FND 100: Fruits and Vegetables Part 2 Flashcards
What are good sources of ascorbic acid?
Citrus fruits, melons, and strawberries
Potatoes
Vegetables
Solubility of ascorbic acid
Water soluble and highly susceptible to oxidation
Loss of ascorbic acid with processing
Losses with cooking and processing and is susceptible with oxidation
L-ascorbic acid vs. L-dehydroascorbic acid
L-ascorbic acid is functionally antioxidant when it is oxidized it is known as L-dehydroascorbic acid
Function of L-dehydroascorbic acid
Need to reduce molecule back to OG because it no longer has aspect of vitamin C
What is all purpose flour fortified with?
B vitamins are removed in the process of producing all purpose/ cake flour
Why is flour fortified with B vitamins?
Done for nutrition and also due to folic acid for the prevention of neural tube defects
What contributes the most ascorbic acid?
Fruits
What do potatoes and sweet potatoes contribute?
Ascorbic acid
What do vegetables contribute ?
Vitamin A and ascorbic acid
What do dry beans and pears contribute?
Niacin and thiamine
What does flour contribute?
Thiamine and niacin
How does vitamin A occur?
In its precursor form such as beta carotene in ‘orange-coloured’ crops as well as dark green leafy vegetables
Is vitamin A water soluble or lipid soluble
Lipid soluble
Where is chlorophyll found?
In chloroplast (which also contain lipid) since chlorophyll is lipid soluble
Carotenoids and chlorophyll
Carotenoids are masked in dark leafy greens due to a larger quantity of chlorophyll in chloroplasts
Why does the high level of provitamin A activity in beta carotene make sense?
Because cleaving bonds right down the center will give two molecules of vitamin A for every molecule of beta carotene.
How many beta carotenes do you need to get 1 vitamin A
Need 6 beta carotene to get 1 vitamin A so not perfectly efficient coversion
Why do you need so many beta carotenes for 1 vitamin A
Your body is not perfect so in order to get 1 molecules l of vitamin A from your food you need 6 molecules of beta carotene
What has the highest provitamin A activity?
Beta carotene
What has the lowest provitamin A activity?
Lycopene (tomato) has basically zero provitamin A activity
Where are B-complex vitamins present?
Present in moderate amount in fruits and vegetables fortified at higher levels in flour
What do carotenoids include?
Beta carotene
Lycopene
Astaxanthin
Beta carotene colour
Orange, yellow colour
Lycopene colour
Red
Asthaxanthin colour
Red
What influences the pigment of our fruits and veggies?
Boiling carrots, sweet potatoes, or squash which can influence and decrease the intensity of the colour
What is the intensity of colour related to?
The bond geometry of the molecule
How is intensity of colour affected?
Conversion of bond geometry
Impact of acids
Acid coverts from trans to cis
What is a conjugated system?
Each double bond is connected to the next group. Different to db structure of fatty acids.
Example of nonconjugated systems
Unsaturated fatty acids like linolenic or linoleic are in non-conjugated systems. There is a carbon in between neighbouring double bonds
Fatty acids vs carotenoid structure
Fatty acids has carbon in between. No carbon in between carotenoids
Why are fruits and vegetables susceptible to oxidation?
Due to conjugated double bond system
Why are carotenoids susceptible to oxidation?
Because of the conjugated double bond structure
What happens if beta carotene colour decreaes?
It means it was used as an antioxidant
Why can beta carotene act as an antioxidant?
Because of the double structure and more specifically the antioxidant ability is due to the capacity of them to act as singlet oxygen clenchers
What is singlet oxygen?
Reactive form of oxygen that may damage DNA or cells
Solubility of chlorophylls
Fat soluble
What are the two forms of chlorophyll
Chlorophyll a and b
Colour of chlorophyll a
Blue-green
Colour of chlorophyll b
Green
What happens to chlorophyll with extensive heating and presence of acid?
With extensive heating and presence of acid the pigments can be altered to pheophytin
Pheophytin colour
Dull, olive green instead of the typically bring green of the fresh veggies
What do typical heme structures do?
Bing magnesium in its structure
What is the phytyl tail of chlorophyll structure
Is a hydrocarbon which makes it lipid soluble
What happens to the structure of chlorophyll when it is exposed to an acid?
The molecule of magnesium is removed and replaced with two hydrogen atoms from the acidic environment and then pigment changes to olive green
Why does the pigment change?
Because hydrogen will not interact with core structure in the Sam way that one molecule of magnesium would
How can loss of chlorophyll colour be prevented?
Through use of a base to preserve bright green colour
What does a base do to veggies?
Destroys cellulose and hemicellulose
What is the trade off of using baking soda and preserving colour?
Prevent conversion of chlorophyll to pthyphytin using baking soda instead of acid in the cooking water. Base will preserve the colour but the trade off is teh base will destroy the cellulose and hemicellulose giving you soft, mushy, broken down, unappealing product
Why are you able to maintain the bright green colour? What is stabilized and what is cleaved off?
Because you have magnesium stabilized which lets you retain colour but the phytyl tail becomes cleaved off
What happens when you lose the phytyl tail?
Becomes hydrophilic so loss of green colour into cooking water and turns mushy. Also loss of vitamins
Structure of anthocyanins
Flavonoid structure
Solubility of anthocyanins
Water soluble
Sensitivity of anthocyanins
PH sensitive
What are the colours of anthocyanins?
Red, blue, and purple colour
Under acidic conditions what colour are anthocyanins?
Red
Colour of anthocyanins at neutral
Purple
Colour of anthocyanins under alkaline conditions
Blue
What are anthocyanins characterized as?
Being antioxidants
Structure of flavonoids
It is two six member rings attached to another 6 member ring
What is key to anthocyanin colour
The double bonds in the structure are key to colour
What may flavylium be occupied by?
Hydrogens, hydroxyl groups, OCH3 (methoxy group), may be linked to a glucose another sugar molecule
What contributes to the pH sensitivty of anthocyanins
Central oxygen is unusual because it has a positive charge associated which gives it the name flavylium cation
Cooking blueberries in baking soda
Blueberries will become more intensely blue
Cooking blueberries of lemon
You will see a more magenta in the more acidic environment
How to reverse pH
You can reverse colour change by readjusting the pH of the environment
What does antioxidant activity tie to?
Flavonoid skeleton and particular the double bonds in the six member rings.
Why are free radicals reactive?
Because of an unpaired electron. If you expose it to an antioxidant can inactivate it with an antioxidant
What is responsible for the inhibition of free radical?
Moisture content
Freeze dried has a greater concentrations of anthocyanins
Berries can be free radical scavengers
What are anthoxanthins responsible for?
White and yellow colour of onions, cauliflower
How are anthoxanthins pH sensitive?
Colour dependent
Colour of anthoxanthins under acidic conditions
White
Colour of anthoxanthins under alkaline conditions
Yellow
What are anthoxanthins also know as?
Leucoxanthins
What can prolonged heating do for leuco anthocyanin?
Pink colour can develop
What is responsible for pink colour?
If over processed a pink colour can development. Molecule cleaved
Betalins
Water soluble, pH sensitive
Betacyanin
Red
Betaxanthin
Yellow
Betalins acidic conditions pH < 3
Violet
Betalins acidic contions pH 3-7
Red
Neutral belalains condition ph >7
Blue
Betalains basic conditions PH > 10
Yellow
What do betalains contain?
Betalains contain nitrogen in their structure (key difference)
What are betalains similar to?
Anthocyanins it has charged groups responsible for pH sensitivity
Key difference of anthocyanins and betalain
Presence of nitrogen
Enzymatic browning
Cut surfaces and bruised areas can turn a brownish red tinge when exposed to air/oxygen
Why does enzymatic browning occur?
Due to conversion of tyrosine to dopa-quinone and finally melanin pigment through a cascade of enzymatic and chemical reactions- Polyphenol oxidases
What does the rusty colour come from?
Conversion of an aromatic amino acid (tyrosine) and the tyrosine is coverted by combo of enzymatic and chemical reactions to give us a melanin pigment (which is the reddish brown colour we see)
What enzyme is responsible for enzymatic browning?
Polyphenol oxidase also referred to as PPO
What is the cascade fo enzymatic reactions up to?
Formation of dopaquinone (after this is formed the reactions no longer require enzymes remaking reactions are chemically based)
How can enzymatic browning be prevented?
PH, water activity, reduce exposure to oxygen, reducing agents
Lemon juice and enzymatic browning
Ascorbic acid and critic acid take the enzyme and exposing it to acidic environment so they acid denatures the enzyme, changing shape of active site which renders it non functional
How does sugar impact enzymatic browning?
If we have sugar (simple table sugar added to the water that we are soaking our apple slices or potato slices in this decreases our water activity.
Water activity with sugar Or salt
Alterting water activity (decreasing it) can be done by adding sugar
You could also decrease water activity using salt
Na+ and Cl- will hydrogen bond with water
Reducing agents
Oxidation which means if you want to prevent an oxidation reaction. Perfect solution is a reducing agent
What is a good reducing agent to prevent browning?
Citrus or any citrus or ascorbic acid
What happens during the ripening process?
Develops to full size and tissues become softer in texture
Post-harvest physiology?
Even when you bring your fruit home, the fruit tissue is still metabolically active and subsequently spoil or change characteristics (example: texture)
What happens to the fruit upon ripening?
Fruit becomes softer/ more pliable upon ripening
Partially a result of changes to the pectins which contribute to the firmess of fruit
What happens to starch content when fruit is ripened?
Hydrolysis enzymes acting on starches present in fruit tissue
Hydrolysis breaks down starch polymers into mono or dissacharide sub units for you to detect as sweetness
What can give ripened fruit aromas?
Development and release of different kind of fruit organic acids can happen as well as release of volatile compounds that give aromas of the ripened fruit
Example: malic acid
What do the changes in the colour of skin do?
Unripened green tomatoes changing into a red colour
Chlorophyll in green tomato broken down in favour of the underlying carotenoids
What is modified atmosphere packaging?
. Being able to export berries. Slightly increasing carbon dioxide to slow metabolism so they can be transported over seas and reach consumers in good quality
What is the ripening hormone?
Ethylene gas
What is ethylene gas?
It is low volatile. Is naturally produced by fruit tissue as it goes through the ripening process
Take paper bag and put unripe avocado into it on its own which will trap ethylene gas or but a ripe banana in the bag with it because the bananas will be emitting ethylene
What does the fridge do to ethylene gas?
alters that gas mixture surrounding the product. Apples are harvested in the fall but sold year round. Need to be stored in a way that controls them and keeps them fresh. Altering gas mixture of the atoms sphere by increasing concentration of carbon dioxide slightly. Combo of decreasing ripening and increasing shelf life
What happens if apples are producing heat?
You want to reduce the temperature so that your apples slow down their metabolism and have a longer shelf life
Fruit respiration post harvest
Fruits use oxygen by plant tissue and produce small amount of carbon dioxide
Vegetables post harvest
After why have been harvested they undergo a decline or decrease in respiration and it continues to decline during storage
What happens once fruit gets past optimal ripeness?
Spoilage and softening of tissues can happen rapidly
What is senescence
Once fruit gets past optimal ripeness it quickly goes into senescence or the stat of decay and overly softening o plant tissues
Respiration and shelf life relationship
Increase in respiration decrease shelf life
Examples of veggies with high and low respiration
Okra or spinach leaves (as opposed to potatoes) have relatively high respiration rates so short shelf life. Less than 1 month keeping time. Brussels have relatively low respiration rate and can be kept for about a month. Tomatoes are harvested mature not ripe so they typically have a long shelf life and lose respiration rates
Why does refrigeration reduce respiration rate?
Fresh produce at room temp in grocery store or farmers market gives high respiration rate. This is why we store in the fridge because it dramatically reduces respiration rate. Give us extended store life during refrigeration
What accelerates the offset of senescence?
When put in the fridge
Climacteric rise”
Sudden increase in respiration rate during ripening
Respiratory quotient
Taking leaves rich in carbohydrates like kale are given a 1 and everything else is in comparison to it. Example everyone on this list is in comparison to kale.
Flax seed otherwise non as linseed we see there can be changes in respiration rate of seeds that are just becoming mature in comparison to seeds that are germinating. Respiration quotient decreases for germinating seeds because the enzymes in the plant tissue are involved with developing the growing embryo in the kernel. Germinating is development of the germ so the metabolism of the grain is involved with producing new plant tissue so not so much concerned with overall respiration of the grain but development of the new plant. Overripe - slightly increased respiration.
Chilling injury
If product is not stored properly post harvest. Chilling injury can result (storing a product in an environment that is too cold). If you cut into the fruit like cantaloupe you can see evidence of damage and on the outside you see pitting
Characteristic of chilling injury
Characteristic pitted on the skin. Underlying carotenoids coming through due to damage of skin resulting in off colour
More impacts of chilling injury
Brown discolouration look slightly brown and fibrous as a result of chilling injury. Damage on citrus skin.
Flesh impacts of chilling injuries
Discoloured flesh and a mealy texture in apples or dry wooly textures (granular)
Where are dry wooly textures due to chilling injury common?
In nectarines and peaches
Storage of pomegranate
5 C Close to refrigeration is better but still not optimal too much pith. If not stored correctly it can have evidence of chilling injury. Exposing it to the freezing point you lose the juice sacks and have a lot of the pith. Slightly above give you more juice seed sacks but still considerable pith which is discoloured.
