Question 12 of 12: Preservatives and Applied Food Microbiology Multiple Choice

Question 12: Preservatives and Applied Food Microbiology Multiple Choice (16.7 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(a) Preservative–food associations

(b) Multiple-choice answers with justification

1. A – Counts in raw milk. Within-batch sampling tests for variability inside one relatively homogeneous bulk lot (a raw-milk tank); the other options are process/environmental checks, not tests of one batch's internal uniformity.
2. B – Probability of customer accepting a batch. The probability of acceptance ($P_a$) from a sampling plan's operating-characteristic curve is, by definition, the chance the plan indicates the lot should be accepted — i.e. from the receiving customer's side of the transaction.
3. A – Increase producers risk. A smaller sample size gives a less discriminating (flatter) operating-characteristic curve, so a genuinely acceptable-quality batch is more likely to be rejected by chance sampling variation — a higher producer's risk.
4. B and C. Chromogenic media let target organisms be read directly by colony colour, which both reduces analysis time versus separate biochemical tests and negates the need for a further confirmation step for many targets; they are not inherently cheaper (D and the "all" options overreach).
5. B – UHT products are packed under vacuum. UHT milk is aseptically, hermetically packaged after sterilization, so no recontamination or growth of any organism (Pseudomonads included) can occur regardless of what the dye-reduction test happens to detect; note A and C are independently false — Pseudomonas grows readily in raw/chilled milk (it is a classic psychrotrophic spoiler) and is an obligate aerobe, not an anaerobe.
6. B – Poor stability. The lipid envelope is fragile and readily disrupted by drying, detergents, bile salts and gastric acid, so enveloped viruses rarely survive the food chain and gut passage intact; non-enveloped viruses (norovirus, hepatitis A) dominate foodborne viral illness precisely because their naked capsid is far more resistant.
7. A and C. Filter-feeding bivalves concentrate viral particles from contaminated water (C, the primary mechanism), and raw or lightly cooked consumption (A, e.g. raw oysters) removes what would otherwise be a lethal thermal step.
8. B and D. Variant CJD (vCJD) is acquired through the food chain (foodborne, linked to BSE-contaminated beef) and typically affects younger individuals, unlike sporadic classic CJD, which is not foodborne and typically presents in older adults; prion resistance to heat inactivation (A) is a shared, not a distinguishing, trait of both forms.
9. Obligate aerobe. Both genera are Gram-negative obligate aerobes that oxidize ethanol to acetic acid, a strictly oxygen-dependent reaction; they are not alkaline-resistant (they are themselves acid producers/tolerant) and are known for pellicle (biofilm) formation, not poor biofilm production.
10. E – Antibiotics. Streptomyces and related actinomycetes are the source of the large majority of clinically and agriculturally used antibiotics.
11. E – Some of the above but not all (A and D). High maintenance-energy demand diverts substrate away from biomass synthesis, lowering yield; a very high growth rate can trigger overflow (Crabtree-type) metabolism that shunts carbon into fermentation products instead of biomass. Growth in complex media (B) and aerobic growth (C) both typically increase yield (more usable nutrients; far more ATP per substrate than anaerobic metabolism), so they are not causes of low yield.
12. A, B and C. A high Staphylococcus count signals potential S. aureus contamination and toxin risk, is a classic indicator of temperature abuse (the organism grows and produces heat-stable enterotoxin in the danger zone), and commonly traces to poor handling by food workers (a major human reservoir/vector); it has no relationship to mycotoxins, which are fungal metabolites (D is unrelated).