Food and Nutrition · 5 min read
Food Science and Preservation
Carbohydrate, Protein, and Fat Chemistry
| Reaction | What Happens | Example |
|---|---|---|
| Gelatinization | Heated starch granules absorb water, swell, and thicken a liquid | Gravy, pudding |
| Retrogradation | Cooled starch molecules realign and squeeze out water | Stale bread, weeping pudding |
| Dextrinization | Dry heat breaks starch into dextrins; browning, less thickening power | Toast, browned flour |
| Caramelization | Sugar alone browns at high heat (about 320°F and above) | Caramel sauce |
| Maillard reaction | Amino acids and sugars react under dry heat; brown color, savory flavor | Seared meat, bread crust |
| Denaturation | Heat, acid, salt, or agitation unfolds a protein | Whipped egg white |
| Coagulation | Denatured proteins bond into a firm network | Cooked egg, custard, cheese curd |
| Gluten development | Glutenin and gliadin in wheat flour form an elastic network when wet and worked | Yeast bread (much); muffins (little) |
| Enzymatic browning | Enzymes and oxygen darken cut produce; slowed by acid, blanching, or excluding air | Cut apples, avocados |
An emulsion disperses one liquid in another that normally will not mix; an emulsifier such as the lecithin in egg yolk holds mayonnaise and salad dressings together. A fat's smoke point is the temperature at which it breaks down and smokes, so refined oils suit frying better than butter. Hydrogenation adds hydrogen to liquid oil to make it solid; partial hydrogenation creates trans fats. Rancidity is the off flavor of fat broken down by oxygen, light, and heat; cool, dark, airtight storage slows it.
Leavening and Thickening Agents
| Agent | How It Works |
|---|---|
| Yeast (biological) | Ferments sugar into carbon dioxide and alcohol; needs time; killed at about 140°F |
| Baking soda (chemical) | Sodium bicarbonate; needs an acid such as buttermilk or lemon juice to release carbon dioxide |
| Baking powder (chemical) | Soda plus acid; single-acting reacts when moistened, double-acting again when heated |
| Ammonium bicarbonate (chemical) | Releases carbon dioxide and ammonia; used in crisp cookies |
| Air and steam (mechanical) | Air is added by creaming, whipping, or folding; steam raises popovers and puff pastry |
| Agent | Characteristics |
|---|---|
| Flour | Contains protein; opaque, stable sauce; cooked in fat as a roux |
| Cornstarch | Pure starch; clear result; thins with prolonged cooking; mixed with cold liquid as a slurry |
| Arrowroot; tapioca | Arrowroot is very clear but thins if overheated; tapioca (cassava) is slightly chewy |
| Eggs; gelatin | Eggs coagulate to set custards; gelatin (from collagen) dissolves in hot liquid and sets when cooled |
| Pectin; agar; gums | Pectin gels jams with sugar and acid; agar is a seaweed gelatin alternative; guar and xanthan gums stabilize |
Ingredient Functions and Mixing Methods
| Ingredient | Main Functions |
|---|---|
| Flour | Structure from gluten and gelatinized starch; bread flour is high in protein, cake flour low |
| Fat | Tenderness (shortens gluten strands), flavor, moisture, flakiness; traps air when creamed |
| Sugar | Sweetness, tenderness, browning, moisture retention; food for yeast |
| Eggs | Structure (coagulation), leavening (foam), emulsifying, color, richness |
| Liquid | Hydrates flour so gluten forms and starch gelatinizes; dissolves sugar and salt; forms steam |
| Salt; leavening | Salt adds flavor, strengthens gluten, and controls yeast; leavening gives volume |
Muffin Method
Mix dry and liquid ingredients separately, then combine just until moistened. Overmixing causes tunnels and peaked tops. Muffins, pancakes.
Biscuit Method
Cut cold solid fat into the dry ingredients, add liquid, and handle lightly for flaky layers. Biscuits, scones, pie crust.
Creaming Method
Cream fat and sugar until light, beat in eggs, then add dry and liquid ingredients alternately. Butter cakes, cookies.
Food Preservation Methods
Preservation removes a condition that microorganisms and enzymes need: it applies heat or cold, removes water, lowers pH, or excludes oxygen. Home canners should use only research-tested recipes from USDA or Cooperative Extension, because botulism toxin gives no warning sign.
| Method | How It Works and Key Points |
|---|---|
| Boiling-water canning | 212°F; high-acid foods only (pH 4.6 or below): fruits, pickles, acidified tomatoes |
| Pressure canning | 240°F destroys C. botulinum spores; required for low-acid vegetables, meat, and poultry |
| Freezing | Slows microbes and enzymes; blanch vegetables first; airtight wrap prevents freezer burn |
| Drying | Sun, oven, or dehydrator removes the water microbes need; store airtight |
| Fermentation; pickling | Acid from beneficial microbes or added vinegar: yogurt, sauerkraut, kimchi, pickles |
| Curing; smoking | Salt, sugar, and nitrites or nitrates preserve meat and fish; smoke adds flavor and preservatives |
| Pasteurization | Mild heat kills pathogens in milk and juice without sterilizing; refrigeration still needed |
| Irradiation | Ionizing energy kills pathogens and insects; food does not become radioactive |
| Vacuum or modified-atmosphere packaging | Removes or replaces oxygen to slow spoilage; anaerobic bacteria can still grow, so keep cold |
Environmental Factors in Food Preparation
Altitude lowers air pressure, so water boils below 212°F (about 2°F lower per 1,000 feet), liquids evaporate faster, and leavening gases expand more. Baking adjustments usually begin at about 3,000 feet.
| Condition | Effect | Adjustment |
|---|---|---|
| High altitude: boiling, canning | Food cooks more slowly | Longer cooking; more processing time or pressure |
| High altitude: baking | Batters overexpand, dry out, and may collapse | Less leavening and sugar; more liquid; oven 15–25°F hotter |
| High humidity | Dry ingredients absorb moisture; candy turns sticky | Slightly less liquid; store airtight |
| Warm kitchen | Yeast works faster; fat softens | Keep fat cold for pastry; watch rising time |
Teaching Connection
Food science labs follow the scientific method: students change one variable (muffins mixed 15, 50, and 150 strokes; acids on cut apples), compare results, and explain the chemistry in a lab report.Exam Focus
Match each term to a food example: gelatinization thickens, caramelization needs only sugar, and the Maillard reaction needs sugar and protein. Low-acid foods require pressure canning. High-altitude baking uses less leavening and sugar, more liquid, and a hotter oven.Finished reading?
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