Baking and roasting are similar processes that use heated air to alter the quality of foods. Baking is typically used for flour-based foods and fruits, while roasting is for meats, nuts and vegetables. Both processes involve heat transfer through radiation, convection and conduction to cook foods internally without exceeding 100°C. This causes surface changes that improve qualities like moisture retention. Ovens can be direct or indirect heating types, and batch, continuous or semi-continuous systems. Frying methods include deep frying by full submersion in hot oil, shallow frying with partial submersion, and stir frying using minimal oil. Frying oils undergo hydrolysis and oxidation over time, producing compounds that degrade quality

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Y.Bavaneethan.
Lecturer
Department of Food Technology
SLGTI.
1/5/2018 Y.BAVANEETHAN

2. Baking and Roasting
Baking and roasting are essentially the same unit
operation.
Both use heated air to alter the eating quality of foods.
Baking is usually applied to flour-based foods or fruits,
• And roasting to meats, nuts and vegetables.
Purpose of baking is;
• Preservation by destruction of micro-organisms and
reduction of the water activity.
Shelf life of most baked foods is short
• Extended by refrigeration or packaging.
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3. In an oven, heat is supplied to the surface of the food;
• by a combination of infrared radiation from the oven
walls.
• by convection from circulating air
• by conduction through the pan or tray.
Baking takes place at;
• Atmospheric pressure and moisture escapes freely from
the food,
• The internal temperature of the food does not exceed
100ºC.
More rapid heating and higher temperatures used in baking;
• Cause complex changes to the components of the food at
the surface. (110–240ºC and a crust )
• These changes effect the eating qualities and retain
moisture in the bulk of the food.1/5/2018 3Y.BAVANEETHAN

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5. Equipment
• Ovens are classified into direct or indirect heating types
1. Direct heating ovens
• Directly heated ovens, air and products of combustion
are recirculated by natural convection or by fans.
• The temperature in the oven is controlled automatically,
by adjustment of air and fuel flow rates
• Natural gas is commonly used
• But propane, butane, fuel oil or solid fuels are also
used.
• If abnormal baking condition, the pressure-relief panels
are fitted to the top of the ovens to protect.
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6. The advantages of direct heating ovens include:
• Short baking times
• High thermal efficiencies
• Good control over baking conditions (using the fan
speed and the rate of fuel consumption)
• rapid start-up, as it is only necessary to heat the air in
the oven.
02. In- direct heating ovens
• Steam tubes are heated by burning fuel or remote
boiler.
• Heated air is commonly recirculated through the
baking chamber and through a separate heat
exchanger.
03. Batch ovens
04. Continuous and semi-continuous ovens1/5/2018 6Y.BAVANEETHAN

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10. Deep frying
Involves the immersion of food in a pan of hot fat. Deep fried
foods are high in Fat but;
• Less fat is absorbed if the oil is very hot when the food is put
into it.
Food that are deep fried ,should be coated to prevent overcooking
and;
• prevent the food breaking up and absorbing too much fat.
When the food is placed in the hot fat;
• Eg: the egg in the coating coagulates rapidly and thus forms a
protective layer around the food.
• The food inside continues to cook by conduction and retains its
flavour and texture.
Deep fat fryers are safer because they control the oil temperature.
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11. Shallow frying
 Involves the cooking of food in layer of hot fat that comes half
way up the food.
 Heat is conducted from the base of the pan to one surface of the
food at a time.
• This means the food has to be turned at regular intervals to
ensure even cooking.
 Food that is shallow fried does not necessarily have to be coated.
Dry frying
 Some foods e.g. bacon and sausages can be fried without the
addition of fat as
• They contain sufficient fat to prevent sticking to the pan.
 Non stick pans are most suitable for this form of frying
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12. Stir Frying
• All ingredients should be finely chopped. into small pieces so
that it cooks quickly.
• A teaspoon of oil is heated in the pan and the food is put in and
stirred continuously to ensure even cooking.
• Few nutrients are lost and the food remains crisp and well
flavoured.
• It is a quick and healthy method of cooking.
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13.  Product flavor
 Product texture
 Product appearance
 Mouthfeel
 Shelf life of the product
 Availability of the oil
 Nutritional requirements
Any selection of frying oil must be
 Low in saturated fat
 Low in linolenic acid
 High oxidative and flavor stability
 Not hydrogenated (trans-fat free)
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14.  In Food
 Loss of moisture
 Development of dark color, firm texture and fried flavor
 In Oil
 Bland flavor at initial frying
 Changes due to chemical reactions
 Dark and viscous
 Unsaturated fatty acids decreases with increasing number or time
of frying
 Oil and food both undergo severe changes due to frying,
=> different frying process, variables of oil, food and
process conditions.
 Understanding new compounds in different oils and their reactions
and functions are important study during the frying process.1/5/2018 14Y.BAVANEETHAN

15. • New compounds formed in oils during frying process
• Frying is a complex process to understand completely and
thoroughly.
Causative agent Change effect New compounds
Moisture Hydrolysis Free fatty acids
Diaclyglycerol
Monoaclyglycerol
Air and Metals Oxidation Oxidized monomers
Oxidized dimers & polymers
Volatile compounds (aldehydes,
ketones, hydrocarbons)
Sterol oxides
High temperature Polymerization Dimers and non-polar polymers
Cyclic monomers
Trans isomers and position isomers
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16.  Hydrolysis in fats and oil due to lipolytic enzymes or moisture
 In Frying
 High moisture in foods to be fried
 Hydrolysis end products
• TAG + H2O Free fatty acids (FFAs) + di or
monoacylglycerol
 More in oil with short-chain unsaturated fatty acids than long
chain saturated fatty acids
 FFAs - Off flavors and decreases smoke point of the oil
• Di- and monogylcerides - Foaming of oil
• Frequent replacement of frying oil with fresh oil slows down the
hydrolysis of frying oil.
• Large amount of water in food being fried hydrolyze the oil
rapidly.1/5/2018 16Y.BAVANEETHAN

17.  Free fatty acid value is used to monitor the quality of frying oil
during a frying process.
 Oil and water do not mix except at high temperature under high
pressure or due to surfactant during frying.
 Presence of surfactant is considered majorly responsible to
facilitate formation of oil and water solution during frying
causing hydrolysis reaction.
 Sources
 Fresh oil can have may be due to chemical refining process,
poor bleaching, washing
 Foods – metal ions reacts with FFAs forms soap
 Poor rinsing of the fryer after cleaning
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18.  Lipid oxidation during frying highly complex,
=> since both oxidative and thermal reaction occur
simultaneously
 Oxidation during frying causes most significant changes in
flavors of fried foods both desired and undesired
 Thermal oxidation mechanism similar to autoxidation, but faster.
 Autoxidation of unsaturated fatty acids initiated by free radicals
in the presence of
 Oxygen – during frying, air pulled into oil
 Metals (iron, copper, nickel etc.) – food or oil
 As the temperature increases, solubility of oxygen in oil
decreases, although the degradation reactions are accelerated.
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