Module 1 – Domain I



Module 1 – Domain: Food Science – Physical and Chemical Properties of Food

After reviewing Module 1 lecture, you should be able to describe the chemical and physical properties of:

• meat, fish, poultry, meat alternatives

• eggs

• milk and dairy products

• flour and cereals

• vegetables and fruits

• fats and oils

Meats, fish, poultry, meat alternatives

Physical Properties of Meats

Meat Composition

• Connective tissue – Collagen- white connective tissue which softens when heated; increased with age and exercise. Elastin - yellow connective tissue, unaffected by heat.

• Fat – may be under skin or around organs; fat layered between tissues or muscles is known as marbling.

• Pigments – Color primarily due to myoglobin and to a lesser extent hemoglobin; color varies with species and age.

Meat Quality

Quality grading is voluntary and includes:

• U.S. Prime – highest quality grade; highest in fat and most expensive but also tends to be the most tender and flavor rich.

• U.S. Choice – follows prime in quality; tends to have less marbling than prime but still good quality

• U.S. Select – lacks some juiciness and quality of higher grades

Inspection

• The Federal Meat Inspection Act of 1906 requires all meat is inspected interstate.

• The Wholesome Meat Act of 1967 requires all meat is inspected, both interstate or intrastate.

Factors affecting tenderness

• Cut of meat - amount of connective tissue – cuts of meat in the rib and loin area contain less connective tissue and are more tender

• Fat and marbling

• Heredity and aging - as animals become older connective tissue increases causing meats to be less tender

Chemical Properties of Meats

Meat Cookery

• Dry Heat – used for tender cuts of meat; includes baking, broiling, pan-broiling, grilling, frying, roasting and stir-frying

• Moist Heat – used for tougher, less tender cuts of meat; includes braising, stewing or cooking in water, and pressure cooking

Physical Composition of Seafood

Seafood can be broken down into two classes - fin fish and shellfish.

• There are two categories of shellfish. Mollusks-soft in structure and enclosed with hardshell (oysters, clams, and scallops). Crustaceans- crust like shell and segmented body (lobster, shrimp).

Seafood Grading

Inspection and grading is voluntary. Quality grades are based on appearance, uniformity, flavor, and odor.

Chemical composition of Seafood

Seafood Cookery

No tenderization is required when preparing seafood due to little connective tissue. Fin fish is quickly cooked and will flake easily and become opaque when done.

Nutritive Value of Seafood

• Most fish is low in fat – light flesh fish tend to be lower in fat in comparison to dark flesh fish. Fish is rich in omega-3 polyunsaturated fatty acids including eicosapentaenoic acid (EPA) which offers several health benefits such as protection of heart health.

Physical Properties of Poultry

• Fat is deposited in muscle tissue, under skin, and the abdominal area. White meat is lower in fat content compared to dark meat.

Inspection

• In 1968, the Wholesome Poultry Products Act was passed and requires all poultry sold in the U.S. be inspected for wholesomeness (sanitary processing and free of disease).

Chemical Properties of Poultry

Poultry Cookery

Because most poultry is tender, both dry or moist heat methods can be used. Stewing hens should be prepared using moist heat methods as they tend to be less tender.

Nutritive Value of Poultry

General composition does not differ from other meats. Poultry breasts are lower in fat and cholesterol in comparison. Dark poultry meats tend to be higher in fat compared to white meat.

Meat Alternatives

• Meat Alternatives aka meat analogs are foods made with soy and other ingredients to imitate meat products.

• Often found frozen or canned.  These items are usually fully prepared and only require heating (ie: imitation burgers, sausage, etc.).  Other alternatives are packaged dried and require some addition of liquid and heating (ie: chili mixes, etc.).

• Nutritional content of meat alternatives differ depending on brand, type, etc.  Generally, such alternatives are good sources of protein and iron.  Some products are also fortified with vitamin B12.

Eggs

Physical Properties of Eggs

Grading

Grading of eggs is conducted via a process known as candling. The egg is held up to a source of light. When the light passes through the egg, it reveals quality of shell, the size of the air cell, position of the yolk. U.S. grades include AA, A, B, and C.

• Grade AA – yolk is firm, white is clear and firm, large proportion of thick white to thin white

• Grade A – yolk is firm and upstanding; white reasonably firm and stands fairly well around yolk; large in proportion of thick to thin white

• Grade B – yolk is enlarged and flattened; white is equal parts thick and thin white

Variations of Eggs

Other forms of eggs include pasteurized (processed egg products), frozen and dried eggs (low bacteria count), egg substitutes (meet needs of low cholesterol diets, subject to same bacteria risk as liquid egg).

Chemical Properties of Eggs

Egg Safety

Egg shells are potentially hazardous food due to salmonella.

• Inspect eggs and discard those with broken shells

• Refrigerate eggs 40 degrees

Egg cookery

Eggs can be cooked (scrambled, boiled, fried, poached) or added to recipe to serve a function (cakes, casseroles, etc.). Eggs can become overcooked quickly leading to a tough, rubbery product.

• When poaching an egg, the addition of vinegar or salt to water can aid in coagulation; egg whites coagulate at lower temperatures than yolks

• An acid (cream of tartar) stabilizes egg whites foam and adds to whiteness; fat prevents proper whipping of egg whites.

Nutritive Value of Eggs

Avidin, a component of raw eggs, binds to biotin if it is not denatured via heat. Cholesterol is found solely in the yolk (212 mg) along with 5 grams of fat.

Milk and Dairy Products

Physical Properties of Milk

Kinds of Milk

1. Fluid Milk

• whole milk - 3-3.8% milk fat

• 2% milk - 2% milk fat

• 1% milk - 1% milk fat (aka low-fat milk)

• Skim milk - less than 0.5% milk fat (aka non fat milk)

• light cream - 18-30% milk fat

• half and half - 10-12% fat

Pasteurization- sanitation process in which milk is heated to kill bacteria and inactivate enzymes.

2. Nonfat dry milk

• contains no more than 5% moisture; made from pasteurized skim milk

3. Concentrated Fluid Milks

• evaporated milk - ~60% water removed

• condensed milk - ~50% water removed; sugar is added

4. Cultured milk products

• yogurt - bacteria is added to milk and incubated; some varieties have active cultures of bacteria as indicated on label

• buttermilk - cultured milk

5. Ice cream

• fine crystals and creamy texture; depends upon fat content - lower fat results in larger crystals and a less creamy texture

• overrun or swell - commercial ice cream increases by 80-100% when frozen; a low overrun results in a compact, course texture, too high of an overrun results in a frothy product

Grading

Grade A milk is the grade supplied to consumers. Grades are based on bacteria count. Grade A milk contains ................
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