Chapter 18 Quiz — The Science of Fruits and Vegetables

15 questions. Answer key with explanations at the bottom.

Multiple Choice (questions 1–12)

  1. Which of the following is a climacteric fruit? a) Lemon b) Strawberry c) Banana d) Grape

  2. Red cabbage juice turns pink when added to which substance? a) Baking soda solution b) Vinegar c) Plain water d) Salt water

  3. The pigment responsible for the orange color of carrots is: a) Anthocyanin b) Chlorophyll c) Carotenoid (β-carotene) d) Flavonoid

  4. Why does cooked broccoli sometimes turn drab olive instead of staying bright green? a) The water is too cold b) Heat degrades chlorophyll, especially in acidic conditions and over time c) Oxygen exposure during cooking d) Salt destroys chlorophyll

  5. Enzymatic browning in a cut apple is caused by: a) Bacteria on the surface b) Polyphenol oxidase (PPO) reacting with phenolic compounds and oxygen c) Maillard reaction d) Caramelization of fruit sugars

  6. Which is the BEST way to slow enzymatic browning of cut apples? a) Refrigerate them b) Coat with lemon juice (acid + ascorbic acid) c) Store them in a dark place d) Sprinkle with salt

  7. Salting cucumbers before adding to a salad makes them weep water primarily through: a) Capillary action b) Osmosis (water moves to higher solute concentration) c) Evaporation d) Diffusion of salt into the cell

  8. Why does adding a small amount of baking soda to cooking greens keep them bright green but ALSO degrade their texture? a) Baking soda is a base — it preserves chlorophyll's magnesium ion but breaks down hemicellulose, softening cell walls b) Baking soda removes chlorophyll c) Baking soda is an acid that brightens color but tenderizes d) Baking soda contains a colorant

  9. Pectin in a fruit jam sets into a gel because of: a) Heat alone b) Sugar + acid + pectin together creating a polymer network c) Boiling pasteurization d) Adding gelatin

  10. Storing a banana in a paper bag with an unripe avocado will: a) Have no effect — banana doesn't ripen the avocado b) Spoil both faster c) Speed up avocado ripening because the banana emits ethylene d) Slow both because of competition for oxygen

  11. Frozen-at-peak-ripeness vegetables compared to "fresh" vegetables that traveled 1,000 miles often have: a) More nutrients (less degradation since freezing) b) Fewer nutrients (always) c) Identical nutrient content d) More water content

  12. Which technique would BEST preserve the bright color of green beans for serving? a) Long simmer in salty water b) Quick blanch (~3 min) followed by ice bath shock c) Slow roast in oven d) Pressure cook for 30 min

Short Answer (questions 13–15)

  1. Explain the chemistry of why a roasted vegetable is sweeter than a steamed vegetable.

  2. The chef Alice Waters is famous for emphasizing seasonal eating. From a food-science perspective, why would in-season tomatoes (peak local) often taste dramatically better than the same variety shipped in winter?

  3. Your kale salad is wilted by the time you serve it. Diagnose the problem using two principles from this chapter and propose a fix.

Answer Key

  1. (c) Banana. Climacteric fruits emit ethylene and ripen after harvest. Lemon, strawberry, grape are non-climacteric.

  2. (b) Vinegar. Anthocyanins (red cabbage's purple pigment) shift to pink in acid, blue/green in base.

  3. (c) Carotenoid (β-carotene). Carotenoids are the orange/red pigments; β-carotene specifically is converted to vitamin A.

  4. (b) Heat degrades chlorophyll, especially in acidic conditions and over time. This is why a quick blanch followed by ice-shock preserves color, while long simmer kills it.

  5. (b) Polyphenol oxidase (PPO) reacting with phenolic compounds and oxygen. PPO is an enzyme; its product is brown melanin-like pigments. Heat denatures PPO; acid lowers its activity.

  6. (b) Coat with lemon juice (acid + ascorbic acid). Acid lowers PPO activity; ascorbic acid (vitamin C) is an anti-oxidant that reverses initial browning. Refrigeration slows but doesn't stop the reaction.

  7. (b) Osmosis (water moves to higher solute concentration). Salt outside the cell creates higher solute concentration — water exits cucumber cells to balance.

  8. (a) Baking soda is a base — it preserves chlorophyll's magnesium ion but breaks down hemicellulose, softening cell walls. A common trick that works for color but loses crunch. Worth knowing — and worth not overusing.

  9. (b) Sugar + acid + pectin together creating a polymer network. All three are needed for high-methoxyl pectin. Low-methoxyl pectin can gel with calcium instead of acid+sugar — used in low-sugar jams.

  10. (c) Speed up avocado ripening because the banana emits ethylene. Ethylene is a plant hormone that triggers ripening in climacteric fruits. The paper bag concentrates the gas.

  11. (a) More nutrients (less degradation since freezing). Vitamins (especially water-soluble C and B's) degrade with time after harvest. Frozen-at-peak captures the produce at maximum nutrition.

  12. (b) Quick blanch (~3 min) followed by ice bath shock. Sets the color, denatures PPO and other enzymes, partial-cooks. Cold shock stops further chlorophyll degradation.

  13. Roasting concentrates the flavors by evaporating water (so sugars and other compounds become more concentrated per bite); high heat triggers caramelization of fruit/vegetable sugars and Maillard reactions on the surface, creating new flavor compounds (Ch 8, 10 callbacks). Steaming does neither — water content stays high, no Maillard, no caramelization. The vegetable remains "watery" tasting.

  14. (a) Climacteric fruit picked unripe and ripened off-vine has time but not the active plant metabolism that produces aromatic compounds — so flavor compounds are fewer. (b) Tomato anthocyanins and aromatic volatiles develop over the last week on the vine; off-vine ripening lacks these. (c) Cold storage during transport (~7-10°C) damages tomato flavor compounds — they become "mealy." (d) Time alone degrades flavor; an in-season tomato is fresher to your kitchen by days.

  15. Diagnosis: Wilted kale = cell turgor lost (Ch 18 cell wall and turgor concept). Either the kale was damaged before serving (osmotic exchange happens once cells are bruised), the salt-and-acid dressing was added too early (osmosis pulls water out — the same chemistry as cucumber-weeping), or the kale was warm-stored (room temperature accelerates respiration and nutrient loss). Fix: Massage kale FIRST with a tiny bit of olive oil and salt, then add dressing JUST before serving (or even at the table). For a sturdy fix, use a sturdier green (lacinato kale, escarole) which holds longer. Or dress just before serving with cold ingredients to slow water loss.