0:04 [music] We welcome you to the week 2 session on heat and cooking. Uh the at the end of this session the students will be able to understand the methods of heat transfer and explain the effects of heat on food. We have discussed about uh food classification of foods and its nutrient composition micronutrients macronutrients, balanced diet and all that. The second week is going to be fully on the cooking part and the moist heat method, dry heat method and the different types of cooking and its effects on the nutrients. First of all to start with heat and cooking. Heat
0:51 acts as a primary driving force in transforming the raw food into edible forms. So most of the time cooking and nutrition has a very uh direct link to play and therefore cooking integrates science which is nothing but heat transfer with culinary practices [snorts] which cooking also determines the nutritional quality, safety and sensory characteristics. There are controlled uh heat application which ensures optimal texture, flavor and stability. This also forms a foundation for understanding food behavior during the uh processing. So coming to the cooking step, cooking is a controlled application of heat causing physiochemical and biochemical changes in the food. As you can see in the picture, you can see how the heat is
1:38 processed while cooking. It enhances the digestibility nutrient bioavailability and the sensory attributes of the food. Uh similarly it ensures the microbial safety enzyme inactivation and improved shelf life. Heat alters macroolelecules influencing the structure function and overall food quality. What is the concept of heat transfer? So as you can see in the picture how the heat flow takes place. The heat transfer is the movement of thermal energy from a higher to a lower temperature region. It occurs due to a temperature gradient within or between the systems. It is fundamental to all cooking and food processing operations. It influences the rate, uniformity and efficiency of the cooking. It also determines the final quality and characteristics of the food.
2:24 Therefore, the concept of heat transfer is very important when we talk about the cooking. How do we understand the methods of heat transfer? Heat transfer in cooking occurs through three primary mechanisms. One is conduction, convection and radiation. So these mechanisms have to be understood before you go on to the next process of the session. Each method differs in its mode of energy transmission and efficiency. Conduction involves heat transfer through direct contact between the surfaces. Whereas convection involves a heat transfer through the movement of fluids like liquids or gases. Radiation involves a heat transfer via electromagnetic waves
3:10 without any physical contact. So these are the major uh methods of heat transfer which is conduction, convection and radiation. So going to the detailed uh process of conduction. Conduction is a transfer of heat through direct contact between surfaces. This process occurs in solid materials during cooking where the heat flows from the hot region to the cooler region within the food. It is slow but at uniform mode of heat transfer. The common methods used for by utilizing the conduction method is frying, sautéing and griddle cooking. So this is the major thing that you should understand is the transfer of heat through direct
3:56 contact between the surfaces. Next is a convection. Convection is a transfer of heat through the movement of liquids or gases and they are occurring due to the circulation of heated particles within the medium. It provides faster and more uniform heat distribution than conduction because in the conduction it we also discussed that it is a slow process and it's a uniform heat distribution whereas convection is a faster process and it's more uniform heat distribution compared to convection process. This convection is natural or forced also. So the common method that we normally follow for convection is steaming and oven cooking.
4:43 Next is the radiation which is the last process which is using the electromagnetic waves without any direct or physical contact. It does not require a material medium for heat transfer and heat is absorbed directly by the surface of the food. It results in rapid heating and surface browning. The common methods in uh coming under radiation include grilling, broiling and microwave cooking which is a very common uh method of cooking. So these three methods like conduction, convection and radiation gives an idea of how the heat is getting transferred and how food is getting cooked via this heat transfer method. Effects of heat on food. Heat induces the physical, chemical and biochemical changes in the
5:30 food components because it alters the structure, the texture, the flavor and the appearance of the food. Uh basically effect of heat improves the digestibility and palatability. It may also lead to the nutrient losses especially the heat sensitive vitamins or the vitamins. Overall impact depends on the temperature, time and the cooking method. Therefore the effect of heat on the food varies with multiple factors. So when we talk about the nutrients micro and macronutrients and their effects of heat there are lot of processes that takes place which I'm going to be dealing in this particular slide where if you see carbohydrates are nothing but starch and starch under goes gelatinization with water whereas dry
6:18 heat causes dextronization and sugars show caramelization which also improves the digestibility of the carbohydrates. In proteins if you see the heat or the temperature causes dennaturation and coagulation that occurs where the structure of the protein gets unfolded and the digestibility increases and excessive heat may reduce the nutritional quality of them under fats. We can observe that when fat is getting heated up, it gets melted and the oxidation takes place at higher temperature and it forms a free fatty acid and it can develop some off flavors. And for all the melting point of the fats, smoking point is very
7:04 important. And when we talk about vitamins, as we discussed in the previous week session also the vitamins have a role to play when they are heat heat is being applied to them. They may lose some vitamins especially B complex and vitamin C because they are very heat sensitive vitamins and they are can be lost during cooking. So that's why we say we have to have a proper way of cooking these kind of uh vitamins which are enriched in uh certain foods. So there may be a destruction due to heat and leeching can happen into the cooking water and we have to identify the method where we can retain these vitamins by covering the uh
7:50 food with the lid and the so that cooking method can loss can be prevented. All that has to be kept in mind while we cook certain uh nutrients which are rich in vitamins. And also when it comes to minerals, minerals are generally heat stable. They can withstand heat and they undergo very minimal structural change and the loss may be mainly through leeching into the water and they can be retained better in dry cooking. So if we see most of the foods which are rich in minerals like iron uh calcium and all that we have to retain them better by applying a dry cooking method. That's why moist heat and dry heat plays a very important role which we'll be looking at in the second week of our videos.
8:37 Okay. What happens to the color and the flavor when the heat is applied? Heat induces my reaction causing a brown color and the flavor development. This is a classic example I would say is caramelization of sugar where you can see that the sugar gets caramelized and there a brown color which you can observe which enhances the sweetness and aroma. Pigments like chlorophyll, keratenoids and anthocyinins also undergo changes. The formation of volatile flavor compounds develop during cooking. Overall these changes on color and flavor would improve the sensory acceptability of any food. So next we move on to the effect of heat on the texture as on the heat can have a impact
9:23 on the flavor color and there can be a change in the structure as well. So if we see softening of plant tissues can happen because of the cell wall breakdown and there may be a gel formation in the starch rich foods especially gelatinization process which we have discussed it uh in the previous slide. Tenderization of meat due to the protein dennaturation can happen. So there will be a texture variation in the protein dennaturation process. Water absorption or loss which affects the firmness and the juiciness. All these things determines the mouth feel and the palatability. So if we see there are lot of effects on the food when it comes to the applying of heat on them. So we can
10:08 see that there will be a change in the color and the flavor and there may be myad reaction and the caramelization reaction and there may be a gel formation softening of the tissues and tenderization of the meat due to protein dennaturation and water absorption or loss because which affects the juiciness or firmness and all these have an impact on the cooking process because the heat is applied to them. Coming to the factors affecting the heat induced changes. As discussed earlier, there are multiple factors which can have a role to play when it comes to the applying of heat in the cooking process. Temperature and duration of heating determine the extent of changes. [snorts] Nature and composition of food influences the heat response because as and when the nature
10:56 of the food and the composition of food can vary, they will definitely have an impact on the heat response. PH of the food system affects reactions like myoord browning where you can understand the pH of the food varies and the browning reactions takes place. Water content and the cooking medium will alter the heat transfer efficiency. Surface area and size of the food also affects the heat penetration. So more the surface area the heat penetration will be and the size of the food also plays an important role. Coming to the advantages of cooking, there are lot more advantages of cooking. As we all know there are foods which can be eaten raw and there are foods which has to be cooked and to enhance the quality to
11:41 enhance the palatability. They improve the digestibility and nutrient ability. They enhance the flavor, texture and appearance. They ensure the bio microbial safety and hygiene when it is cooked properly. increases the variety and palatability of foods and it also facilitates the food preservation and storage. So these are some of the major advantages of cooking when we talk about uh the heat and cooking process. What are the disadvantages? As discussed, there may be a loss of heat sensitive nutrients like B complex and vitamin C. There may be possible formation of undesirable compounds on overheating because it may give you that charred feel or uh of flavor which
12:29 develops on overheating. There may be a changes in natural color and flavor. So there may be a little bit uh overheating process which may occur and there may be a risk of over cooking also which may affect the texture and quality of the food. So any food for example if you take biryani when it is overcooked you may understand that how the flavor gets changed and overcooked biryani may not be palatable to all of us. So we have to understand the correct method of cooking and the cooking process to be appropriate. Nutrient loss through leeching may also occur when it is leeched into the cooking water. So there are lot of disadvantages also when we talk about cooking. Nevertheless,
13:14 advantages of cooking and uh the correct method of cooking will help us to correct these disadvantages or demerits. Advantages of heat processing. When it comes to heat processing, it promotes the structural modification of the food or better assimilation. So, always applying heat, it may be a dry heat or a moist heat, but it helps in the structural modification of the food or better assimilation of the food. Similarly, it enhances the development of desirable sensory characteristics. So, it helps in the enhancing of the flavor. It enhances the odor. It enhances the texture as well. Heat processing enables safe consumption because it may be affected. Uh there may be some microbes which are present in
14:00 the food. But if you heat the food, it may the microbes may be killed. So these things ensure that we have a safe consumption through microbial and enzyatic control. Similarly, heat processing helps us to improve the functional properties of food components and there may be diversified food products and we can also develop culinary techniques with regard to heat processing. All these combinations of moist heat, dry heat and application of different types of uh cooking methodology can improvise a food and make it a better food for us to enhance the quality nutritional efficiency and thereby have a proper palatable food. Coming to the nutritional implications
14:46 of cooking. Cooking either uh by moist heat or dry heat naturally improves the digestibility and nutrient ability availability and uh it may cause some loss of heat sensitive nutrients. Over cooking can reduce the nutritional quality as well. For in order to prevent all this we have to have a proper selection of method which is crucial for any kind of nutrient to be retained in the food. So anybody can go through any type of cooking process. Unless you know the method of cooking to retain the nutrients, it may be of loss. If the nutrients are not in the food, then whatever food you eat may not be applicable or may not be bioavailable to your body. So better understand the
15:32 method of cooking to retain the nutrients and to get the proper nutrition from the food. Therefore, I would like to conclude uh this session by telling that heat application is a critical determinant of food quality and safety. Thereby we should understand the heat application in a very proper way whether it's a dry heat or a moist heat or a combination of dry heat and a moist heat cooking uh heat type of cooking. So you should understand the heat transfer which is effectively used in efficient cooking processes or practices. Thermal processing causes both beneficial and adverse changes. Optimization is essential for nutritional and sensory balance. Therefore, in order to achieve all this, we need to understand that we
16:20 have to have some proper scientific knowledge to enhance the food utilization in terms of clinical nutrition. So having heard about nutrition, food, food groups and also the method of heat transfer, how the food has to be cooked by moist heat or dry heat or combined method of cooking. We have to understand that cooking also plays an important role to retain the nutrient that is needed for our body and also to enhance the nutritional quality and availability to our body. Cooking plays a very important role when it comes to food and nutrition. Thank you for patient listening and happy learning.
