lec 8 plant tissue based foods

Question 1

what are Types of plant structures?

Answer 1

• Fruits
• Seeds and pods
• Bulbs, roots and tubers
• Flowers, buds, stems and leaves

Question 2

what is the difference between Above ground structures and Below ground (e.g. Roots and tubers)?

Answer 2

Above ground structures develop wax coatings, Below ground has no coating

Question 3

what is the plant cell wall made of and what purpose does it have?

Answer 3

Rigid cell wall
Solid-like structure of cellulose, pectic substances, other polysaccharides, lignin and proteins.
Supports the cell membrane (plasmalemma) against the hydrostatic pressure of cell components
Gives structural support to the plant tissue.
The cell wall is permeable to water and solutes.

Question 4

what is the composition of the primary cell wall for cereals and vegetables?

Answer 4

cellulose, pectin, arabinoxyloan, mixed linkage glucan, xyloglucan, extensin

Question 5

Cytoplasm

Answer 5

Continuous medium Kept together by a “skeleton” of microfilaments (actin polymers, approx. 6 nm). The elastic properties of the cells are related to the microfilament network

Question 6

Organells

Answer 6

Surrounded by lipid membranes
Kept in place by the microfilaments

Question 7

Vacuoles

Answer 7

Fluid reservoirs with a semi-permeable membrane (tonoplast) containing
solutes (sugars, salts, amino and organic acids)

Question 8

what does the tonoplast do?

Answer 8

maintains the osmotic pressure of the cell

Question 9

Turgidity

Answer 9

presses the plasmalemma against the cell wall
The turgor pressure is responsible for the stiffness and crispness in fruits and vegetables

Question 10

what are Other components in the plant cell?

Answer 10

Chloroplasts – chlorophyll
Chromoplasts – carotenoids (yellow-red)
Amyloplasts – starch granules
(Lipid droplets – fat storage)

Question 11

how is The mushroom cell wall very different from the plant cell wall?

Answer 11

Non-structural carbohydrates in mushrooms are different from those of plants
The 3 dominating: mannitol, trehalose, glycogen-similar polysaccharide
Mushrooms are primarily consumed for flavour –>1-octene-3-ol (“mushroom alcohol”)

Question 12

what is the Chemical composition of fruit & veg

Answer 12

-Water: most Common > 80 wt %
Some > 95 wt % (cucumbers, melons, lettuce etc.)
Starchy tubers and seeds usually > 50 wt%

-Carbohydrates (Energy and structure)
Typically 2-40 wt %
High in starch rich produce
Low in for instance cucumbers

-Protein (Majority is enzymes and storage proteins) Typically 1-2 wt %, In Brassica vegetables and legumes typically 3-5 wt %
Majority is enzymes or storage proteins

-Lipids, Typically < 1 wt%
Exceptions: avocado (20 wt%) and olives (15 wt%)

-Organic acids, Content varies. High in lemon, lime, passion fruit and black currant (> 3 wt%)
Important for the taste in balance with sugars

-Vitamins & Minerals; Vitamin C, Vitamin A precursors, Folic acid. Major mineral is K (highest in green, leafy vegetables)

-Other compounds
Polyphenols and anthocyanins
Volatiles –> esters, alcohols, acids, aldehydes and ketones

Question 13

how does the Respiration of plants continue after harvest?

Answer 13

Uptake of O2
Release of CO2 and heat

Question 14

what is Transpiration

Answer 14

Loss of water – no longer attached to the plant
Varies depending on the produce
Examples: Fruits with waxy layers, onions, cucumber
Optimal relative humidity (RH) during storage
Too high–> risk of patogens

Question 15

what happens during Ripening of fruits?

Answer 15

All fruits generate ethylene during
developmet. High in climacteric fruits
Low in non-climacteric fruits. Ethylene can be added to hasten ripening.
0.1 µL/L atmosphere for 1 day -> sufficient for full ripening of climateric fruits.

Question 16

what are climacteric and nonclimacteric fruits

Answer 16

Climacteric fruits are those that continue to ripen after they have been harvested.
Non-climacteric fruits do not continue to ripen significantly after they have been harvested.

Question 17

Examples of climacteric fruits

Answer 17

bananas, apples, tomatoes, avocados, peaches, and pears.

Question 18

Examples of non-climacteric fruits

Answer 18

strawberries, citrus fruits (such as oranges, lemons, and limes), grapes, cherries, pineapples, and watermelons.

Question 19

what are the Changes during fruit ripening

Answer 19

-Colour, Most common change is loss of green colour–> degradation of chlorophyll. Ripe colour can be given by anthocyanins

-Aroma development, Increased synthesis of volatiles

-Structural changes,
Degradation of the pectin in the middle lamellae
Enzymatic degradation of cell wall polysaccharides
Weakens the cell wall
Rate of pectin degradation directly correlated to rate of softening

Question 20

how does the storage life vary with the respiration rate?

Answer 20

inversely, low respiration rate gives long storage life, high respiration gives low storage life.

Question 21

what are the Most important factors influencing respiration?

Answer 21

-Temperature
* Profound effect on rate of respiration and metabolism
* van ‘t Hoff rule: The rate of a biological reaction increases 2-3 fold for every 10°C
Chilling stress= Too low temperature may induces damages to tissue – related to
crystallization of membrane lipids
* Certain fruits of tropical or subtropical origin can display increased respiration at low temperatures (< approx. 10°C)

-Atmospheric composition
Adequate level of O2 is important to maintain but reduce respiration, Typically 2-3 % O2.
CO2 can reduce respiration and delay senescence in some fruits

-Physical stress
Signals from physical stress migrates from injury to non-wounded tissue
Induces a wide range of physiological changes

Question 22

what happens with Enzymatic activity during storage?

Answer 22

Post-harvest: gradual degradation of membrane lipids–>off-flavours
Also occurs in produce with low lipid content
Example: strawberries
Some forms of lipid oxidation gives desired aroma
Example: oxidation of linolenic acid to cis-3-nonenal and hexanal in cucumbers
For long storage: inactivation of enzymes is often necessary
Lipases, lipoxygenases, peroxidases etc.
Blanching in hot water or with steam
Also necessary for frozen storage
Example: Non-blanched frozen peas develop off-flavours within
three weeks

Question 23

what is the Eating texture of fruit and vegetable tissue determined by?

Answer 23

primarily by the
manner in which the cell-wall skeleton deforms and ruptures

The disruption and release of cell contents upon cell disruption results in juciness.
Forces holding cells together are stronger than the cell wall–>cell wall breaks.
If the opposite, cells will separate. In uncooked vegetables and unripe fruit cell adhesion is strong. A high level of turgor gives crispness.

Question 24

what does heat treatment cause?

Answer 24

Heating causes membrane disruption and loss in turgor –> softening
Cooking and ripening decreases cell adhesion
–> softening
In highly softened tissue, cells become completely separated
Example: over-ripe apple, boiled potatoe
Cell separation occurs mainly in non-lignified tissue
Tissues that fail to soften typically consist of cells that have secondary walls and lignification.

Question 25

what is the Hard-to-cook phenomenon?

Answer 25

Do not imbibe sufficient amounts of water
In soft beans the middle lamellae is largely dissolved (cell separation) while remaining in hard beans.

Question 26

what similarities and differences do Fruit juices and vegetable purees have?

Answer 26

-have similar chemical composition to their
sources
-have Very different physical properties, rheological behaviour and sensory properties

Structure influences bioavailability of nutrients
Cell disruption –> nutrient release
Examples : carotenoids from carrots
lycopene from tomatoes (paste -> 20-380% increase in uptake)
Cell disruption influences formation of flavours, off-flavours and browning
Example: onions – flavour precursors are converted into flavours