GATE — Life Sciences (XL), Section U Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)
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)
GATE — Engineering Sciences (XE), Section G Food Technology
Section 3 names hurdle technology and intermediate-moisture foods and packaging; Section 1 names chemical changes during processing; Section 4 names permeability through films. Expect numericals on first-order kinetics and half-lives, Q10 and Arrhenius, and film-limited moisture gain.
GATE — Life Sciences (XL), Section U Food Technology
Same scope as XE-G; questions often link aw and microbial growth limits to shelf life.
How our questions for GATE spread across the units of Shelf-life Science & Food Stability. Difficulty: 6 easy, 13 medium, 7 hard.
| Kinetics of quality loss: zero- and first-order reactions | 7 | |
| Temperature dependence: Arrhenius equation and Q10 | 6 | |
| Water activity, sorption isotherms and moisture-limited shelf life | 5 | |
| Shelf-life concepts: safety-limited and quality-limited shelf life | 4 | |
| Packaging-limited shelf life and permeability calculations | 3 | |
| Shelf life of specific product groups | 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
The hurdle concept explains the stability of intermediate-moisture foods by
D. several moderate barriers combined
Moderate aw reduction, pH, preservatives and packaging combine to inhibit microbes while keeping quality.
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
For a first-order quality loss, a straight line is obtained by plotting
D. ln A against time
ln(A/A0) = −kt; a plot of A against t is linear for zero order.
Further reading: Labuza, Shelf-life Dating of Foods
Using the same product (30 days at 35 °C, Q10 = 2.5), the estimated shelf life at 20 °C is closest to
B. 119 days
ts(20) = 30 × 2.5^((35 − 20)/10) = 30 × 2.5^1.5 = 119 days. 113 uses 2.5 × 1.5 × 30; 94 uses a linear guess; 45 multiplies by 1.5 only.
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
In a moist cake with crisp biscuit pieces, moisture moves from
B. the cake to the biscuit, from higher to lower aw
Water migrates down the aw gradient until aw is equal; matching aw or a barrier prevents sogginess.
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
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
Enzymatic browning of cut apples during storage is an example of
B. enzymatic deterioration
Polyphenol oxidase oxidises phenolics to brown pigments.
Further reading: Kilcast and Subramaniam, The Stability and Shelf-Life of Food
Ten here, 26 in the app. The Laisha app has every practice question we have written to GATE in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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