Vegetables Flashcards
What are vegetables? What is the structure of their cell wall?
- Edible part of a plant
- Some fruit (ripened seed and adjacent fleshy tissue) are eaten as vegetables (tomatoes, pumpkin, squash, cucumber, eggplant, peppers)
- Parts include leaves, steams, roots, tubers, flowers, bulbs, seeds
- High proportion of cellulose and hemicellulose, low proportion of pectic substances
- Contain more lignin (woody material not softened by cooking, indigestible, dietary fibre)
What are the effects of cooking the cell walls?
- Cooking in water
- Cellulose and hemicellulose absorb water
- Vegetables become softer, but don’t lose shape - Cooking in acidic conditions (added or organic in the fruits that come out cooked, diffusion happening, organic acids diffuse out and in cooking medium and in contact with hemicellulose and cellulose)
- Slow softening of cellulose and hemicellulose
- Vegetables retain some firmness - Cooking in alkaline conditions (adding baking soda or use of hard water)
- Guelph water has pH = 8.0
- Solubilizes (break down) hemicellulose
- Vegetables become mushy and slimy
- B-vitamins (especially thiamin or B1) are destroyed
What are the factors influencing the cooking method of vegetables?
- Composition of veggie
- Water-soluble vitamins
- Flavour
- Pigment
How does composition of vegetables influence cooking method?
- Leafy vegetables (kale, spinach)
- Waterless cooking (steam cooking)
- Use only water clinging to leaves after washing spinach
- Use pot with tight fitting lid
- Cooking time of 2-3 minutes - Starchy vegetables (potatoes, turnips, rutabaga, beets)
- Cooking time of 20+ minutes
- Cook until soft, need to eliminate taste of raw starch
How do water-soluble vitamins influence cooking method? What are the water soluble vitamins?
- Vitamin C, B vitamins (thiamin, niacin, folic acid, biotin, riboflavin)
- To retain water-soluble vitamins, use other cooking methods instead of boiling them in water/liquid
- Steaming, stir-frying, microwave pressure cooking, broiling, grilling, BBQ, baking (skin on)
What are mild flavoured vegetables (give examples) and how are they cooked?
- Bland or sweet flavour due to sugars in cell sap
- Carrots, green peas, corn, potatoes, zucchini, eggplant, beets parsnips
- Sugars diffuse across totally permeable cell membrane into cooking medium = flavour loss
- Use small amount of water
- Cook with lid on
- Cook for as short a time as possible (“tender crisp”)
What are distinctive flavoured vegetables (give examples) and how are they cooked?
- Spinach, asparagus, fiddleheads only
- Flavour is due to organic compounds other than those containing sulfur
- Flavour compounds can diffuse across totally permeable cell membrane
- Same method for mild vegetables
What are strong flavoured vegetables (give examples) and how are they cooked? Mention the families.
- Strong odours and flavours due to sulfur compounds produced in enzyme-catalyzed reactions
- Cabbage, rutabaga, cauliflower, onions, broccoli, leeks
- Try to minimize production of sulfur compounds
- Brassica (cabbage family) or Allium (lily family)
- Use large amount of water to dilute the sulfur compounds
- Lid off to allow volatile sulfur compounds to escape and not stay in with water
- Short period of time to minimize production of sulfur compounds (produced due to heat)
What determines pigments in vegetables?
- Conjugated double bond system
- Alternating single and double bonds in a repeating pattern, with no interruptions in pattern
- Allows pigments to absorb light in the visible range of the spectrum = COLOUR
What are the categories of pigments in vegetables?
Any Body Can Cook Food Anthocyanin Betalin Chlorophyll Carotenoid Flavenoid
What colour is anthocyanin and what happens when you cook it? Talk about methods and conditions.
Red to blue to purple
- Acid conditions: becomes reddish (eg. braised red cabbage changed from purple to purple-red)
- Alkaline conditions: becomes bluish or greenish
- Metal ions: coloured complexes form between the pigment and the metal ion (cooking pans, etc.)
o Aluminum: blue coloured complexes
o Iron: green coloured complexes
o Tin: grey coloured complexes
Eg. red cabbage is strong flavoured so cook in a lot of water however anthocyanin is water soluble and pigment will diffuse across totally permeable cell membrane.
Instead add little bit of water, and add ingredients (bacon, vinegar, wine, spices) to cover up sulfur flavour
What colour is betalin and what happens when you cook it? Talk about the 2 groups.
- Beets only
- Made up of 2 groups of pigments
- Betacyanins: purple-red (+anthocyanin)
- Betaxanthins: yellow
- Maintain colour in beets by not peeling or slicing before cooking (if you do, steam it)
- Leaving roots and stem attached
- Cook in minimum amount of water in short period of time (using pressure cooker)
- Stable in different pH and metal conditions
What colour is flavenoid and what happens when you cook it? Mention the groups.
- 3 groups: flavone, flavonol, flavanone
- Acid conditions: colour fades (may not be noticeable)
- Alkaline conditions: colour intensifies (may not be noticeable), turns white to yellow
- Metal ions: coloured complexes form between the pigment and metal ion
o Aluminum: yellow coloured complexes
o Iron: blue-black coloured complexes
o Copper: red/brown coloured complexes
What colour is chlorophyll and what happens when you cook it? Talk about the structure of the molecule.
- Phytol group: gives fat solubility to molecule
- Chlorophyll b gives the yellow-green colour
- Centre of chlorophyll molecule is the Mg ion
- Alkaline and heat conditions: Chlorophyllin (phytol group is removed, pigment turns water soluble): turns bright green, Magnesium ion is still there
- Acid and heat conditions: Pheophytin (still fat soluble as phytol group remains): turns olive green, acid donates 2 hydrogen ions to magnesium ions to cause this reaction above
What colour is carotenoid and what happens when you cook it? Talk about the 2 types.
- Carotenes (orange to orange-red)
- Beta-carotene (orange): 1 molecule converts into 2 molecules of vitamin A
- Alpha-carotene (yellow-orange): 1 molecule converts into 1 molecule of vitamin A
- Lycopene (orange-red): contains 2 extra double bonds, found in tomatoes, watermelon, pink grapefruit, cannot be converted into vitamin A - Xanthophylls (yellow)
- Eg. corn, butter, egg yolks
- Contain oxygen
- Slightly water soluble
- Acid and heat conditions: slight fading (eg. beta carotene changes from orange-red to paler colour)
- Alkaline and heat: no effect
Which pigments are water soluble? What does this mean?
- Water soluble pigments are anthocyanin, betalin, and flavonoid
- Dissolved in cell sap in vacuole
- Diffuse into cooking water through totally permeable cell membrane = colour loss
Which pigments are fat soluble? Where are these found?
- Fat soluble pigments are chlorophylls and carotenoids
- Found in plastids, which are floating in cytoplasm of cell
Which coloured vegetables contain which vitamins?
- Dark green veggies are good sources of minerals, iron, calcium (however may not be available due to organic acid oxalic acids)
- Good sources of ascorbic acid (vitamin C) and B vitamins
- Green and yellow veggies are good sources of pigment carotene (converts in body to vitamin A)
Why does wilting occur and what happens to flavour?
- Vegetables stored in fridge may wilt due to water passing into surrounding air through semi-permeable cell membranes
- Osmosis reduces turgor pressure causing cells to collapse
- Flavour will deteriorate due to enzyme action in tissues
How do you combat wilting? What is one caveat?
- Storing veggies in small closed container allows equilibrium to be reached
- Surrounding air becomes saturated with water vapour
- However, encourages microbial spoilage
- Frost-free fridges remove moisture from air to prevent ice thus uncovered foods wilt
What are all the methods of cooking veggies?
- Baking
- Time required
- Form steam quickly in vegetable, giving better texture to starchy vegetables
- Potatoes, sweet potatoes, winter squash, onions - Frying
- Can be dipped in batter or parboiled
- Potatoes, onions, eggplant, zucchini, parsnips - Stir-frying/panning
- Thin cuts so heat will penetrate quickly
- Helps retain vitamins and minerals
- Should be slightly firm - Boiling
- Water-soluble vitamins are lost
- Flavour may be lost
- Covering veggies may make it possible for less water to be used - Steaming/pressure cooking
- Take longer to cook
- Retains water soluble nutrients
- Loss of colour due to long cooking time
- Pressure cooking cooks food faster - Microwave cooking
- Better colour and sometimes flavour
- Should be uniform in size
- Skins should be pierced to allow steam to escape
- Tender parts of vegetables would be arranged toward centre of dish
- Vegetables should be cooked until almost done
