CFS Food Chemistry & Biochemistry Flashcards

During starch gelatinization, what physical change occurs when starch granules are heated in water?

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.

What is the isoelectric point (pI) of a protein, and why is it relevant to food processing?

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.

Enzymatic browning in cut fruits and vegetables is primarily catalyzed by which enzyme?

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.

In food emulsions, which type of molecule acts as an emulsifier by possessing both hydrophilic and hydrophobic regions?

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.

Retrogradation of starch refers to which post-gelatinization process?

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.

The saponification value of a fat indicates which characteristic?

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.