Handling and storage quality Flashcards
factors affecting quality changes during handling and storage (8)
temperature
gaseous atmosphere
plant hormones
physical damage
moisture
micro-organism
light
biochemical reactions
relationship between temp and respiration
as one increases so does the other
what is Q10
the ratio of the rate of reaction at the given temperature/ rate of reaction at -10C
Q10 of most f and v at temps > 10C
2-3
what can lowering the temperature do to f and v (3)
-reduce the rate of undesirable physiological changes
-reduce microbial activity
-reduce water loss
physiological disorders associated with temperature extremes (3)
high heat injury
chilling injury
freezing injury
result of high heat injury
inactivated enzymes
abnormal metabolism
-breakdown of membrane structure and integrity
-disruption of cellular organisation and rapid deterioration
-loss of pigments
what component of the membrane structure causes the breakdown
pectin is attacked by polygalacturonase
result of chilling injury (3)
loss of fluidity in membrane
imbalance of metabolic reactions
undesirable quality changes
what does the extent of a chilling injury depend on
duration of exposure
extreme of temperature
can fruit with chilling injury be eaten?
YES, but has changes in its sensory properties
example of chilling injury in capsicum
pitting
what is the affect a chilling injury has on ripening
it can no longer ripen
some general symptoms of chilling injury (4)
surface lesions
internal browning
accelerated internal senescence
loss of growth capacity
what does the freezing temperature of F and V depend on
conc of solutes
effect of freezing
initiates desiccation and osmotic stress
solvent water loss due to ice crystal formation
physical disruption from ice crystals
Controlling which factor will result in the biggest difference for maintaining quality
temperature
4 types of cooling methods
cold air (room cooling, forced air/pressure)
cold water
ice
evaporation of water
most common type of cooling
room cooling
what does room cooling involve
Produce that has been packed into boxes being exposed to cool air in a store room
advantage of room cooling
cool and store in the same place (simple)
Disasvantage to room cooling
low efficiency
large space required
disadvantage ot room cooling
low efficiency
requires large storage area
describe pressure cooling
cold air forced through packages
the advantage to pressure cooling
faster
describe hydro cooling
water is used as a heat transfer medium
advantages to hydro cooling
increased surface exposure increases efficiency
allows for cleaning from the environment
purpose of icing
pre-cooling or transport
describe vacuum cooling
reduced pressure decrease water BP so it evaporates
advantage to vacuum coolig
rapid
describe evaporative cooling
dry air is blown across wet surface
disadvantage to evaporative cooling
requires low RH and quality water
advantage to evaporative cooling
low energy cost
how can changing the gaseous atmosphere slow respiration
reducing O2
low levels of CO2
normal composition of air
21% O2
78% nitrogen
0.034% CO2
what % is O2 generally reduced to
<10%
what is important to consider when changing the air composition
critical levels for different fruits
what does a yellow door mean
gas composition is being controlled
types of technology used to control atmosphere
CA-contorlled atmosphere
MA-modified atmosphere
what is CA
proportion of gases is carefully controlled throughout storage
what is MA
packaging of f and v is changed then allowed to respire normally
what is MA good for
short term storage
methods to minimize ethylene concentration
hypobaric chamber
ventilation
when should climateric products be harvested
maximum cell enlargement and enough starch to convert to sugar during maturation
when should non-climacteric products be harvested
when mature
what kinds of treatments can be used for eythlene
ethylene-action inhibitors:
2, 5 nobornadiene
1-methyl cyclopropane (1-MCP)
what will physical damage/stress cause
localised bursts in respiration
ethylene formation
accumulation of secondary metabolites
what does wounding lead to
undesirable colour and flavour changes
what causes the wounding changes
release of enzymes and substrates from damaged cells
more susceptible to microbial invasion
draw wound flow diagram on paper
wound ->
respiration
-heat
-ripening->softening
-reduced CHO, organic acids and ascorbic acid-> poor flavour
ethylene-> ripening-> softening
phenolic metabolism
-PPO + O2 + phenolic compounds-> browning
-PAL-> phenolic compounds->browning or lignin -> toughening
wound healing
-suberin
-peridium -> cell division
Classes of metabolites formed form physical stress/damage
protective
stress
lipid
what do protective metabolites do
form a waxy or lignified layer to prevent microbial invasion
examples of stress metabolites
isoflavonoids, diterpenes, polyacetylenes, glycoalkaloids
effect of stress metabolites
antibiotic
reduced quality
can be toxic
precursor to enzymatic browning
how do lipid metabolites form
stress causes PUFA breakdown and autolysis of cell membranes
which enzymes are involved in lipid metabolism
lipoxygenase, peroxidase, lipase, phopholipase
what doe enzymatic reactions caue
off flavours
-even in frozen of dehydrated produce
how are hydroperoxides involved in lipid metabolism
formed by lipogenases
what do hydroperoxides do
cause bleaching of carotenoids and chlorphyll
react with other consituents
technologies to prevent physical injury
hand harvesting
corrugated fiberboard packing
separated layers/padding
what does low humidity cause in f and v
water loss
how is water lost
transpiration
evaporation
adverse affects of waterloss
wilting
decreased crispness + saleable weight
factors that affect water loss
surface volume affect
surface coatign
mechanical damage to tissue
what can high humidity cause
excess water
-microbial growth
-fogging of packaging
technologies to control moisture
coatings(waxes)
use water vapour to increase RH
water scrubbers in packaging
maintain temp gradient in storage
what does microbial invasion cause in f and v
stress reposnse
what kind of barriers to plants have as microbial invasion barriers
physcial and chemcial
what can happen to plants barriers during processing
comprimised
describe two natural chemical and physical barriers plant use to protect against microorganisms
skin/fuss
phenolic and benzoic acids
what are phytoalexins toxic to
microbes
how to reduce exposure to micro attack
minimise processing
washing
chilling
-fungicide treatments (not in NZ)
adverse effects of light on the quality
formation of glycoalkaloids
photo-oxidation of chlorophyll
what does the formation of glycoalkaloids do to potatoes
makes them go green
what does the photo-oxidation of chlorophyll cause in broccoli and spinach
yellowing
positive effect of light on f and v
ripening
-i.e tomatoes
what does the photo-oxidation of chlorophyll cause in broccoli and spinach
yellowing
technologies to protect from light exposure
dark storage (light excluded packaging)
irradiation
positive effects of irradiation
inhibition of sprouting
destruction of pests + insects in grains
ripening delay
negative effects of irradiation
irradiation injury
-blemishes, accelerated yellowing
interferes with wound healing
biochemical processes that affect the quality
cell wall changes
starch-sugar transformation
pigment metabolism
aroma compounds
what changes occur in the cell wall during processing
softening
-loss of turgor
-depolymerisation, demethylation, and loss of calcium in cell wall polysaccharides
hardening
-lignin formation
describe some starch-sugar transformation
synthesis of starch
starch degradation to simple sugars
Why do potatoes stored below 5C for too long go brown during frying
they have been allowed to ripen for too long and the starch has been converted to simple sugars which causes the Maillard reaction to occur during frying
what happens during pigment metabolism
anthocyanins are lost due to polyphenol oxidase and peroxidase enzymes
what happens to aroma compounds during process/storage
biosynthesis and degradation of volatiles
technologies to protect from biochemical reactions during processing
plant hormones
coatings
how do plant hormones protect from biochemical reactions
delay senescence
improve quality + shelf life
how do coatings protect from biochemical reactions
control water loss
slow respiration and ripening
reduce surface injury
