Principle Of Food Science And Processing 2024 Lect. 5 PDF

Eggs and vegetable 5th lecture Dr. Mohamed Elsaadany 1 Eggs Dr. Mohamed Elsaadany 3 Definition Composition of Eggs Cuticle (bloom) A waxy coating on an eggshell that seals the pores from bacterial contamination and...

Eggs and vegetable 5th lecture Dr. Mohamed Elsaadany 1 Eggs Dr. Mohamed Elsaadany 3 Definition Composition of Eggs Cuticle (bloom) A waxy coating on an eggshell that seals the pores from bacterial contamination and moisture loss. Dr. Mohamed Elsaadany 4  Nutritional value Eggs are a naturally nutrient-rich food, containing all essential amino acids. Eggs provide an excellent source of vitamin B12, biotin (B7), iodine, selenium, and choline; riboflavin (B2) and pantothenic acid (B5); as well as the carotenoids lutein and zeaxanthin Yolk The yolk makes up just over one-third of an egg. It provides three- fourths of the calories, all of the fat-soluble vitamins (A, D, E and K), and all of the choline, lutein, and zeaxanthin. The yolk also provides most of the phosphorus, iron and folate and almost half of the protein and riboflavin. It also contains omega 3 and 6 fatty acids The white (albumen) provides more than half of the total protein and riboflavin. Complete protein Eggs contain the highest quality protein and are often used as a standard to measure the quality of other protein sources. Eggs have the highest biological value, meaning the essential amino acids they provide are used very efficiently by the body. Because eggs are very easy to digest, they are frequently included in therapeutic diets. Dr. Mohamed Elsaadany 5  Protein types and contents Definition About 3 grams of protein are also found in the egg yolk in the form of lipoproteins— lipovitellin and lipovitellinin—which act as emulsifiers in food preparation. Dr. Mohamed Elsaadany 6  Purchasing Eggs Inspection Ensure that egg products be: – Wholesome – Un adulterated – Truthfully labeled Grading The best-quality eggs are graded USDA Grade AA, followed by USDA Grade A. USDA Grade B, the lowest grade. Dr. Mohamed Elsaadany 7  Purchasing Eggs Haugh Units The freshness of an egg can be Candling: A method of determining egg detected by cracking it open onto a flat surface quality based on observing eggs against a and looking at the height of its thick albumen. light. Fresh egg whites sit up tall and firm, while older ones tend to spread out. Dr. Mohamed Elsaadany 8  Purchasing Eggs Definition Grading Sizing is not related to grading in any way. Eggs are sold in cartons by various sizes determined by a minimum weight for a dozen eggs in their shell. Dr. Mohamed Elsaadany 9  Eggs in Foods preparation Eggs are often combined with other ingredients for – Flavor – Color – Emulsify – Thicken – Bind – Foam – Interfere – Clarify Dr. Mohamed Elsaadany 10  Eggs in Foods preparation Definition Changes in Prepared Eggs The key to cooking eggs is to keep the temperature low and/or the cooking time short. Egg whites and yolks coagulate at different temperatures. Egg white protein coagulates between (62.2° C and 65° C); egg yolk protein coagulates between (65° C and 70° C); and whole egg protein coagulates (62.2° C and 70° C). In all cases, eggs are cooked at simmering temperatures (71-80 °C ). Dr. Mohamed Elsaadany 11 Hard and soft boiled Definition Dr. Mohamed Elsaadany 12  Storage of Eggs Definition (1) Whole eggs Eggs retain their moisture better and keep longer if they are stored in the fridge in the carton. The carton also prevents flavours and odours from being absorbed through the eggs' porous shells. (a) Signs of aging in eggs 1 Causes egg white to thin 2 Chalazae are not so prominent and viscous 3 Vitellin membrane weakens and yolk migrates or breaks 4 Air cell increases in (b) Shelf life of refrigerated eggs. Whole About a month. Yolk stored under water 2 days. Whites kept tightly covered in a glass container 4 days (c) Storage period Eggs may be stored for up to 6 months. Dr. Mohamed Elsaadany 13  Storage of Eggs Definition Washing eggs is not recommended Unopened liquid egg products can be stored for up to 7 days. Once opened, they should be used or discarded within 3 days. Dried egg mix should be used within 7 to 10 days of opening Freezing a whole egg is not possible because it will crack under the expanding liquids. The egg contents can be frozen; Whole (whites and yolk mixed together) or Separated as whites or yolks Dr. Mohamed Elsaadany 14 2 Vegetables Dr. Mohamed Elsaadany 15  Handling Vegetables Definition Vegetables selection and purchasing Good color, non-wilted vegetables Buy in season for best value Buy medium sized, heavy vegetables Avoid sprouts on root vegetables Washing and Soaking Root vegetables should be cleaned with a stiff vegetable brush. Wash green, leafy vegetables in several changes of cold water. After washing, drain well and refrigerate lightly covered. Do not soak vegetables for long periods as flavor and nutrients leach out. Dr. Mohamed Elsaadany 16  Handling Vegetables Definition Peeling and Cutting Peel most vegetables as thinly as possible. Cut vegetables into uniform pieces for even cooking. Peel and cut vegetables as close to cooking time as possible. Treat vegetables that brown easily with an acid, such as lemon juice, or an antioxidant solution or hold under water until ready to use Dr. Mohamed Elsaadany 17  Handling Vegetables Definition For processed Vegetables Canned – Checking Quality Reject damaged , Puffed or swollen cans that indicate spoilage. Know the drained weight. Check the grade. Storage Fresh Vegetables Potatoes, onions, and winter squash are stored at cool temperatures. – (50–65°F/10–18°C) in a dry, dark place Other vegetables must be refrigerated. Peeled and cut vegetables need extra protection from drying and oxidation. – Cover or wrap, and use quickly to prevent spoilage. Dr. Mohamed Elsaadany 18  Handling Vegetables Definition Storage Frozen Vegetables – Store at 0ºF (–18ºC) or colder, in original containers, until ready for use. – Do not refreeze thawed vegetables. Leftovers – Not to put them in the first place. – Do not mix batches. Dried Legumes Dried legumes are soaked for several hours before cooking to replace moisture lost in drying. – Dried beans absorb their weight in water. Dr. Mohamed Elsaadany 19  Cooking changes Definition Cooking is affects vegetables in four ways – Texture – Flavor – Color – Nutrients Texture Fiber The amount of fiber varies depend on – Type of vegetables. – In mature vs. younger vegetables. – Parts of the same vegetable. Fiber become firmer by acids and sugars. Fiber softened by heat and alkalis. Starch Dry starchy foods must be cooked in enough water Doneness A vegetable is become done when it reaches the desired degree of tenderness. Dr. Mohamed Elsaadany 20  Cooking changes Definition FLAVOR CHANGES Flavor loss can be controlled in four ways: 1. Cook for as short a time as possible. 2. Use boiling salted water: 3. Use just enough water to cover food to minimize leaching of flavor, color and nutrients. 4. Steam vegetables whenever appropriate: 5. Try to serve young, fresh vegetables that have been stored as short a time as possible to keep their sweet taste. Dr. Mohamed Elsaadany 21  Cooking changes Definition Color Changes Overcooking produces undesirable changes. White Vegetables contain pigments called anthoxanthins and flavonoids range from pale yellow to white. White pigments stay white in acid and turn yellow in alkaline water Red Vegetables contained contain pigments, called anthocyanins, are found in only a few vegetables, mainly red cabbage and beets. – Acids turn anthocyanins a brighter red. – Alkalis turn anthocyanins blue or blue-green (not a very appetizing color). Dr. Mohamed Elsaadany 22  Cooking changes Definition COLOR CHANGES Green Vegetables contain Chlorophyll that present in all green plants. Acids are enemies of green vegetables. Both acid and long cooking turn green vegetables a drab olive green. To protect the color of green vegetables : – Cooking uncovered to allow plant acids to escape. – Cooking for the shortest possible time. – Cooking in small batches rather than holding for long periods Do not use baking soda to maintain green color. – Alkalis destroy vitamins and makes texture unpleasantly mushy and slippery. Dr. Mohamed Elsaadany 23  Cooking changes Definition COLOR CHANGES Yellow and Orange Vegetables contain Carotenoids are yellow and orange pigments: – These pigments are very stable. – Little affected by acids or alkalis. – Short cooking prevents dulling of the color and preserves vitamins and flavors. Dr. Mohamed Elsaadany 24  Cooking changes Definition Nutrient Losses factors are responsible for most nutrient loss: 1. High temperature 2. Long cooking 3. Leaching (dissolving out) 4. Alkalis (baking soda, hard water) 5. Plant enzymes (which are active at warm temperatures but destroyed by high heat) 6. Oxygen 7. Using a lot of liquid increases vitamin loss by leaching. Dr. Mohamed Elsaadany 25  General Rules in Cooking Vegetable Cooking General Rules in Cooking Vegetable Do not overcook. Cook as close to service time as possible, and in small quantities. Avoid holding for long periods on a steam table. If the vegetable must be cooked ahead of time: – Undercook slightly and chill rapidly. – Reheat at service time. Never use baking soda with green vegetables. Cut vegetables uniformly for even cooking. Start with boiling, salted water when boiling green vegetables Roots and tubers are started in cold, salted water for more even cooking. Cook green vegetables and strong-flavored vegetables uncovered Dr. Mohamed Elsaadany 26