CFS CFS Food Chemistry & Biochemistry 2 — Questions and Answers
Question 1: During starch gelatinization, what physical change occurs when starch granules are heated in water?
- Granules crystallize and shrink
- Granules swell irreversibly and absorb water (Correct answer)
- Amylose chains form helical complexes with lipids only
- Starch depolymerizes into glucose monomers
Correct answer: Granules swell irreversibly and absorb water
During gelatinization, starch granules absorb water, swell irreversibly, and lose their crystalline structure, causing a dramatic increase in viscosity.
Question 2: What is the isoelectric point (pI) of a protein, and why is it relevant to food processing?
- The pH at which net charge is zero and solubility is minimal (Correct answer)
- The temperature at which the protein denatures
- The pH at which the protein has maximum positive charge
- The molecular weight at which proteins precipitate
Correct answer: The pH at which net charge is zero and solubility is minimal
The isoelectric point is the pH at which a protein carries no net charge, resulting in minimum solubility and maximum tendency to aggregate or precipitate — critical in dairy and soy processing.
Question 3: Enzymatic browning in cut fruits and vegetables is primarily catalyzed by which enzyme?
- Amylase
- Polyphenol oxidase (PPO) (Correct answer)
- Lipase
- Protease
Correct answer: Polyphenol oxidase (PPO)
Polyphenol oxidase (PPO) catalyzes the oxidation of phenolic compounds to quinones, which polymerize into brown melanin pigments when plant tissue is cut and exposed to oxygen.
Question 4: In food emulsions, which type of molecule acts as an emulsifier by possessing both hydrophilic and hydrophobic regions?
- Polysaccharides
- Amphiphilic molecules (e.g., lecithin) (Correct answer)
- Simple sugars
- Saturated fatty acids
Correct answer: Amphiphilic molecules (e.g., lecithin)
Amphiphilic emulsifiers like lecithin have a polar head (hydrophilic) and a nonpolar tail (hydrophobic), allowing them to stabilize oil-water interfaces and prevent phase separation.
Question 5: Retrogradation of starch refers to which post-gelatinization process?
- Starch granules dissolving in hot water
- Re-crystallization of starch polymers upon cooling (Correct answer)
- Enzymatic hydrolysis of amylose chains
- Maillard reaction between starch and proteins
Correct answer: Re-crystallization of starch polymers upon cooling
Retrogradation occurs when gelatinized starch cools and amylose/amylopectin chains re-associate into ordered crystalline structures, causing staling in bread and firming in gels.
Question 6: The saponification value of a fat indicates which characteristic?
- Degree of unsaturation of fatty acids
- Average molecular weight of triglycerides (Correct answer)
- Level of free fatty acids present
- Oxidative stability index
Correct answer: Average molecular weight of triglycerides
The saponification value represents the milligrams of KOH required to saponify one gram of fat, which is inversely proportional to the average molecular weight of the constituent triglycerides.
CFS CFS Food Chemistry & Biochemistry 2
During starch gelatinization, what physical change occurs when starch granules are heated in water?