2. Food Composition, Structure and Functional Properties

Introduction and context

Food is not simply a collection of nutrients. It is a structured, dynamic system in which water, carbohydrates, proteins, lipids, minerals, vitamins, enzymes and bioactive compounds interact with one another and with processing conditions. These interactions determine whether a sauce is smooth or lumpy, bread is soft or stale, meat is tender or tough, a beverage remains stable, or a dessert develops the desired body and flavour.

For hospitality professionals, food composition is directly connected with purchasing, menu planning, recipe standardisation, cooking control, quality assurance and guest satisfaction. A chef who understands the composition of an ingredient can predict how it will respond to heat, mechanical action, acidity, salt, freezing, drying and storage. Similarly, a food and beverage manager can make more informed decisions about product specifications, shelf life, allergen control and nutritional communication.

The functional properties of food components arise from their chemical structure and from the way they are organised within cells, tissues, dispersions and emulsions. Composition therefore cannot be studied independently from structure. The same molecule may behave differently depending on concentration, temperature, pH, water availability and the presence of other components.

Learning objectives

After studying this chapter, the learner should be able to:

1. Describe the major components of foods and their chemical characteristics.

2. Explain the relationship between molecular structure and functional behaviour.

3. Analyse the roles of water, carbohydrates, proteins, lipids, vitamins, minerals, enzymes and bioactive compounds.

4. Predict how heating, cooling, mixing, acidity and water activity affect food quality.

5. Apply compositional knowledge to cooking, formulation, menu planning and food service operations.

6. Evaluate common processing problems and recommend technically appropriate solutions.

7. Discuss professional, regulatory and emerging technological issues related to food composition.

Food as a structured system

Food structure exists at several levels. At the molecular level, water molecules associate with sugars, salts and proteins. At the microscopic level, starch granules, fat droplets, air cells and protein networks form dispersions or matrices. At the macroscopic level, these structures are perceived as viscosity, crispness, tenderness, juiciness, creaminess and appearance.

A food may be a solution, suspension, emulsion, gel, foam or combination of these systems. Salt dissolved in soup forms a solution; flour particles dispersed in batter form a suspension; mayonnaise is an oil-in-water emulsion; jelly is a gel; whipped cream is a foam. Their stability depends on particle size, interfacial forces, viscosity, temperature and chemical environment.

Two important concepts are concentration and availability. A component may be present in substantial quantity but have limited functional activity if it is bound, encapsulated or chemically unavailable. Water illustrates this distinction particularly well. Total moisture does not indicate how much water is available for microbial growth or chemical reactions. This is expressed through water activity, a measure of the escaping tendency of water relative to pure water. Lowering water activity through drying, freezing, salting or sugaring generally improves stability, although it may alter texture.

Water: the principal medium of food reactions

Water is commonly the largest component of fresh foods. It acts as a solvent, reaction medium, plasticiser, heat-transfer medium and determinant of texture. Its polarity enables it to dissolve ionic substances and many polar molecules. It also participates directly in hydrolysis reactions and influences the mobility of food constituents.

Water is present in two broad forms. Free water is relatively mobile and can support microbial growth, dissolve solutes and migrate during processing. Bound water is associated with proteins, starches, fibres, salts or surfaces and is less mobile. The distinction is not absolute; water exists across a continuum of binding strengths.

Water contributes to cooking in several ways. During boiling, it transfers heat efficiently and hydrates starches and proteins. In baking, steam contributes to expansion and crust formation. During freezing, ice crystals concentrate solutes in the unfrozen phase and may damage cellular structures. Slow freezing usually forms larger crystals, causing greater tissue rupture and drip loss after thawing; rapid freezing generally produces smaller crystals and better texture retention.

Water activity is particularly important in hospitality operations. A moist cake may remain microbiologically stable if its solutes reduce water activity sufficiently, while a dry product can still deteriorate through lipid oxidation or enzymatic reactions. Packaging, humidity control and temperature management must therefore be matched to the food’s moisture characteristics.

Carbohydrates: sweetness, body and structural transformation

Carbohydrates include sugars, oligosaccharides, starches and non-starch polysaccharides such as cellulose, pectin and some gums. They supply energy but are also major structural and sensory agents.

Simple sugars such as glucose, fructose and sucrose contribute sweetness, browning and solids. Their sweetness differs, and their behaviour depends on concentration, temperature and the presence of acids or other ingredients. Sugars bind water, lower the freezing point and increase viscosity. These properties are central to ice cream, confectionery, preserves and beverages.

Starch consists mainly of amylose and amylopectin. When starch is heated in water, granules absorb water, swell and lose their organised structure. This process, gelatinisation, increases viscosity and produces body in sauces, soups, custards and bakery products. On cooling, starch chains may reassociate, a process known as retrogradation. Retrogradation contributes to firming and bread staling, although it can also help set certain gels.

Dextrinisation is the breakdown and browning of starch under dry heat, as seen on the surface of toast or roasted flour products. Caramelisation is the thermal degradation of sugars, producing colour and complex flavour compounds. The Maillard reaction involves reducing sugars and amino groups, usually from proteins or amino acids. It creates desirable roasted aromas and brown colour in bread crust, seared meat and baked goods, but excessive reaction can produce bitterness and undesirable compounds.

Dietary fibre includes indigestible carbohydrate components. Soluble fibres may increase viscosity and form gels, while insoluble fibres contribute bulk and water-holding capacity. Pectin, alginate, carrageenan and modified starches are used as hydrocolloids to control viscosity, suspension, gel strength and mouthfeel. Their performance depends strongly on pH, ionic concentration, temperature and shear.

Proteins: networks, emulsions and food texture

Proteins are polymers of amino acids folded into specific three-dimensional structures. Their functional behaviour derives from peptide bonds, charged groups, hydrophobic regions and the ability to interact with water, lipids and other proteins.

Protein denaturation is the unfolding or reorganisation of native structure without necessarily breaking the peptide backbone. Heat, acids, salts, alcohol, mechanical action and pressure can cause denaturation. Once unfolded, proteins may aggregate and form a network. Egg white illustrates this process: heating converts a transparent liquid into an opaque, firm gel. Excessive heating, however, can produce a tough or rubbery texture because the network contracts and expels water.

Proteins contribute to gelation, emulsification, foaming, water binding and elasticity. In meat, myofibrillar proteins help bind water and fat in sausages and emulsified products. Gluten proteins in wheat form an elastic network when hydrated and mixed, retaining gas during bread fermentation. Milk proteins stabilise emulsions and participate in cheese manufacture. Egg proteins stabilise foams in meringues and emulsions in custards.

Protein functionality is influenced by pH. Near the isoelectric point, the protein carries minimal net charge and often has reduced solubility and water-holding capacity. This principle contributes to curd formation in dairy products. Salt can improve solubility at certain concentrations but may promote aggregation at higher levels. Enzymatic proteolysis can tenderise meat or weaken a protein network, but uncontrolled hydrolysis may produce poor texture.

Lipids: energy, flavour and physical character

Lipids include triglycerides, phospholipids, sterols and related compounds. They are largely hydrophobic and therefore do not mix naturally with water. Their culinary functions include heat transfer, lubrication, flavour carrying, tenderness, aeration and formation of emulsions.

The fatty-acid composition of a fat determines its melting behaviour. Saturated and longer-chain fatty acids generally increase melting temperature, whereas unsaturation introduces bends that reduce close packing and lower melting temperature. This explains why butter, coconut fat and vegetable oils differ in spreadability, mouthfeel and cooking performance.

Lipids provide richness and carry fat-soluble flavour compounds. In pastry, solid fat interrupts gluten development and contributes shortness. In frying, the medium transfers heat rapidly and produces dehydration and crust formation. Repeated heating can promote oxidation, hydrolysis and polymerisation, leading to off-flavours, darkening, foaming and increased viscosity.

Emulsions require energy to disperse one liquid into another and usually need an emulsifier or stabilising system. Mayonnaise is an oil-in-water emulsion stabilised mainly by egg-yolk components; butter is a water-in-oil system. Emulsion failure may result from insufficient emulsifier, large droplet size, excessive temperature, incompatible ingredients or inadequate mixing. Lecithin, mono- and diglycerides, proteins and some hydrocolloids are used to improve stability.

Lipid oxidation is accelerated by oxygen, heat, light, metal ions and unsaturated fatty acids. It causes rancidity and nutritional loss. Protection includes oxygen-barrier packaging, low temperatures, light exclusion, antioxidants and careful control of frying oil turnover.

Vitamins, minerals and bioactive compounds

Vitamins are organic micronutrients required in small amounts. Fat-soluble vitamins A, D, E and K can be stored in body tissues, while water-soluble vitamins such as the B-group and vitamin C are generally less extensively stored. Processing may cause losses through heat, oxidation, leaching and exposure to light. Water-soluble vitamins are especially vulnerable to losses when vegetables are boiled in excess water and the cooking liquor is discarded.

Minerals are inorganic elements such as calcium, iron, sodium, potassium, magnesium and zinc. They contribute to bone structure, fluid balance, nerve function, enzyme activity and food structure. Calcium supports pectin and protein interactions and can strengthen some gels. Sodium affects flavour, preservation and protein extraction. Iron and copper may catalyse lipid oxidation, although they are nutritionally essential.

Bioactive compounds are constituents that may influence physiological processes beyond basic nutrition. Examples include polyphenols, carotenoids, phytosterols, glucosinolates and certain peptides. Their concentration and activity can change during cooking, fermentation, milling and storage. Bioavailability is not identical to content: a compound may be present but poorly absorbed because it is bound to fibre or affected by antinutritional factors.

Hospitality professionals should avoid overstating health effects. Nutrient and health claims must be scientifically supported and comply with applicable food-labelling regulations. Menu descriptions should distinguish between a naturally occurring component and a clinically proven benefit.

Enzymes and controlled change

Enzymes are biological catalysts that accelerate specific reactions without being consumed. In foods, they may be naturally present or added deliberately. Their activity depends on temperature, pH, water availability and substrate concentration.

Polyphenol oxidase causes enzymatic browning in cut apples, bananas and potatoes when tissue damage exposes enzymes to oxygen. Acidulated water, blanching, refrigeration and exclusion of oxygen can reduce this reaction. Pectinases soften fruit tissues and clarify juices. Proteases tenderise meat and modify dairy or cereal proteins. Amylases break down starch and influence bread volume, sweetness and staling.

Enzyme control is often a balance rather than complete elimination. Ripening depends on enzyme activity, but excessive activity creates mushiness or quality loss. Blanching vegetables briefly inactivates enzymes before freezing, while overcooking can degrade colour, flavour and nutrients. Commercial food processing uses enzymes to improve yield, clarification, texture and consistency, subject to regulatory approval and process control.

Interactions that determine food quality

Food properties rarely arise from one component alone. In a custard, egg proteins form a heat-set network while sugar delays coagulation, water acts as the continuous phase, and fat contributes richness. In bread, gluten provides structure, yeast produces gas, starch gelatinises, sugars support browning and water controls dough development. In a sauce, starch thickening may be modified by fat, acid, salt and shear.

A useful analytical approach is to consider five questions:

• Which component provides the primary structure?
• Where is the water located, and how mobile is it?
• What transformations are expected at the processing temperature?
• Which interactions may stabilise or destabilise the system?
• What sensory and safety outcomes are required?

This approach helps predict failures. A broken emulsion suggests a problem at the interface; a watery gel may indicate inadequate polymer concentration or unsuitable pH; a tough protein product may reflect excessive denaturation; a stale bakery product may involve moisture migration and starch retrogradation.

Applications in hospitality and food product formulation

Recipe formulation should begin with the intended sensory and functional outcomes rather than with ingredient substitution alone. Replacing sugar with an intense sweetener, for example, may preserve sweetness but remove bulk, water binding, browning and freezing-point effects. Replacing butter with oil changes melting, aeration and pastry structure. Reducing salt alters flavour as well as protein extraction and preservation.

Standardised recipes should specify ingredient form, temperature, mixing sequence, cooking time, endpoint and holding conditions. Mise en place is not merely an organisational practice; it controls the timing of enzymatic reactions, hydration and temperature changes. Batch size also matters because heat penetration, evaporation and mixing efficiency change with scale.

In menu engineering, composition supports informed decisions about allergens, dietary patterns and product claims. Gluten, milk, egg, peanut, tree nuts, fish, shellfish, soy and other regulated allergens require careful specification and cross-contact control. Nutrient-dense formulations may incorporate pulses, whole grains, vegetables, nuts and fermented foods, but their effects on texture, flavour and guest acceptance must be tested rather than assumed.

Illustrative case study: stabilising a dairy-based dessert sauce

Background

A hotel pastry kitchen develops a vanilla dessert sauce for banquet service. The intended product is smooth, glossy and pourable for two hours under chilled holding.

Situation and problem

The first batch is initially smooth but becomes watery and slightly grainy after chilling. A second batch is thick but develops a cooked-egg flavour when reheated.

Analysis

The sauce contains milk, egg yolks, sugar and starch. Egg proteins provide thickening through heat-induced coagulation, while starch gelatinisation increases viscosity. Sugar competes for water and delays protein coagulation. Chilling increases viscosity but may also encourage starch retrogradation. Excessive heating causes protein aggregation and syneresis, the expulsion of liquid from a gel network.

The watery appearance indicates either inadequate starch hydration, weak structure or syneresis. The graininess and cooked flavour indicate that the second batch exceeded the desired coagulation temperature or was held too long at high heat. Poor cooling may also have allowed continued cooking.

Approach and solution

The pastry team standardises the starch dispersion, mixes sugar with the starch before adding liquid, heats the sauce gradually with continuous agitation, and removes it at the target endpoint rather than relying only on time. The sauce is strained, rapidly cooled in shallow containers and covered to minimise evaporation and contamination. A small formulation trial compares different starch levels and evaluates viscosity after both immediate service and chilled holding.

Outcome

The revised process produces a smoother sauce with stable body during the service period. The team records batch size, heating endpoint and cooling time in the standard recipe. The formulation is not judged solely by hot viscosity; it is evaluated after the complete holding cycle.

Learning points

The case demonstrates that composition, structure and process cannot be separated. Sugar, protein and starch perform different but interacting roles. Temperature control is essential, and a product must be assessed under actual service conditions rather than immediately after preparation.

Limitations, risks and common mistakes

A frequent mistake is to treat ingredient substitutions as nutritionally or functionally equivalent. Low-fat products may have less lubrication and may require stabilisers; gluten-free flours may lack the network needed for bread; plant-based proteins may respond differently to heat and pH. Another error is to assume that a recipe behaves identically at every scale.

Other risks include uncontrolled allergen cross-contact, inaccurate labelling, excessive reliance on sensory judgement without records, overheating of oils, inadequate cooling, and confusing total moisture with water activity. Natural ingredients can also vary in maturity, cultivar, composition and storage history. Professional control therefore requires specifications, calibrated equipment, documented procedures and verification.

Technology, analytics and emerging developments

Modern kitchens and food manufacturers increasingly use digital thermometers, data loggers, texture analysers, refractometers, water-activity meters and rapid quality tests. These tools support evidence-based decisions about cooking endpoints, concentration, shelf life and batch consistency. Near-infrared and other spectroscopic methods can estimate composition rapidly in industrial settings, while predictive models help assess microbial and chemical stability.

AI and data analytics may assist with recipe optimisation, allergen databases, waste reduction and sensory prediction. However, algorithmic recommendations depend on reliable input data and should not replace professional validation. Emerging formulation trends include plant-based foods, precision fermentation, clean-label stabilisation, reduced-sugar products, upcycled ingredients and personalised nutrition. Their success depends on achieving acceptable texture, flavour, safety, cost and regulatory compliance simultaneously.

Best practices for professional application

1. Define the desired sensory, nutritional and safety outcomes before changing a formulation.

2. Identify the principal structural component and the role of water in the system.

3. Control pH, temperature, time, shear and concentration rather than relying on intuition alone.

4. Evaluate products after realistic holding, reheating, freezing or transport conditions.

5. Use standardised specifications and document deviations.

6. Protect against oxidation, moisture migration, enzymatic browning and microbial growth.

7. Verify allergen information and regulatory claims.

8. Combine sensory evaluation with instrumental or analytical measurements where appropriate.

Chapter Summary

Food quality results from the interaction of composition, structure and processing. Water controls solubility, heat transfer, texture and reaction rates, while water activity helps explain stability. Carbohydrates provide sweetness, viscosity, browning and gel formation; proteins create networks, emulsions, foams and water-binding structures; and lipids contribute richness, lubrication, flavour delivery, heat transfer and emulsion behaviour. Vitamins and minerals support nutritional and structural functions, whereas bioactive compounds may influence physiological processes but require responsible communication. Enzymes drive important changes such as browning, ripening, tenderisation and starch modification.

Understanding these components enables professionals to predict the effects of heat, pH, mixing, freezing, drying and storage. It also supports recipe standardisation, product development, allergen management, quality assurance and informed use of technology. The central principle is that ingredients do not act independently: food performance emerges from interactions within a changing system.

Key Terms

Water activity: The effective availability of water for chemical reactions and microbial growth.

Bound water: Water associated with food constituents and less mobile than free water.

Gelatinisation: Swelling and structural disruption of starch granules during heating with water.

Retrogradation: Reassociation of starch molecules during cooling or storage.

Caramelisation: Thermal degradation of sugars producing colour and flavour compounds.

Maillard reaction: Reaction between reducing sugars and amino groups that produces browning and aroma.

Denaturation: Unfolding or reorganisation of a protein’s native structure.

Isoelectric point: pH at which a protein has minimal net electrical charge.

Gelation: Formation of a three-dimensional network that immobilises liquid.

Emulsion: A dispersion of one immiscible liquid within another.

Emulsifier: A substance that promotes or stabilises an emulsion.

Lipid oxidation: Reaction of fats with oxygen, often causing rancidity.

Hydrocolloid: A water-interacting polymer used to modify viscosity, suspension or gelation.

Enzyme: A biological catalyst that accelerates a specific chemical reaction.

Syneresis: Expulsion of liquid from a gel or structured food system.

Bioactive compound: A food constituent that may influence physiological processes beyond basic nutrition.

Water-soluble vitamin: A vitamin that dissolves in water and is generally less extensively stored.

Fat-soluble vitamin: A vitamin that dissolves in lipid and may accumulate in body tissues.

Protein network: An interacting structure of proteins responsible for properties such as elasticity or firmness.

Review Questions

Short Answer Questions

1. Distinguish between free water, bound water and water activity.

2. What is starch gelatinisation, and where is it used in hospitality products?

3. State two functional roles of proteins in food systems.

4. Why are unsaturated fats generally more prone to oxidation?

5. Define enzymatic browning and name one method of controlling it.

Long Answer Questions

1. Explain how carbohydrates contribute to sweetness, viscosity, browning and gel formation.

2. Discuss the effects of heat, pH and salt on protein functionality.

3. Describe the composition and stability requirements of food emulsions, using suitable examples.

4. Analyse the roles of water in cooking, freezing, storage and food safety.

5. Explain how vitamins, minerals and bioactive compounds should be considered in menu planning and product communication.

Analytical / Application Questions

1. A cream sauce separates after prolonged hot holding. Analyse the likely compositional and process causes and recommend corrective measures.

2. A bakery replaces butter with vegetable oil but obtains a flatter, less tender pastry. Explain the functional changes and propose formulation adjustments.

3. A cut fruit platter browns rapidly during a banquet. Design a control strategy using knowledge of enzymes, oxygen, acidity, temperature and service timing.

22. Multiple Choice Questions with Answers

Question 1

Which property most directly explains why reducing water activity can improve the storage stability of a food?

A. It increases the total moisture content

B. It reduces the water available for microbial growth and reactions

C. It guarantees that all enzymes are destroyed

D. It prevents all lipid oxidation

Correct Answer: B. It reduces the water available for microbial growth and reactions

Question 2

A custard becomes rubbery and releases liquid after excessive heating. Which explanation is most appropriate?

A. Insufficient sugar caramelisation

B. Starch retrogradation before heating

C. Excessive protein aggregation and network contraction

D. Complete inhibition of protein denaturation

Correct Answer: C. Excessive protein aggregation and network contraction

Question 3

Which transformation is primarily responsible for the thickening of a starch-based sauce during heating with water?

A. Gelatinisation

B. Lipid oxidation

C. Proteolysis

D. Caramelisation

Correct Answer: A. Gelatinisation

Question 4

Why does replacing butter with oil commonly alter pastry texture?

A. Oil contains no water-soluble vitamins

B. Oil changes the fat’s solid-to-liquid behaviour and gluten-interruption pattern

C. Oil always increases protein denaturation

D. Oil prevents all starch gelatinisation

Correct Answer: B. Oil changes the fat’s solid-to-liquid behaviour and gluten-interruption pattern

Question 5

Mayonnaise is best described as which type of system?

A. Water-in-oil foam

B. Oil-in-water emulsion

C. Solid fat suspension

D. Protein gel without a continuous phase

Correct Answer: B. Oil-in-water emulsion

Question 6

Which condition would generally accelerate lipid oxidation?

A. Exclusion of oxygen and low temperature

B. Protection from light and use of antioxidants

C. Exposure to heat, oxygen and metal ions

D. Rapid freezing in oxygen-barrier packaging

Correct Answer: C. Exposure to heat, oxygen and metal ions

Question 7

A cut apple is treated with lemon juice mainly to reduce which process?

A. Starch retrogradation

B. Enzymatic browning

C. Protein gelation

D. Lipid crystallisation

Correct Answer: B. Enzymatic browning

Question 8

Near its isoelectric point, a protein commonly shows which behaviour?

A. Maximum net charge and maximum solubility

B. Minimal net charge and often reduced solubility

C. Complete resistance to heat

D. Conversion into a carbohydrate

Correct Answer: B. Minimal net charge and often reduced solubility

Question 9

In the dessert-sauce case, rapid cooling after cooking was important primarily because it helps to:

A. Continue protein coagulation gradually

B. Limit carry-over cooking and improve safety and stability

C. Increase enzymatic browning

D. Prevent all starch hydration

Correct Answer: B. Limit carry-over cooking and improve safety and stability

Question 10

Which statement best reflects responsible use of bioactive-compound claims?

A. Any naturally occurring compound can be described as a cure

B. Content and physiological benefit are always identical

C. Claims should be scientifically supported and comply with applicable regulations

D. Bioactive compounds have no relevance to formulation

Correct Answer: C. Claims should be scientifically supported and comply with applicable regulations