Food chemistry Study Guide

📖 Core Concepts Food Chemistry – study of chemical processes & interactions of all food components (bio‑ and non‑biological). Water Activity (aw) – measures how much water is available for microbial growth; directly ties to shelf life. Carbohydrate Formula – monosaccharides follow $CnH{2n}On$ (n ≥ 3). Lipid Amphiphilicity – lipids possess a non‑polar (hydrophobic) core and a polar (hydrophilic) region, making them surface‑active. Proteins – macromolecules of C, H, O, N, S (± Fe, Cu, P, Zn); >50 % of dry cell mass; provide essential amino acids. Enzymes – biological catalysts that lower activation energy, speeding reactions in food processing. Vitamins – divided into water‑soluble (e.g., C) and fat‑soluble (e.g., E); essential for disease prevention. Minerals – bulk (Ca, Mg, K > 200 mg/day) vs. trace (Fe, Cu, Zn < 200 mg/day). Food Additives – substances (often identified by E‑numbers or GRAS status) that preserve/enhance flavor, appearance, etc. --- 📌 Must Remember aw < 0.6 → most bacteria cannot grow; important for preservation. Monosaccharide general formula: $CnH{2n}On$ (n ≥ 3). Sucrose formation: glucose + fructose → glycosidic bond → disaccharide (loss of H₂O). Degrees Brix = % (w/w) sucrose; standard for sugar concentration. Lipids are amphiphilic → can form micelles & emulsions, crucial for vitamin absorption. Complete protein = all essential amino acids; can be achieved by combining complementary plant sources. Enzymes lower activation energy, thus reducing required temperature/time in baking, brewing, etc. Water‑soluble vitamins are excreted quickly → need regular intake; fat‑soluble vitamins accumulate → risk of toxicity. Bulk minerals: Ca, Mg, K > 200 mg/day RDI; Trace minerals: Fe, Cu, Zn < 200 mg/day RDI. E‑numbers identify additives in the EU; GRAS indicates FDA‑approved safety in the U.S. --- 🔄 Key Processes Water Activity Reduction Dehydration → lower moisture → ↓ aw. Freezing → immobilizes water, limiting microbial activity. Refrigeration → slows microbial metabolism (doesn’t change aw much). Disaccharide (Sucrose) Synthesis Glucose + Fructose → condensation reaction → glycosidic bond + H₂O released. Polysaccharide Formation Repeated glycosidic linkages → long chains (e.g., pectin, agar). Digested polysaccharides → hydrolyzed to monosaccharides; dietary fiber → fermented in large intestine. Lipid Micelle Formation (Amphiphilic Action) In aqueous environment, hydrophobic tails cluster inward, hydrophilic heads face water → micelle → solubilizes fat‑soluble vitamins. Enzyme‑Catalyzed Food Processes Baking: amylase → breaks down starch → sugars for Maillard browning. Brewing: proteases → degrade proteins → clarify wort. Dairy: rennin (chymosin) → coagulates casein → cheese curd. --- 🔍 Key Comparisons Water‑Soluble vs. Fat‑Soluble Vitamins Solubility: dissolve in water vs. dissolve in lipids. Storage: excess excreted quickly vs. stored in body fat/liver. Toxicity risk: low vs. higher. Bulk Minerals vs. Trace Minerals RDI magnitude: >200 mg/day vs. <200 mg/day. Physiological role: structural/electrolyte balance vs. enzyme co‑factors. Dehydration vs. Freezing (Preservation) Mechanism: removes water → lowers aw vs. immobilizes water → slows metabolism. Effect on texture: can cause shrinkage/drying vs. preserves texture. Monosaccharide vs. Disaccharide vs. Polysaccharide Size: single unit vs. two units vs. many units. Digestibility: generally rapid vs. moderate vs. variable (fiber). --- ⚠️ Common Misunderstandings “Low water = no spoilage.” – Low aw inhibits most bacteria, but xerophilic molds can still grow. “All lipids are fats.” – Lipids include waxes, phospholipids, glycolipids, etc., not just triglycerides. “Vitamin C is the only water‑soluble vitamin.” – B‑complex vitamins are also water‑soluble. “Fiber is indigestible.” – Some fibers are fermented by gut microbiota, yielding short‑chain fatty acids. “E‑numbers are always harmful.” – E‑numbers simply label approved additives; many are harmless. --- 🧠 Mental Models / Intuition “Water activity = microbial buffet.” – Think of aw as the number of seats at a table; fewer seats (lower aw) → fewer microbes can sit and eat. “Amphiphile = Janus molecule.” – One face loves water, the other hates it → explains emulsification. “Protein completeness = puzzle pieces.” – Different plant proteins provide complementary amino‑acid “shapes”; combine to fill the whole picture. “Enzyme as a shortcut road.” – Lowers the energy hill (activation energy), letting reactants bypass the steep climb. --- 🚩 Exceptions & Edge Cases Xerophilic molds can grow at aw as low as 0.65. Some vitamins (e.g., B₁₂) are water‑soluble but stored in the liver, so deficiency can develop slowly. Polysaccharide digestibility varies: cellulose is indigestible to humans, while starch is readily hydrolyzed. GRAS status is not a guarantee of safety for all populations (e.g., infants, pregnant women). --- 📍 When to Use Which Choose preservation method: Want long shelf life & maintain texture → freeze. Need lightweight, dry product → dehydrate. Require minimal processing → refrigerate. Select vitamin supplement type: Immediate need & risk of excess → water‑soluble (excreted quickly). Need sustained release → fat‑soluble (stored). Determine protein source for vegetarians: If only one source → may lack essential AA → combine legumes + cereals. Pick additive labeling: In EU‑based product → refer to E‑numbers. In US‑based product → look for GRAS designation. --- 👀 Patterns to Recognize Low aw ↔ high shelf life (unless xerophilic mold is present). Glycosidic bond formation always involves loss of one H₂O molecule. Amphiphilic molecules → micelle formation → solubilize fats/vitamins. Enzyme‑added foods often show faster reaction rates and lower required temperatures. E‑numbers beginning with “E1” are typically food‑preserving additives; “E3” often colorants. --- 🗂️ Exam Traps “Water activity of 0.8 guarantees safety.” – Wrong; many bacteria thrive up to aw ≈ 0.85. “All sugars are monosaccharides.” – Incorrect; disaccharides (sucrose) and polysaccharides exist. “All fats are hydrophobic.” – Misleading; phospholipids have hydrophilic heads. “GRAS means no regulation.” – False; GRAS substances still undergo safety review. “Bulk minerals are more important than trace minerals.” – Both are essential; deficiency of a trace mineral (e.g., iron) can be severe. ---