Editors’ note: This is the second in a series of three articles on frying. Part 1, “How To Ensure Quality in Fried Foods,” was published in the June/July issue of FQ&S, and Part 3 will be published in the October/November issue.
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In 1991, Blumenthal and Stier stated that optimum frying occurs when the frying process is economic and superior quality fried food is produced. The best means for evaluating a frying operation, whether an operator is a food processor or producing fried food in a restaurant environment, is to conduct a comprehensive frying study. It is simply not possible to optimize a system if the fryer operator does not understand the system or does not understand that a fryer operation is a system. Components of the system are the fryer, the food, and the people operating the system. In addition, frying is the most dynamic food preparation system around, given that the frying oil is constantly changing, thanks to the interactions of food, water, temperature, oxygen, and the condition of the fryer.
So, what are the reasons for conducting a frying study? The first is to establish a baseline for oil degradation under normal operating parameters. Frying studies should include the following elements:
- Evolving oil chemistry;
- Food quality over time;
- Amount of food being fried; and
- Frying operating parameters.
The greater the number of chemical tests that are done, the better one understands the system. When establishing a baseline, one of the operator’s main goals is to establish a relationship between the oil chemistry, or chemical markers of oil degradation, and the sensory parameters of the food being fried. So, the operators need to be involved, as they are the ones who best understand what would be deemed quality fried food.
Once an operator has established a baseline, they have the first tool necessary for optimizing their operation. There is now a yardstick against which they can compare changes to the system: a new oil, a filter system, the use of a new oil additive, a change in food mix, a change in a formulation, or any other change.
The reasons to conduct a frying study using a standard format include the following:
- To ensure proper evaluation of the system;
- To allow the gathering of technical data to demonstrate benefits/concerns to potential users;
- To develop performance data to demonstrate benefits/concerns to potential users;
- To ensure food safety/adequate processing or process lethality;
- To understand the operations to maximize benefits or minimize concerns; and
- To allow operators and users to make intelligent, well-informed decisions on direction.
Developing a Baseline for a Fryer
Prior to conducting any scientific study, it is imperative to establish a baseline. In deep-fat frying operations, this consists of determining the chemical, physical, and sensory parameters of oil and food in existing frying operations. Once this data has been gathered, any changes to the frying system can be evaluated against the baseline intelligently and without prejudice. The baseline for any fryer operator will be current practices. When conducting a baseline study, it is vital that nothing be changed before or during the study. Lastly, prior to initiating a baseline study or any other frying study, the researchers must determine what endpoint will be utilized—that is, a chemical measurement, sensory testing, or a quality parameter.
A frying study can be done in a restaurant, in a technical center, or in an industrial processing operation. When embarking on such a study, operators must be aware that these will be time consuming and can be quite expensive. If conducting the work in a restaurant or plant, one of the challenges is to minimize disruption of normal operations.
When putting together a frying study to develop baseline data, the organizers need to determine which chemical tests will be done, which physical tests will be done, how sensory work will be done, and what sampling plan to establish. It’s essential that the fresh oil be fully characterized. Tests on fresh oil may include the following:
- Polar materials
- Free fatty acids
- Oxidative stability index (OSI)
- Peroxide value
- Anisidine value
- Fatty acid profile
- Trace metal
At least two samples should be tested. Once the testing has been completed, the results should be compared with the oil specification to determine whether or not the samples meet established specifications.
Once the fresh oil has been characterized, the next step is to prepare for the baseline study. The fryer must be completely cleaned, which means ensuring that all residual cleaner is completely removed. Rinse with water and check the pH to ensure that the pH of the rinse water matches that of fresh water. The researchers performing the study must also confirm frying times and temperatures, determine the foods to be fried, and decide how records will be kept.
The sampling schedule must also be established. Table 1 shows a recommended sampling schedule.
Testing the hot oil immediately after startup but before frying is initiated is extremely important. It will let the researchers know whether or not the fryer was properly cleaned. If residual detergent and water remain in the fryer, the metals in the detergent will form soaps, which act as prooxidants during frying and will damage the oil.
Collect oil samples at the intervals noted in Table 1 on each day of the study until you reach the endpoint. When it comes time to add oil to or top up the fryer, be sure to collect the sample before adding oil. Adding oil will dilute the oil in the fryer and will affect test results. When collecting samples of hot oil, the person collecting the samples should wear the appropriate personal protective equipment (PPE), which should include gloves, eye protection, and a protective smock of some sort.
Sensory work on the fried food should be done at the same intervals. The sensory testing should be done with input from the company conducting the study. They know the products better than anyone else and are, therefore, the experts on the sensory parameters of food. The oil samples must be collected and placed in properly labeled containers in preparation for delivery to the testing laboratory. The number of chemicals tests that are done depends on the operator. The more tests that are done, the more you will learn about the system. The same tests that were highlighted for fresh oil are the ones that can be done on the heated oils, with the exception of oil flavor. The focus should be food quality and not the taste of hot oil. At minimum, tests for free fatty acids, soaps, polar materials, and polymers should be conducted. If a company is using a rapid test of some sort, that test should be incorporated into the study.
During frying, be sure to monitor the amount of food fried, frying temperatures, how much oil is added to the fryer, and whether there were any deviations during the study. It’s also a good idea to observe what goes on during frying operations. If the oil begins to foam or to become significantly darker, record these observations. It is also useful to record anecdotal information during a baseline study. For example, if a restaurant operator’s baseline includes using a system or practice that the workers find hard to use for some reason, record that information and the problem or problems. A proposed change may make life easier for the workforce, and any change in protocol that makes life easier for people will be appreciated. In fact, if something is easier to do, there is a greater chance that the procedure will not only be done, but will be done properly.
Research personnel should also be available throughout the study to assist and help keep the study on track. This is especially important when working in a restaurant or a food processing facility. The study should continue until you reach the endpoint established prior to initiating the work. This could be poor food quality or one of the chemical markers of oil degradation.
Types of Frying Tests
So, what do the different tests mean? Let’s take a look at a few of them.
Free fatty acids (FFA). Free fatty acids by themselves have no impact on the oil or fried food flavor. In fact, it is possible to fry foods in 100% free fatty acid mixtures. Fatty acids are, however, more prone to oxidation reactions, which create problems in foods and cooking oils. They are easy to measure, so they are often used as a quality indicator in frying operations, especially in snack foods such as potato chips.
Soaps. Soap is produced in the oil during chemical refining. This is subsequently removed completely from the refined oil using special adsorbents that remove the soap, along with the trace metals and residual phosphatides, from the oil. In frying oils, soaps will form through the reaction of free fatty acids and metals in the presence of water. These metals include calcium, magnesium, sodium, and potassium. Sources of metals are food and residual caustic from cleaning operations. Soaps are surfactants and will be absorbed onto frying food. Many active filter media are designed to reduce soaps in oils. Soap is a detergent. Presence of soap causes rapid rise in FFA in the oil during frying and also causes more rapid oxidation in the oil.
Total polar materials (TPM). The simplest definition for total polar materials is all non-triglyceride materials soluble in, emulsified in, or suspended in oil. Fresh oil typically contains 2 to 4 percent polar compounds but may contain less. Once oil is exposed to frying conditions, conversion of trigylcerides is initiated and is irreversible during the frying process. Proper oil management can slow polar material formation and extend the life of the oil. There are many who consider polar materials the single most important test for degrading restaurant cooking oils. In fact, Spain, Portugal, Italy, Belgium, France, and various states/cantons in Switzerland and Germany have established regulatory limits for polar materials in restaurant frying oils. In 2000, the DGF (German Society for Fat Research) stated that polar materials and polymeric triglycerides were the best indicators of oil abuse. This statement was made as part of the published summary of the 3rd International Symposium on Deep-Fat Frying held in Hagen, Germany. Unfortunately, testing for TPM requires a skilled technician, and the test itself is expensive.
Polymeric triglycerides. Polymers are the single largest class of degradation materials in frying oils. They include dimers, trimers, polymers, tetramers, and others, and are formed through both oxidative and thermal reactions. They manifest themselves as lacquers or brown buildup on fryers or in oil. Polymers are complex and generally indigestible. As noted above, polymeric triglycerides, along with polar materials, are excellent indicators of oil abuse.
Para-anisidine value (pAV). For every molecule of peroxide that breaks down, twice the equivalent amount of anisidines are formed; however, some of these will disappear through further oxidation reactions, forming dimers and trimers. This test is valuable for the detection of reprocessed edible oils. If an oil producer further processes their oils to reduce levels of free fatty acids, the end result will be an increased anisidine value.
Once the baseline data has been compiled and reviewed, the operator should have a good idea of how the oil degrades over time. The sensory data and chemistry can also be reviewed, and one or more of the chemical markers of oil degradation may now be selected as endpoint indicator. Operators will also have a good picture of how their frying systems run, giving them the background data to properly evaluate any proposed changes aimed at system optimization.
Frying Studies for System Optimization
Once a food processor or restaurant operator has established a solid baseline for frying performance, they are set up to properly evaluate any change to their frying system. As noted above, the change can be anything, including a different filter system, a change in food formulation, or the addition of an oil additive. The procedure for evaluating the change will mirror that used to establish the baseline data. The only change between the baseline study and the system or material being evaluated will be what is being evaluated. The sampling schedule will remain the same, the test protocol will remain the same, and the way that the data is analyzed will remain the same.
Once the data has been reviewed, the operator will have a good idea of the potential benefits of the change. Among the potential benefits such studies have been able to demonstrate include, but are not limited to, the value of switching to an active filter system, the problems inherent with multi-pot frying (frying in which products are switched from fryer to fryer), oil life extension by dropping temperatures in a fryer, and the value of adopting a rapid test kit as an endpoint indicator. These are also benefits that operators can put a number on, that is, a return on investment or information that shows a change is not only technically solid, but a cost savings. Figure 1 shows the benefits of the use of an active filter system on controlling soaps in an industrial frying system. This was deemed to be a significant contributor to enhanced shelf life and improved oil life.
Operators that follow this disciplined approach will be able to develop information that is essential for making scientifically sound decisions in a business environment. They can help processors work to continuously improve their operations from a quality and safety standpoint, which is one of the basic principles of the food safety management system known as the hazard analysis and critical control points system.