Lecture 2 - Health and nutrition
FV are healthy because
- Low in calories [veggies]
- Low in fat [no saturated fats]
- Non digestible fibre [good for digestive health]
- Lots of water [up to 90% - cucumber]
- Minerals [Ca/K/Se/Mn/Fe/Zn]
- Some essential vitamins [Vit C/E/K]
The zero-sum relationship describes the trend that if you eat more FV, you are likely to eat less of something else, like candy
Antioxidants (AO)
- Examples are: Vitamins, polyphenols, carotenoids etc
- The production of free radicals is a part of a normal metabolism. AO neutralise these radical by forming a double bond
peroxyl radicals, hydrogen peroxide, Oz-, OH*
- Superfoods are known of the amount of AO [good marketing tool], however there is little evidence that these AO really
work in disease prevention
E-numbers
- Code for a food additive that is allowed in the EU [citric acid=E330]
- They are safe! [however, not always healthy. Candy contains lot of E-numbers, but is bad because of the sugar content]
- A lot of E-numbers in FV
Nutrient levels after harvest aka in shop
- Dark induced senescence (PCD) is the process during storage of FV in the dark, that the
chlorophyll, protein and CH generally decrease. Also other compounds can decrease
over the days
- Ex. Broccoli starts turning yellow and the VitC concentration starts to decline [let op:
when stored in darkness and not cold]
- The shelf life of products can be kept longer when the FV are stored cold and with light
how cold depends on the FV
- Boiled FV lose their vitamins the compounds leak into the water
Flavour life is often shorter than shelf life based on visual appearance [discoloration,
senescence, browning, lesions, firmness etc]. Maintaining flavour postharvest is a challenge
Taste + aroma = flavour
- Taste [by tongue] 10.000 taste buds, each about 100 taste cells
o Sweet sugars, esters etc
o Sour organic acids: citric acid etc
o Salt NaCl
o Bitter glucosinolates etc [sprouts]
o Unami
o Hot/peppery glucosinolates, capsisic acid
o Receptors
Hot/cold receptor
G-coupled receptors integrated in your brain taste perception
- The basic taste compounds interact + interact with aroma’s. the effect of changes in a single component is therefore
hard to predict. Well trained taste panels are very important for flavour profiling of new products
- Aroma’s provide unique characteristics and have very dynamic components (change rapidly during ripening, storage,
ageing etc) indicator of quality (ripeness, spoilage)
- Over time the volatiles change during storage (too cold), which can cause depletion or off-odour production smell
bad
- Aroma [nose]
o Esters, alcohols, aldehydes, ketons etc
, o Important volatiles methyl salicylate, guaiacol, eugenol, beta-ionone, geranyl acetone
o 100 million taste neurons which contain receptors for different volatile compounds
Tasty products
- Dependent on the combination of level of sugars and organic acids, low bitter compounds, sufficient aroma volatiles
and crispness
- During ripening the conversion from starch into sugars, the breakdown of acids and the production of aroma volatiles is
often synchronized
- Breeding for taste is not yet really possible. Flavour is changed during cultivation and postharvest. However, there are
tools to select the best tasty products
o Screen breeding [populations] taste panels or instrumental measurements for levels of certain compounds
[proton transfer reaction mass spectroscopy, ‘live’ measurements possible]
Lecture 3 – Postharvest quality
Mechanical damage [bruises, discoloration, stains] - deterioration
- Disruption of cell membranes
o Mixing enzymes and substrates
o Release of elicitors
o Browning
o Release of aromas
- Disruption of cuticle
o Increase in water loss [wound formation]
o Increase in weight loss [paid per kilo, so a problem]
o Shrivelling
o Pathological infection [pathogens can enter the wound]
- Tomatoes damaged (dropped) at the mature green stage and ripened at 20 degrees increase in respiration and
increase in ethylene production faster ripening
Physiology/biochemistry – deterioration
- Same consequences as mechanical damage, but it will also occur without (after time, banana)
- Senescence Developmental stage towards death
o Endogenously controlled processes leading to death [leaves on a tree turns yellow/red first, on the floor it
stays green]
o Genetically programmed cell death
o Initiation of gene expression and enzymes activities
o Nucleus stays intact up to an advanced state of senescence
o Ethylene also involved
- Aging
o Not programmed chronic degeneration, accumulation over time of sub-lethal damage
o Exhausting of carbohydrates as respiratory substrate respiration of proteins
o Respiration rate: index of potential storage life [more respiration is faster aging]
Potato lowest respiration rate and flower(petals) the highest
- Necrosis
o Passing boundaries of excessive stress [freezing, burning, chilling, anaerobic conditions, high CO2, ethylene]
Phyto pathological [diseases] - deterioration
- Pathological decay dependent on preharvest infection pressure, latent infection, natural resistance
- Conditions after harvest [spreads very quickly when put together]
- Pathogens often get access through damaged spots [combination with mechanical damage]
- Insects eggs in fruit will develop after a few weeks in a container
Interaction of mechanical damage + physiology/biochemistry + Phyto pathological deterioration leads to deterioration
Quality
- Science: fitness for consumption and use
- Business: whatever the customer wants each customer can have other quality specs
,Value [financial loss] – postharvest quality
- Direct product losses (investments, water, nutrients, land, personnel)
- Higher quality has higher value [selling bad quality (because too long on stock) has high costs (import/handing/storage)
and you get a low price]
Desirability [superior quality + shelf life] – postharvest quality
- Increased demands for high quality [attractiveness more important than taste sometimes]
- Higher quality reduces losses [longer shelf life]
- We also want more processed food which can be difficult for quality [mango chunks/precut fresh mango]
Waste – postharvest quality
- Vs. increasing world population [most FV]
- Low income countries [distribution phase]
o Focus on the chain improve postharvest infrastructure [holes in ways increase mechanical damage] +
educate to improve postharvest management
o Focus on consumer improve remaining shelf life and product quality [how to store food] + search for new
high value markets
- High income countries [consumer phase]
o Focus on consumer phase remaining shelf life, how old is the product? + consumer awareness [government
campaigns] + quality aspects should match needs and expectations
o Focus on the chain improve postharvest management [shorter chain] + improve communication within the
chain + education: chain monitoring systems
- Optimize postharvest chain
o Great effort is put in…
Optimizing growing/breeding (pest resistance/yield/quality]
Education (cultivation/agriculture/horticulture)
Advisory networks for growers
5% increase is major challenge
o A lot to gain in postharvest
Optimizing handling and distribution
5% less postharvest spoilage is relatively easy goal
5% more profit in postharvest is a relatively easy goal
Lecture 4 – Growing quality
Genotype selection:
- Good postharvest traits: slow deterioration, long shelf life, colour, uniformity, flavour/aroma
- Modern breeding technology mapping populations, sequence info, QTLs
- Quality measurements metabolites, phenomics, shelf life
All to select good varieties for good postharvest traits
Preharvest
- Time of harvest determines developmental stage, climacteric and initiation of ripening
- Season effect on tomato taste. At every time of the year, the levels of acid/sugars are different
- Tree factor - fruit on tree is stone hard, not ripening on the tree [ethylene blockers]. After harvest they ripe differs
per FV
- Environmental conditions T and light and cultivation operations soil type, irritation, nutrition, pruning/thinning and
spacing are important preharvest factors
- Manipulating growth conditions can lead to an increase nutritional content, flavour/taste, and affect colour [vertical
farming – LED, hydroponics etc]
- Stress more stress will give more vitamin C + sweetness [water gift, flower removal. Additional light]
- LEDs volatile aroma can be changed using different light conditions + at higher light conditions the quality is higher +
more sustainable growth + more control on growth conditions
- Next generation cultivation higher RH =reduced vase life
What is quality?
, - Everybody looks different to quality [different standards] Quality is assigned by the customer
- Based on product properties [each product has different quality values and agreements]
- Affected by
o Consumer/user preferences
o Economic circumstances
o Social circumstances
- Quality means acceptance
Models provide understanding of behaviour and interpretation of results in all circumstances [storage/distribution/retail,
prediction of behaviour and growing seasons/conditions]. Every researcher has models in his mind.
Kinetic modelling
- Modelling the processes occurring in nature [not applying some fancy mathematical function]
- Nature is lazy some processes/same kinetics + sticks to the laws of nature same processes in different fruits [but
other formulas]
- Use other functions of processes, do not reinvent the wheel
- That makes describing nature in models not very difficult, but very complex
- The only constant is change
- Example: first order kinetic model mathematical description of the combination of all underlying processes
[substrate transforms into product]
Example models
- Firmness model often looks like an exponential decay [softer]
- Colour mechanism
o Often sigmoidal behaviour (green to red or yellow)
o Autocatalytic conversion
o Differential equations
o Analytical solution
- Colour model rate constant (depends on T)
Keeping quality system
- Time a product remains acceptable for majority of consumers
- Example for exponential quality decay
- Q0 is the initial quality, and Ql the quality limit
o Shelf life – time when Q0 reaches Ql
Lecture 5 – Transpiration
Role of transpiration
- Plants/trees have a driving force for uptake of minerals + way to regulate the T of the leaves
- A full-grown oak may transpire up to 400 litre per day
- Stomata opening increases PS but also increases water loss balance is needed
- Cohesion and adhesion pull the water upwards
- Fruits differ from trees since there is no water uptake (because no roots/not attached to tree) continuously losing
water, but how much can be different
https://www.youtube.com/watch?v=mc9gUm1mMzc&feature=related
What determines transpiration
- Transpiration= loss of water through the gas phase [function of VP difference]
- Vapor pressure (VP) is the pressure exerted by a vapor in equilibrium with solids or liquids
- A substance with high VP at normal T is often referred to as volatile (alcohol has larger VP as water)
- High VP = high evaporation rate
- VP difference (VPD) between water in the gas
phase (plant) and water in the gas phase (air) [driving force of
diffusion] higher VPD is more water loss
- If VP in plant is higher than VP in surrounding air,
product will lose water through diffusion
FV are healthy because
- Low in calories [veggies]
- Low in fat [no saturated fats]
- Non digestible fibre [good for digestive health]
- Lots of water [up to 90% - cucumber]
- Minerals [Ca/K/Se/Mn/Fe/Zn]
- Some essential vitamins [Vit C/E/K]
The zero-sum relationship describes the trend that if you eat more FV, you are likely to eat less of something else, like candy
Antioxidants (AO)
- Examples are: Vitamins, polyphenols, carotenoids etc
- The production of free radicals is a part of a normal metabolism. AO neutralise these radical by forming a double bond
peroxyl radicals, hydrogen peroxide, Oz-, OH*
- Superfoods are known of the amount of AO [good marketing tool], however there is little evidence that these AO really
work in disease prevention
E-numbers
- Code for a food additive that is allowed in the EU [citric acid=E330]
- They are safe! [however, not always healthy. Candy contains lot of E-numbers, but is bad because of the sugar content]
- A lot of E-numbers in FV
Nutrient levels after harvest aka in shop
- Dark induced senescence (PCD) is the process during storage of FV in the dark, that the
chlorophyll, protein and CH generally decrease. Also other compounds can decrease
over the days
- Ex. Broccoli starts turning yellow and the VitC concentration starts to decline [let op:
when stored in darkness and not cold]
- The shelf life of products can be kept longer when the FV are stored cold and with light
how cold depends on the FV
- Boiled FV lose their vitamins the compounds leak into the water
Flavour life is often shorter than shelf life based on visual appearance [discoloration,
senescence, browning, lesions, firmness etc]. Maintaining flavour postharvest is a challenge
Taste + aroma = flavour
- Taste [by tongue] 10.000 taste buds, each about 100 taste cells
o Sweet sugars, esters etc
o Sour organic acids: citric acid etc
o Salt NaCl
o Bitter glucosinolates etc [sprouts]
o Unami
o Hot/peppery glucosinolates, capsisic acid
o Receptors
Hot/cold receptor
G-coupled receptors integrated in your brain taste perception
- The basic taste compounds interact + interact with aroma’s. the effect of changes in a single component is therefore
hard to predict. Well trained taste panels are very important for flavour profiling of new products
- Aroma’s provide unique characteristics and have very dynamic components (change rapidly during ripening, storage,
ageing etc) indicator of quality (ripeness, spoilage)
- Over time the volatiles change during storage (too cold), which can cause depletion or off-odour production smell
bad
- Aroma [nose]
o Esters, alcohols, aldehydes, ketons etc
, o Important volatiles methyl salicylate, guaiacol, eugenol, beta-ionone, geranyl acetone
o 100 million taste neurons which contain receptors for different volatile compounds
Tasty products
- Dependent on the combination of level of sugars and organic acids, low bitter compounds, sufficient aroma volatiles
and crispness
- During ripening the conversion from starch into sugars, the breakdown of acids and the production of aroma volatiles is
often synchronized
- Breeding for taste is not yet really possible. Flavour is changed during cultivation and postharvest. However, there are
tools to select the best tasty products
o Screen breeding [populations] taste panels or instrumental measurements for levels of certain compounds
[proton transfer reaction mass spectroscopy, ‘live’ measurements possible]
Lecture 3 – Postharvest quality
Mechanical damage [bruises, discoloration, stains] - deterioration
- Disruption of cell membranes
o Mixing enzymes and substrates
o Release of elicitors
o Browning
o Release of aromas
- Disruption of cuticle
o Increase in water loss [wound formation]
o Increase in weight loss [paid per kilo, so a problem]
o Shrivelling
o Pathological infection [pathogens can enter the wound]
- Tomatoes damaged (dropped) at the mature green stage and ripened at 20 degrees increase in respiration and
increase in ethylene production faster ripening
Physiology/biochemistry – deterioration
- Same consequences as mechanical damage, but it will also occur without (after time, banana)
- Senescence Developmental stage towards death
o Endogenously controlled processes leading to death [leaves on a tree turns yellow/red first, on the floor it
stays green]
o Genetically programmed cell death
o Initiation of gene expression and enzymes activities
o Nucleus stays intact up to an advanced state of senescence
o Ethylene also involved
- Aging
o Not programmed chronic degeneration, accumulation over time of sub-lethal damage
o Exhausting of carbohydrates as respiratory substrate respiration of proteins
o Respiration rate: index of potential storage life [more respiration is faster aging]
Potato lowest respiration rate and flower(petals) the highest
- Necrosis
o Passing boundaries of excessive stress [freezing, burning, chilling, anaerobic conditions, high CO2, ethylene]
Phyto pathological [diseases] - deterioration
- Pathological decay dependent on preharvest infection pressure, latent infection, natural resistance
- Conditions after harvest [spreads very quickly when put together]
- Pathogens often get access through damaged spots [combination with mechanical damage]
- Insects eggs in fruit will develop after a few weeks in a container
Interaction of mechanical damage + physiology/biochemistry + Phyto pathological deterioration leads to deterioration
Quality
- Science: fitness for consumption and use
- Business: whatever the customer wants each customer can have other quality specs
,Value [financial loss] – postharvest quality
- Direct product losses (investments, water, nutrients, land, personnel)
- Higher quality has higher value [selling bad quality (because too long on stock) has high costs (import/handing/storage)
and you get a low price]
Desirability [superior quality + shelf life] – postharvest quality
- Increased demands for high quality [attractiveness more important than taste sometimes]
- Higher quality reduces losses [longer shelf life]
- We also want more processed food which can be difficult for quality [mango chunks/precut fresh mango]
Waste – postharvest quality
- Vs. increasing world population [most FV]
- Low income countries [distribution phase]
o Focus on the chain improve postharvest infrastructure [holes in ways increase mechanical damage] +
educate to improve postharvest management
o Focus on consumer improve remaining shelf life and product quality [how to store food] + search for new
high value markets
- High income countries [consumer phase]
o Focus on consumer phase remaining shelf life, how old is the product? + consumer awareness [government
campaigns] + quality aspects should match needs and expectations
o Focus on the chain improve postharvest management [shorter chain] + improve communication within the
chain + education: chain monitoring systems
- Optimize postharvest chain
o Great effort is put in…
Optimizing growing/breeding (pest resistance/yield/quality]
Education (cultivation/agriculture/horticulture)
Advisory networks for growers
5% increase is major challenge
o A lot to gain in postharvest
Optimizing handling and distribution
5% less postharvest spoilage is relatively easy goal
5% more profit in postharvest is a relatively easy goal
Lecture 4 – Growing quality
Genotype selection:
- Good postharvest traits: slow deterioration, long shelf life, colour, uniformity, flavour/aroma
- Modern breeding technology mapping populations, sequence info, QTLs
- Quality measurements metabolites, phenomics, shelf life
All to select good varieties for good postharvest traits
Preharvest
- Time of harvest determines developmental stage, climacteric and initiation of ripening
- Season effect on tomato taste. At every time of the year, the levels of acid/sugars are different
- Tree factor - fruit on tree is stone hard, not ripening on the tree [ethylene blockers]. After harvest they ripe differs
per FV
- Environmental conditions T and light and cultivation operations soil type, irritation, nutrition, pruning/thinning and
spacing are important preharvest factors
- Manipulating growth conditions can lead to an increase nutritional content, flavour/taste, and affect colour [vertical
farming – LED, hydroponics etc]
- Stress more stress will give more vitamin C + sweetness [water gift, flower removal. Additional light]
- LEDs volatile aroma can be changed using different light conditions + at higher light conditions the quality is higher +
more sustainable growth + more control on growth conditions
- Next generation cultivation higher RH =reduced vase life
What is quality?
, - Everybody looks different to quality [different standards] Quality is assigned by the customer
- Based on product properties [each product has different quality values and agreements]
- Affected by
o Consumer/user preferences
o Economic circumstances
o Social circumstances
- Quality means acceptance
Models provide understanding of behaviour and interpretation of results in all circumstances [storage/distribution/retail,
prediction of behaviour and growing seasons/conditions]. Every researcher has models in his mind.
Kinetic modelling
- Modelling the processes occurring in nature [not applying some fancy mathematical function]
- Nature is lazy some processes/same kinetics + sticks to the laws of nature same processes in different fruits [but
other formulas]
- Use other functions of processes, do not reinvent the wheel
- That makes describing nature in models not very difficult, but very complex
- The only constant is change
- Example: first order kinetic model mathematical description of the combination of all underlying processes
[substrate transforms into product]
Example models
- Firmness model often looks like an exponential decay [softer]
- Colour mechanism
o Often sigmoidal behaviour (green to red or yellow)
o Autocatalytic conversion
o Differential equations
o Analytical solution
- Colour model rate constant (depends on T)
Keeping quality system
- Time a product remains acceptable for majority of consumers
- Example for exponential quality decay
- Q0 is the initial quality, and Ql the quality limit
o Shelf life – time when Q0 reaches Ql
Lecture 5 – Transpiration
Role of transpiration
- Plants/trees have a driving force for uptake of minerals + way to regulate the T of the leaves
- A full-grown oak may transpire up to 400 litre per day
- Stomata opening increases PS but also increases water loss balance is needed
- Cohesion and adhesion pull the water upwards
- Fruits differ from trees since there is no water uptake (because no roots/not attached to tree) continuously losing
water, but how much can be different
https://www.youtube.com/watch?v=mc9gUm1mMzc&feature=related
What determines transpiration
- Transpiration= loss of water through the gas phase [function of VP difference]
- Vapor pressure (VP) is the pressure exerted by a vapor in equilibrium with solids or liquids
- A substance with high VP at normal T is often referred to as volatile (alcohol has larger VP as water)
- High VP = high evaporation rate
- VP difference (VPD) between water in the gas
phase (plant) and water in the gas phase (air) [driving force of
diffusion] higher VPD is more water loss
- If VP in plant is higher than VP in surrounding air,
product will lose water through diffusion
