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Cameroon GCE A-Level Food Science & Nutrition study materials
Cameroon GCE A-Level Food Science & Nutrition study resources

Cameroon GCE A-Level Food Science & Nutrition practice questions

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Question 1Food Chemistry and Composition

Which macronutrient is the principal structural component of cell membranes in foods of animal and plant origin?

  1. Cellulose
  2. Starch
  3. Triglycerides
  4. Phospholipids Correct answer.

Explanation

Phospholipids are amphipathic molecules with a hydrophilic phosphate head and hydrophobic fatty acid tails, so they spontaneously form the bilayer that constitutes the membrane framework. Triglycerides are storage lipids, while cellulose and starch are structural and storage polysaccharides respectively.

Question 2Food Chemistry and Composition

Which bond links two amino acids in a protein chain?

  1. Glycosidic bond
  2. Hydrogen bond
  3. Peptide bond Correct answer.
  4. Ester bond

Explanation

A peptide bond forms by condensation between the carboxyl group of one amino acid and the amino group of the next, releasing water. Glycosidic bonds join sugars, ester bonds join glycerol and fatty acids, and hydrogen bonds are weaker secondary interactions.

Question 3Food Chemistry and Composition

Which monosaccharide is the basic repeating unit of both starch and cellulose?

  1. Ribose
  2. Fructose
  3. Glucose Correct answer.
  4. Galactose

Explanation

Both starch and cellulose are homopolymers of glucose; they differ in the anomeric linkage and branching, which explains their very different digestibility. Fructose, galactose and ribose are other sugars that do not form these polymers.

Question 4Food Chemistry and Composition

What is the principal solvent that supports biochemical reactions and nutrient transport in fresh foods?

  1. Water Correct answer.
  2. Acetic acid
  3. Glycerol
  4. Ethanol

Explanation

Water is the dominant component of most fresh foods and acts as the universal solvent, allowing enzymes, salts and sugars to dissolve and react. Its high polarity and hydrogen bonding underpin its solvent and transport functions.

Question 5Food Chemistry and Composition

Which vitamin is water-soluble and therefore most easily lost during blanching of vegetables?

  1. Vitamin A
  2. Vitamin D
  3. Vitamin E
  4. Vitamin C Correct answer.

Explanation

Vitamin C (ascorbic acid) is highly water-soluble and heat-labile, so it leaches into blanching water and is readily oxidised. Vitamins A, D and E are fat-soluble and much less affected by aqueous leaching.

Question 6Food Chemistry and Composition

Which mineral is the central atom of the chlorophyll molecule?

  1. Calcium
  2. Magnesium Correct answer.
  3. Zinc
  4. Iron

Explanation

Chlorophyll is a porphyrin ring chelating a magnesium ion at its centre, which is essential for light absorption. Iron is central to haem in haemoglobin, not chlorophyll.

Question 7Food Chemistry and Composition

Which type of fatty acid has no double bonds in its hydrocarbon chain?

  1. Trans fatty acid
  2. Saturated fatty acid Correct answer.
  3. Monounsaturated fatty acid
  4. Polyunsaturated fatty acid

Explanation

Saturated fatty acids contain only single carbon-carbon bonds, giving a straight chain that packs tightly and tends to be solid at room temperature. Mono- and polyunsaturated acids contain one or more double bonds, and trans acids are unsaturated isomers.

Question 8Food Chemistry and Composition

Which process describes the uptake of water by dry starch granules when heated in water, causing them to swell?

  1. Gelatinisation Correct answer.
  2. Retrogradation
  3. Syneresis
  4. Caramelisation

Explanation

Gelatinisation occurs when heat and water disrupt starch crystallinity, allowing granules to absorb water, swell and eventually rupture, thickening the mixture. Retrogradation is the reverse reordering on cooling, caramelisation is sugar pyrolysis and syneresis is liquid weeping from a gel.

Question 9Food Chemistry and Composition

Which protein fraction of wheat flour is chiefly responsible for gluten formation?

  1. Casein
  2. Albumin
  3. Glutenin and gliadin Correct answer.
  4. Globulin

Explanation

When hydrated and worked, the storage proteins glutenin and gliadin associate to form gluten, which gives dough its elastic and extensible character. Albumins and globulins are soluble metabolic proteins, and casein is a milk protein.

Question 10Food Chemistry and Composition

Which change in protein structure is described as denaturation?

  1. Addition of a phosphate group to a serine residue
  2. Loss of secondary, tertiary and quaternary structure without breaking peptide bonds Correct answer.
  3. Hydrolysis of peptide bonds into free amino acids
  4. Formation of new peptide bonds between side chains

Explanation

Denaturation disrupts the weak non-covalent interactions that maintain higher-order structure, unfolding the molecule while leaving the primary sequence intact. Hydrolysis cleaves peptide bonds and is a different, more destructive change.

Question 11Food Chemistry and Composition

A cook notices that a mayonnaise separates after standing. Which phenomenon best explains this?

  1. Maillard browning
  2. Gelatinisation of starch
  3. Protein hydrolysis
  4. Coalescence of dispersed oil droplets Correct answer.

Explanation

Mayonnaise is an oil-in-water emulsion stabilised by egg lecithin; over time droplets collide, the interfacial film fails and droplets merge, leading to phase separation. This process is coalescence, distinct from chemical browning or starch changes.

Question 12Food Chemistry and Composition

Which statement correctly describes the Maillard reaction?

  1. It is the enzymatic browning caused by polyphenol oxidase
  2. It involves condensation between a reducing sugar and an amino group, producing brown pigments Correct answer.
  3. It is the thermal decomposition of sucrose alone above 160 degrees Celsius
  4. It is the oxidation of ascorbic acid in the presence of light

Explanation

The Maillard reaction begins with the carbonyl group of a reducing sugar reacting with an amino group of a protein or amino acid, followed by complex rearrangements that yield melanoidins and aroma compounds. It requires both reactants and is non-enzymatic.

Question 13Food Chemistry and Composition

Which factor most directly lowers the water activity of a food without changing its moisture content?

  1. Increasing the pH
  2. Whipping in air
  3. Adding sodium chloride Correct answer.
  4. Raising the temperature

Explanation

Dissolved solutes such as sodium chloride bind water through hydration, reducing the proportion available as solvent and thus lowering water activity at constant moisture. Temperature and pH changes do not bind water in this way.

Question 14Food Chemistry and Composition

Which lipid fraction is most susceptible to oxidative rancidity during storage?

  1. Saturated triacylglycerols
  2. Monoglyceride emulsifiers
  3. Sterol esters
  4. Polyunsaturated triacylglycerols Correct answer.

Explanation

Oxidative rancidity proceeds by free-radical attack at bis-allylic methylene groups between double bonds, so the more double bonds a fatty acid has, the faster it oxidises. Saturated chains lack these reactive sites and resist oxidation.

Question 15Food Chemistry and Composition

Which enzyme is responsible for the browning of cut apples and potatoes?

  1. Polyphenol oxidase Correct answer.
  2. Amylase
  3. Pepsin
  4. Lipase

Explanation

Polyphenol oxidase catalyses the oxidation of phenolic compounds to quinones, which polymerise into brown melanins when tissue is cut and exposed to oxygen. Amylase, lipase and pepsin act on starch, lipids and proteins respectively.

Question 16Food Chemistry and Composition

Which statement about the isoelectric point of a protein is correct?

  1. The isoelectric point is unaffected by the amino acid composition
  2. At its isoelectric point the net charge is maximal and solubility is highest
  3. At its isoelectric point the net charge is zero and solubility is usually minimal Correct answer.
  4. The isoelectric point is always at pH 7 for food proteins

Explanation

At the isoelectric point the positive and negative charges on the protein balance, reducing electrostatic repulsion between molecules so they aggregate and precipitate. This principle is used to isolate casein by acidification to about pH 4.6.

Question 17Food Chemistry and Composition

Which sugar alcohol is commonly used as a low-calorie sweetener and humectant in confectionery?

  1. Lactose
  2. Sucrose
  3. Maltose
  4. Sorbitol Correct answer.

Explanation

Sorbitol is a sugar alcohol with about two-thirds the sweetness of sucrose and a strong water-binding capacity, making it useful as a humectant in sugar-free confectionery. Sucrose, lactose and maltose are digestible sugars, not polyols.

Question 18Food Chemistry and Composition

Which statement best explains why unsaturated fats are liquid at room temperature?

  1. They are always shorter in chain length than saturated fats
  2. They have a higher proportion of glycerol backbone
  3. They contain more carbon atoms than saturated fats
  4. Cis double bonds create kinks that prevent tight packing of the chains Correct answer.

Explanation

Cis double bonds introduce a bend in the hydrocarbon chain, disrupting orderly crystal packing and lowering the melting point so the fat remains liquid. Chain length and glycerol content do not explain the difference.

Question 19Food Chemistry and Composition

Which analytical measure is used to express the degree of unsaturation of a fat?

  1. Peroxide value
  2. Saponification value
  3. Iodine value Correct answer.
  4. Refractive index

Explanation

The iodine value measures the grams of iodine absorbed by 100 g of fat, which is proportional to the number of double bonds present. Saponification value reflects average chain length, peroxide value indicates oxidation and refractive index is a physical property.

Question 20Food Chemistry and Composition

A flour dough is enriched with the enzyme transglutaminase. Which change is expected?

  1. Hydrolysis of starch into maltose, weakening the dough
  2. Oxidation of lipids to aldehydes, producing rancidity
  3. Denaturation of gluten by heat, reducing elasticity
  4. Formation of covalent cross-links between glutamine and lysine residues, strengthening the dough Correct answer.

Explanation

Transglutaminase catalyses an acyl transfer reaction between the gamma-carboxamide of glutamine and the epsilon-amino group of lysine, creating isopeptide bonds that reinforce the protein network. This increases dough strength and elasticity.

Question 21Food Chemistry and Composition

Which explanation accounts for the thickening of a starch sauce when it cools after cooking?

  1. Sucrose crystallises and forms a rigid network
  2. Amylose chains reassociate into ordered junction zones that trap water Correct answer.
  3. Fat droplets solidify and bind the liquid phase
  4. Starch granules continue to absorb unlimited water

Explanation

On cooling, leached amylose molecules aggregate through hydrogen bonding into double-helical junction zones, forming a three-dimensional network that immobilises water and sets the gel. This is the early stage of retrogradation.

Question 22Food Chemistry and Composition

Which statement about water activity and microbial growth is correct?

  1. Water activity has no influence on microbial growth once the food is refrigerated
  2. All microorganisms grow equally well at any water activity above 0.50
  3. Bacteria tolerate lower water activity than any mould or yeast
  4. Most spoilage bacteria require a water activity above about 0.90, while xerophilic moulds can grow near 0.65 Correct answer.

Explanation

Water activity determines the amount of water available for microbial metabolism; most bacteria need values above roughly 0.90, yeasts tolerate about 0.88 and xerophilic moulds can grow near 0.65. Below these limits growth is inhibited, which is why drying and salting preserve food.

Question 23Food Chemistry and Composition

Which interaction is chiefly responsible for stabilising the tertiary structure of a globular protein in an aqueous environment?

  1. Glycosidic linkages between serine residues
  2. Peptide bonds between distant residues
  3. Hydrophobic interactions between non-polar side chains Correct answer.
  4. Ionic bonds between phosphate groups

Explanation

In water, non-polar side chains cluster in the interior to minimise contact with solvent, and these hydrophobic interactions, together with hydrogen bonds and disulfide bridges, stabilise the folded conformation. They are weak individually but numerous and collectively dominant.

Question 24Food Chemistry and Composition

Which change explains the loss of green colour when vegetables are heated in hard water?

  1. Carotenoids are destroyed, revealing chlorophyll
  2. Magnesium in chlorophyll is replaced by hydrogen ions, forming pheophytin Correct answer.
  3. Iron in chlorophyll is oxidised to ferric hydroxide
  4. Chlorophyll is hydrolysed into glucose and phytol only

Explanation

Heat and acidity labilise the chlorophyll molecule so that the central magnesium is displaced by two hydrogen ions, producing olive-brown pheophytin. Hard water and acids accelerate this replacement, while brief cooking in alkaline water preserves colour.

Question 25Food Chemistry and Composition

Which statement correctly distinguishes gelatinisation from gelation in starch systems?

  1. Both terms describe the enzymatic hydrolysis of starch
  2. Gelatinisation is heat-driven granule swelling, whereas gelation is network formation on cooling Correct answer.
  3. Gelatinisation requires fat, whereas gelation requires protein
  4. Gelatinisation occurs only on cooling, whereas gelation occurs only on heating

Explanation

Gelatinisation describes the irreversible uptake of water and swelling of granules during heating, whereas gelation is the subsequent formation of an ordered three-dimensional network as amylose reassociates on cooling. The two stages are sequential but mechanistically distinct.

Question 26Food Chemistry and Composition

A sample of groundnut oil is analysed and found to contain a high proportion of linoleic acid. To which class of fatty acids does linoleic acid belong?

  1. Polyunsaturated fatty acid Correct answer.
  2. Monounsaturated fatty acid
  3. Trans fatty acid
  4. Saturated fatty acid

Explanation

Linoleic acid has two cis double bonds in its hydrocarbon chain (18:2), so it is classified as a polyunsaturated fatty acid. Fatty acid classes are defined by the number of double bonds: none for saturated, one for monounsaturated, two or more for polyunsaturated.

Question 27Food Chemistry and Composition

A food technologist wishes to express the total ash content of a dried fish sample as a percentage of its dry matter. Which calculation gives the correct result?

  1. (mass of dried sample ÷ mass of ash) × 100
  2. (mass of ash ÷ mass of crucible) × 100
  3. (mass of ash ÷ mass of dried sample) × 100 Correct answer.
  4. (mass of ash ÷ mass of fresh sample) × 100

Explanation

Ash represents the inorganic residue left after complete incineration of organic matter, and expressing it on a dry-matter basis requires dividing the ash mass by the mass of the dried sample used. Multiplying by 100 converts the ratio to a percentage. This value is used to estimate total mineral content.

Question 28Food Chemistry and Composition

During storage, a biscuit made with a high level of glucose syrup becomes sticky and loses crispness. Which property of glucose syrup best accounts for this behaviour?

  1. Its ability to act as an oxidising agent in the dough
  2. Its high protein content, which binds water strongly
  3. Its low solubility, which causes crystallisation on the surface
  4. Its hygroscopic nature, which attracts and retains moisture from the air Correct answer.

Explanation

Glucose syrup contains glucose, maltose and higher saccharides that are strongly hygroscopic, so they absorb moisture from the surrounding atmosphere. The absorbed water plasticises the biscuit structure and reduces crispness. Controlling the proportion of such syrups is therefore important in baked confectionery.

Question 29Food Chemistry and Composition

Two loaves are baked from the same flour, one with added salt and one without. The salted loaf shows a firmer, less extensible dough. Which explanation best accounts for this observation?

  1. Sodium chloride increases starch gelatinisation temperature, hardening the crumb
  2. Sodium chloride denatures gluten proteins irreversibly, destroying the network
  3. Sodium chloride shields charges on gluten proteins, promoting protein-protein association and a tighter gluten network Correct answer.
  4. Sodium chloride inhibits yeast activity, so less gas is produced and the dough stays firm

Explanation

Salt ions screen electrostatic repulsion between charged groups on glutenin and gliadin, allowing the proteins to associate more closely and forming a stronger, tighter gluten network. This reduces extensibility and increases dough resistance. Salt also affects flavour and yeast activity, but the rheological change described is mainly a protein-charge effect.

Question 30Food Chemistry and Composition

A protein isolate is heated in an aqueous medium at pH 4.5, close to its isoelectric point, and a dense coagulum forms. Which combination of factors best explains this behaviour?

  1. Minimal electrostatic repulsion between neighbouring protein molecules at the isoelectric point favours aggregation when heat unfolds the chains Correct answer.
  2. The isoelectric point increases the solubility of the protein, which then crystallises out of solution
  3. Heat cleaves peptide bonds, producing short peptides that precipitate as a coagulum
  4. Maximum net charge at the isoelectric point causes the proteins to attract water and swell into a stable gel

Explanation

At the isoelectric point the net charge on the protein is zero, so electrostatic repulsion between molecules is minimal. Heating unfolds the globular structure and exposes hydrophobic groups, allowing the chains to associate and coagulate. Away from the isoelectric point, residual charge keeps the molecules apart and the dispersion is more stable.

Question 31Food Microbiology and Food Safety

A batch of cooked rice left at room temperature overnight develops a sweetish, slightly sour smell and is linked to a food poisoning case. Which organism is most likely responsible?

  1. Salmonella enterica
  2. Listeria monocytogenes
  3. Bacillus cereus Correct answer.
  4. Clostridium botulinum

Explanation

Bacillus cereus is the classic cause of illness linked to cooked rice that is cooled slowly and held warm, because its heat-resistant spores survive cooking and germinate. The emetic toxin produces vomiting within a few hours, and the diarrhoeal form follows ingestion of vegetative cells. The other organisms are not characteristically associated with this specific cooked-rice scenario.

Question 32Food Microbiology and Food Safety

Which of the following is the most reliable indicator of faecal contamination of a water supply used in a food processing plant?

  1. Presence of lactic acid bacteria
  2. Presence of thermophilic spore-formers
  3. Presence of yeasts and moulds
  4. Presence of coliform bacteria such as Escherichia coli Correct answer.

Explanation

Escherichia coli and other coliforms are used as indicator organisms because they are abundant in the intestines of warm-blooded animals and their presence signals faecal contamination. Lactic acid bacteria, yeasts, moulds and thermophilic spore-formers occur widely in foods and environments and do not specifically indicate faecal pollution. Testing for indicators is cheaper and safer than testing for every pathogen.

Question 33Food Microbiology and Food Safety

In food preservation, the term 'water activity' (aw) refers to which property?

  1. The rate at which water evaporates from the food surface during drying
  2. The volume of water absorbed by a food when soaked in excess liquid
  3. The total moisture content of the food expressed as a percentage by mass
  4. The ratio of the vapour pressure of water in the food to that of pure water at the same temperature Correct answer.

Explanation

Water activity is defined as the ratio of the water vapour pressure of the food to that of pure water at the same temperature, giving a measure of the water available for microbial growth. It is not the same as moisture content, because water can be bound to solutes and unavailable. Most bacteria require aw above about 0.91, while many moulds can grow at lower values.

Question 34Food Microbiology and Food Safety

Which temperature range represents the 'danger zone' in which foodborne bacteria multiply most rapidly?

  1. 5 °C to 63 °C Correct answer.
  2. -18 °C to 0 °C
  3. 70 °C to 100 °C
  4. 0 °C to 5 °C

Explanation

The danger zone is generally taken as about 5 °C to 63 °C, where mesophilic foodborne bacteria grow fastest, with optimum growth around 37 °C. Foods should be kept below 5 °C or above 63 °C to limit multiplication. The other ranges are either frozen, chilled or hot enough to inhibit or destroy most pathogens.

Question 35Food Microbiology and Food Safety

Which type of food is most frequently implicated in botulism associated with Clostridium botulinum?

  1. Dry pasta
  2. Pasteurised milk
  3. Home-canned low-acid vegetables Correct answer.
  4. Fresh citrus juice

Explanation

Clostridium botulinum spores germinate in anaerobic, low-acid conditions such as home-canned vegetables, where they produce a potent neurotoxin. Proper canning with adequate heat treatment and acidity control prevents this. High-acid, dry or pasteurised products do not support growth of this anaerobe.

Question 36Food Microbiology and Food Safety

Which practice best prevents cross-contamination between raw poultry and ready-to-eat foods in a kitchen?

  1. Storing raw poultry above cooked foods in the refrigerator
  2. Washing raw chicken under running water before cooking
  3. Using separate colour-coded chopping boards and utensils for raw meat Correct answer.
  4. Reusing the same cloth to wipe benches and plates

Explanation

Separate colour-coded boards and utensils prevent transfer of pathogens such as Campylobacter and Salmonella from raw poultry to ready-to-eat foods. Washing raw chicken spreads droplets, and storing raw meat above cooked food allows drip contamination. Reusing the same cloth spreads microorganisms around the kitchen.

Question 37Food Microbiology and Food Safety

Which of the following is a spore-forming bacterium of significance in canned foods?

  1. Staphylococcus aureus
  2. Clostridium perfringens Correct answer.
  3. Campylobacter jejuni
  4. Escherichia coli

Explanation

Clostridium perfringens forms heat-resistant spores that can survive cooking and germinate in slowly cooled foods, causing illness. It is also relevant to canned and vacuum-packed products because it grows anaerobically. The other listed organisms are non-spore-forming vegetative bacteria.

Question 38Food Microbiology and Food Safety

What is the main purpose of pasteurisation in food processing?

  1. To reduce pathogenic vegetative microorganisms to a safe level while extending shelf life Correct answer.
  2. To sterilise the food completely by destroying all microorganisms and their spores
  3. To remove all water from the food to prevent microbial growth
  4. To add preservative chemicals that inhibit microbial growth

Explanation

Pasteurisation uses controlled heat to destroy pathogenic vegetative cells and reduce spoilage organisms, thereby improving safety and shelf life. It does not achieve sterility because spores and some heat-resistant enzymes survive. It is not a drying or chemical preservation process.

Question 39Food Microbiology and Food Safety

A food manufacturer wants to reduce the risk of Staphylococcus aureus intoxication in a ham product. Which control measure is most directly aimed at this hazard?

  1. Increasing the final cooking temperature to 80 °C for ten minutes
  2. Packing the ham in modified atmosphere with high oxygen
  3. Adding more salt to the brine without controlling temperature
  4. Rapid chilling of cooked ham to prevent toxin formation during cooling Correct answer.

Explanation

Staphylococcus aureus intoxications arise when the organism grows and produces enterotoxin in food, and the toxin is heat-stable, so it survives later cooking. Rapid chilling limits the time the product spends in the danger zone and prevents toxin formation. Raising the cooking temperature does not destroy any toxin already formed.

Question 40Food Microbiology and Food Safety

In a HACCP plan, what is a critical control point (CCP)?

  1. The final point at which the finished product is packaged
  2. Any stage in the process where a quality check is performed
  3. A supplier from whom raw materials are purchased
  4. A step at which control can be applied to prevent, eliminate or reduce a significant hazard to an acceptable level Correct answer.

Explanation

A CCP is a specific step where a control measure is applied and a critical limit is set to prevent, eliminate or reduce a significant hazard. It must be distinguishable from general quality checks and from supplier selection, which are not CCPs. Monitoring at a CCP is essential for food safety verification.

Question 41Food Microbiology and Food Safety

A batch of jam with a pH of 3.2 and 65% soluble solids is prepared. Which statement best explains its microbiological stability?

  1. The high sugar content provides nutrients that encourage pathogen growth
  2. The combination of high sugar and low pH inhibits most bacteria, yeasts and moulds Correct answer.
  3. The low pH sterilises the product by killing all spores present
  4. The product is stable only because it is stored frozen

Explanation

Jam stability relies on a combination of low water activity from high sugar and low pH, which together inhibit most spoilage organisms and pathogens. Neither factor alone sterilises the product, and some osmophilic yeasts and moulds may still spoil it. The product is shelf-stable at ambient temperature, not dependent on freezing.

Question 42Food Microbiology and Food Safety

Which factor most directly explains why Listeria monocytogenes is a particular concern in chilled ready-to-eat foods?

  1. It is destroyed by low pH
  2. It can grow at refrigeration temperatures Correct answer.
  3. It requires anaerobic conditions to survive
  4. It forms heat-resistant spores

Explanation

Listeria monocytogenes is psychrotrophic, meaning it can multiply at normal refrigeration temperatures, so chilled ready-to-eat foods with long shelf lives pose a risk. It does not form spores and is relatively acid-tolerant. Control therefore relies on strict hygiene, short shelf life and adequate heat treatment.

Question 43Food Microbiology and Food Safety

A laboratory performs a total viable count on a food sample and obtains a high count. Which conclusion is most appropriate?

  1. The food contains only beneficial microorganisms
  2. The food definitely contains pathogens capable of causing illness
  3. The food may have poor hygiene or spoilage potential, but the count alone does not identify pathogens Correct answer.
  4. The food has been correctly pasteurised

Explanation

A total viable count measures the number of colony-forming units able to grow under the test conditions and indicates general hygiene and spoilage potential. It does not identify species, so it cannot confirm the presence of pathogens. Additional specific tests are needed to detect pathogens or toxins.

Question 44Food Microbiology and Food Safety

Which of the following best describes the role of nitrites in cured meats?

  1. They increase the water activity of the product
  2. They neutralise all bacterial toxins present in the meat
  3. They act as the main cooking medium for the meat
  4. They inhibit Clostridium botulinum and contribute to colour and flavour development Correct answer.

Explanation

Nitrites in curing salts inhibit outgrowth of Clostridium botulinum spores and contribute to the characteristic pink colour and cured flavour. They are not a cooking medium and do not raise water activity. They also do not neutralise pre-formed toxins, so they cannot make unsafe meat safe.

Question 45Food Microbiology and Food Safety

A caterer prepares a large quantity of stew and must cool it quickly before refrigerated storage. Which method is most appropriate?

  1. Adding ice directly to the stew and leaving it at room temperature
  2. Dividing the stew into shallow containers and cooling rapidly in a blast chiller Correct answer.
  3. Placing the whole pot in the refrigerator with the lid on
  4. Leaving the pot on the counter to cool overnight

Explanation

Rapid cooling in shallow containers or a blast chiller reduces the time the food spends in the danger zone, limiting growth of spore-formers such as Clostridium perfringens. A large covered pot cools too slowly in the centre, and leaving food out overnight is unsafe. Adding ice does not reliably control the cooling rate and may introduce contamination.

Question 46Food Microbiology and Food Safety

Which statement correctly distinguishes food infection from food intoxication?

  1. Infection results from toxins in the food, while intoxication results from living pathogens
  2. Infection results from ingestion of living pathogens, while intoxication results from toxins already present in the food Correct answer.
  3. Infection occurs only with canned foods, while intoxication occurs only with fresh foods
  4. Both terms describe illness caused only by viruses

Explanation

A food infection occurs when living pathogenic microorganisms are ingested and multiply in the body, as with Salmonella. A food intoxication occurs when a pre-formed toxin in the food is consumed, as with Staphylococcus aureus enterotoxin. The distinction matters because cooking may kill pathogens but cannot destroy heat-stable toxins.

Question 47Food Microbiology and Food Safety

A fermented milk product is being produced and the manufacturer wants to suppress undesirable spoilage bacteria. Which mechanism is most important in this fermentation?

  1. Reduction of salt concentration to zero
  2. Production of lactic acid lowers pH and inhibits competing bacteria Correct answer.
  3. Increase in water activity to above 0.99
  4. Production of oxygen encourages desirable bacteria

Explanation

Lactic acid bacteria convert lactose to lactic acid, lowering the pH and suppressing many spoilage and pathogenic bacteria. This competitive exclusion is central to the safety of fermented milk. Oxygen, low salt or high water activity would not provide the same protective effect.

Question 48Food Microbiology and Food Safety

Which of the following is the best example of a physical hazard in food?

  1. Aflatoxin produced by Aspergillus flavus
  2. Cleaning chemical residue on a surface
  3. A fragment of glass from a broken light fitting Correct answer.
  4. Salmonella enterica on raw chicken

Explanation

Physical hazards are foreign objects such as glass, metal, stones or bone that can cause injury. Salmonella is a biological hazard, aflatoxin is a biological toxin, and cleaning chemicals are chemical hazards. Correct classification guides the choice of control measures in a HACCP plan.

Question 49Food Microbiology and Food Safety

A sample of dried fish is found to contain a high level of histamine. Which cause is most likely?

  1. Use of a vacuum pack that excludes oxygen
  2. Exposure of the fish to strong sunlight during drying
  3. Addition of too much sodium chloride during drying
  4. Growth of bacteria that decarboxylate histidine during poor temperature control Correct answer.

Explanation

Histamine forms when bacteria such as Morganella or Klebsiella decarboxylate histidine in fish tissues, usually because the fish was held at warm temperatures before processing. Salt, sunlight and vacuum packing are not the direct cause. Proper chilling from catch to processing prevents histamine formation.

Question 50Food Microbiology and Food Safety

Which cleaning and disinfection sequence is most appropriate for a food contact surface?

  1. Clean with detergent only and skip disinfection
  2. Pre-rinse, clean with detergent, rinse, apply disinfectant, then allow to drain or dry Correct answer.
  3. Apply disinfectant first, then clean with detergent without rinsing
  4. Rinse with water only and dry with a shared cloth

Explanation

Effective cleaning removes food residues and biofilm with detergent before disinfection, because soil reduces disinfectant efficacy. The surface is then rinsed and treated with a suitable disinfectant, followed by draining or drying. Disinfectant applied to dirty surfaces is largely inactivated, and detergent alone does not reduce microorganisms adequately.