it disappears. So, as restaurants and food manufacturing companies in which frying food is part of the processing or preparation of finished product, it is important to consider not only how to respond to the trends for healthier end products but to consider what constitutes quality and safety in this unit operation. By transitioning to other types of fats and oils, are we somehow changing the frying process such that other food safety or quality challenges emerge?
Quality in Deep-Fat Frying
The ultimate yardstick of any food is consumer acceptance. As noted, fried foods taste good. In the past decade, there have been hundreds of low-fat, reduced fat and no-fat products introduced to the marketplace. The failure rate has been enormous simply because they did not meet customer expectations for taste or other quality-related attributes, including mouthfeel, texture or color. There are likely people who still pine for the “good old days when fast food fries were cooked in tallow.”
Fried food quality is a function of oil quality. If the cooking oil is abused or damaged, it affects the texture, taste and overall flavor perception of the food. The Europeans are the leaders when it comes to research pertaining to deep-fat frying. They have organized five symposia since 1973 on this cooking process, and in 2000, the symposium’s number one recommendation was: “The principle index for deep-fat frying should be sensory parameters of the food being fried.”
In other words, focus on the food. This is precisely what Dr. Michael Blumenthal did in the late 1980s. He developed what he called the surfactant theory of frying that addressed how changing oil chemistry and food quality are interrelated. One of his first assumptions was that frying is a dehydration process, that is, the process drives water from the food. In an effort to explain this, he took an engineering approach. He believed that changes in oil chemistry affected how heat was transferred from the oil to the food. He felt that what brought about these changes in heat transfer was the formation of surfactant compounds. As cooking oil is increasingly abused, more surfactant compounds are formed, and hence, contact between food and oil is increased, resulting in excessive drying and darkening of the food. Dr. Blumenthal was not the first to realize that surfactant materials had a role in frying, but he was the one who determined that they were crucial to the process. In 1959, Stern and Roth from DCA (Doughnut Corp. of America) observed that surfactant compounds could be formed in degrading oils.
Frying is a dynamic process. In other forms of cooking, the heating medium—hot air, hot water or steam—does not change, whereas frying oil changes from a medium that is almost pure triglyceride when fresh to a product that can have literally thousands of different compounds that form due to interactions between the oil, food, heat and oxygen. Fritsch developed a diagram that has become a classic reference in frying that shows the complexity of frying and the myriad of reactions that occur.
So, how does one control quality in such a dynamic system? Back in 1967, Robertson proposed basic principles for maintaining frying oil quality:
• Proper design, construction and maintenance of equipment
• Proper cleaning of equipment
• Minimize exposure to UV light
• Keep salt and other sources of metal away from oil
• Filter regularly
These principles are valid today. Many also believe that it is important to monitor oil quality during frying. It is also important to maintain and monitor oil temperatures. Keeping a fryer at elevated temperatures during extended downtimes can severely damage oil.
Following these principles will maintain oil quality and allow processors and restaurant operators to maximize oil life. One tool that can help processors to better understand frying is the Frying Oil Quality Curve, developed by Dr. Blumenthal (Figure 1). The curve describes five stages of oil degradation: break-in, fresh, optimum, degrading and runaway. If one looks at French fry cooking, these changes can be seen throughout the life of the oil. When frying is initiated in a clean fryer with fresh oil, fries are light in color and do not have the rich smell one would expect in the product. This fresh oil has few surfactants, so the oil and food do not remain in contact long enough to properly cook the food. Water that escapes from the potato pushs the oil away from the product surface so the surface does not brown and the interior is not properly cooked.
As surfactants build in the oil, food quality increases to a point at which the oil is considered “optimum.” This is where one gets quality fried foods. The goal of both industrial and foodservice frying is to maintain the oil in this condition for the longest possible time. This is easier to accomplish in industrial operations, especially when cooking foods that absorb a great deal of oil such as potato chips. Such operations literally reach a steady state and can be maintained If users allow the oil to go beyond this stage to degrading and runaway stages, food quality becomes progressively worse. Products become darker, surfaces are case hardened, coatings are lost and taste is poor. Figure 2 shows French fries that have been fried in progressively degraded oils.
Once oil begins to break down, the process is irreversible. Failure to follow the basic quality guidelines noted will speed up the process of degradation. If one fails to properly clean a fryer, residual soaps will react with the oil and speed the breakdown process. The presence of metals, particularly metals such as copper and bronze, can destroy oil in a very short time. One industrial operator discovered this the hard way. The company was losing several fryer vats of oil each week and couldn’t figure why. What they eventually found was that a night shift employee was cooking his dinner in the industrial fryer. He would lower his food into the oil using a brass clothes hanger. The little bit of metal from the hanger was enough to start a cascading degradation reaction. So, if repairs are required on your fryer, don’t use a brass fitting.
Oil Filtration and Treatment
The use of oil treatment or filtration systems is regarded as an essential step for maintaining oil quality. According to Chow and Gupta, oil must be treated from the very beginning so that breakdown components of the oil, which act as catalysts for further oil degradation, are continuously removed without accumulating in the oil. There are two types of oil filtration systems: passive and active. Passive systems simply remove particulates; that is, they simply act as sieves to remove particulates from the oil. These systems include the metal screens, rolling (indexing) paper filters, paper cones, plastic cloths, plate and frame systems, systems using diatomaceous earth, and leaf filters. Active systems remove specific oil soluble chemical compounds from heated oils. These active filters or systems remove or trap not only the particulates but also remove or reduce certain non-filterable chemicals or breakdown compounds.
There are pros and cons to adopting an active filter system. Potential benefits of filtration include reduced energy usage, improved food quality, reduced oil usage, enhanced shelf life, reduced down time, oil life extension, reduced cleanup time, the use of healthier oil for frying and the potential for having a safer and more comfortable work place. When evaluating any filter material, take a look at these benefits and work to put numbers on them.
Potential concerns with oil treatments are leaching of powders into the oil, leaching of metals into the oil, the lack of good filtration equipment, potential legal issues in different countries, the capital expenditures and safety of the system. With foodservice or restaurant frying, there is another issue that needs to be factored into the equation: the worker. Any system that is introduced into a restaurant must be easy to use and field rugged. Just as one must look at the benefits, it is essential that one must look at the negatives. The bottom line is whether the benefits outweigh the costs. The supplier of the system needs to work closely with the vendor to evaluate costs and benefits. Why? The oils used for frying and foods that are fried affect how these systems per-form, but more importantly, only the users understand what constitutes quality fried food in their businesses.
Test Your Oil
There are a number of different rapid oil tests available in the marketplace. The use of rapid tests or instruments for monitoring fats and oils can provide significant benefits to food processors. Potential benefits of improved monitoring and control include reduced lab work and all activities involved with laboratory testing, more rapid detection and response to process deviations, reduced product costs thanks to enhanced operating efficiencies, reduced waste through faster startups and lower rework volumes, faster release and clearance of finished goods, lower labor costs, and most important, happier customers—customers who will continue to buy your products and ingredients.
Among the rapid tests for fats and oils commercially available, there are several physical and chemical instruments and kits that can help determine oil quality and degradation markers. Viscosity meters and electronic-based physical tests such as the Fri-Check (Belgium) help to monitor frying oil at all stages of its useful life and the point at which the operator should discard overused oil. On the chemical side, there are various handheld, portable instruments that rapidly measure (in a matter of seconds) the quality of cooking oils by determining the total polar materials (TPM) based on changes in the dielectric constant (Testo 265, Ebro FOM 200, Mir-Oil OptiFry), on a color reaction that indicates the presence of free fatty acids (FFA) (Merck Fritest, 3M LRSM, MP Biomedicals ACI-SAFE), oxides (Merck Oxifrit-Test), or multiple parameters such as TPM, FFA and water emulsion titratables (WET) (Test Kit Technologies; Libra Labs Veri-Fry), and on the observation of more polar degradation compounds through the migration of a colored spot on a silica strip (3M PCT 120).
However, like filter systems, users of these analytical tools need to work with suppliers to determine how to monitor quality. The endpoint that is used in one operation may not be appropriate for your operation. The goal is to maintain quality of the food and ensure that the oil does not go past what is considered optimum for frying. Selecting an endpoint that is too conservative or wrong can waste oil and money. Endpoints that are established using rapid tests should be established using food quality as the primary index.
Ensuring Food Safety in Frying
One would think that frying foods in oils that range in temperature from 350F to 400F would be a no-brainer when it comes to food safety. What self-respecting pathogen could survive such temperatures? As with any other food processing operation, processors and foodservice operators need to take a Hazard Analysis and Critical Control Points (HACCP)-based approach to their frying operations and determine if there are any significant risks. How many people are aware that there was recently a Salmonella outbreak that was attributed to potato chips? The cause was a contaminated seasoning, so it is important that operators take a long look at frying to determine if foods are truly safe.
Pathogens. There are many foods that are fried. These range literally from fish to fowl to vegetables to potatoes to pastries. Is there a chance that a fried food could harbor a potential pathogen? The Almond Board of California recently funded work to evaluate the effects of different processing methods on almonds in response to two outbreaks of salmonellosis attributed to consumption of raw almonds. The work indicated that normal industrial frying processes would be adequate to ensure over a 5-log reduction of Salmonella.
There are no documented outbreaks that have been attributed to fried foods, but there may be potential concerns. According to Blumenthal, there is a potential that pathogens may survive frying if oils are not maintained properly. A study that addresses this is being prepared for publication. Remember how we discussed heat transfer earlier? Abused oils may not adequately cook foods, such as breaded chicken, allowing pathogens such as Salmonella to survive what would normally be considered an adequate and safe cook. Blumenthal used differential scanning calorimetry (DSC) followed by fluorescence microscopy to better understand water migration and pooling. These studies showed that due to migration of water from frying foods, particularly near the bone of meats, there is a chance that foods could be undercooked.
Allergens. What may pose a greater risk in frying is food allergens. At the 5th International Symposium on Deep-Fat Frying, this author warned that allergens could pose a potential risk in frying, in particular restaurant operations. There are many operations that fry different products in a single fryer. There is, therefore, a potential that allergens from one food may be transferred to the oil and onto some other item. These concerns were echoed by Dr. Steve Taylor of the University of Nebraska at a short course on deep-fat frying sponsored by the Institute of Food Technologists. According to Taylor, there have been allergen incidents that have been linked to foodservice frying. These are anecdotal and very few are cited in the literature.
Both urged that the industry conduct studies to determine what kind of risk such operations do pose and whether there are processes that might minimize these potential risks. The most obvious issue is to ensure that foods are fried in separate fryers and that operators pay close attention to cleanup operations. Risks in industrial frying would be less, but there is still a chance for cross-contamination; for example, if a fish processor reused old oil from shellfish frying when doing a fin fish. That oil could contain shellfish proteins and could elicit an allergic response from a sensitive individual. One possible means of reducing allergen risks is filtration. Filters will remove particulates but is there a chance that smaller molecules might get through a product. Active systems have greater capacities to remove materials, so they might be a more effective option. Unfortunately, the work has yet to be done to demonstrate whether such processes will minimize risk.
Concerns with Abused Oil. In the early 1970s, German regulatory agencies received a number of complaints from consumers about fried food quality. This prompted scientists in that country to initiate studies into the quality of oil in restaurant frying. Researchers were never able to establish a direct link between abused oil and a health problem, but they did determine that many operators were abusing their oil. This work set the stage for the establishment of both regulations and guidelines for deep-fat frying in Europe. Regulatory limits and guidelines for restaurant frying oils may be seen in Table 1. The most common index index of oil abuse is total polar materials. The simplest definition of polar materials is the non-triglyceride materials found in heated oils. Fresh oils are almost pure triglyceride. If an operator abuses his oil to the point that the operation is out-of-compliance (24-25% polars), there is a good chance that the food being produced is of very poor quality.
So, What Other Worries?
Since the April 24, 2002 announcement by researchers at the Swedish National Food Administration and Stockholm University that acrylamide can be found in a variety of fried and oven-baked foods, scientists from all over the world have joined to look at how this compound forms in foods and determine whether it is a truly a food safety risk. The initial Swedish research indicated that acrylamide formation is particularly associated with traditional high-temperature cooking processes for certain carbohydrate-rich foods. In response to concerns about the potential risk of foodborne acrylamide based on the known toxicity of acrylamide at much higher doses than those seen in foods, the FDA and other agencies have collected data on the levels of acrylamide in different foods.
When one examines data collected by FDA, one will see that their findings agree with those of the Swedish team. As of yet, the U.S. has not established a regulatory limit for the product. Thanks to public commentary, California has yet to apply Proposition 65 to foods containing the compound and companies who manufacture these foods. In reality, this would be very difficult, because it forms in all foods containing carbohydrate that are cooked, even organic, all-natural breads and snacks. Unfortunately, some major players have caved in to pressure and will place acrylamide warnings in their operations.
Processors and research scientists are hard to work looking for ways that will effectively reduce the formation of acrylamides in fried foods, including changes in formulations, the use of additives, and changes to the process itself. Factors such as the presence of low molecular weight protein components (amino acids), reducing sugars and low water availability all affect acrylamide formation in some way. However, these materials are also crucial components in Maillard browning, which is essential to production of baked and fried food traits that are desirable. Matthaus et all have reported that potato variety, raw product storage temperatures and frying temperature affect formation of acrylamide. Reducing frying temperature can reduce the concentration of acrylamides in foods. This is also a step that can help minimize damage to the oil.
To date there is no definitive answer on acrylamide control. Projects that succeed at the bench do not translate to the production floor, but the work goes on. The most important piece of the puzzle is that based on consumption data, the compound does not appear to be a significant risk at this time.
New Oils/Trans Fats. This piece started with trans fatty acids so it seems fitting that it should end with the same topic. The changeover to trans-free or low-trans fat containing oils for frying has taken on added impetus in the last year, especially with cities like New York mandating that users phase trans fats out of their products. The no- or low-trans oils being adopted are generally vegetable oils that have been produced to meet a need, such as modified sunflower or soy oils. There are some operators who have made the switch to oils that were traditionally used only as salad oils. The use of oils such as these could create problems down the road. These oils have low levels of saturated fatty acids and often relatively high levels of polyunsaturated fatty acids.
Companies that took the time and made the effort to conduct extensive frying and consumer studies before adopting low and no trans alternatives should not have problems. Those who allowed the decision making to be driven by marketing, and did not do their homework, so to speak, may have problems. In fact, the author has already heard reports from the field about oils that are not performing properly. Users are seeing greater formation of polymers and fry life is compromised. According to Dr. Paul Addis of the University of Minnesota, saturated or monounsaturated oils are far better for fry life, health and safety than the more polyunsaturated oils. Addis believes that the change to low trans oils could create issues related to lipid oxidation products (LOPs). The resulting compounds can create other health issues such as arteriosclerosis and rheumatoid arthritis.
Restaurant operators and food processors who decide to adopt low or no trans alternatives need to do comprehensive frying studies so they will understand how these changes will affect processes, food quality and oil chemistry. Without this background information, it is very likely that operators will be in for some unpleasant surprises.
The dynamic nature of frying and the sea changes that the industry is experiencing with trans fatty acids means that processors and restaurant operators must take even greater care to follow good quality practices. Filter regularly (and maybe take a closer look at active systems), maintain and clean your equipment properly, do not do things that will damage oils such as expose them to metals, salts and UV lights, consider reducing frying temperatures, and monitor oil quality. And, perhaps most importantly, conduct proper training. Be sure that operators, especially those in foodservice, train staff on the importance of these quality and safety elements. Properly followed frying processes ensure the production of safe and high quality foods, and protect the oil, which can ensure maximum usage—and put money into the pockets of the operator.
Richard F. Stier is a consulting food scientist with international experience in food safety (HACCP), food plant sanitation, quality systems, process optimization, GMP compliance and food microbiology. He has worked with a wide range of processing systems and products, including canning, freezing, dehydration, deep-fat frying, and aseptic systems. He can be reached at firstname.lastname@example.org.
1. German Society for Fat Science. 2000. Recommendations for the 3rd International Symposium on deep-fat frying – optimal operation.” Euro J Lipid Sci Tech, 102: 8-9, 594.
2. Blumenthal, M.M. 1991. A new look at the chemistry and physics of deep fat frying. Food Tech 45:1, 68-74.
3. Stern, S. and H. Roth. 1959. Properties of doughnut frying fat. Cereal Sci Today, 4, 176-179.
4. Fritsch, C.W. 1981. A measurement of frying fat deterioration: a brief review. J AOCS,”55:10, 718-727.
5. Robertson, C.J. 1967. The practice of deep-fat frying. Food Tech, 21:1, 34-36.
6. Chow, C.K. and M.K. Gupta. 1994. “Technological Advances in Improved and Alternative Sources of Oil.” Chapter 11 in Technological Advances in Improved and Alternative Sources of Lipids. B.S. Kamel and Y. Kakuda, eds. Blackie Academic & Professional, London.
7. Stier, R.F. 2004. Tests to monitor quality of deep-frying fats and oils. Euro J Lipid Sci Tech, 1006:11, 766-771.
8. CDC. 2004. “Outbreak of Salmonella serotype Enteritidis infections associated with raw almonds – United States and Canada, 2003 – 2004.” MMWR, Dispatch 4, June 2004.
9. Blumenthal, M.M. 2007. Personal correspondence.
10. Stier, R.F. Presentation: Safety in Frying. 5th International Symposium on Deep-Fat Frying, San Francisco, CA, Feb. 20-22, 2005.
11. Taylor, S.L. Presentation: “Food Allergen Issues and Deep-Fat Frying Operations.” IFT-sponsored Short Course, Science & Technology of Frying, April 5-7, 2006, Chicago, IL.
12. DGF. 1973. Meeting summary: German Society for Fat Research. Fette Seifen Anstrichm., 75:49.
13. Stier, R.F. “The Measurement of Frying Oil Quality and Authenticity.” Chapter 8 in Frying: Improving Quality. Woodhead Publishing, Cambridge, England.
14. U.S. FDA CFSAN Office of Plant & Dairy Foods. Survey Data on Acrylamide in Food: Individual Food Products. 2002-2006. www.cfsan.fda.gov/~dms/acrydata.html.
15. Matthaus, B., N.U. Haase and K. Kosman, K. 2004. Factors affecting the concentration of deep-fat frying potatoes. Euro J Lipid Sci Tech, 1006:11, 793-801.
16. Addis, P. 2007. Personal communication.