Can we re-use cooking oil, once it is utilized for frying foods?
- By:Aiman Zaidi
Frying is one of the most common methods used for the preparation of food such as French fries, chips, samosas, patties, pakodas and various other products. Frying temperatures can range from 170–190°C. Fried Foods are good in texture, flavor, aroma and taste. Soft foods become crispy when fried and so are liked by all. Nowadays, fried foods are not considered healthy and are regarded as nutritional villains. However, not all researches show that the consumption of fried foods is unhealthy; there are some which report high level of antioxidant content in fried foods.
Whether fried food is healthy or unhealthy depends on the following factors-
(a) Individual’s Age :Children require more fat than adults as they are growing and more active. On the other hand, adults require less fat. Those who have heart problems should not consume oils having high content of saturated fatty acids. As per World Health Organisation (WHO) recommendation, the total fat intake as % of Energy should not be less than 15% and should not exceed 30%. The intake of Saturated Fat (SFA) as % of Energy should not exceed 10% (7% for cardiac patients) respectively.
(b)Types of oils and fats used for frying :Cooking oils with more saturated fatty acids such as palm oil are usually more stable than the oils with more unsaturated fatty acids such as soybean oil which decomposes easily at high frying temperature, leading to the formation of Polar Compounds. So oils with more saturated fatty acids can be used for frying, provided it is occasional. On the other hand, oils with higher levels of unsaturated fatty acids are far healthier, provided they are used only once for frying.
(c) Overall dietary pattern Fried foods consumed occasionally may not be as unhealthy as when consumed regularly along with processed or junk foods and,
(d) Re-use of frying medium- The oil if used once for frying is ideal. However, if used repeatedly for frying is considered a bad practice.
Repeated frying causes several oxidative and thermal reactions which result in change in the physicochemical, nutritional and sensory properties of the oil. These changes include development of dark color, increase in viscosity and free fatty acid content, decrease in iodine value and surface tension, changes in refractive index and an increased tendency to foam. The flavor and stability of compounds present in the oil are also changed.
Numerous by-products that are volatile and non-volatile in nature such as free fatty acids, alcohols, cyclic compounds, dimers and polymers are produced during frying. The majority of the non-volatile by-products are generally categorized as the Total Polar Compounds (TPC). The TPC constituents include dimeric fatty acids, triglyceride monohydroperoxides, polymerized triglycerides (PTG), cyclic fatty acid monomers and aldehydic triglycerides.
The toxicity of these compounds is due to their high reactivity with proteins, nucleic acids, DNA and RNA and reports have related them to the cause of several diseases such as hypertension, atherosclerosis, Alzheimer’s disease and liver disease. A probable human carcinogen, acrylamide is produced when the food containing starch such as potato chips are heated above 120°C, due to a reaction between amino acids (e.g., asparagines) and reducing sugars (glucose and fructose).
Therefore, it is essential to monitor the quality of used cooking oil which in turn affects the quality of fried foods.
Guidelines in Food Safety and Standards (Licensing and Registration of Food Businesses), Regulations 2011-
At Present, following are the provisions in Schedule 4 Part-V- Specific Hygienic and Sanitary Practices to be followed by Food Business Operators engaged in catering/ food service establishments -
|S. No.||Clause No.||Provisions|
|1.||(Part -V)(II)(3)(e)||Re-use of cooking oil should be avoided.|
|2.||(Part -V)(II)(3)(J)||In case of reheating of oil, use maximum three times to avoid the formation of trans fat. It is ideal to use once if possible.|
|3.||(Part -V)(VI)(7)(4)||Re-heating and reuse of oil should be avoided as far as possible. Avoid using leftover oil wherever possible.”|
The above mentioned provisions are subjective. There is need to have quantitative limits for relevant parameters beyond which a vegetable oil is not safe for further use. In order to safeguard consumer health, FSSAI has therefore fixed a limit for Total Polar Compounds (TPC) at 25% beyond which the vegetable oil shall not be used. This is based on the reference to international regulations and scientific advice. The draft notification has been made (available on FSSAI Website www.fssai.gov.in) and comments received from stakeholders are being considered. Enforcement of the said standard by the enforcement agencies will come into effect after the final gazette notification of the standard.
Total Polar Compounds
The estimation of Total Polar Compounds (TPC) is a widely accepted parameter to decide whether the oil is safe for further use or not. The TPC Value is considered a better indicator since it refers to all degraded products from the initial triglycerides present in the oil.
Methods for determining polar compounds in cooking oil
The Total Polar compounds are determined by reference methods such as ISO 8420:2002 and AOAC Official Method 982.27 which are generally recognized as standard methods for measurement of oil deterioration during frying. However, these methods are time consuming for on-site measurements of Total Polar Compounds for frying operation businesses. For this purpose, hand-held devices (cooking oil tester based on the dielectric method which records all polar and non-polar components and thus monitors the overall polarity) are available in market to enable rapid on-site TPC measurements. Such devices measure TPC content in the oil and display this as a percentage. These are available in the market in the range of Rs. 40,000 to Rs. 50,000 each.
Good Practices for maintaining the quality of fried foods:
From the standpoint of food acceptability and wholesomeness, it is desirable to minimize extensive oxidative decomposition, and avoid development of objectionable flavors and extensive formation of polar compounds during frying. Following good practices should be followed to control the formation of such compounds at household level-
- ✔Choice of good quality frying oil (oil having high saturated and monounsaturated fatty acids are good for frying).
- ✔Selection of the lowest frying temperature consistent with producing a fried product of good quality. The perfect temperature for frying would be that lowest temperature when the product comes up on the surface of the oil once the batter is dropped into the frying oil. The oil should not reach its smoke point. (The smoke point of an oil or fat is the temperature at which it gives off smoke).
- ✔Frequent filtering of the oil to remove food particles.
- ✔Use of fryer or utensils made of god material for frying. Stainless Steel is the ideal material to use. Avoid iron pans as it accelerates oxidation resulting in rancidity.
- ✔At household level, Oil once used for frying foods can be filtered and used for curry preparation in order to make it economical. Used oil should not be stored for longer time as the rate of deterioration is higher than the unused oil and should be consumed in a day or two.
At commercial level, following practices may be followed in addition to prescribed above-
- ✔Frequent shut down and cleaning of equipment. Sodium hydroxide and other alkalis used for cleaning a fryer increase the oil hydrolysis deteriorating the oil.
- ✔Frequent testing of the oil throughout the frying process.
- ✔Replacement of oils as needed to maintain high quality.
- ✔Adequate training of personnel.