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
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
Metabolism
Collective term for all the chemical reactions that are continually occurring inside living cells to sustain life
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)
Catabolism
degradative (destructive) reactions e.g. respiration - conversion of starch →sugars →CO2
- Release energy as kinetic energy
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.
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
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
Refractometer measures amount of sugar
- Squeeze a drop
- Peek at the screen
- Check the chart
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
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
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.
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
Regulating O2 and CO2
- Controlled atmosphere (CA) storage
- Modified atmosphere storage include modified atmosphere packaging (MAP) - Can be artificial or natural
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
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)
- (red/purple/blue)
