Ch.5: Edible Plants

Chapter 5 of the book "On Food and Cooking: The Science and Lore of the Kitchen" by Harold McGee (1984) Plants as Food Plant Foods and Health Composition of Fruits and Vegetables Handling and Storing Fruits & Vegetables Cooking Fresh Fruits and Vegetables Preserving Fruits and Vegetables

317 flashcards · Other · by lakesare

Part of Public › Books › On Food and Cooking (Harold McGee) · 16 courses

1. [Edible Plants] Why do plants produce so many strong colors, tastes and aromas?

   Plants can't move, so they defend and spread themselves with chemicals. Their compounds repel enemies, attract helpers such as pollinators and seed carriers, and protect the plant against chemical stress.Many of those compounds are what we perceive as flavor, color and aroma, and some protect us too.

2. [Edible Plants] About when did humans begin to farm plants?

   About 10,000 years ago. Before that, people foraged a wide range of wild fruits, leaves and seeds for a million years and more.

3. [Edible Plants] Which kinds of plants did humans domesticate first?

   A few grains, beans and peas, and tubers. These are among the richest plant sources of energy and protein, and they can be grown and stored in large quantities, which made settlement and the first cities possible.

4. [Edible Plants] What did agriculture, and later industrialization, do to the variety of plants in the human diet?

   Both reduced the variety drastically. Foragers ate a wide range of wild fruits, leaves and seeds; in the modern Western diet, fruits and vegetables became marginal foods.

5. [Edible Plants] Apart from ethics, why have most people in history eaten mainly plant foods?

   Meat costs far more to produce than grains and tubers. Some, from Pythagoras onward, also chose plant foods to avoid killing animals that can feel pain.

6. [Plants as Food] What is the difference between an autotroph and a heterotroph?

   An autotroph makes its own food from simple materials; a heterotroph eats other living things. Plants are autotrophs: they build themselves from water, minerals, air and sunlight. Animals are heterotrophs.

7. [Plants as Food] What is the overall equation of photosynthesis?

   6 CO2+6 H2O+light→C6H12O6+6 O2\boldsymbol{6\,\mathrm{CO_2} + 6\,\mathrm{H_2O} + \text{light} \to \mathrm{C_6H_{12}O_6} + 6\,\mathrm{O_2}}6CO2​+6H2​O+light→C6​H12​O6​+6O2​ Carbon dioxide and water, with light energy, give glucose and oxygen. The green pigment chlorophyll captures the light and starts the process.

8. [Plants as Food] How did photosynthesis make life on land possible?

   Its oxygen formed the ozone layer, which blocks most ultraviolet light. Oxygen ( O2\mathrm{O_2}O2​ ) is turned into ozone ( O3\mathrm{O_3}O3​ ) by radiation in the upper atmosphere.Before that, UV rays reached the ground and several feet into the ocean, so life survived only in deeper water. Photosynthetic bacteria appeared more than 3 billion years ago.

9. [Plants as Food] Why are plants made mostly of carbohydrate, while animals are made mostly of protein?

   Plants stay put and build stiff carbohydrate walls; animals move, which takes muscle protein. McGee: "Plants are essentially stationary chemical factories."

10. [Plants as Food] What kinds of chemical weapons do plants make against animals and microbes?

    Irritants Example: mustard oil, capsaicin of chillis, the tear-inducing factor of onions Bitter, toxic alkaloids Example: caffeine in coffee, solanine in potatoes Cyanide compounds Example: lima beans and many fruit seeds Digestion blockers Example: astringent tannins, inhibitors of digestive enzymes

11. [Plants as Food] If plants are full of toxins, how do animals avoid being poisoned?

    Smell and taste warn them: animals instinctively dislike bitter and like sweet. Smell and taste detect these compounds even at tiny concentrations.Bitterness is typical of alkaloids and cyanide; sweetness signals nutritious sugars. Some animals also have detoxifying enzymes for one plant.Example: koalas eat eucalyptus leaves, monarch butterfly caterpillars eat milkweed.

12. [Plants as Food] How have humans made toxic plants edible?

    By breeding less toxic varieties, and by cooking. Heat destroys many toxins, and boiling water draws others out.Example: the wild ancestors of cabbage, lima beans, potatoes and lettuce were more toxic than today's cultivated forms.

13. [Plants as Food] Why do people enjoy pungent spices such as mustard and pepper?

    We have learned to enjoy warning signals (burning, irritation) that are fairly harmless. The compounds of mustard, pepper and onions exist to repel animals; humans seek them out.

14. [Plants as Food] Why do plants make fruits that taste good to animals?

    So animals eat them and carry the seeds away from the parent plant. The seeds often end up in a pile of manure.Seeds dropped beside the parent would compete with each other and with the parent for light and minerals. The seeds survive by being large and armored, tiny, or poisonous.

15. [Plants as Food] What is the biological purpose of ripening?

    To keep the fruit unappealing until its seeds are mature. Leaves, roots and stalks can be eaten any time (usually the younger the tenderer); fruit signals readiness by changes in color, texture and flavor.

16. [Plants as Food] What does a flower do for a plant?

    It attracts an animal, usually an insect, to carry pollen between plants. Its shape, color and scent attract a particular pollinator, which collects nectar or pollen as food.

17. [Plants as Food] What is a herbaceous plant?

    A small, delicate plant that produces its seeds and dies within one growing season. Such plants spread widely only a few million years ago, around the time the human species appeared. Most food plants are herbaceous.

18. [Plants as Food] Why have herbaceous plants (which seed and die within one growing season) suited human farming so well?

    They grow to a harvest in months, so crops and varieties can change quickly. Plantings can change from year to year, and new varieties can be bred fast.Also, their parts are tender, since they are not built to last for years.

19. [Plants as Food] What is a fruit in the botanist's sense?

    The seed-enclosing organ that grows out of the ovary of a flower. So capsicum peppers, pea pods, cucumbers and corn kernels are botanically fruits, though cooks call them vegetables.

20. [Plants as Food] What does vegetable mean in its current sense?

    Plant material that is neither fruit nor seed. The word took on this sense only a few centuries ago.

21. [Plants as Food] How did the US Supreme Court classify tomatoes in the 1890s?

    As vegetables, because they are served with the main course, not as dessert. An importer had claimed duty-free status for tomatoes as fruits; the court kept the cook's definition, so he paid the duty.

22. [Plants as Food] In the kitchen, what three qualities set fruits apart from vegetables?

    High sugar content It satisfies the liking for sweetness that all animals share. Pronounced, complex aroma Often several hundred different volatile chemicals, more than any other natural ingredient. Self-softening Ripe fruit becomes tender and moist on its own. Vegetables stay firm and taste either very mild (green beans, potatoes) or too strong (onions, cabbage), so they need a cook. McGee calls fruits "the natural world's soft drinks and candies".

23. [Plants as Food] "Vegetable" comes from the Latin verb vegere, to invigorate; "fruit" comes from Latin fructus, meaning gratification or enjoyment.

24. [Plants as Food] What is the difference between an herb and a spice?

    Herbs are leaves and other green parts; spices are seeds, bark, roots and other tough parts. Both are flavorings used in small amounts. Herbs: parsley, thyme, basil. Spices: black pepper, cinnamon, ginger. Spices were durable enough for long-distance trade.

25. [Plants as Food] The word "spice" comes from medieval Latin species, meaning "kind of merchandise".

26. [Plants as Food] Which common vegetables are recent inventions, not eaten since prehistory?

    Broccoli, cauliflower, brussels sprouts, celery. Nearly all other common vegetables have been eaten since before recorded history.

27. [Plants as Food] Which spice became the most popular of the ancient world, from about 500 BCE?

    Black pepper, from the Far East. Egyptian records of about 1200 BCE already list large offerings of cinnamon from Sri Lanka.

28. [Plants as Food] What were Columbus, Vasco da Gama, Cabot and Magellan looking for?

    A new sea route to the spices of the Indies. Venice and the Arab traders held a monopoly on the spice trade.The sought-after spices were cinnamon, cloves, nutmeg and black pepper. Instead, the voyages opened the Americas to Europe.

29. [Plants as Food] Which important foods came to Europe from the New World?

    Potatoes, tomatoes, corn, chillis and peppers, beans, squashes. Also sweet potatoes, avocados, pumpkins, pineapple, vanilla and allspice. Most of the vegetables grew well in Europe and became staples there.

30. [Plants as Food] Why did the quality of fresh produce decline through much of the 20th century?

    Crops were bred for yield and toughness, not flavor, and picked hard and early. Breeders aimed for productivity, uniformity and durability; produce was harvested weeks or months before being eaten.They had to survive mechanical harvesting, long shipping and storage. A few varieties took over the market and thousands disappeared.

31. [Plants as Food] About how many plant species are farmed for food, at least on a small scale?

    Perhaps 2,000. Out of about 300,000 edible species.

32. [Plant Foods and Health] For which vitamins are fruits and vegetables our main source?

    Vitamin C (almost entirely), vitamin A (about half) and a large share of folic acid. They contribute only modestly to protein and calories.

33. [Plant Foods and Health] What does vitamin C do in our cells?

    It keeps many enzymes working, and helps build collagen (connective tissue). It returns the metal atoms in these enzymes to their working chemical state.It is also an antioxidant.

34. [Plant Foods and Health] From what do we make our vitamin A?

    From beta-carotene and related orange-yellow plant pigments. These pigments are called carotenoids.

35. [Plant Foods and Health] What does vitamin A do in the body?

    It lets the eye detect light, and helps control the growth of cells. The light-detecting receptor molecule of the eye contains vitamin A.

36. [Plant Foods and Health] What does folic acid do in our cells?

    It clears away homocysteine, a by-product that harms blood vessels. Folic acid turns homocysteine into the amino acid methionine.Built-up homocysteine may contribute to heart disease and stroke. The name comes from Latin for "leaf".

37. [Plant Foods and Health] Which three vitamins are also antioxidants?

    Vitamins A, C and E.

38. [Plant Foods and Health] Which crops supplied most genetically modified ingredients in US processed foods?

    Soybeans, canola and corn. Modified to resist insect pests or weed killers. As of 2004, about 75% of US processed foods contained such ingredients.The only other significant engineered US crop was virus-resistant Hawaiian papaya. Much cheese is coagulated with rennet made by microbes carrying the cattle gene for the enzyme.

39. [Plant Foods and Health] How did the goal of nutritional science change toward the end of the 20th century?

    From avoiding deficiencies to finding a diet that prevents long-term diseases. Cancer and heart disease turned out to be influenced by diet, including by minor, nonessential components such as plant phytochemicals.

40. [Plant Foods and Health] What are free radicals?

    Highly reactive molecules that damage the cell's own molecules. The damage is called oxidative, because most free radicals come from reactions involving oxygen.

41. [Plant Foods and Health] Which processes in the body produce free radicals?

    Mainly the cell's use of oxygen to get energy from sugars and fats. Ultraviolet light also makes them, for example in the eye.

42. [Plant Foods and Health] Give three examples of oxidative damage in the body.

    DNA damage A cell may multiply uncontrollably and form a tumor. Damage to cholesterol-carrying particles in the blood They irritate the artery lining, starting damage that leads to heart attack or stroke. UV damage in the eye Free radicals damage proteins of the lens and retina: cataracts, macular degeneration.

43. [Plant Foods and Health] What is an antioxidant?

    A molecule that reacts harmlessly with free radicals before they do damage. The body makes some (including enzymes), but benefits from more supplied by food.

44. [Plant Foods and Health] Why are green leaves especially rich in antioxidants?

    Photosynthesis makes more free radicals than any other process in living things. It splits water with the energy of sunlight.The antioxidants keep these high-energy reactions from damaging the leaf's DNA and proteins.

45. [Plant Foods and Health] What are the main kinds of plant antioxidants?

    Carotenoid pigments Example: orange beta-carotene, yellow lutein and zeaxanthin, red lycopene of tomatoes Chlorophyll Vitamins C and E Phenolic compounds Thousands of compounds built from rings of 6 carbon atoms. The more pigmented and astringent a food, the richer it tends to be in them. Example: anthocyanins of grapes and berries, the phenolics of tea

46. [Plant Foods and Health] Why is eating many different fruits and vegetables better than taking antioxidant supplements?

    Each antioxidant guards against only some damage, and a high dose of one can harm. Each fruit and vegetable has its own mixture of antioxidants.

47. [Plant Foods and Health] Besides acting as antioxidants, what are some other beneficial effects of phytochemicals?

    Moderating inflammation Example: salicylates (aspirin-like) in raisins, dates, chillis, tomatoes Blocking the body's production of DNA-damaging chemicals Example: glucosinolates of broccoli and the cabbage family; flavonoids Inhibiting the growth of cancer cells Example: isoflavones of soybeans, lignans of rye and flaxseed Feeding beneficial gut bacteria Example: inulin of the onion family and sunchokes Preventing bacteria from adhering to the urinary tract Example: proanthocyanidins of cranber…

48. [Plant Foods and Health] How can you judge by eye how healthful a fruit or vegetable is?

    The deeper its color, the more healthful it is likely to be. Leaves that get more light need more pigments and antioxidants. Skins are especially rich.Example: dark romaine leaves have nearly 10 times the lutein and zeaxanthin of pale iceberg lettuce.

49. [Plant Foods and Health] What is dietary fiber?

    Plant material that our own enzymes cannot digest. It passes to the large intestine, where bacteria break down some of it and the rest is excreted.

50. [Plant Foods and Health] What are the four main components of dietary fiber?

    Cellulose, lignin, pectins and hemicelluloses. All four come from plant cell walls.Minor components include uncooked starch, gums, the chitin of mushrooms, the agar and carrageenan of seaweeds, and inulin.

51. [Plant Foods and Health] Which of the four main fiber components (cellulose, lignin, pectins, hemicelluloses) dissolve in water?

    Pectins and hemicelluloses. Cellulose and lignin stay solid. Example: wheat bran is rich in insoluble cellulose; oat bran in soluble glucan; ripe fruits in soluble pectins.

52. [Plant Foods and Health] How do insoluble and soluble fiber act differently in the intestine?

    Insoluble fiber adds bulk and speeds things up; soluble fiber thickens and slows them. Soluble fiber lowers blood cholesterol and slows the rise of blood sugar after a meal, helping protect against heart disease and diabetes. Both may bind toxins.

53. [Plant Foods and Health] Why is orange or carrot juice not as valuable as the whole fruit or vegetable?

    Juicing removes most of the fiber.

54. [Plant Foods and Health] What are alkaloids?

    Bitter-tasting plant toxins; nearly all are poisonous in high doses. At low doses most of them change how an animal's body works: hence the attraction of caffeine and nicotine.

55. [Plant Foods and Health] Which common food can build up harmful amounts of alkaloids?

    The potato, when it turns green or sprouts. Greened potatoes and potato sprouts are bitter and toxic.

56. [Plant Foods and Health] How do cyanogens in plants release cyanide?

    When the plant is chewed, an enzyme splits cyanide off them. The damage mixes cyanogens with a plant enzyme that releases hydrogen cyanide ( HCN\mathrm{HCN}HCN ).HCN poisons the enzymes animals use to generate energy.

57. [Plant Foods and Health] How are cyanogen-rich foods such as manioc, bamboo shoots and tropical lima beans made safe?

    Open boiling, leaching in water, and fermentation.

58. [Plant Foods and Health] Why are the seeds of stone fruits prized as a flavoring despite their cyanogens?

    The same cyanogens also release benzaldehyde, the smell of almond extract.

59. [Plant Foods and Health] Why might mushrooms be best eaten in moderation?

    They contain hydrazines, which cause cancer in mice; their effect on humans is unknown. Hydrazines survive cooking and also cause liver damage in mice.The common white mushroom contains about 500 parts per million. In rats hydrazines have no effect. McGee advises moderation until more is known.

60. [Plant Foods and Health] How do the protease inhibitors and lectins of raw beans harm us?

    Both block digestion: one stops protein-digesting enzymes, the other nutrient uptake. Protease inhibitors block our protein-digesting enzymes; lectins bind to the cells of the intestine and keep them from absorbing nutrients.Found mainly in soy, kidney and lima beans. Lectins can also make red blood cells stick together.

61. [Plant Foods and Health] How are the protease inhibitors and lectins of beans made harmless?

    By prolonged boiling. In raw or undercooked beans they survive and can cause symptoms like food poisoning.

62. [Plant Foods and Health] Which plant flavor chemicals can harm in large amounts?

    Safrole Main aromatic of sassafras (traditional root beer); damages DNA, banned as an additive in 1960. Myristicin Main flavor of nutmeg; causes intoxication and hallucinations in large amounts. Glycyrrhizin Intensely sweet compound of true licorice root; raises blood pressure. Coumarin Sweet aroma of sweet clover, lavender and tonka beans; interferes with blood clotting.

63. [Plant Foods and Health] Which bean can cause favism, an anemia in susceptible people?

    The fava bean. Its toxic amino acids vicine and convicine destroy red blood cells in susceptible people.A similar toxic amino acid, canavanine, in alfalfa sprouts, has been associated with lupus.

64. [Plant Foods and Health] Why can oxalates (in spinach, chard, beets, rhubarb) be harmful?

    They form sharp crystals with calcium: irritating in the gut, kidney stones in the kidney. Oxalates are salts of oxalic acid. A few grams of oxalic acid can be fatal.

65. [Plant Foods and Health] What do psoralens do to us?

    In sunlit skin they damage DNA and cause blistering. They enter the skin by handling the vegetable, or by eating it.

66. [Plant Foods and Health] When do celery, celery root, parsley and parsnips contain psoralens?

    After stress: cold close to freezing, very strong light, or a mold infection. So buy these vegetables as fresh as possible and use them quickly.

67. [Plant Foods and Health] Why should fiddleheads be eaten in moderation?

    Bracken fern causes cancer in grazing animals, and other ferns are little studied. Bracken (Pteridium) also causes blood disorders in grazing animals.Ostrich fern (Matteuccia) fiddleheads are thought to be safer.

68. [Plant Foods and Health] Besides the plant's own defense chemicals, which other toxins can fruits and vegetables carry?

    Toxins from molds, agricultural chemicals, and pollutants from soil and air. Example: patulin in apple juice comes from a Penicillium mold on damaged fruit.

69. [Plant Foods and Health] How can we take in fewer of the mold toxins, farm chemicals and pollutants on produce?

    By washing it, peeling off its surface layers, and buying certified organic produce.

70. [Plant Foods and Health] Why are fruits and vegetables a significant cause of food poisoning?

    They grow in microbe-rich soil and are often eaten raw. They are also easily contaminated during harvest and packing.Salad bars and fresh juices are common sources; nearly all US juice is now pasteurized.

71. [Plant Foods and Health] By about how much does washing reduce the microbes on raw produce?

    About a hundredfold. Soapy water and produce washes work better than water alone. Wash even fruit to be peeled: knives and fingers carry surface bacteria to the flesh.

72. [Plant Foods and Health] Why can't washing remove all the microbes from raw produce?

    Some microbes sit in tiny pores and cracks that water can't reach. Even heavily chlorinated water doesn't reach them.

73. [Plant Foods and Health] Which homemade vegetable preserve carries a risk of botulism?

    Garlic in oil. The oil cuts off air, and the botulism bacterium (Clostridium botulinum) grows without oxygen.

74. [Composition of Fruits and Vegetables] What are the main parts of a plant cell?

    Cell wall, membrane, cytoplasm, nucleus, a large vacuole, and plastids. Plastids are small bodies such as chloroplasts, chromoplasts and amyloplasts. Cross-section through a typical plant cell.

75. [Composition of Fruits and Vegetables] What is the vacuole of a plant cell?

    A big watery sac that fills most of the cell and holds most of its flavor. Often 90% of the cell volume. It holds sugars, acids, enzymes, proteins, water-soluble pigments and waste or defensive compounds.It presses the cytoplasm and nucleus against the cell membrane.

76. [Composition of Fruits and Vegetables] What do chloroplasts, chromoplasts and amyloplasts in plant cells contain?

    Green chlorophyll; yellow-to-red pigments; starch. Chloroplasts: chlorophyll, for photosynthesis. Chromoplasts: fat-soluble yellow, orange and red pigments. Amyloplasts: starch granules.Leaf cells have dozens to hundreds of chloroplasts; chromoplasts are typical of fruits, amyloplasts of storage cells.

77. [Composition of Fruits and Vegetables] What do plant cells have that animal cells lack entirely?

    A strong, rigid cell wall around the membrane. The outer layers of neighboring walls hold cells together. Some strengthening cells become mostly wall and keep working after they die.Example: the grit in pears, celery fibers, a peach stone and bean seed coats are mainly cell-wall material.

78. [Composition of Fruits and Vegetables] What are the four basic plant tissues?

    Ground tissue The main mass of cells, with thin walls, so tender; photosynthesis in leaves, storage elsewhere. Most fruits and vegetables are mainly ground tissue. Vascular tissue Tubes that transport fluids: xylem and phloem. Often tough and fibrous. Dermal tissue The protective, moisture-retaining surface: epidermis (with cutin and wax) or corky periderm. Example: periderm forms the skins of potatoes and beets. Secretory tissue Isolated cells that make and store aroma compounds. Example: glan…

79. [Composition of Fruits and Vegetables] In vascular tissue, the xylem carries water and minerals up from the roots, and the phloem carries sugars down from the leaves.

80. [Composition of Fruits and Vegetables] What makes many fruits naturally shiny?

    Wax secreted by the epidermis (long molecules of fatty acids joined to alcohols). The epidermis also secretes a fatty material called cutin.

81. [Composition of Fruits and Vegetables] Most roots are tough and fibrous. What makes edible roots such as carrots and sweet potatoes different?

    They are swollen with soft storage cells that feed the plant through winter or drought. Winter, to flower in the second year: carrots, parsnips, radishes. Tropical dry season: sweet potatoes, manioc.

82. [Composition of Fruits and Vegetables] How do carrot and beet roots differ in structure?

    A carrot has one central core; a beet has alternating rings. Carrot: storage tissue around a central core of fluid-carrying tubes (vascular tissue). Beet: rings of storage tissue alternating with rings of vascular tissue.The carrot's core is less flavorful; striped beet varieties have different pigments in different layers.

83. [Composition of Fruits and Vegetables] Why do asparagus and broccoli stems often need peeling, and celery stalks deveining?

    Stems conduct nutrients and support the plant, so they become fibrous.

84. [Composition of Fruits and Vegetables] What is the hypocotyl of a plant?

    The part where the stem meets the root. In turnips, celery root and beets the hypocotyl swells into a storage organ.These vegetables are part stem, part root.

85. [Composition of Fruits and Vegetables] What is the difference between a tuber and a rhizome?

    A tuber is a swollen underground stem tip; a rhizome is a horizontal underground stem. Both store food and let the plant clone itself. Tubers: potato, true yam. Rhizomes: sunchoke, ginger.

86. [Composition of Fruits and Vegetables] Why do leafy greens shrink so much when cooked?

    Leaves are full of air pockets, which collapse in heat. Some leaves are up to 70% air by volume. The air pockets expose inner cells to the carbon dioxide that photosynthesis needs. Heat also wilts leaves so they pack together.

87. [Composition of Fruits and Vegetables] What are the layers of an onion, botanically?

    Swollen leaf bases. They sit around a small inner stem; the tops of the leaves die and fall off.They store water and carbohydrate in the first year for flowering and seed in the second. Onions are the main exception to leaves having no storage tissue.

88. [Composition of Fruits and Vegetables] Which common vegetables are flower buds or their stalks?

    Broccoli, cauliflower, artichokes.

89. [Composition of Fruits and Vegetables] Why is ripe fruit usually the most flavorful and tender part of a plant?

    It has no other job than to appeal to animals. Fruit does no supporting, transporting or feeding for the plant, so it is almost all soft storage tissue full of attractive substances.

90. [Composition of Fruits and Vegetables] What two factors determine the texture of raw fruits and vegetables?

    The construction of the cell walls and the amount of water inside them. Texture reflects how the tissue breaks apart as we chew.

91. [Composition of Fruits and Vegetables] What are plant cell walls made of?

    Cellulose fibers held in a jelly-like "cement". The cement is water, carbohydrates (hemicelluloses, pectins), minerals and proteins.The cement cross-links the fibers, and holds neighboring cells together where their walls meet.

92. [Composition of Fruits and Vegetables] What makes a fruit or vegetable turgid (full and firm)?

    Water pressure inside the cells, pushing out against their walls. The water-filled vacuoles press each cell against its wall, at up to 50 times atmospheric pressure. Left: well-watered tissue. Right: after water loss the vacuoles shrink and the walls sag, so the tissue goes limp.

93. [Composition of Fruits and Vegetables] Why is a turgid vegetable crisp and juicy, but a limp one chewy?

    Taut cells burst when bitten; limp cells just squash. In turgid tissue the stressed walls break easily and release juice; in limp tissue chewing only presses the walls together.

94. [Composition of Fruits and Vegetables] How can you restore and enhance the crispness of a vegetable?

    Soak it in water for a few hours, and serve it icy cold. The cells absorb water and reinflate; cold stiffens the cell-wall cement, so it breaks in a brittle way.

95. [Composition of Fruits and Vegetables] What gives a fruit or vegetable a mealy texture?

    Cells come apart whole instead of breaking open. The material holding neighboring cells together is weak.The mouth fills with many tiny separate cells, which feels grainy and dry.

96. [Composition of Fruits and Vegetables] What gives a ripe peach or melon its soft, melting texture?

    Its cell walls have nearly fallen apart, so juice flows out at a touch.

97. [Composition of Fruits and Vegetables] Why is cooked starchy tissue (a potato) never juicy?

    Starch absorbs the water when heated, so the tissue becomes moist but mealy or pasty.

98. [Composition of Fruits and Vegetables] What are hemicelluloses?

    Cell-wall carbohydrates that link the cellulose fibers together. They are built from sugars such as glucose and xylose.Cooking partly dissolves them out of the walls.

99. [Composition of Fruits and Vegetables] How does a fruit soften as it ripens?

    Its enzymes modify the pectins in its cell walls, which weakens the walls. Pectins form a gel that fills the spaces between the cellulose fibers of the wall.

100. [Composition of Fruits and Vegetables] What are pectins?

     Cell-wall carbohydrates that form a gel between the cellulose fibers. Pectins are branched chains of galacturonic acid.Cooking can dissolve them or firm them up. Their gel sets jams and jellies. In boiling water the cellulose stays intact, but pectins and other amorphous materials are partly extracted, which softens the walls.