22-Agric-A7 Chemistry and Microbiology of Foods · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. 04-Agric-A7 Chemistry and Microbiology of Foods, National Exams December 2013 — a three-hour closed-book exam (approved Casio/Sharp calculator permitted; one aid sheet, both sides). The paper is in two sections: Section I (Food Chemistry, Questions 1–7) and Section II (Food Microbiology, Questions 8–14); candidates answer any four questions from each section for a 100-mark paper (each question worth 12.5 marks). All fourteen questions are worked here so the set is a complete study resource.
Reference texts. S. Damodaran, K.L. Parkin and O.R. Fennema (eds.), Fennema's Food Chemistry, 5th ed. (Maillard/enzymatic browning, water activity and sorption isotherms, lipid oxidation and rancidity, sucrose glass transition, protein denaturation at interfaces, myoglobin chemistry); R.P. Singh and D.R. Heldman, Introduction to Food Engineering, 5th ed. (reaction kinetics in food processing, thermal process lethality); J. Jay, M. Loessner and D. Golden, Modern Food Microbiology, 7th ed. (microbial growth curve, intrinsic/extrinsic factors, Listeria monocytogenes, food preservation hurdles, irradiation, spoilage patterns); C. Mortimore and C. Wallace, HACCP: A Practical Approach, 3rd ed. (CCP identification/monitoring/verification for milk pasteurization).
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.
| Item | Answer | Justification |
|---|---|---|
| Q1 | B, D | Aseptic (UHT) processing sterilises the product outside the container in seconds, so total heat exposure — and hence sensory/nutritional damage — is much lower than in-container retort canning; lethality target and relative cost are not the distinguishing factors. |
| Q2 | B, C, D | Low-dose pasteurizing irradiation is tailored to the specific pathogen-reduction target (product specific) and avoids the radiolytic by-products, oxidation and sensory changes that higher sterilizing doses cause, making it more consumer-acceptable; cost savings are a secondary, not primary, driver. |
| Q3 | C | Pasteurization is not sterilisation; typical plate counts on correctly pasteurized, good-quality milk run on the order of $10^3$ cfu/mL, well under the regulatory Grade-A maximum. |
| Q4 | E | Prerequisite programs (GMPs/SSOPs) underpin HACCP by ensuring a sanitary, structurally sound facility with GMP compliance in place before hazard analysis even begins — all four listed roles apply. |
| Q5 | E (specifically A and B) | Enrichment culture raises low/injured pathogen numbers to detectable levels and lets sub-lethally injured cells repair and become culturable; it does not itself distinguish live from dead cells (that needs a separate viability method), so "all of the above" over-states it. |
| Q6 | A, B | Chlorine was adopted historically for being cheaper and easier to apply/handle at scale, and for leaving a persistent disinfecting residual; ozone is actually the stronger oxidant/antimicrobial and decomposes without leaving a residual, so C is false, and chlorine's own halogenated by-products rule out D. |
| Q7 | E | Manure run-off, wash water, field workers and wildlife are all well-documented, independent contamination routes for fresh produce. |
| Q8 | E | High staff turnover, limited time, inadequately trained management and limited resources are all real, commonly cited barriers, but they do not all apply with equal force at every facility, so "more than one but not all" is the accurate choice. |
| Q9 | D | SO$_2$ in wine simultaneously suppresses/inactivates spoilage microbes, inhibits the enzymatic browning enzyme polyphenol oxidase, and binds acetaldehyde and other carbonyls — all three functions are genuine. |
| Q10 | E | Direct microscopic counts (e.g. Breed smear, haemocytometer) give rapid, low-cost, in-process results, are feasible because dairy/fermentation cell densities are high enough to see directly, and reveal cell morphology (yeast budding, cell type) that a plate count alone would not. |
| Q11 | E (specifically A, B and C) | A sanitation plan itself covers the cleaning schedule, verification method and Standard Operating Procedures; end-product sampling is a separate finished-product/HACCP verification activity, not part of the sanitation plan proper. |
| Q12 | C | Standard outbreak-investigation protocol requires confirming that an outbreak has genuinely occurred (a validated case definition/excess of cases) before any company/retailer contact, sampling or hypothesis work begins. |
| Q13 | A, B, C | High pressure processing, pulsed electric fields and irradiation are all non-thermal; aseptic processing is fundamentally a heat-sterilisation technology (product is heat-treated, then aseptically packaged), so it does not belong in the non-thermal group and "all of the above" is therefore incorrect. |
