Preservation Principles Quiz
What this quiz covers
Before the machines and the chemicals come the principles — the “why it works” underneath every preservation method. Why does blanching brighten a vegetable’s colour? Why does honey never ferment? Why does a plate heat exchanger, and not a shell-and-tube, sit at the heart of every milk pasteurizer? This quiz rewards people who can derive the practice from the physics: water activity from mole fractions, refrigeration load from latent heat, sterilization choice from heat sensitivity.
Twenty questions connect theory to plant floor. You will estimate honey’s water activity from first principles (0.725 — the worked calculation is in the quiz), define cold sterilization as irradiation, name cobalt-60 as the workhorse source, explain why meat irradiation targets salmonellosis, and trace the heat-stable proteinase of Pseudomonas fluorescens that survives pasteurization only to spoil milk later. Refrigeration principles run through the set: the pressure–enthalpy chart, the ton of refrigeration, net refrigeration effect.
Principles, not procedures
Each question asks for the mechanism. Blanching works by inactivating peroxidase and lipoxygenase — the brightening and cleaning are bonuses. Honey’s 0.725 a_w comes straight from Raoult’s law: mole fraction of water in an 80% sugar solution. Liquid egg must be pH-stabilized before pasteurization because heat would otherwise wreck its functional properties. Follow the mechanism and the answer is rarely the most complicated option.
How to use this quiz
Twenty seconds per question, one attempt. Work the honey calculation yourself — it is the single best test of whether you own water activity or just recognize the term. Revisit every miss at the principle level before retaking.
Answer explanations
Through the set? Here is the principle behind each correct answer — the mechanism each question was really testing.
- Blanching of vegetables results in ___.
Correct answer: Enzyme inactivation, surface cleaning, colour brightening — Hot water or steam inactivates the enzymes, washes the surface, and brightens colour by expelling intercellular gases. - Honey is roughly an 80% (w/w) aqueous sugar solution, with about 90% of the sugars as hexoses and 10% as disaccharide. Taking the molecular weights of water, hexose and disaccharide as 18, 180 and 342, estimate the water activity of honey.
Correct answer: 0.725 — Mole fraction of water: 20 g of water (1.11 mol) over total moles including hexoses and disaccharide gives X_w ≈ 0.725 — below the growth range of nearly all microbes. - The stabilization step carried out before egg pasteurization is meant to
Correct answer: Adjust the pH — Liquid egg is pH-adjusted (stabilized) before pasteurization so the heat does not damage its functional properties. - What is the main sugar that microbes ferment in milk?
Correct answer: Lactose — Lactose is milk’s fermentable carbohydrate — the substrate for every lactic fermentation. - Which chart is the most useful for refrigeration work?
Correct answer: Pressure-enthalpy chart — Refrigeration engineers read the whole vapour-compression cycle — pressures, enthalpies, COP — off the p–h diagram. - In an ice-bank system of refrigeration, the usual value of the COP is:
Correct answer: 3 — This is the cited typical coefficient of performance for ice-bank refrigeration systems. - One ton of refrigeration is defined as a heat-absorption rate of:
Correct answer: 12000 Btu/h — Defined as the heat absorbed in melting one ton of ice in 24 hours. - Which refrigeration cycle has the minimum COP?
Correct answer: Air cycle — The air (reversed Brayton) cycle is the least efficient of the practical refrigeration cycles. - Which heat exchanger was originally developed for milk pasteurization?
Correct answer: Plate — The plate heat exchanger’s thin channels and easy cleaning made it the pasteurizer standard — it was developed for dairy. - How does a food’s water content affect its freezing time?
Correct answer: More water means longer freezing time — Water’s high latent heat dominates the load: more water means more heat to remove, hence longer freezing. - Cold sterilization refers to
Correct answer: sterilization using irradiation — “Cold” sterilization kills microbes without heat — and ionizing radiation is the industrial meaning of the term. - Which of these can serve as a source of radiation for food irradiation?
Correct answer: Cobalt-60 — Cobalt-60 gamma is the standard food-irradiation source: penetrating, reliable, and well characterized. - What is meant by the net refrigeration effect?
Correct answer: The heat absorbed by the refrigerant per unit mass during each cycle — The refrigerating effect is the enthalpy the refrigerant picks up in the evaporator, per unit mass. - Salted egg yolk does not require pasteurization when it contains
Correct answer: 1.4% acetic acid — At this acidity the yolk is preserved without any heat pasteurization. - Stabilization of liquid egg before pasteurization is done by
Correct answer: Adding aluminum salts — The cited stabilization treatment applied to liquid egg before pasteurization. - Pink discoloration of salt-cured fish is caused by
Correct answer: Halobacterium, Halococcus and Pseudomonas salinaria — Halophilic archaea and bacteria pigment salt-cured fish pink. - Irradiation of meat is used to prevent outbreaks of
Correct answer: Salmonellosis — Irradiation’s headline public-health win in meat is the elimination of Salmonella. - The heat-stable proteinase that survives milk pasteurization, though the bacterium itself is killed, is produced by
Correct answer: Pseudomonas fluorescens — Its psychrotrophic proteases survive pasteurization and later gel or embitter the milk. - Which of these chemical changes can occur in food as a result of irradiation?
Correct answer: Sugar breakdown, fat oxidation, vitamin C loss — Ionizing radiation can break down sugars, oxidize fats, and destroy vitamin C — dose permitting, all three occur. - Which statement about retort pouches is NOT correct?
Correct answer: They should not withstand high temperature — Retort pouches must survive retort temperatures, block oxygen and moisture, and usually include an aluminium barrier layer — so this option contradicts the requirements.