Fruit and Vegetables part 1 Flashcards
What are fruits?
The ripened ovary of a plant. A seed baring structure.
What is a vegetable?
Herbaceous plant containing an edible portion, such as leaf, shoot, root, tuber, flower, or stem.
Properties of berries:
generally small and quite fragile
Properties of melons:
large and have tough outer rind
Properties of apricots, cherries, peaches, and plums:
contain single pits
Properties of apples, pears, and quinces (“pomes”):
contain many pits
Properties of oranges, lemons, and grapefruits (citrus):
high in citric acid
Properties of bananas, mangos, papayas, and pineapples (tropical & sub-tropical fruits):
require warm climates for growth
Properties of vegetables:
name derived from part of plants.
huge genetic diversity - numerous varieties selected for different characteristics
some vegetables are genetically closely related, but totally different tissue types
Composition of fruit and vegetables:
depends on:
- botanical variety
- cultivation practices
- weather
- degree of maturity prior to harvesting
- condition of ripeness (continues after harvest & influenced by storage conditions)
General composition of fruit and vegetables:
- high in water
- low in protein
- low in fat (exc. sweet corn and avacado)
- important source of digestible carbohydrates
- important source of fermentable carbohydrates
- important source of minerals & vitamins
Structural features of F & V
same fundamental structure
parenchyma cell (plant cell) = structural unit of edible portion of most fruit & vegetable
Vacuole
- contained within the cell
- size depends on cell’s function
- composed of water soluble substances dissolved within it (e.g. sugars, acids, volatile esters, aldehydes, ketones & water-soluble pigments)
Chloroplasts & mitochondria
energy conversion
- carry out energy conversion in the cell
- chloroplasts = through photosynthesis
- mitochondria = through cellular respiration; contain fats, proteins & enzymes
- Leucoplats (colourless plastids) also can store starch = energy source for plants
Nucleus
- embedded within the cytoplasm
- controls reproduction & protein synthesis
- needed for continued cell life (w/ mitochondria
Cell walls
critical components
- primary and secondary cell walls joined by middle lamella
- cellulose, hemicellulose and pectic substances (complex cho) (pectic substances give gel like structure
Plant tissues in fruits & vegetables
4 main types:
- Dermal (protect) - epidermis & endodermis
- Vascular (transportation) - xylem & phloem
- Supporting (stand upright)
- Storage (starch, sugar, nutrients, vitamins etc)
Dermal tissue
- protect, first defence against parasites, diseases, rot etc
- forms skin/peel/rind
- secretes waxy cutin on leaves, stems or fruits (water impermeable)
- contains valve-like structures (stomata), through which moisture and gasses pass through on leaves and young stems
Vascular tissue
two clearly defined structures (picture celery stalk):
- xylem = transfers water
- phloem = transfer food
Supporting tissue
in addition to parenchyma cells:
- collenchyma = tissue of living cells; particularly in young plants; lack primary cell walls (think of asparagus)
- sclerenchyma = hardened & rigid tissue (think stem of asparagus)
Storage tissue
making up most of the edible portion of F & V, contained in the cytoplasm, all referred to as plastids:
- leucoplast - fatty acids and amino acids
- amyloplast - sugars and starch
- elaioplast - lipds and oils
- aleuroneplasts/proteinoplasts - proteins
Texture
texture largely explained by changes in specific plant cell components.
- cells start dying, plant tissues generally contain more than 2/3 water, start losing water through respiration process and moisture leaching out (which fridge slows down), get wilting, pockmarked appearance
Turgor
Osmotic forces are key to state of turgor
parenchyma cell is stretchy/elastic, has flexibility, plant cell can expend (water enters cell)
texture & turgor
affected when plant tissues are damaged, killed by storage, freezing, cooking
- denaturation of cell membrane proteins occurs = loss of perm-selectivity
- without perm-selectivity, osmotic pressure in cell vacuoles cannot be maintained
- water & dissolved substances diffuse out of cells = remaining tissue left in soft & wilted conditions
Other cell constituents affecting texture - cellulose, hemicellulose & lignin:
- secondary cells forming, making it more fibrous, bark is secondary cell walls. we consume primary cell walls.
- young plants = cell walls are very thin and largely composed of cellulose
- as plants age, cell walls thicken & become higher in hemicellulose and lignin
- as such, cell walls are fibrous & tough = not significant;y softened by cooking
Other cell constituents affecting texture - cellulose, hemicellulose & lignin:
- secondary cells forming, making it more fibrous, bark is secondary cell walls. we consume primary cell walls.
- young plants = cell walls are very thin and largely composed of cellulose
- as plants age, cell walls thicken & become higher in hemicellulose and lignin
- as such, cell walls are fibrous & tough = not significantly softened by cooking
Other cell constituents affecting texture - Pectic substances:
- complex polymers of sugar acid derivatives
- “glue” found especially in the middle lamella; helps hold plant cells to one another and are water-insoluble
- yeilds water under mild hydrolysis - soluble pectin which can form gels or viscous colloidal suspensions with sugar & acid
- certain water-soluble tupes react with metal ions (e.g. calcium), forming water-insoluble salts (e.g. calcium pectate) - increase structural rigity when produced within F & V
- common commercial practice is to add low levels of calcium salts to tomatoes, applles & other fruits & veges prior to canning or freezing = firms the texture
- when cooking: some water-insoluble pectin hydrolysed into water-water soluble oectin, results in degree of cell separation in tissues, contributes to tenderness
- soluble pectins = form colloidal suspensions = thicken juices/pulp (due to acid & sugar present)
Other cell constituents affecting texture -
starch:
When making potato mash
- Cube potatoes, boil, cells swell because of water and heat (contributing to firm texture & plumpness), starch swells, cell rupture, starch leaching out, colloidal starch suspension, water getting thick/viscous. Over mashing gives gooey pasty mess
Colour
- appeal of F & V in our diets
- mostly occur in cellular plastid inclusions
- lesser extent dissolved in fat droplets or water within cell vacuole & protoplast
- four main groups: chlorophylls, carotenoids, anthocyanins, anthozanthins
Chlorophylls:
largely contained within chloroplasts
- primary role in photosynthetic production of cho from co2 and h2o
- gives leaves and other plants bright green colour
- oil soluble & binds to proteins in highly organised complexes
Carotenoids:
- fat soluble, often occuring along with chlorophylls, but present in other chromoplasts, may occur free in fat droplets
- ranging in colour from yellow through orange to red
- important carotenoids: carotenes of carrots, corn, apricot, peach, citrus fruits (orange), lycopene of tomato, watermelon, apricots (red), xanthophyll of corn, peach, paprika (yellow/orange)
- some serve as a precursor of vitamin A (1 molecule of beta-carotene converts to 2 molecultes of vitamin A in body)
- fairly resistant to heat, pH changes & water leaching during food process (due to being fat soluble)
- sensitive to oxidation by range of free radicals = results in colour loss & destruction of vitamin A activity
Anthocyanins
- water soluble (easy leaching of pigment when cut)
- belong to plant chemical group called flavonoids
- water-soluble & commonly present in juices of fruits & veggies
- include purple, blue & red pigments of grapes, berries, plums, eggplant, purple cabbage
- colour depends on pH (acid/basic environment). violet or blue in alkaline conditions, red in acidic conditions
- can react with metal ions (like cans) causing red anthocyanins to become more violet/blue/colourless, coating preserves colour
Tannins
- complex mixture of phenolic compounds
- colourless in most cases, reactions with metal ions form range of dark-colour complexes of red, brown, green, grey, or black
- shade depends on particular tannin, specific metal ion, and pH
- water-soluble tannins in grape & apple juices; tea & coffee brews
- colour & clarity of tea influenced by hardness and pH of brewing water
- possess astringency = influences flavour & contributes to body of tea, coffee, wine, apple cider…
- excessive astringency = puckery sensation in the mouth = produced when over brewing tea
