ICAR AIEEA-PG / PGS — Code 18 Food Science Technology · India · ICAR through the National Testing Agency
Original practice questions written to the published syllabus · not past papersPredicting and proving how long a food stays safe and acceptable: the kinetics of quality loss, temperature and water-activity effects, accelerated shelf-life testing, packaging-limited shelf life, challenge tests and date labelling.
In the exams: ICAR AICE 35.a Unit 5 (shelf-life studies) and 37 Unit 3 (water activity, sorption, hurdle technology); GATE XE-G Section 3 (hurdle technology, intermediate-moisture foods)
ICAR AIEEA-PG / PGS — Code 18 Food Science Technology
Unit I names physicochemical changes during processing and storage; Unit IV names intrinsic and extrinsic factors in microbial growth. MCQs test aw limits, reaction orders, date-marking terms and hurdle concepts.
How our questions for ICAR AIEEA-PG / PGS spread across the units of Shelf-life Science & Food Stability. Difficulty: 13 easy, 21 medium, 4 hard.
| Shelf life of specific product groups | 9 | |
| Kinetics of quality loss: zero- and first-order reactions | 5 | |
| Water activity, sorption isotherms and moisture-limited shelf life | 5 | |
| Shelf-life concepts: safety-limited and quality-limited shelf life | 4 | |
| Temperature dependence: Arrhenius equation and Q10 | 4 | |
| Date marking: use-by, best-before and expiry | 4 | |
| Packaging-limited shelf life and permeability calculations | 3 | |
| Accelerated shelf-life testing and its limits | 1 | |
| Microbial challenge tests and durability studies | 1 | |
| Sensory end-points and survival analysis | 1 | |
| Time-temperature integrators | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Biscuits that become soft but remain safe are an example of
D. quality-limited shelf life
Loss of crispness is a quality change; the product remains safe.
Further reading: Kilcast and Subramaniam, The Stability and Shelf-Life of Food
Vitamin C in a juice degrades by first-order kinetics with k = 0.010 per day. The time to fall to 80 % of its initial value is about
C. 22.3 days
t = ln(1/0.80)/0.010 = 0.2231/0.010 = 22.3 days. 20.0 assumes zero order (0.20/0.010); 8.0 and 80.0 are slips.
Further reading: Labuza, Shelf-life Dating of Foods
Q10 is defined as
A. the rate ratio for a 10 °C rise
Q10 = k(T + 10)/k(T) = ts(T)/ts(T + 10).
Further reading: Labuza, Shelf-life Dating of Foods
A pack holds 200 g dry solids at 2.0 % moisture (dry basis); the critical moisture is 3.5 %. Area is 0.04 m² and WVTR 2.0 g/m² day. The constant-rate moisture-limited shelf life is
A. 37.5 days
Allowed gain = 200 × 0.015 = 3.0 g; daily gain = 2.0 × 0.04 = 0.08 g; ts = 37.5 days. 87.5 uses 3.5 % as the allowance; 1.5 omits area and mass; 75.0 uses 0.04 g/day.
Further reading: Labuza, Shelf-life Dating of Foods
Lipid oxidation in a dry food is slowest at about
C. the monolayer water activity
Below the monolayer oxidation speeds up; at intermediate aw it also rises.
Further reading: Labuza, Shelf-life Dating of Foods
Taking 1 cm³ of oxygen at standard conditions as 1.43 mg, 8 cm³ of oxygen weighs about
B. 11.4 mg
8 × 1.43 = 11.4 mg. 5.6 divides by 1.43; 8.0 ignores the factor.
Further reading: Labuza, Shelf-life Dating of Foods
A 'sell-by' or 'display until' date is
B. a retailer's stock-control date
It is not intended for consumers and can add to confusion and waste.
Further reading: Codex CXS 1-1985 (revised 2018), date marking
Codex allows some foods to carry no date mark, such as
B. salt, sugar and vinegar
Very stable foods and fresh fruit and vegetables may be exempt; perishable foods are not.
Further reading: Codex CXS 1-1985 (revised 2018), date marking
Xerophilic moulds and osmophilic yeasts can grow down to a water activity of about
A. 0.61
They are the most tolerant organisms; no microbial growth occurs below about 0.6.
Further reading: Labuza, Shelf-life Dating of Foods
Chocolate shelf life is commonly limited by
B. fat bloom and sugar bloom
Fat migration and polymorphic change, or surface sugar recrystallisation, dull the surface.
Further reading: Kilcast and Subramaniam, The Stability and Shelf-Life of Food
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