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 papersThe chemistry a food scientist uses every day: bonding, acids and bases, buffers, organic functional groups and reaction mechanisms, chemical kinetics and thermodynamics, and the physical chemistry of solutions, surfaces and colloids. Students who take GATE XL (Life Sciences) sit a compulsory chemistry section alongside the Food Technology section.
In the exams: GATE XL-P (compulsory chemistry section for XL candidates who choose XL-U Food Technology); background for ICAR AIEEA-PG Code 18 Unit I
How our questions for ICAR AIEEA-PG / PGS spread across the units of Chemistry for Food Science (General, Organic & Physical). Difficulty: 10 easy, 35 medium, 3 hard.
| Coordination chemistry and metal ions in foods | 7 | |
| Organic reaction mechanisms relevant to food: oxidation, hydrolysis, esterification and condensation | 6 | |
| Chemical thermodynamics: enthalpy, entropy and free energy | 5 | |
| Colligative properties: freezing-point depression, boiling-point elevation and osmotic pressure | 5 | |
| Acids, bases, pH, buffers and the Henderson-Hasselbalch equation | 4 | |
| Organic functional groups and nomenclature | 4 | |
| Surface chemistry, adsorption and an introduction to colloids | 4 | |
| Stoichiometry, concentration units and solution preparation | 3 | |
| Atomic structure, periodicity and chemical bonding | 2 | |
| Chemical equilibrium and solubility | 2 | |
| Chemical kinetics: rate laws, reaction order and the Arrhenius equation | 2 | |
| Stereochemistry and optical activity | 2 | |
| Electrochemistry and redox potential | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A 10.0 g sample of juice needs 12.0 mL of 0.1 N NaOH to reach the phenolphthalein end point. What is its titratable acidity as anhydrous citric acid (meq. factor 0.064)?
D. 0.768%
Acidity = V × N × meq × 100/mass = 12.0 × 0.1 × 0.064 × 100/10 = 0.768%. 1.080% uses the lactic acid factor (0.090); 7.680% forgets to divide by the 10 g sample mass; 0.077% slips the decimal point by a factor of ten.
Further reading: Nielsen, Food Analysis; Housecroft and Sharpe, Inorganic Chemistry
In alcoholic fermentation, C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂. What is the theoretical maximum mass of ethanol from 90 g of glucose? (Molar masses: glucose 180, ethanol 46 g/mol.)
D. 46 g
90 g glucose = 0.5 mol, giving 1.0 mol ethanol = 46 g. 23 g ignores the 2 : 1 mole ratio; 92 g is the yield from 180 g; 90 g assumes all the mass becomes ethanol, ignoring the CO₂ (44 g).
Further reading: Nielsen, Food Analysis; Housecroft and Sharpe, Inorganic Chemistry
A buffer contains 0.2 M sodium acetate and 0.1 M acetic acid (pKa 4.76). What is its pH?
A. 5.06
Henderson-Hasselbalch: pH = pKa + log([A⁻]/[HA]) = 4.76 + log 2 = 4.76 + 0.30 = 5.06. 4.46 inverts the ratio; 4.76 assumes equal amounts; 5.76 adds a whole unit as if the ratio were 10.
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
Sorbic acid has a pKa of about 4.8. In which product is a given dose most effective as an antimicrobial?
A. A fruit filling at pH 3.5
The undissociated acid crosses microbial membranes; at pH 3.5, more than 95% of sorbic acid is undissociated, against under 10% at pH 5.8 and less above that. The higher-pH products need more preservative for the same effect.
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
Why are many white wines chilled close to freezing and filtered before bottling?
C. To crystallise tartrate before bottling
Potassium hydrogen tartrate is less soluble at low temperature; cold stabilisation drives it out of solution so that consumers do not find crystals later. Chilling does not kill yeast reliably, SO₂ does not crystallise, and the malolactic conversion is a bacterial fermentation favoured by warmth.
Further reading: Atkins' Physical Chemistry; Fennema's Food Chemistry
In the propagation step of lipid autoxidation, what does a peroxyl radical (LOO•) do?
C. Abstracts a hydrogen from another lipid, forming a hydroperoxide and a new radical
LOO• + LH → LOOH + L•, so the chain continues. Radical combination is termination; initiation needs a radical or a sensitiser; release of free fatty acids is hydrolysis, not oxidation.
Further reading: Clayden, Greeves and Warren, Organic Chemistry; Fennema's Food Chemistry
What are the products of saponification of a triacylglycerol with sodium hydroxide?
D. Glycerol and sodium salts of fatty acids
Alkaline hydrolysis of esters gives the alcohol (glycerol) and carboxylate salts (soaps) and goes to completion. Free fatty acids form in acid or enzymatic hydrolysis; methyl esters need methanol (transesterification).
Further reading: Clayden, Greeves and Warren, Organic Chemistry; Fennema's Food Chemistry
What is the first step of the Maillard reaction?
B. Condensation of a reducing-sugar carbonyl with an amino group to form a glycosylamine
The carbonyl of a reducing sugar condenses with a free amino group (losing water) to form a Schiff base and glycosylamine, which rearranges to an Amadori or Heyns product. Caramelisation needs no amino group; lipid oxidation and proteolysis are different reactions.
Further reading: Clayden, Greeves and Warren, Organic Chemistry; Fennema's Food Chemistry
Which amino acid found in proteins is not chiral?
A. Glycine
Glycine has two hydrogens on its α-carbon, so the carbon does not carry four different groups. The other proteinogenic amino acids are chiral and occur in the L form in proteins.
Further reading: Clayden, Greeves and Warren, Organic Chemistry; Fennema's Food Chemistry
Why do green vegetables turn olive-brown when cooked for a long time in acidic water?
B. Acid replaces the magnesium of chlorophyll with hydrogen, forming pheophytin
H⁺ displaces Mg²⁺ from the porphyrin ring, forming olive-brown pheophytin. Magnesium does not go to +3; copper substitution gives a stable green colour; carotenoids are separate pigments that become visible but are not formed from chlorophyll.
Further reading: Nielsen, Food Analysis; Housecroft and Sharpe, Inorganic Chemistry
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