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.
(i) Applying the CCP decision-tree logic to each step, Pasteurization is the only CCP in this process. Receiving/holding, centrifugation, homogenization, packing and cold holding/distribution are all important quality or good-manufacturing-practice steps, but none of them is designed specifically to eliminate or reduce a microbiological hazard to an acceptable level — a step upstream of pasteurization (raw-milk receiving) can control hazard level but cannot eliminate it, and steps downstream (packing, cold storage) merely preserve whatever safety pasteurization has already achieved. Pasteurization (a regulated minimum heat treatment, e.g. HTST at $\ge$72°C for $\ge$16 s under Canadian dairy regulations) is the one step whose entire purpose is to destroy the target vegetative pathogens (Coxiella burnetii, Mycobacterium bovis, and other pathogens of concern in raw milk) to a safe level, and no later step can compensate if it fails — the textbook definition of a CCP.
(ii) The pasteurization CCP is monitored continuously, not by periodic sampling: a calibrated temperature-recording device (with a chart or digital data logger) on the holding tube records milk temperature throughout the run, paired with verification that the holding time in the holding tube meets the minimum contact time for the flow rate in use. An automatic flow-diversion valve (FDV) is interlocked to the temperature sensor so that any milk falling below the set temperature is automatically diverted back to the raw side for reprocessing rather than allowed to proceed to packing — this makes the monitoring system also a real-time corrective-action mechanism, not just a record.
(iii) Verifying that the whole HACCP plan is actually performing as intended combines several independent checks: routine calibration of the temperature recorder/sensor and the FDV against a certified reference thermometer; the classic regulatory phosphatase test — alkaline phosphatase, naturally present in raw milk, is slightly more heat-resistant than the target pathogens, so a negative (inactivated) phosphatase result confirms the pasteurization temperature/time combination was actually adequate; periodic microbiological testing of the finished product (standard plate count, coliform count) against regulatory limits; and periodic audit of the time/temperature charts themselves and of record-keeping/corrective-action logs to confirm the CCP was continuously in control, not merely that isolated checks happened to pass.
