Practice Questions

Question 1

Explain the different forms of water in food (bound, vicinal, and free water) and their impact on microbial growth, texture, and preservation.

Answer 1

Bound water:
Tightly associated with food molecules (e.g. proteins, polysaccharides).
Not free to move or freeze.
No microbial growth supported.
Maintains structure in low-moisture foods (e.g. crackers).
Preservation role: Helps in shelf stability.

Vicinal water (multilayer water):
Loosely bound in multiple layers around molecules.
Limited mobility, partially unavailable.
Can slightly support microbial activity.
Affects texture and mouthfeel (e.g. firmness).

Free water:
Not bound; behaves like bulk water.
Supports microbial growth, enzymatic activity.
Major contributor to texture (e.g. juiciness in fruit).
Easily removed in drying or freezing.

Question 2

What is water activity (aw) and how does it differ from moisture content? Why is aw more useful than moisture content for predicting microbial growth?

Answer 2

Water Activity (aw):
Ratio of vapor pressure of water in food to that of pure water at the same temp.
Ranges from 0 (dry) to 1 (pure water).
Reflects the availability of water for microbial use.

Moisture Content:
Total amount of water (bound + free) in a food.
Expressed as a percentage (%).

Key Differences:
Moisture content doesn’t indicate water’s availability.
Foods can have high moisture but low aw (e.g. jam, honey).
Why aw is more useful:

Directly correlates with microbial growth thresholds.

Better predictor for shelf life and spoilage risk.

Question 3

Microbial growth thresholds

Answer 3

Bacteria: grow at aw > 0.90
Yeasts: aw > 0.85
Moulds: aw > 0.70

Question 4

Discuss the roles of water in food, including:
Texture
Microbial stability
Heat transfer
Include: forms of water, measurement techniques (e.g. Karl Fischer), and preservation/storage examples.

Answer 4

Texture:
Determines mouthfeel (e.g. crunchiness vs. softness).
Water loss (e.g. staling of bread) affects firmness.
Gelation, emulsions, and foam stability depend on water interaction.

Microbial Stability:
Microorganisms require available water to grow.
Low aw = longer shelf life (e.g. dried fruits, powdered milk).
Preservation methods: drying, adding sugar/salt to reduce aw.

Heat Transfer:
Water has a high specific heat, effective at distributing heat during cooking (e.g. boiling, steaming).

Karl Fischer Titration:
Measures total water content (bound + free).
Accurate for low-moisture foods.
Water activity meters:
Measure aw using vapor pressure sensors.

Question 5

What happens during freezing that causes cellular damage and drip loss in foods?

Answer 5

Osmotic Stress:
Ice forms extracellularly first, concentrating solutes outside the cell.
Water leaves the cell to balance concentration → cell shrinkage.

Membrane Puncture:
Ice crystals can form inside cells if frozen slowly.
Crystals pierce membranes, causing leakage on thawing.

Structural Damage:
Ruptured membranes → loss of turgor, poor texture.
Proteins may denature.
On thawing, water is lost as drip loss → reduced juiciness, weight, and quality.

Prevention:
Use rapid freezing to minimise crystal growth (e.g. IQF).
Cryoprotectants (e.g. sugars) help stabilise membranes.

Question 6

What are the main structural differences between amylose and amylopectin in starch?

Answer 6

Amylose:
Linear polymer of α(1→4)-linked glucose.
Forms tight, helical structures → less soluble.
Slower to gelatinise; contributes to firm textures.

Amylopectin:
Highly branched with α(1→4) and α(1→6) linkages.
More soluble and rapidly gelatinises.
Contributes to viscosity and thickening in foods.

Question 7

Dietary Fibre
structural components and digestibility

Answer 7

Soluble Fibre:
Dissolves in water, forms gels.
Includes pectins, gums, β-glucans.

Insoluble Fibre:
Does not dissolve; remains intact through digestion.
Includes cellulose, lignin, some hemicelluloses.

Insoluble fibre: largely undigested, low fermentability.
Increases stool bulk, promotes regular bowel movements.

Soluble fibre: fermentable by gut bacteria → SCFAs (e.g. butyrate).
Prebiotic effects → promotes healthy microbiota.

Question 8

What is starch retrogradation and how does it affect food texture in products like bread or rice?

amylose vs amylopectin

Answer 8

linear chains realign and crystallize upon cooling, causing firmness and staling.

Amylopectin, being highly branched, retrogrades much more slowly and contributes less to this process than amylose

Question 9

What are FODMAPs and how are they metabolised in the gut? Explain their effects in individuals with IBS.

Answer 9

FODMAPs are short-chain carbs poorly absorbed in the small intestine. They reach the large intestine where gut bacteria ferment them, producing gas, Fermentation also draws water into the gut lumen due to their osmotic effect. In people with IBS, this can cause bloating, pain, and altered bowel habits

Question 10

Key Functional Roles of Starch in Food Processing:

Answer 10

Thickening and gelling: Starch absorbs water and swells when heated, thickening sauces, soups, and fillings.
Texture modification: Provides structure and firmness in baked goods and gels.
Stabilising emulsions: Helps maintain consistency in products like salad dressings.
Water retention: Improves moisture in products such as bread and cakes.

Question 11

Differences between amylose and amylopectin in Food Processing:

Answer 11

Amylose:
Linear chains that form firm gels and contribute to gel strength.
More prone to retrogradation, leading to staling in bread and firming in cooked rice.

Amylopectin:
Highly branched and prevents firm gel formation.
Provides viscosity and smooth textures; less retrogradation means softer textures over time.
Examples:

High amylose starch (e.g., some types of rice) results in firmer, less sticky cooked grains.
High amylopectin starch (e.g., waxy corn starch) gives creamy, smooth textures in sauces and puddings.

Question 12

Compare caramelisation, the Maillard reaction, and amino acid degradation

Answer 12

1. Caramelisation
   Process: Thermal breakdown of sugars at high temperatures without amino acids.
   Flavour: Produces sweet, nutty, and caramel-like flavours.
   Colour: Leads to brown to dark brown colours.
2. Maillard Reaction
   Process: Chemical reaction between reducing sugars and amino acids/proteins during heating.
   Flavour: Creates complex, roasted, meaty, and toasted flavours.
   Colour: Produces brown pigments called melanoidins.
3. Amino Acid Degradation (Non-Maillard)
   Process: Breakdown of amino acids by heat, independent of sugars.
   Flavour: Can produce off-flavours or bitter compounds.
   Colour: Typically less browning than Maillard or caramelisation.

Question 13

Comparison of Saturated vs. Unsaturated Fatty Acids:
Roles in Food Processing

Answer 13

1. Roles in Food Processing
   Saturated fats:
   Solid at room temperature, provide structure and firmness (e.g., in butter, chocolate).
   More stable, longer shelf life.
   Unsaturated fats:
   Liquid at room temperature, contribute to fluidity and softness (e.g., vegetable oils).
   Used for dressings, frying oils, and emulsions.
2. Behaviour During Frying
   Saturated fats:
   More heat-stable, less prone to oxidation and rancidity.

Unsaturated fats:
Less stable, prone to oxidation and formation of harmful compounds during frying (especially polyunsaturated fats).

Question 14

Comparison of Saturated vs. Unsaturated Fatty Acids:
Health Impacts

Answer 14

Saturated fats:
Linked to increased LDL cholesterol and higher risk of cardiovascular disease.

Unsaturated fats:
Considered healthier; can lower LDL cholesterol and support heart health (especially mono- and polyunsaturated fats).

Question 15

Chemical Structure of Fats

Answer 15

Fats are triglycerides: glycerol backbone + three fatty acid chains.
Fatty acids vary by chain length and degree of saturation (saturated, mono- or polyunsaturated).

Question 16

Hydrogenation:

Answer 16

Addition of hydrogen to unsaturated bonds to make fats more saturated.
Increases melting point and stability (e.g., converting liquid oils to solid margarine).
Can create trans fats

Question 17

Interesterification:

Answer 17

Rearrangement of fatty acids on the glycerol backbone without changing saturation.
Modifies melting behavior and texture without producing trans fats.
Used to create specialty fats for spreads, baking.

Question 18

Fractionation:

Answer 18

Physical separation of fats by melting points (cooling and crystallisation).

Question 19

Lipid Degradation:

Answer 19

Includes oxidation (rancidity), hydrolysis (free fatty acid formation), and polymerization.
Leads to off-flavors, decreased shelf life, and nutritional loss.

Question 20

Analytical Techniques fats

Answer 20

Iodine Value: Degree of unsaturation.
NaOH titration: amount of FFAs

Question 21

Why are trans fats a health concern? How can their formation be minimised during processing?

Answer 21

Trans fats raise LDL (bad) cholesterol and lower HDL (good) cholesterol, increasing the risk of heart disease.

They are linked to inflammation, insulin resistance, and higher risk of type 2 diabetes, strokes

use fully hydrogenated oils with interesterification instead of partial hydrogenation, avoid high frying temperatures or choose stable oils

Question 22

How is oil stabilised

Answer 22

Antioxidants: Natural (e.g., tocopherols) or synthetic antioxidants are added to delay oxidation.
Proper Storage: Keep oil away from light, heat, and oxygen by storing in cool, dark, airtight containers.
Refining: Removes impurities and free fatty acids that promote rancidity.
Packaging: Use opaque or vacuum-sealed packaging to limit oxygen exposure.

Question 23

How does oil go “bad”

Answer 23

Oxidation:
Unsaturated fatty acids react with oxygen to form peroxides and secondary compounds like aldehydes and ketones, causing rancid off-flavors and odors.

Hydrolysis: Breakdown of triglycerides by moisture, releasing free fatty acids that contribute to off-flavors.

Polymerisation: Occurs during repeated heating, leading to increased viscosity and off-flavors.

Question 24

List three functional roles of lipids in food systems

influence structure, stability, and sensory properties.

Answer 24

Texture and Structure:
Lipids contribute to the firmness, creaminess, and mouthfeel of foods (e.g., butter in baked goods).

Stability:
Lipids act as barriers to moisture and oxygen, helping preserve food freshness and shelf life.

Sensory Properties:
Lipids carry and enhance flavors and aromas, improving taste perception.

Question 25

Why is the isoelectric point (pI) of a protein important in food processing?

Answer 25

The pI is the pH at which a protein has no net electrical charge and is least soluble, leading to aggregation and precipitation. This property is crucial for controlling protein solubility, texture, and coagulation in food products. Example: Milk Protein (Casein) Casein has a pI around 4.6. At this pH (e.g., during cheese-making or yogurt production), casein precipitates and forms a gel or curd, essential for texture and structure.

Question 26

How do proteins contribute to foaming and emulsification in food systems? Provide examples.

Answer 26

Proteins stabilize foams by forming films around air bubbles, like egg whites in meringues, act as emulsifiers by coating oil droplets to keep mixtures stable, such as milk proteins in cream or dressings.

Question 27

What are anti-nutritional factors? Provide examples (e.g. phytates, oxalates) and explain how they affect nutrient absorption and how processing can reduce their effects.

Answer 27

Compounds in foods that interfere with nutrient absorption or digestion, reducing nutritional value. Oxalates: Bind calcium, forming insoluble complexes that reduce calcium bioavailability. Soaking, fermenting, sprouting, and cooking can degrade or reduce anti-nutrients. Fermentation, for example, breaks down phytates, improving mineral absorption. Heat treatments can inactivate some anti-nutrients like tannins.

Question 28

How does food processing impact the bioavailability of vitamins and minerals? Include: heat, pH, light exposure, fortification

Answer 28

Heat: Can degrade heat-sensitive vitamins like vitamin C and some B vitamins (e.g., in boiling vegetables). May increase mineral availability by breaking down cell walls (e.g., cooking spinach increases iron bioavailability). pH: Acidic conditions can enhance mineral solubility and absorption (e.g., vitamin C in citrus aids iron absorption). Light Exposure: Exposure to light degrades photosensitive vitamins like riboflavin (vitamin B2) in milk. Fortification: Adding vitamins/minerals (e.g., vitamin D in milk, iron in flour) boosts nutrient content and bioavailability.

Question 29

DPPH Assay:

Answer 29

Uses the stable free radical DPPH* (purple color) to measure antioxidant activity. Antioxidants donate electrons or hydrogen to DPPH*, reducing it to a colorless or pale yellow compound.

Question 30

Folin–Ciocalteu Method:

Answer 30

Measures total phenolic content based on the reduction of the Folin–Ciocalteu reagent by phenolics, producing a blue complex. The intensity of the blue color, is proportional to phenolic concentration.

Question 31

Discuss how fermentation affects the nutritional quality, safety, and sensory properties of food. Use examples like kombucha, yoghurt, sourdough. Include: Microbial roles Nutrient bioavailability Shelf-life extension

Answer 31

Microbial Roles: Beneficial microbes convert sugars into acids, alcohol, or gases. These microbes improve food safety by lowering pH and producing antimicrobial compounds, inhibiting pathogens. Nutrient Bioavailability: Fermentation can increase bioavailability of nutrients by breaking down anti-nutrients like phytates. Enzymatic activity may partially digest proteins and carbohydrates, improving digestibility. Shelf-life Extension: Acid production lowers pH, creating an environment hostile to spoilage microbes. Organic acids, alcohol, and bacteriocins act as natural preservatives. Sensory Properties: Fermentation develops unique flavors, aromas, and textures (e.g., tangy yogurt ) Gas production creates texture changes like the crumb structure in sourdough.

Question 32

What makes fermentation an effective preservation method? Discuss: pH drop (e.g. lactic acid) Salt and water activity Anaerobic conditions Role of starter cultures

Answer 32

pH Drop: Fermentation produces organic acids (e.g., lactic acid) that lower pH, creating an acidic environment hostile to many spoilage organisms and pathogens. Salt and Water Activity: Salt draws water out of microbes via osmosis, inhibiting their growth. Reduced water activity (aw) further limits microbial activity, enhancing preservation. Anaerobic Conditions: Many fermentation processes occur in low-oxygen environments, which inhibit aerobic spoilage microbes and favor beneficial fermentative microbes. Role of Starter Cultures: Starter cultures ensure rapid acid production and consistent fermentation. They outcompete undesirable microbes, improving safety, flavor, and shelf life.

Question 33

Digestion, Absorption, and Metabolism of Dietary Fats

Answer 33

Digestion: Begins mainly in the small intestine. Emulsified by bile salts from the gallbladder to increase surface area. Pancreatic lipase breaks triglycerides into monoglycerides and free fatty acids. Absorption: Lipid digestion products form micelles for transport to enterocyte surfaces. Absorbed into intestinal cells, re-esterified into triglycerides, then packaged into chylomicrons. Post-absorptive metabolism: Triglycerides broken down by lipoprotein lipase for uptake by tissues. Fatty acids used for energy, storage, or membrane synthesis.

Question 34

Digestion, Absorption, and Metabolism of Dietary Proteins

Answer 34

Digestion: Begins in the stomach with pepsin breaking proteins into peptides. Continues in the small intestine with pancreatic proteases breaking peptides into smaller peptides and amino acids. Absorption: Amino acids and small peptides absorbed by active transport into enterocytes. Transported via portal vein to the liver. Post-absorptive metabolism: Used for protein synthesis, energy production

Question 35

Digestion, Absorption, and Metabolism of Dietary carbohydrates

Question 36

Crystalline vs. Amorphous Structures

Answer 36

Crystalline (e.g. table sugar, chocolate): Ordered molecular structure. Sensory: Crunchy, brittle textures; important for snap/melting in chocolate. Nutritional: Slower digestion and sugar release compared to amorphous forms. Amorphous (e.g. boiled sweets, gummy lollies): Disordered structure. Sensory: Chewy, sticky textures. Nutritional: Rapid digestion and sugar absorption → higher glycaemic impact.

Question 37

Emulsions

Answer 37

Structure: Mixtures of two immiscible liquids (e.g. oil-in-water), stabilised by emulsifiers (often proteins or phospholipids). Sensory effects: Create smooth, creamy textures (e.g. mayonnaise, ice cream). Affect mouthfeel and appearance (e.g. glossiness in salad dressings).

Question 38

Gels and Foams

Answer 38

Gels: Structured networks formed by proteins (e.g. gelatin) or polysaccharides (e.g. pectin). Sensory: Provide firmness, chewiness, or jelly-like texture (e.g. yoghurts, jams). Foams: Gas dispersed in a liquid/solid, stabilised by proteins (e.g. egg whites). Sensory: Light, airy textures (e.g. mousses, meringues).

Question 39

What are common packaging techniques (e.g., vacuum, MAP) and how do they extend shelf life?

Answer 39

1. Vacuum Packaging What it is: Removes air (especially oxygen) from the package before sealing. How it extends shelf life: Reduces oxygen → slows oxidation of fats, colour changes, and vitamin loss. Inhibits aerobic microbial growth (e.g. moulds, spoilage bacteria). Maintains moisture and flavour. Modified Atmosphere Packaging (MAP) What it is: Replaces air in the package with a specific gas mix (e.g. N₂, CO₂, O₂).

Question 40

Why might a cake or bread not rise properly? Discuss leavening agents, protein structure, and moisture.

Answer 40

1. Leavening Agents Insufficient or expired leavening (e.g. baking powder, yeast, baking soda): Can’t produce enough gas (CO₂) to lift the batter or dough. Protein Structure (Gluten or Egg Protein) Weak gluten network (in bread): Insufficient kneading = poor gas retention. Low-protein flour = weak gluten = flat bread. Overmixed cake batter (using wheat flour): Too much gluten development → dense texture. Moisture & Batter/Dough Balance Too much liquid: Makes the batter too runny to hold gas. Too little liquid: Gas bubbles can’t expand well. Incorrect oven temperature: Too low → slow rise and collapse. Too high → crust forms too fast

Question 41

Why has meat gone stiff after storage? Include: cold shortening, muscle structure, and prevention/fix strategies.

Answer 41

Cold shortening: Meat chilled too fast before rigor mortis → calcium release + low ATP → severe muscle contraction. Muscle structure: Tight actin-myosin bonds form without ATP, making meat tough. Age the meat (wet or dry aging). Use mechanical tenderization (e.g. pounding). Apply marinades (acidic or enzymatic). Cook slowly with moisture (e.g. stewing).

Question 42

Compare fat bloom and sugar bloom in chocolate—what causes each and how can they be prevented?

Question 43

Why has a tomato spoiled at room temperature? Consider ethylene production, microbial growth, and temperature effects.

Answer 43

1. Ethylene Production (Ripening Hormone) Tomatoes naturally produce ethylene gas, which accelerates ripening. At room temperature, ethylene activity increases → faster ripening → overripening → spoilage. 2. Microbial Growth Warm temperatures (~20–25°C) create ideal conditions for bacteria, yeasts, and moulds. 3. Temperature Effects Enzymatic activity increases at room temp, degrading texture and flavour.

Question 44

What is invert sugar?

Answer 44

A mixture of glucose and fructose formed by hydrolysing sucrose (table sugar). Hydrolysis happens via heat + acid or the enzyme invertase Sweeter taste enhances flavour with less sugar. Prevents sugar crystallisation, keeping jam smooth. Improves moisture retention, giving a better spreadable texture.

Question 45

What happens when sugar is removed from a food product? Consider: texture, Maillard reaction, preservation, mouthfeel, microbial stability.

Answer 45

Texture: Sugar contributes to bulk, tenderness, and moisture retention. Without it, products may become dry, crumbly, or hard. Maillard Reaction: Sugar participates in Maillard browning with amino acids, so removing sugar can reduce browning and flavor development during cooking or baking. Preservation: Sugar lowers water activity, helping inhibit microbial growth. Without sugar, microbial spoilage risk increases, reducing shelf life. Mouthfeel: Sugar adds sweetness, viscosity, and smoothness. Its absence may result in a product that feels less rich or less palatable. Microbial Stability: Reduced sugar means higher water activity, promoting growth of bacteria, yeasts, and moulds

Question 46

Texture Profile Analysis (TPA)

Answer 46

What it is: An instrumental method that simulates the action of chewing by compressing a food sample twice. How it works: A texture analyzer presses down on the food sample, measuring force over time during two compression cycles. Key parameters measured: Hardness: Force required to compress the food. Cohesiveness: How well the food withstands a second deformation relative to the first. Springiness: How well the food recovers its shape after compression. Chewiness: Energy required to chew a solid food (calculated from hardness, cohesiveness, and springiness).

Question 47

organoleptic testing

Answer 47

texture, colour, taste

Question 48

shortening

Answer 48

Fat, solid at room temperature. interfere with gluten development, leading to a crumbly or flakey texture, coats flour partials, preventing them from fully absorbing water in which is necessary for gluten development

Question 49

Aeration

Answer 49

adding very small pockets of air to lead to lighter, fluffier texture and contribute to rise of baked goods

Question 50

creaming

Answer 50

beating softened butter and sugar together As butter and sugar are beaten together, the sugar crystals act as tiny mechanical levers, puncturing the butter and trapping air pockets within the mixture. The fat molecules in the butter help to disperse the sugar and create a smooth, homogeneous blend.