Food Processing Lecture Notes PDF

Why foods are processed? Foods are processed to: 1. Improve their palatability. 2. Extend their life time (shelf life), especially by the destruction of microorganisms causing food deterioration. Processing methods vary in the temperatures used and in the contact time with w...

Why foods are processed? Foods are processed to: 1. Improve their palatability. 2. Extend their life time (shelf life), especially by the destruction of microorganisms causing food deterioration. Processing methods vary in the temperatures used and in the contact time with water or oil as heat transfer media. Other parameters that affect the rate of destruction of nutrients are the presence of oxygen, light, and pH of the aqueous phase.  What are the different methods of food processing? 1) Baking. 2) Frying. 3) Grilling. 4) Smoking. 5) Boiling. 6) Fermentation.  1-Baking Baking: involves cooking cakes, pasting, potatoes or fruits in a dry oven at temperature in the range 170-230оC. The surface of the food reaches the oven temperature, but in most foods e.g. potatoes or fruits, the high water content limits the internal temperature to 100оC or less.  What are the effects of backing process on food? 1. Some loss of nutrients e.g. vitamin C, may occur from the surface layer, but the bulk of the nutrients are retained. 2. Thiamin can be lost (average loss 15%) if pH of the products rises above 6. 3. Some of the amino acid Lycine can be destroyed by baking due to the browning reactions between protein and carbohydrates that contribute to the brown color and aroma of baked products.  2-Frying Frying: involves cooking in oil at temperature in the range 160-200оC. Oil gives better heat transfer than air, so cooking time tends to be shorter than for baking.  What are the effects of frying process on food? During the process of frying, foods are dipped in flour, egg, breadcrumbs, milk etc. and then fried. These ingredients add more calories to the fried foods. Eating high calorie food is the main cause of obesity. Frying of foods destroys the health benefits of nutrients present in the food. Examples: EX1: Frying of potatoes cause loss of nutrients especially vitamin C, where about 80% of ascorbic acid was converted to dehydroascorbic acid (DHA) during frying for 5 minutes at 180оC. DHA is reduced in cells, and this change should not be reducing the bioactivity of ascorbic acid from fried food. Longer fried period can cause complete loss of ascorbic acid due to oxidation.  EX2: Lean meat, fish, and chicken are healthy. However, frying of these foods causes losing of thiamin and riboflavin, with reductions up to 72% and 55%, respectively.  3-Grilling o Grilling is a popular cooking method, which can be a healthy alternative to other cooking methods, because some of the meat's saturated fat content is reduced by the grilling process. o However, grilling also presents a health risk. Two types of carcinogenic compounds are produced by high-temperature grilling. (They Will be discussed later)  4-Smoking Smoking is a process of slowly cooking food indirectly near a fire. “Indirectly” means that the food is not placed directly over the heat source but over a drip pan of water placed under the food on the grill. Steam from the water helps destroy harmful bacteria that can cause food borne illness.  To ensure that food are smoked safely: 1-Two types of thermometers are needed, one for the food and the other for the smoker to : Monitor the air temperature in the smoker to be sure that, the heat stays between 225 and 300 °F throughout the cooking process. Keep the air hot enough to destroy bacteria as the meat cooks.  2-Cook food to a safe minimum internal temperature: Beef, veal and lamb steaks should be cooked to 145 °F. Ground beef, veal, and lamb should be cooked to 160 °F. All poultry should reach a safe minimum internal temperature of 165 °F.  What are the effects of boiling process on food? 1. Water soluble vitamins such as vitamin C, thiamin, riboflavin and minerals leach out of the food. Losses increase with the amount of added water, and also if the food is over-cooked. For example: boiling of chicken led to loss up 52%of thiamin, and 37% of riboflavin. Moreover, mashing of boiled potatoes increases losses of vitamin C by oxidation due to the increased exposure to oxygen.  5-Boiling Boiling: involves cooking in water at about 100оC. It commonly applied to vegetables and starch rich foods such as rice or potatoes. How can we minimize loss of vitamin C during boiling of vegetables? BY Immersing small amount of vegetable into rapidly boiling water. WHY immersing small amount of vegetable into rapidly boiling water minimizes loss of vitamin C? Due to rapid denaturation of enzymes, that catalyze oxidation of ascorbic acid.  Toxic The components processing of foodsformed by processing is essential to inactivate microorganisms and toof allow foodsflavor and texture development. However processing may lead to the formation of toxic or carcinogenic components under certain conditions. A wide range of chemical reactions occur at high temperatures such as those that occur during frying or grilling of food.  The following compounds are examples of toxic Ex1: products that may be formed: 3-Monochloropropane-1,3,diol (3-MCPD) It can be formed during industrial processing of foods such as hydrolyzed vegetable protein or soy sauce. Also it can be formed during domestic cooking or it may transfer in foods from packing material. MCPD has been shown to be a carcinogen by laboratory animal studies.  The European Commission Scientific Committee on Food (SCF) have proposed a tolerable daily intake 2µg MCPD /kg body weight. The reaction between chloride and lipids of the processed food is thought to be an important route for the formation of MCPD.  Ex2: Acrylamide It is found in fried and baked foods at levels up to 3mg/kg. Highest levels are found in crisp-bread, chips and fried potatoes. The WHO classifies acrylamide as a probable human carcinogen. The reaction between the amino acid asparagine (which occurs in potatoes and cereals) and glucose is thought to be an important route for the formation of acrylamide.  Ex3&4: HCAs and PAHs are another two types of carcinogenic compounds that are produced by high-temperature grilling: Ex3: Hetero –Cyclic- Amines (HCAs) HCAs are formed when a meat is directly exposed to a flame or very high-temperature surface. The Creatine in meat juices react with heat to form different HCAs which have been shown to cause DNA mutation, and may be a factor in the development of certain cancers.  Ex4: Polycyclic Aromatic Hydrocarbons (PAHs) PAHs are formed in smoke that's produced when fat from the meat drips on the hot coals of the grill. PAHs present in the resulting smoke, adhere to the outside surface of the grilled meat. PAHs exposure is also believed to be linked to certain cancers.  How can we reduce the amount of HCAs and PAHs formed by processing? 1. Select leaner meats. Leaner parts of meat are less likely to drip fat on the grill and produce PAH-laden smoke. 2-Marinate meats before grilling. Researchers have determined that, marinating meat before grilling, even for just a few minutes, can reduce HCAs formation by 90% or more. It's believed that the marinade forms a protective barrier for the meat juices that prevents the HCAs reaction from occurring. 3- Grill at lower temperatures. Lower temperature "roasting" also greatly reduces HCAs formation. 4-Prevent flare-ups. Flames from grill flare-ups cause the formation of both HCAs and PAHs. Turn meats frequently to minimize the chance of flare-ups. 5- Don't overcook meats. While it's important to cook poultry and ground meats thoroughly, be careful not to overcook any meat. Well-done or burnt meats contain higher levels of HCAs.  Overview on Nutritional Effects of Food Processing As mentioned before nearly every food preparation process reduces the amount of nutrients in food. In particular, processes that expose foods to high levels of heat, light, and/or oxygen cause the greatest nutrient loss. Nutrients can also be "washed out" of foods by fluids that are introduced during a cooking process. The following tables compares the typical maximum nutrient losses for common food processing methods. These tables are included as a general guide only. Actual losses will depend on many different factors, including type of food and cooking time and temperature. For additional data on specific preparation methods, see the USDA Table of Nutrient Retention Factors (2003)  HOW TO MINIMIZE NUTRIENT WATER INPUT AND OUTPUT 1- Choose fresh foods that are not over-ripe, cut or scraped. 2- Store foods in a cool, dark place. 3- Cook the food whole, unless the outer layer is unpalatable, or contaminated. 4- When slicing the raw food, try to keep the pieces as large as possible. 5- When boiling, add the raw food to the boiling water rather than to cold water. 6-Use the smallest amount of water as possible; it is not needed to cover the food. 7- If possible use the cooking water for sauces or soups as it is a source of water-soluble vitamins and minerals. 8-Cook for the minimum time needed to make the food palatable and safe. 9- Do not use baking soda to help keep the green color of vegetables, as this increases loss of vitamin C. 10- Do not use copper utensils, because copper helps to destroy vitamin C.