For Degree and Diploma

1. 1
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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