USE OF LIPIDS in FRYING

31st October 2009 2009/10

B.K.K.K.Jinadasa GS/MSc/FOOD /3608/08

Use of Lipids in Frying

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Use of lipids in frying Introduction Cooking oil is purified fat of plant origin, which is liquid at room temperature. Some of the many different kinds of edible vegetable oils include: olive oil, palm oil, soybean oil, canola oil, pumpkin seed oil, corn oil, sunflower oil, safflower oil, peanut oil, grape seed oil, sesame oil, argan oil and rice bran oil. Many other kinds of vegetable oils are also used for cooking. Oil can be flavored by immersing aromatic food stuffs such as fresh herbs, peppers, garlic and so forth in the oil for a period of time. However, care must be taken when storing flavored oils to prevent the growth of Clostridium botulinum. Lipids of both plant and animal origin are used for the frying purposes. Normally the fats can be classified as saturated such as coconut oil and unsaturated such as Soya bean oil. In the course of deep-fat frying, food contacts oil at about 180°C and is partially exposed to air for various periods of time. Thus frying, more than any other standard food processor handling method, has the greatest potential for causing chemical changes in fat, and sizeable amounts of this fat are carried with the food ( 5- 40% fat by weight is absorbed) A variety of physical and chemical changes can be observed in the oil during frying. These changes include increase in viscosity and free fatty acid content, development of a dark color etc. During frying water is continuously released from the food into the hot oil. Volatiles (e.g. sulphur compounds and pyrazine derivatives in potato) may develop in the food itself or from the interactions between food and oil. Food absorbs varying amounts of oil during deep-fat frying (potato chips have final fat content of about 35%) resulting in the need for frequent or continuous addition of fresh oil. The food itself can release some of its endogenous lipids into the frying fat. The presence of food causes the oil to darken at an accelerated rate. A 2001 parallel review of 20-year dietary fat studies in the United Kingdom, the United States of America and Spain concluded that polyunsaturated oils like soya, canola, sunflower and corn degrade easily to toxic compounds when heated up. Palm oil is edible plant oil derived from the pulp of the fruit of the oil palm Elaeis guineensis. Palm oil is naturally reddish because it contains a high amount of beta-carotene (though boiling palm oil destroys the beta-carotene rendering the oil colorless). Palm oil is one of the few vegetable oils relatively high in saturated fats (like palm kernel oil and coconut oil). Palm oil contains several saturated and unsaturated fats in the forms of lauric (0.1%, saturated), myristic (0.1%, saturated), palmitic (44%, saturated), stearic (5%, saturated), oleic (39%, monounsaturated), linoleic (10%, polyunsaturated), and linolenic (0.3%, polyunsaturated) acids. Like any vegetable oils, palm oil is designated as cholesterol-free; however saturated fat intake increases LDL cholesterol.

Use of Lipids in Frying

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3.1. Examination of physical properties: 3.1.1. Materials Beakers Sample oils 3.1.2. Method Palm oil sample was transferred into beaker and examined them for their colour, odour and consistency. Samples were warmed to a slightly higher temperature in a beaker (60ºC) and reexamined as before. 3.1.3. Results At room temperature Character Palm oil Color Pale yellow Odor No odour Consistency Slightly viscous

At 60o C Character Palm oil Color Yellow Odor No odour Consistency Viscosity changed

3.1.4. Discussion When oil is heated lot of chemical and physical changes take place. These changes depend on the temperature that the oil is been heated. At low temperatures there would not be any significant changes when compared with oil at room temperature, but for certain oils when they are heated they can give oily smell than when they are at room temperature. This is may be due to the decomposition reactions of particular oil. 3.1.5. Conclusion The temperature affects the characters of oil such as odour, consistency and color.

Use of Lipids in Frying

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3.2. Change of physical properties on heating 3.2.1. Material Samples (Palm oil) Beakers (100mL) Thermometer (Glass – Mercury) 3.2.2. Method 20 mL of each sample was transferred into 100 mL beaker and heated up to 100 ºC and examined for physical changes and odour. Heating was continued until the oil decomposed. Smoke point of the sample was measured using a thermometer. 3.2.3. Results Sample Smoke point (ºC) Palm oil 290

3.2.4. Discussion When the oil is heated to a higher temperature thermo degradation reactions take place which leads to the decomposition of oil and smoke begin to evolve. This temperature is the smoke point or other vice the smoke point of an oil or fat is the temperature at which it gives off smoke. The smoke point of oil depends to a very large extent on its purity and age at the time of measurement. In general vegetable oils have a higher smoke point than animal fats and solid fats have low smoke points than oil fats. In the case of palm oil smokes at 2900 C. In this experiment the smoke point is 290(ºC). This may be due to the practical errors and the oil, which used must be adulterated. For any oil the smoke point must be higher than 185o C. Due to the practical reasons unable to find the flash point (maximum measurement of thermometer was 3000 C, it was not enough to measure the flash point) Different fats and oils shows different smoke point value which is given below table. Fats or Oils Type of Fat Smoke Point °C Almond Oil Monounsaturated 216 Avocado Oil Monounsaturated 271 Butter Saturated 177 Butter (Ghee), clarified Saturated 190-250 (depending on purity) Canola Oil (Rapeseed oil) Monounsaturated 204 Coconut Oil Saturated 177 Corn Oil Polyunsaturated 232 Cottonseed Oil Polyunsaturated 216 Grapeseed Oil Polyunsaturated 200 Palm Oil Saturated 230 Sunflower Oil Polyunsaturated 232 Soybean Oil Polyunsaturated 232

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3.2.5. Conclusion High temperatures change the physical properties of oil.

Use of Lipids in Frying

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3.3. Effect of hydrolytic products and water on smoke point 3.3.1. Materials Beakers Thermometers (Hg-Glass) Water Samples (Palm oil) 10% glycerol 10% stearic acid 10% Glycerol monostearate 3.3.2. Method 10% Glycerol, 10% stearic acid, 10% glycerol mono stearate solutions were prepared and 20mL of each was added into separate 100mL beakers which contains 20mL of two samples, coconut oil and sunflower oil. Appearance of solutions were examined and heated till the smoke point and flash point obtained. Experiment was repeated with water. 3.3.3. Results Palm oil With 10%

Glycerol With 10% Stearic acid

With 10%glyceryl monostearate

Appearance of the solution

Yellow colour Pale yellow colour Bright yellow colour.

Smoke Point (o C)

190

150

210

3.3.4. Discussion When lipids are over heated they begin to decompose. The temperature of this particular point is considered as smoke point of the fat. Low smoke points were observed with glycerol and stearic acid since any impurities in oils such as glycerol and high free fatty acid content reduce the smoke point of oil. Hydrolysis is the major chemical reaction during frying when there is water with oil. It increases the free fatty acid content and this leads to the reduction of smoke point. Also presences of water in food cause the oil hydrolysis and develop off flavors 3.3.5. Conclusion Presence of hydrolytic products reduces the smoke point of oils. 3.4. Lipid absorption during frying 3.4.1. Materials Deep fryers Wire baskets Perforated spoon

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Potato peelers Weighing scale Thermometers (Hg-Glass) Fat/oil (Palm oil) Potatoes 3.4.2. Method Potatoes were peeled and sliced (equal slices); and were divided into three equal portions and weighed. Palm oil was heated to about 150, 160 and 170o C in deep fryer and equal portion of sliced potatoes were submerged into the fryer with the help of wire baskets. Potatoes were fried till they became yellow brown color and the time taken for frying was noted for oils. Then the wire baskets were taken off from the fryer and let them stand for two minutes for draining. Finally fried pieces (in three different temperature) were weighed and lipid absorption was calculated by using the following equation. Lipid absorption = Weight of fried pieces (g) – Weight of unfired pieces (g) * 100 Weight of unfired pieces (g) 3.4.3. Results 1500C 1600 C 1700 C Wt of fresh potatoes (g) 149.97 150.64 150.08 Wt of fried potatoes (g) 41.96 34.52 49.76 g %of lipid absorption -72.02 -77.08 -66.84 Time (min) 16 12 7

3.4.4. Discussion When food is frying water is continuously release from the food in to the hot oil. This produces a steam distillation effect, sweeping volatile oxidative products from the oil. The released moisture also agitates the oil and hastens hydrolysis. And also the food absorbs varying amounts of oil during deep frying. In the above experiment lipid absorption seems to be a negative answer since the water in the potato chips had been released to the frying medium and palm oil had been absorbed to the potatoes. But here relationship was not clear in three different temperatures, because the level of frying was varied as our vision decision. 3.4.5. Conclusion Lipid of the frying medium is absorbed into the food while frying and water is released to the medium.

Use of Lipids in Frying

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3.5. Moisture content of unfired potatoes 3.5.1. Materials Fresh potato pieces Stainless steel dishes Desicator Oven 3.5.2. Method 5g of unfried potato pieces were taken and weighed with porcelain dishes. Both samples were kept in the oven for two and half hours then in the decicator for 20 min. The weights of both samples were measured (empty dish + sample). Finally the moisture content of the sample was calculated. The same procedure was done for the fried potato pieces in both coconut and sun flower oil. 3.5.3. Results Moisture content = Weight lost × 100 Fresh weight Fresh sample (I) Fresh sample (II) Weight of empty dish 44.5878 g 47.4849 g Wt of dish + potatoes 49.4451g 52.1120 g Weight of sample 4.8573 g 4.6271 g Wt of dish+fried potatoes[after drying]

45.3685g 48.2378 g

Wt of sample after drying/ frying

0.7807 g 0.7529 g

Weight lost 4.0766 g 3.8742 g Moisture content 83.93 % 83.73 % Mean Value of Moisture content

83.83 %

3.5.4. Discussion Moisture content in the fresh sample is very high. This continuous formation of bubbles from frying food is a proof that moisture is escaping as steam. 3.5.5. Conclusion Moisture releases from food when frying and part of the lipids get absorbed into the food.

Use of Lipids in Frying

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3.6. References: Atanu B. Bhattacharya, Sajilatha M.G., Rekha S. Singhal (2008) Lipid profile of foods fried in thermally polymerized palm oil, Food chemistry journal, volume 108, issue 4. Laboratory manual on analytical methods and procedures for fish and fish products, 2nd edition, (1992), SEAFDEC The Culinary Institute of America (1996); The New Professional Chef, 6th edition, John Wiley & Sons