CFTRI M.Sc. (Food Technology) Chemistry Flashcards

24 sample cards from the Chemistry deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Why is water activity important for food stability?

   It controls microbial growth and chemical reactions; most bacteria need aw > 0.90, yeasts > 0.88, molds > 0.80, so lowering aw preserves food. Minimum for most spoilage is around aw 0.60.

2. Differentiate monosaccharides and disaccharides with examples.

   Monosaccharides are single sugar units (e.g. glucose, fructose, galactose); disaccharides are two monosaccharides joined by a glycosidic bond (e.g. sucrose, lactose, maltose).

3. What are the monosaccharide units of sucrose, lactose, and maltose?

   Sucrose = glucose + fructose; lactose = glucose + galactose; maltose = glucose + glucose.

4. What defines a reducing sugar and how is it tested?

   A reducing sugar has a free aldehyde or ketone group (free anomeric carbon) that can reduce Cu²⁺ to Cu₂O. Tested positive with Fehling's, Benedict's, or Tollens' reagent.

5. Why is sucrose a non-reducing sugar?

   Both anomeric carbons (of glucose and fructose) are involved in the glycosidic bond, leaving no free aldehyde/ketone group to act as a reducing agent.

6. Define mutarotation.

   Mutarotation is the change in optical rotation of a sugar solution as the α- and β-anomers interconvert through the open-chain form until equilibrium is reached (e.g. α- and β-D-glucose).

7. Describe the structure of starch and its two components.

   Starch is a plant storage polysaccharide of glucose with two fractions: amylose (linear, α-1,4 linkages) and amylopectin (branched, α-1,4 with α-1,6 branch points).

8. How does cellulose differ structurally from starch?

   Cellulose is a linear glucose polymer joined by β-1,4 glycosidic bonds (versus α-1,4 in starch), giving rigid fibres that humans cannot digest (dietary fibre).

9. What are pectins and where are they found?

   Pectins are structural polysaccharides composed mainly of galacturonic acid units; found in the cell walls/middle lamella of fruits, they form gels and are used as gelling agents in jams and jellies.

10. Name three common plant (organic) acids found in foods and their sources.

    Citric acid (citrus fruits), malic acid (apples), and tartaric acid (grapes); also oxalic acid (spinach) and lactic acid (fermented foods).

11. What is the primary structure of a protein?

    The linear sequence of amino acids joined by peptide bonds in a polypeptide chain, determined by the gene; it dictates all higher levels of structure.

12. Describe the secondary structure of proteins and its two main forms.

    Secondary structure is local folding stabilized by hydrogen bonds between backbone C=O and N–H groups; main forms are the α-helix and the β-pleated sheet.

13. What is the tertiary structure of a protein and what stabilizes it?

    The overall 3D folding of a single polypeptide, stabilized by interactions among side chains: hydrogen bonds, ionic (salt) bridges, hydrophobic interactions, and disulfide bonds.

14. Define quaternary structure of proteins with an example.

    The assembly of two or more folded polypeptide subunits into a functional protein, e.g. hemoglobin (four subunits).

15. What is protein denaturation?

    The disruption of secondary, tertiary, and quaternary structure (without breaking peptide bonds), causing loss of native shape and biological function; primary structure remains intact.

16. List four agents that cause protein denaturation.

    Heat, extremes of pH (acids/alkalis), organic solvents (alcohol), heavy metal ions, urea, mechanical agitation, and high salt concentrations.

17. What is a peptide bond and how is it formed?

    A peptide bond is an amide linkage (–CO–NH–) formed between the carboxyl group of one amino acid and the amino group of another, with the loss of a water molecule (condensation).

18. What are the key structural features of a peptide bond?

    It is planar and rigid due to partial double-bond character (resonance), usually in the trans configuration, and cannot rotate freely.

19. Draw/describe the general structure of an α-amino acid.

    A central α-carbon bonded to an amino group (–NH₂), a carboxyl group (–COOH), a hydrogen atom, and a variable side chain (R group).

20. What is the zwitterion form of an amino acid and the isoelectric point (pI)?

    A zwitterion has both a protonated amino group (–NH₃⁺) and a deprotonated carboxyl group (–COO⁻), carrying no net charge. The pI is the pH at which the amino acid exists predominantly as a zwitterion with zero net charge.

21. Classify amino acids based on their side chains.

    By polarity: nonpolar/hydrophobic, polar uncharged, acidic (negatively charged, e.g. aspartate, glutamate), and basic (positively charged, e.g. lysine, arginine, histidine).

22. What is an essential amino acid? Give examples.

    One the body cannot synthesize and must obtain from the diet. Examples: leucine, isoleucine, valine, lysine, methionine, phenylalanine, threonine, tryptophan, histidine.

23. What is the Maillard reaction and which food components react?

    A non-enzymatic browning reaction between a reducing sugar's carbonyl group and a free amino group of an amino acid/protein, producing brown colour and flavour compounds on heating.

24. Why does cellulose serve as dietary fibre while starch is an energy source?

    Human digestive enzymes (amylase) can hydrolyze the α-1,4 bonds of starch into glucose, but cannot break the β-1,4 bonds of cellulose, so cellulose passes undigested as fibre.

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