WK 6 Fruit and Veg

Storage of veg - refrigeration

- Cooler temps slow respiration - Leaves draw moisture from rest of plant so if we chop off the leaves, the celery will last longer as the leaves aren't drawing the moisture from the stems.

fruit classification - multiple fruits

- Develop from a cluster of several flowers • Pineapples, figs

fruit classification - aggregate fruits

- Develop from several ovaries in one flower • Blackberries,raspberries,strawberries

Composition of veg - acidity

- Low content of organic acids

Composition of veg - fibres

- Pectic substances - Cellulose & hemicelluloses

Fruits - transport + indigenous

- Pineapples were indigenous to South America - Lemons/limes indigenous to India - Oranges indigenous to SE Asia - Kiwi fruit indigenous to NZ? -transportation can occur due to changes in storage conditions and advances in food processing

acid pH

- Polyphenol oxidase's activity is inhibited in acidic environments (works best at pH 7) - Coat fruit in lemon/lime/orange juice or cream of tartar solution

Plant Cell Structures - cell walls

- Provide structural support (animal cells have skeleton for this) - Strength contributed to by fibrous compounds - all indigestible • Cellulose, pectic compounds, hemicellulose, lignin, gums • Lignin (non-CHO fibre) increases as vegetable matures • Gums absorb & swell with water (carrageenan , guar gum...) - Substances between cell walls acts as intra/inter-cellular cement • Pectic compounds & hemicellulose - Outer layer of skin/peel has more cellulose/hemicellulose

composition of veg - vitamins

- Some vitamin A,C, E, but also folate

Fruit composition - pectic substances

- There are 3 primary types • Protopectin • Pectin (Pectinic Acids) • Pectic Acid -"pectin" is used to describe them all -act as a cementing substance b/n cell walls & contribute to plant's firmness & structure -Protopectin - immature fruit - no gel -pectin - ripe fruits - gels -pectic acid - overripe fruit - no gel - The compound responsible for gelling is Methyl Pectate - Has high water binding capacity - Repeating chains of galacturonic acid - Under right conditions, forms a net like structure that is able to trap water & form a gel - Only found in cell walls, not juice

fruit classification - exceptions

- Tomatoes - Squash - Green beans - Cucumbers (All botanically fruits)

Functions of Plant Parts - roots, tubers, bulbs

- Uptake & transport of water & nutrients - Energy storage

Storage of veg - maintaining moisture

- Use of crisper - Plastic bags with tiny holes

fruit classification - simple fruits

- all develop from 1 flower - Drupes • Fruits with seeds encased in a pit • Apricots, cherries, peaches, .... - Pomes • Fruit with seeds contained in a central core • Apples, pears, .....

Denaturing enzymes

- blanching -not often done with fruits

Fruit Composition - phenolic compounds

- responsible for browning & bruising behaviour of fruits -also called "tannins" -found predominantly in unripe fruits = gives a bitter taste and astringent mouth feel -fruits contain them include: •Apples,apricots,avocadoes,bananas,cherries,dates,grapes, nectarines, peaches, persimons, pears, strawberries

fruits

-Fruits are ripened ovaries & adjacent parts of plant's flowers -There are several different ways in which fruits develops - this forms a means of classification

Other types of fruit browning

-Maillard reaction -caramelisation

Prep of fruits - changes during heating

-Pigments colouring fruit = same as those in vegies. -During ripening, chlorophyll breaks down so the underlying pigments are more exposed. The colours then become more brilliant -During cooking, changes to colour are generally related to the changes in pH or the reaction with metal salts or ethylene gas

Plant Pigments

-carotenoids -chlorophyll -flavenoids -betalains

fruit composition

-cell structure & cell components = very similar to veg -The organic acids, pectic substances & phenolic compounds (found in both fruit & veg) have more relevance to fruits

Pectin used extensively in FI

-setting agent -emulsifiers -thickeners -texturisers -e.g. Helps control ice crystal size in frozen foods, thus preventing loss of syrup on thawing Harvesting fruit at the appropriate stage of development is critical in optimising pectin content

Fruit composition - organic acids

-tart flavour component = partially due to organic acids located in cell sap -acidity varies with ripeness (usually ↓) -acids = volatile or non-volatile but can leach out when cooked in water -common acids: • Citric Acid: citrus fruits, tomatoes, ... • Malic Acid: apples, apricots, cherries, peaches, pears, strawberries • Tartaric Acid: grapes • Oxalic Acid: rhubarb • BenzoicAcid:cranberries

antioxidants

-these use up available O -inc vitamin C, sulfur compounds -pineapple juice = ^ in sulfur compounds

Classification of Vegetables

1 method- based on the part of the plant from which they originated Vegetables may be derived from almost any part of a plant • Roots (e.g. carrot) • Tubers (e.g. potato, beetroot) • Bulbs (e.g. onions, garlic) • Stems (e.g. celery, asparagus) • Leaves (e.g. lettuce, bok choy) • Seeds (e.g. beans, peas) • Flowers (e.g. artichoke, broccoli)

fruit classification - nuts

Are fruits but as they are seeds instead of fleshy fruit, are grouped separately

Composition of veg - energy source

Energy source = Starches or Sugars - Some store oils

Dietary fibre

Fibre Content per 1⁄2 cup cooked unless indicated. kidney beans - 7 lentils - 4 corn - 3 potato - 3 broccoli - 2 carrots - 2 spinach - 2 sweet pot - 2

difference b/n fruit and veg

Fruits contain seeds.

Composition of veg - minerals

Mainly potassium, but also sodium, calcium, magnesium, iron and zinc.

prep of fruits - control of enzymatic browning

Most are prone to this when sliced or peeled. Can be controlled by: 1. Denaturing the enzymes 2. Adding acid 3. Lowering storage temp 4. Blocking exposure to oxygen

Phytochemicals

Non-nutritive compounds found in foods that possess health protective effects • Best if in natural food source • Cruciferous vegetables notoriously rich - Includes broccoli, brussel sprouts, cabbage, cauliflower, turnips - So called because of their cross shaped blossoms

Functions of Plant Parts - leaves

Photosynthesis - conversion of CO2 + H2O to carbohydrate (also uses the green pigment chlorophyll)

Enzymatic browning - fruit

Requires 3 substances: 1. Phenoliccompounds 2. Polyphenol Oxidase enzymes 3. Oxygen The brown substances produced (melanins) are safe to consume on an apple.

storage of veg - freezing

Suitable vegetables need to be blanched first

Functions of Plant Parts - stems

Support, transport of water & nutrients

coating with sugar or water

a protective layer from O

Cold temps

decreases rate of enzyme activity

fruit define

is a seed-bearing structure that develops from the ovary of a flowering plant, whereas vegetables are all other plant parts, such as roots, leaves and stems'. • Part of the plant that contains its seed • The mature ovaries of plants • Derived from flower(s), usually a fruit

fruit classification - rhubarb

is actually a vegetable

commercial jam prep

pectin acts as a preservative and reduces bacterial growth and enzymatic breakdown.

Composition of veg - pigment compounds

pigment compounds

Functions of Plant Parts - Blossoms, seeds, fruits

used as energy stores for plant reproduction

Storage of veg

• After harvesting still respire, contributing to deterioration • Variations in respiration affects rate of decline - Potatoes yield 8 ml CO2/hr @ 15C - Green beans yield 250 ml CO2/hr • Loss of moisture - Wilting, accelerated decomposition affects veges with highest water content (tomato/lettuce) • Overall, need to slow respiration & moisture loss

Flavenoids

• Anthocyanins - Red/purple/blue colours - Not common in vegetables (red cabbage, egg plant, radishes) - Affected by pH • Colour intensifies with acidity, weakens in alkaline • Anthoxanthins - Composite compounds - Give white/cream colours - Whitened in acidity and yellowed in alkaline - Can darken in intense heat and/or presence of iron/copper

vegetables define

• Any plant or part of a plant used as food • "the edible part of a plant (raw or cooked) accompanying the main course of a meal"

dry heat prep - veg

• Baking • Roasting • Stir Frying • Deep Frying

Preparation of Vegetables - colour

• Both fat & water soluble pigments are affected by pH, heating and the presence of metals • Adding baking soda to green vegies makes them appear greener, however damages B vitamins & texture • Other than pigment, other reactions occur affecting colour - Maillard reactions - Caramalisation of sugars - Enzymatic browning

Betalains

• Deep red/purples of beetroot • Best kept unpeeled when cooking to prevent bleeding • Acidity causes brighter red • Alkaline cause red shift to yellow

Carotenoids

• Found in plastids • Fat soluble • Can be affected by heat - overheating may cause loss of colour as well as loss of Vit A

Chlorophyll

• Found in plastids • Fat soluble • Essential to photosynthesis • Colour changes of leaves caused by variation in chlorophyll content • Volatile acids found in plants can destroy chlorophyll - Best to have lid off for first few minutes - Avoid heating in pan with lid on • Colour of green vegies enhanced by blanching - how/why? enzymes activity is stopped - increases shelf life. gases in the cell walls of the plants hide the chlorophyll. As you boil it, the acids evaporate off and uncovers the chlorophyll and then the ice water stops the chlorophyll from breaking down. • Cooking induced colour changes - Heat - Membranes separating acids & pigments are disrupted

Preparation of Vegetables - texture

• High temps gelatinise starch, decrease bulk (softens cellulose) & causes reduction in turgor (water loss) • Other than baking potatoes or cooking legumes, most vegies should be heated until barely cooked to maintain texture (and nutrients) • Adding acidic ingredients should be done towards end of cooking time - acidity makes vegies more resistant to softening, and they precipitate pectins which increases heating time • Alkaline ingredients cause cellulose to break down, producing a mushy texture

Preparation of Vegetables - nutrient retention

• Leaching is the most significant cause of mineral loss in vegetables - Use as little water as possible or steam/braise/microwave - Also minimised by cutting into fewer/larger pieces & cooking until just done • Note that some nutrients may actually increase as a result of cooking - Heating legumes destroys protease inhibitors, making more protein available - Heat softens fibre content

Plant Cell Structures - Parenchyma cells

• Most common cell type in vegetables - lots of functions (storage, support, photosynthesis, transfer cells) • Within their jelly like cytoplasm are the compounds responsible for the plants starch content, colour, water volume & flavour • Within these cells are 3 organelles called plastids • Plastids are the site of manufacture and storage of important chemical compounds. They often contain pigments used in photosynthesis, and the types of pigments in a plastid determine the cell's colour. - Leucoplasts - Hold starch & some water, the major digestible part of the plant - Chloroplasts - Contain green pigments (chlorophyll) - Chromoplasts - Contain the orange/yellow pigments of certain vegies (carotene & xanthophyll) • Also contain sacs called vacuoles that store water • Size of the cell largely determined by water content - Juiciness of fruits & veges is also determined by amount of fluid • Potatoes/bananas → tomatoes/watermelon • Optimal water content provides turgor & crunchiness to leafy veges • Vacuoles also contain red-blue pigments (anthocyanins) & many flavour compounds (salts, organic acids, saccharides) • Organic acids found in plants contribute to its pH, flavour & acidity - Most veges have pH 5 - 5.6 (tomatoes 4 - 4.6, corn/spuds 6.1 - 6.3)

Fruit composition - acidity

• Most have pH < 5 • pH ≈ 2.0 → very tart • pH > 4.5 → often served as veg squash 5.2 bananas, figs 4.6 tomatoes 4.2 blueberries 3.7 orange juice, peaches 3.5 apples 3.1 lemon juice 2.3 lime juice 2.2

Preparation of Vegetables - flavour

• Originates from volatile oils, organic acids, sulfur compounds, mineral salts, CHO's & polyphenolic compounds • Best retained when heated as quickly as possible & with minimal water • Exceptions - Onions: best with long/gentle heat yielding milder flavour - Garlic: cooking mellows/sweetens, best at low/med heats • Other vegetables require degorging - Egg plant - peeling eliminates the bitter taste substances below the skin

Plant Cell Structures - Intercellular spaces

• Plant cells do not fit tightly together - Spaces filled with air (adding volume & crispness) - Amount of space alters texture • Apples 20 - 25 % spaces • Peach 15 % space • Potatoes 1 % space

Moist heat prep - veg

• Simmering - Use minimal water & slightly salted - Vegies added to boiling water (not potatoes) - Potatoes in cold salted water • Steaming - Takes longer - Better retention properties - Wrapping in foil in oven effectively the same • Pressure Cooking - Not recommended • Braising • Microwaving

Preparation of Vegetables - odour

• Sulfur compounds present in cruciferous & allium vegies (onions, garlic, shallots, leeks, and chives) can give their pungent odour • What causes the odour from allium vegies to activate? oxygen activates the odours in the particular veggies. • Cabbage & onion odours can be reduced by shortening heating time and/or adding a little vinegar to cooking water and/or removing lid occasionally during cooking to let volatile organic acids to escape

Fruits masquerading as vegetables

• Tomatoes, squash (pumpkin, zucchini, eggplant), cucumbers, avocados • Olives, water chestnuts, peppers (capsicum)