THE SCIENCE OF COOKING: MODE OF HEAT TRANSFER IN RELATIONSHIP WITH NUTRIENT RETENTION IN SELECTED FOODS..( Egg, Vegetable)
BY: Olalekan Solomon O.
BY: Olalekan Solomon O.
INTRODUCTION
According to the Online Etymology, Science can be defined as knowledge arranged in an organized manner. Science can also be defined as the knowledge or study of the natural world based on facts learned through experiments and observation. ( Etymology. 2014).
According to Mitchell et al, (2003). Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanation and prediction about the universe.
Science is about asking question, According to Nola,R,. et al,(2005), in science you can ask about absolutely anything. It then follows that the question: is there any science of cooking? Is scientifically significant.
Cooking is the art and science, technology and craft of preparing food for consumption with the use of heat.(Wayt R. et al, 2006)
According to Nola,R. et al, (2009), cooking is the application of heat to food for the purpose of making the food more digestible, safer to eat, more palatable and to change its appearance.
Although some foods especially fruits and vegetable are eaten raw, we prefer to cook most of the items in our diet. The process of cooking not much necessity since the digestion of nutrient such as starch and some of the proteins is aided by decomposition mechanisms induce by chemical reactions that release flavors and produce coloring reactions whereas some vitamins and minerals are either destroyed or rendered inactive respectively on heat.
Cooking can be simply defined as the heat treatment of food, that is been carried out to improve its palatability, digestibility and safety (Hot, C. et al, 2007).
Drastically speaking, for cooking to take place in food preparation processing, heat must be added to the food materials. To cook food, is the art of impacting or introduced heat into the food (willett, W. 2006). It then means that such process as washing, freezing, slicing etc. of food items is never the art or science of cooking process but rather cookery because according to (Hot, C.2007) for cooking process to occur, heat must be transferred from the heat source to the food through the principle of heat and heat transfer.
The science of cooking is been used in most areas of food preparation and processing however simple and all these methods depend on utilization of heat energy.
Heat is the amount of energy flowing from one body of matter to another spontaneously due to their temperature difference, or by any means other than through work or the transfer of matter.
Heat can be thought of as a structureless, even unwanted form of energy, since many devices that produce useful energy such as electrical or mechanical energy also produce heat as a waste product. This fact is noticeable in an electric light bulb or food mixer (cortell, R. 2007)
Heat is been applied to food according to( Zheng 2002) in which is been defined as the degree of hotness, which is more expressed as temperature
History OF Cooking
Homo erectus had begun cooking food as early as 500,000 years ago. In which the degree of hotness,which is more expressed as temperature is been applied to food. Phylogenetic analysis suggests that human ancestors may have invented cooking as far back as 1.8 million to 2.3 million years ago. Re-analysis of burnt bone fragments and plant ashes from the Wonderwerk Cave, South Africa, has provided evidence supporting control of fire by early humans there by 1 million years ago. There is evidence that Homo erectus was cooking their food as early as 500,000 years ago. Evidence for the controlled use of fire by Homo erectus beginning some 400,000 years ago has wide scholarly support. Archeological evidence from 300,000 years ago, in the form of ancient hearths, earth ovens , burnt animal bones, and flint , are found across Europe and the Middle East. Anthropologists think that widespread cooking fires began about 250,000 years ago, when hearths started appearing. More recently, the earliest hearths have been reported to be at least 790,000 years old.(Luke Kim, 2013).
Method Of Coking
Cooking can be perform by using the four basic method of cooking e.g cooking by steaming, cooking by boiling, cooking by frying, cooking by baking. Microwave cooking.
2.3 A Brief History Of Heat
The history of heat has a prominent place in the history of science . It traces its origins to the first hominids to make fire and to speculate on its operation and meaning to modern day
physicists who study the microscopic nature of heat . The phenomenon of heat and its definition through mythological theories of fire, to heat, to Terra pinguis, phlogiston , to fire air , to caloric , to the theory of heat , to the mechanical equivalent of heat , to Thermos-dynamics (sometimes called energetics ) to thermodynamics . The history of heat is a precursor for developments and theories in thehistory of thermodynamics.
Early Views Of Heat
The ancients viewed heat as that related to fire . The ancient Egyptians in 3000 BC viewed heat as related to origin mythologies. One example, is the theory of the Ogdoad,or the “primordial forces”, from which all was formed. These were the elements of chaos , numbered in eight, that existed before the creation of the sun.
The first to have put forward a semblance of a theory on heat was the Greek philosopherHeraclitus who lived around 500 BC in the city of Ephesus in Ionia, Asia Minor. He became famous as the "flux and fire" philosopher for his proverbial utterance: "All things are flowing." Heraclitus argued that the three principal elements in nature were fire, earth, and water. Of these three, however, fire is assigned as the central element controlling and modifying the other two. The universe was postulated to be in a continuous state of flux or permanent condition of change as a result of transformations of fire. Heraclitus summarized his philosophy as: "All things are an exchange for fire."(philosopher Heraclitus 500 BC)
Heat Transfer
Heat is been transfer to food from a heat source by three principal methods: Conduction, Convection and Radiation.
Nutrient In Food
A nutrient is a component in foods that an organism uses to survive and grow. Macronutrients provide the bulk energy an organism's metabolic system needs to function while micronutrients provide the necessary cofactors for metabolism to be carried out. Both types of nutrients can be acquired from the environment. (Francis et al, 2007).
Essential Nutrient
[1] Micronutrients are used to build and repair tissues and to regulate body processes while macronutrients are converted to, and used for, energy
Organic nutrients consist of carbohydrates, fats, proteins (or their building blocks, amino acids), and vitamins. Inorganic chemical compounds such as dietary minerals, water (H2O), and oxygen may also be considered nutrients.
(Luke k. 2013).
[2] A nutrient is considered essential if it must be obtained from an external source either because the organism cannot synthesize it or because insufficient quantities are produced. Nutrients needed in very small amounts are called micronutrients while those needed in large quantities are called macronutrients. The effects of nutrients are dose-dependent; shortages are called deficiencies. (Luke k. 2013).
Methods Of Cooking
In other for the food to be nutritious it must be prepared in a form that would enable the nutrient to be available in a substantial amount.
There are many methods of cooking and each method has its own advantages over others. The only substance that aid cooking is heat. (w.wayt gibbs, 2006)
Cooking by Steaming: steaming method of cooking can be defined as the preparation of food by steaming under varying degree of pressure.
Cooking by Boiling: boiling can be defined as the method of cooking in a liquid at the boiling point of the liquid.in which it posses the temperature of about 100c
Cooking by frying: frying can be defined as a method of preparing food in which oil is been used to cook
Cooking by baking: this is another method of cooking food. Baking can be defined as the cooking of food by dry heat in oven in which the action of dry oven heat is modified by steam.
Cooking Time
The time required to cook food is a function of temperature, specific heat capacity and thermal conductivity of the food and the thickness of the food.
Examples for cooking time methods
Cooking by Moist Heat
Heat transfer from energy source to food surface with water or steam by convection.
BOIL
Cooking of food in the presence of high quantity of water or containing liquid in a pot.
Temperature of cooking liquid and of food: ~ 100°C; pressure: ~ 0.1 MPa.
PRESSURE BOIL
Cooking of food in the presence of high quantity of water or containing liquid in pressure cooker.
Temperature of cooking liquid and of food: ~ 102 -120°C; Pressure: ~ 0.11-0.20 MPa.
MICROWAVE BOIL
Cooking of food in the presence of high quantity of water or containing liquid in a pot by using microwave oven.
Temperature of cooking liquid and of food: ~ 100°C; Pressure: ~ 0.1 MPa.
STEAM
Cooking of food in vapour from boiling water in an atmospheric steamer pot.
Temperature of steam and of food: ~ 100°C; Pressure: ~ 0.1 MPa.
Cooking By Dry Heat
Heat transfer from energy source to food surface with air, fat, radiation (e.g. infra red) and conduction (e.g. contact grill). Temperatures of cooking medium (fat) or area or metal surface resp. are between 140 °C and 350 °C. The surface of food is usually browned.
FRY IN PAN,
Cooking of food in a pan with a small quantity of added fat. The food surface will mostly brown.
Temperature of fat or oil: 160 °C to 200 °C
Temperature of food core: <100°C 26
Cooking time: 2-8 min for eggs
4-20 min for meat and fish
3-15 min for vegetables and other foods
FRY IN OVEN
Cooking of meat in oven with and without added fat; by hot air. The food surface will mostly brown.
Temperature of air in oven: 160 °C to 250 °C
Temperature of food core: <100°C
Cooking time: 30-240 min for meat and meat products
BAKE IN OVEN
Baking in oven will usually applied to cook starch reach foods and dishes such as bread, cake, pizza, vegetables, fruits and potatoes.
Temperature of air in oven: 160 °C to 250 °C
Temperature of food core: <100°C
Cooking time: 10-60 min for vegetables, fruits
20-70 min for bread, cake, pizza, potatoes
MODES OF HEAT TRANSFER:
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems.(S.A.Al-sanea,2003)
Heat is transfer to food from a heat source by three principal methods: Conduction, Convection and Radiation. Induction and electric heating are also possible are used rarely or only an experimentally in cookery.
To better understanding what take place during the transmission of the three principal methods of heat transfer.
(a)Transmission of heat- Conduction:
This simply means the flows of heat flowing in physical content. In which heat flows from hot things to cold thing. The flow of heat through a substance from hot to cold parts of it is called the conduction of heat.
Difference substance conduct heat at different rates is their thermal conductivities are different. Generally metals are good conductors of heat liquid,gases and non-metals such as wood, polystyrenes and glass are poor conductor of heat.
Conduction and insulation may be simply explained using the kinetic theory. Hot plates are ones where there is more vibration of the hot molecules with the cooler one next to them. Conductor transfer this vibration easily, insulators do not (S.A.AL-Sanea, 2003).
(b) Transmission of heat- Convection:
This is the process whereby the heat transfer due to motion of a fluid (liquid or gas (Al-Sanea, 2003)
Convection is a method of heat flow that only takes place in fluid by means of the movement of warm parts of the fluid. A fluid is a substance, which can flow. Liquid and gases are fluid.
(C)Transmission of heat- Radiation:
This is the heat transfer by electromagnetic wave.
Radiation involves the emission of heat from high temperature source in the form of waves. Such waves pass through air in straight line to reach the surface of the food without any intermediate medium being involved (cortell, R. (2007).
Mode of heat transfer
DIRECT HEAT TRANSFER:
In this process heat penetrate into the food without the aid of an intervening medium and it involves radiation e.g grilling. A very strong heat is encountered in grilling because there is no circulation or dissipation of heat by an intervening medium. The surface of the food quickly reaches a high temperature as it absorbs the radiant heat whereas the surface heat penetrate the bulk of the food relatively slowly leading to the common observation the grilling can over cook the outside of the food leaving the inside underdone.
Method of cooking which utilize radiant heat such as grilling and infrared cooking is therefore liable to overcook the outside of food. While leaving the inside under done where such a result is desirable as in cooking steak, grilling may be the preferred method of cooking (Zheng L.C and Zhang X.X, 2002).
INDIRECT HEAT TRANSFER:
The presence of an intervening medium serves to maintain and regulate the flow of heat to food. The physical properties of the medium such as boiling point, specific heat and thermal conductivity will all influence the rate of heat transfer(Zheng et.al, 2002)
THE MODE OF HEAT TRANSFER IN RELATIONSHIP WITH NUTRIENT RETENTION IN SOME FOODS E.g(EGG, AND VEGETABLE)
Egg
Nutrient content is often altered during cooking. Cooking food improve digestion and absorption of nutrient.
The mode of heat transfer in cooking of eggs, occur as a result in transmission of heat CONDUCTION. In which the heat that present in the boiling water,is then transferred to the egg. As the outer parts of the egg heat up, the heat is transferred inward, so that the hotter parts of the egg end up in cooking the cooler, interior parts of itself. The transfer of heat from one part of an object to another part of the same object is also considered as conduction(Sweeney, et.al,2007)
Nutrient Retention in Vegetable
There are many ways to prepare vegetables for a meal, but some might be better than others, depending on what vegetable is used, and how it is been prepared.
Usually when cooking vegetables, it is important to use a little water as possible because water-soluble vitamins will leak out of vegetables when cooking. Adding water to cooked vegetables causes them to becoming mushy, which is only ideal in a creamy soup. For vegetable that are not made into a cream soup, try methods like microwaving, steaming, and baking. In which all are method that do not use much water, so the vegetables themselves do not charge in texture, color or taste.(wayt W. 2006).
COOKING METHOD USED FOR NUTRIENT RETENTION IN VEGETABLE
•Microwave
Cooking of food in the presence of high quantity of water or containing liquid in a pot by using microwave oven.
Temperature of cooking liquid and of food: ~ 100°C; Pressure: ~ 0.1 MPa.
*Steam
Cooking of food in vapour from boiling water in an atmospheric steamer pot.
Temperature of steam and of food: ~ 100°C; Pressure: ~ 0.1 MPa.
*Bake in Oven
Baking in oven will usually applied to cook starch reach foods and dishes such as bread, cake, pizza, vegetables, fruits and potatoes.
Temperature of air in oven: 160 °C to 250 °C
Temperature of food core: <100°C
Cooking time: 10-60 min for vegetables and fruits
20-70 min for bread, cake, pizza and potatoes
CONCLUSIONS
Cooking of food is not so much of choice as a requisite due to its numerous advantages. In which Cooking act as the heat treatment of food, that is been carried out to improve its palatability, digestibility and safety.
Heat is been applied to food in home and industry, in which is been express as the degree of hotness, which is more expressed as temperature.
The scientific and Technologist explanation on the numerous complexity in cooking is highly accepted to allow for improvement in cooking. At this point, we can then conveniently conclude that:
Usually when cooking vegetables, it is important to use a little water as possible because water-soluble vitamins will leak out of vegetables when cooking. Adding water to cooked vegetables causes them to becoming mushy, which is only ideal in a creamy soup. For vegetable that are not made into a cream soup, try methods like microwaving, steaming, and baking. In which all are method that do not use much water, so the vegetables themselves do not change in texture, color or taste.
Finally, it is required that water for vegetables be brought to boil before adding vegetables to shorten the cooking time and hence reduce nutrient loss through leaching.
RECOMMENDATION
This research work showed that, the numerous complexity in cooking is highly accepted to allow the improvement of nutrient in Food. It will therefore be recommended that cooking should be carried out in other to improve it’s palatability, digestibility and safety. It also be recommended that, it is required that water for vegetables be brought to boil before adding vegetables to shorten the cooking time and hence reduce nutrient loss through leaching.
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