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FOOD2000 > week 6 > Flashcards

week 6 Flashcards

1
Q

Factors affecting quality of F&V

A
  • Preharvest – genetic, agronomic, environmental - Harvest – maturity, physical damage
  • Immediate postharvest – temperature, handling - Postharvest storage – temperature, atmosphere - Transportation – packaging, temperature
  • Human – skilled personnel, extension
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2
Q

Horticultural produce

A
  • Fruits (there for dispersing the seed) and vegetables
  • Once we harvested plant food they are still metabolically active
    Long term viability depends on global competitiveness and cultivation of export markets
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3
Q

Metabolism

A

Collective term for all the chemical reactions that are continually occurring inside living cells to sustain life

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4
Q

Anabolism

A

synthetic (constructive) metabolic reactions e.g. protein synthesis, photosynthesis and cell wall formation
- Require energy input from reduced nucleotides such as ATP and NADPH
- Energy is used and stored as potential energy (macromolecules)

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5
Q

Catabolism

A

degradative (destructive) reactions e.g. respiration - conversion of starch →sugars →CO2
- Release energy as kinetic energy

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6
Q

Products of photosynthesis

A

Polysaccharides: cellulose, pectin and hemicellulose
Cellulose - B1-4, linked D glucose units
- Pectin & hemicellulose have a key role in texture & viscosity
- Form a network that cements the cellulose microfibrils in the cell wall - Pectin breaks down during ripening & softening process
- Hydrolytic cleavage of a long chain increases solubility, making bonds between adjacent cell walls looser.

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7
Q

Polysaccharides: starch

A

Many plant parts are high of it, water insoluble - allows high cellular conc without influencing osmotic potential (good storage in plants)
- Stored in large quantities in roots, stems, bulbs, seeds, smaller qualities in leaves
- Amylose: a-1,4-linkage
- Amylopectin: a-1,4 linkage and 1-6 linkage

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8
Q

Products of photosynthesis

A

Sucrose = Glucose + Fructose Disaccharide
- Water soluble – major portion of soluble solids in many fruit
- % total soluble solids (TSS) is often measured as a way to test maturity e.g. citrus,
grapes, melons
- (TSS = sugar + organic acids + salts)
Sucrose is main transport sugar around plant (in most cases) – drawn to actively growing regions eg. fruit, flower, growing point
- Sugar is the major contributor to flavor in fruit & veg combined with organic acids and volatiles: Flavour = balance of sugars, acids & volatiles

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9
Q

Refractometer measures amount of sugar

A
  1. Squeeze a drop
  2. Peek at the screen
  3. Check the chart
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10
Q

Substrate for respiration

A
  • Respiration involved degradation of sugars to release energy
  • Starch, protein and lipids can all be degraded to release CO2, H20, ATP
  • STARCH is main
  • In presence of O2, pyruvate enters krebs cycle
  • In abscess of O2 ethanol or lactic acid is produce → off-flavors
    Problem is bulky storage organs e.g. alcoholic melons
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11
Q

Respiration rate and age of tissue

A
  • Young tissues are actively growing and require high inputs of energy - Developing organs have a higher rate than mature ones
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12
Q

Respiration rate and temperature

A
  • It increases just above freezing and ceases at thermal death point
  • Within certain temperature limits (usually 0-20C), respiration rate approximately
    doubles for every 10 C rise in temperature
  • Cold chain is one of the simplest and most effective ways to maximize shelf-life of
    perishable produce.
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13
Q

Respiration and gas atmosphere

A

O2 and CO2
- Low O2 retards respiration rate
- But too low O2 leads to anaerobic respiration & off-flavors - High CO2 retards respiration
- High CO2 also controls pathogen growth

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14
Q

Regulating O2 and CO2

A
  • Controlled atmosphere (CA) storage
  • Modified atmosphere storage include modified atmosphere packaging (MAP) - Can be artificial or natural
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15
Q

Respiration rate and ripening

A
  • Ethylene is a hormone synthesised by all cells during normal cell development
    It is also produced during fruit ripening, causing a characteristic rise in respiration rate known as climacteric
  • Fruit are classifies as climacteric or non-climacteric according to their response to ethylene
  • Non climacteric can only be harvested when they are ripe while climacteric doesn’t
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16
Q

Ripening process

A
  1. Changes in carbohydrate composition, resulting in sugar accumulation and increased sweetness
  2. Change in colour
  3. Flesh softening and textural change
  4. Formation of aroma volatiles
  5. Accumulation of organic acids with associated development of flavour
17
Q

Preharvest factors affecting quality

A

Preharvest factors affecting quality
- Genetics
- Climate
- Crop nutrition
- Agronomy
- Pollination
- Pest and disease

18
Q

Internal dryness in imperial mandarins

A
  • Non detectable by external inspection
  • Caused by granulation - related to water potential in cells - Juice sacs hardened, gelled, or granular and opaque
    white-decreased carotenoids
  • Build of of structural carbohydrates e.g. pectin - uses
    sugars and acids
  • Thickened walls-restricts water movement out of cells
    (increased turgor)
  • Lower extractable juice but total moisture content same or
    higher
  • Soluble solids lower-tasteless fruit
19
Q

Post harvest temperature management

A
  • The first step is removal of field heat immediately after harvest
  • Main methods are hydro-cooling, vacuum cooling and forces air cooling
20
Q

Management of ripening

A
  • Ethylene is suppressed by: - Low temperature
  • CA storage (high CO2 and low O2)
  • Hypobaric storage (reduced pressure)
  • however, once started it can’t be stopped only slowed
  • Ethylene is deliberately administered to induce ripening:
    • -
      Tomatoes & avocados (10 mL/L), mango & banana (1 mL/L)
      Bananas - C2H4 and manipulate temp (from 12 – 13oC to 17 – 18oC); Avos put on shelf with 2 – 3 days to go
  • Enables fruit to be harvested while green-mature, thus avoiding damage during transport and handling
21
Q

Ethyl management and quality

A
  • Ethylene may be controlled in non-climacteric as well as climacteric fruit as it increases respiration rate and reduces shelf life
  • Ethylene can have a detrimental effect on produce shelf-life and quality even at concentrations as low as 0.5 ppm incl. bitterness in carrots & parsnips
22
Q

Ethylene inhibitors

A
  1. 1-MCP is a gas that blocks ethylene receptors
  2. SmartFresh only on apple and pears
  3. AVG inhibits ACC synthase activity and is applied preharvest to delay ripening and
    fruit drop
  4. ReTain only on stone fruit and apples
23
Q

manipulating apple maturity

A

starch converted to sugars at apple maturity - measured using iodine staining pattern

earliest time apples can be harvest (within a week after first signs of starch conversion) - retain should be applied 21-28 days prior to delay maturity and allow further growth

24
Q

Factors affecting visual quality - colour

A

Colour results form composition of pigmented phytochemicals especially: - Chlorophyll (green)
- Carotenoids (chromoplasts)
- 1. Hydrocarbon carotenes (red/orange)
- Oxygen-containing Xanthophylls (yellow)
- Phenolics (water soluble in cytoplasm and vacuole)

    1. (red/purple/blue)
25
Q

Colour change during ripening

A
  • Banana yellowing is due to loss of chlorophyll, not increase in carotenoids
  • Tomato reddening is due to increase in carotenoids and degradation of chlorophylls - In most F&V, degradation of chlorophyll and biosynthesis of carotenoids &
    anthocyanins occurs simultaneously
  • Dulling may be due to degradation or isomerisation of carotenoids: naturally occurs
    most commonly in trans form, but can be isomerised due to heat, light, processing
26
Q

Degreening of citrus

A
  • Citrus needs minimum temperatures below 15C for chlorophyll in skin to break down - Mature green fruit can be de-greened with ethylene treatment
  • Set of guidelines to do this include: fungicide treatments, good air ventilation, control
    of temperature and humidity to reduce postharvest disease.
27
Q

Enzymatic browning

A
  • Cut-edge browning is caused by release of phenolic oxidising enzymes form breakdown of cell membranes or mechanically damaged tissues
  • Associated with physical injuries and chilling injury
  • Can use citric and ascorbic acid, lemon or pineapple juice - oxidised instead
    of polyphenol and acidic pH reduces enzyme activity
28
Q

Bruising

A
  • Physical damage due to mishandling is a major cause of postharvest loss - Mechanical damage increases respiration rate - wound response
  • Vibration damage - prolonged vibration associated with transport
  • Excessive pressure on fruit or pressure from other fruit
29
Q

Factors affecting textural quality

A
  • Textural change is often associated with softening
  • F&V that soften greatly as they ripen… e.g. apricot, strawberry… have a soft,
    melting texture
  • F&V that soften moderately as they ripen… e.g. apple, capsicum,
    watermelon… have a more crisp, fracturable texture
  • Texture not directly correlated with climacteric or non-climacteric grouping
  • Firmness and texture are most closely associated with cell wall structure and composition
  • Postharvest change in texture is mostly explained by cell wall changes during ripening
30
Q

Post harvest changes in cell wall

A

Primary cell walls have rigid cellulose microfibrils held together by networks of hemicelluloses & pectins, with smaller aunts of structural proteins and phenolics
- During ripening, cell wall structure and strength are modified by enzymes, depolymerisation of matrix hemicelluloses and pectins. This all weaken the cell wall

31
Q

Loss of water and texture

A
  • Desiccation causes textural change
  • During storage water moves to the atmosphere - Results in:
  • Shrivelling, softening, loss of appearance
  • The greater the surface area to volume ratio of the produce the faster the rate of
    water loss
  • Wate ross varies with skin properties
32
Q

What determines flavour:

A

What determines flavour:
1. sugar/acid balance
2. Production of aroma volatile compounds (mixture of volatile acids, aldehydes,
alcohols, esters, terpenoids and aromatics)
GC-MS ripe fruit may contains more volatile compounds that contribute to their flavour
- Often not related to concentration
- Sometimes compounds found at very low levels

33
Q

Factors affecting flavour

A

Genetics, environment, production, post harvest conditions
- Harvest at optimal maturity is critical to achieve maximum flavour quality for the right
time
- Synthesis of aroma volatile increases dramatically during ripening
- Enzymes involved in generation of fruit aroma volatiles
- Manipulation of enzymes for ripening can affect flavour development
- 1-MCP treatment of climacteric fruit can suppress synthesis of aroma volatiles - At RT malate decreases and citrate increases while quinate reminds the
same. However during cool storage malate increase
- The longer the time between harvest and eating, the greater the loss is aroma and
risk of off-colour development
- Decreased flavour is caused by loss of sugars, acids and volatiles
- Off-odours caused by fermentative metabolism and associated with exposure
to environmental contaminants during post-harvest

FOOD2000 (13 decks)

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