week 6 Flashcards by Bianca Perillo

Factors affecting quality of F&V

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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Horticultural produce

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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Metabolism

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

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Anabolism

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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Catabolism

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

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Products of photosynthesis

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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Polysaccharides: starch

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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Products of photosynthesis

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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Refractometer measures amount of sugar

Squeeze a drop
Peek at the screen
Check the chart

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Substrate for respiration

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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Respiration rate and age of tissue

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

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Respiration rate and temperature

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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Respiration and gas atmosphere

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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Regulating O2 and CO2

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

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Respiration rate and ripening

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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Ripening process

Changes in carbohydrate composition, resulting in sugar accumulation and increased sweetness
Change in colour
Flesh softening and textural change
Formation of aroma volatiles
Accumulation of organic acids with associated development of flavour

Preharvest factors affecting quality

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

Internal dryness in imperial mandarins

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

Post harvest temperature management

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

Management of ripening

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

Ethyl management and quality

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

Ethylene inhibitors

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

manipulating apple maturity

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

Factors affecting visual quality - colour

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)

Colour change during ripening

- 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

Degreening of citrus

- 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.

Enzymatic browning

- 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

Bruising

- 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

Factors affecting textural quality

- 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

Post harvest changes in cell wall

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

Loss of water and texture

- 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

What determines flavour:

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

Factors affecting flavour

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