Fruits and vegetables Flashcards

Question

[Part 2 -- strategies for shelf-life extension : MAP] What is MAP, and what are the concentrations of gases?

Answer 1

Modified atmosphere packaging - O2 : <10%, but should not fall below 2% - CO2 : increase composition but should not reach 20%

Answer 2

- **H2O** **scrubber** – reduce water activity and prevent mold growth - **C2H4** (ethylene) **scrubber** – slow down rate of senescence - **Impermeable package** to **reduce** exposure to surrounding **O2** (irl have vents to prevent condensation and mold growth, bc don’t have H2O scrubbers) - Gas composition : **0.03% CO2 + 21% O2** - Cold storage to reduce rate of biochemical reactions

Answer 3

1 – MCP is complexed with α-cyclodextrin, a water soluble powder When powder is mixed with water, it disperses around the produce and 1 – MCP is generated as gas

Answer 4

Temporary : climacteric fruits - climacteric fruits need to ripen later on --> delay ripening during post harvest + transport etc, until reach supermarkets then let it continue ripening Persistent : vegetables / non-climacteric fruits

Answer 5

True, since it binds to receptor and ethylene cant bind --> signal transduction cascade cannot be passed down --> ripening inhibited

Answer 6

process to remove field heat of freshly harvested produced, usually within **24h or less** after harvest

Answer 7

difference in temperature of harvested produce and optimal storage temperature

Answer 8

- Suppress enzymatic degradation (leading to softening) and respiratory activity [aka slow down rate of biochemical reactions] [BIOCHEMICAL] - Slow / inhibit water loss (wilting) -- If temperature high, resp high → stomata open → transpiration also high → loss of water - Slow / inhibit growth of decay-producing **microbes** [BIOLOGICAL] - Reduce production of ethylene (due to reduced respiration) or minimise produce’s reaction to ethylene [CHEMICAL]

Answer 9

- Produce is placed in an insulated room equipped with refrigeration units to chill air - Produce packaged in well-vented packaging and stacked in small crates - Cool air is circulated by convection, with help of fans **Suited for types of fresh produce that are tolerant of slow heat removal (does not dehydrate easily)**

Answer 10

- Clean & simple - Low installation and maintenance cost - Provides temporary storage space after pre-cooling

Answer 11

- Slow - **Uneven cooling at the beginning** - May not be suitable for produce that are sensitive to dehydration due to a prolonged cooling period

Answer 12

A kind of modified room cooling. - Exposing produce to higher air pressure on one side than on the other side - Cold fan at one side to blast cool air in (high pressure) - Fans to pull out the warm air, creating a lower pressure on top and causing hot air to rise and get pulled out **Suitable for most leafy, fruited and root produce**

Answer 13

- Clean & simple - Low installation and maintenance cost - Rapid (faster than room cooling) - High rate of heat transfer

Answer 14

Slower than vacuum cooling

Answer 15

- produce are subject to low pressure with **fans sucking hot air out** - reduces pressure on the headspace of produce, causing **vaporization of water at low temperatures** - water from produce evaporates, thus produce loses heat (since it has a high heat capacity and can carry a lot of heat) **Suitable for mushrooms and (some) leafy vegetables** ## Footnote Similar forced air cooling, just that no additional cool air

Answer 16

- Rapid - Uniform cooling - High energy efficiency

Answer 17

- Risk of wilting due to moisture loss - High cost - Requires packaging with holes for water evaporation

Answer 18

- usage of chilled water or cold water to cool produce - produce can be flooded / immersed in water, or water can be sprinkled **Suitable for most fresh fruits and vegetables** Note : contact between water and product surface must be uniform

Answer 19

- Rapid - High energy efficiency - Provides means to clean vegetables (chlorinated water) → reduces spoilage

Answer 20

- Additional drying step required (wet produce – susceptible to microbial growth) - Additional effort to **monitor water quality and cleanliness** of cooler daily.

Answer 21

- produce is cooled with crushed / fine granular ice - the ice is either packed around produce cartons or sacks, or it is made into a slurry with water and injected into waxed cartons packed with produce. The ice then fills the voids around the produce. - Ice removes heat rapidly, and continue to absorb heat as it melts **Suited for broccoli, carrots, Chinese cabbage, green onions, and commodities that have a high respiration rate (prone to drying)** - High respiration rate = stomata open - If use room cooling / forced-air cooling / vacuum cooling → will drive transpiration as water in air is taken away → causing wilting

Answer 22

- Rapid - High heat transfer performance - Prevents moisture loss

Answer 23

- Additional weight from crushed ice and high water content from melting ice → increased risk of physical injury + rotting - Risk of chilling injury if period of icing is prolonged.

Answer 24

It is the amount of atmospheric moisture present relative to the amount of moisture that would be present if air was saturated - R.H. = (actual vapour density / saturation vapour density) x 100%

Answer 25

Temperature at which air becomes saturated with water

Answer 26

When temperature decreases, water-holding capacity (WHC) of air decreases. Thus, with the same amount of water but lower capacity (air cannot hold as much water), condensation occurs

Answer 27

1. Water loss leads to loss in turgor pressure and freshness, esp for leafy greens 2. Wilting, shrivelling, poor appearance 3. Increased respiration (moisture stress), shorter shelf life - Cuz water travels from high humidity to low humidity, transpiration increases, stomata open, thus respiration rate also increase to produce water (C6H12O6 + 6O2 → 6CO2 + 6H2O)

Answer 28

stress that occurs when the moisture levels in plant tissues are reduced

Answer 29

1. Increased ethylene production and increase in ACC + ACC oxidase activities - _1-Aminocyclopropane-1-carboxylic acid oxidase (ACC oxidase) : enzyme that catalyzes the final step in the production of the plant hormone ethylene_ 2. Faster ripening due to increased respiration (+ increased ethylene) 3. Hasten senescence : increased formation of free radicals, deterioration of cell membranes, softening, decreased insoluble pectin + increased soluble pectin

Answer 30

1. Condensation on surface of fruits occurs → microbial growth (mould etc) 2. Surplus turgor pressure may lead to cracking of fruit 3. Inhibition of gas exchange (water covers the leaves / skin of fruit → blocking stomata, making it harder for gaseous exchange)

Answer 31

mass transfer process in which **water vapour** moves from **surface** of plant / organ to surroundings through openings present in tissue (stomata)

Answer 32

small, lens-shaped openings on the surface of fruits, stems, and tubers to allow air to pass through (water vapour can be lost through lenticels during transpiration)

Answer 33

1. Pressure gradient in intercellular spaces and in ambient atmosphere 2. Surface area of plant organ 3. Resistance (thickness of surface layer) ## Footnote Like FST2109 -- pressure : driving force ; resistance : opposing force that prevents water vapour from escaping

Answer 34

Pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system. - It's an indication of a liquid's thermodynamic tendency to evaporate.

Answer 35

The difference in water vapour pressure (wvp) of normal air and wvp of saturated air

Answer 36

- increased temperature → increased free energy of water molecules (breaking of H bonds between H2O molecules, becoming from liquid state in fruit and loss as vapour) → increased potential to transfer and evaporate away as vapour - this increased temperature → high WVP

Answer 37

- Most fruits (tropical / subtropical / temperature / fruit-type vegetables) : **RH 85-95% (~90%)** - Most vegetables: **95-100% RH**, esp **leafy** greens *Dormant storage organs – don’t need so high RH as there is a thick layer of dry skin outside to protect from water loss* - Roots/tubers: 85-90% RH - Bulb (garlic/onion), ginger, jicama, pumpkin, winter squashes : 65%-75% RH (~70%)

Answer 38

**1. Produce characteristics** - Surface area to volume ratio, properties (pore size, presence of protective wax), size, respiration rate **2. Postharvest handling** Injuries and damage to protective layers increases respiration and transpiration **3. Environmental factors** **a. Air Relative Humiditty (RH) – affects VPD** **b. Temperature **– affects WHC (water holding capacity) of air, VPD, transpiration **c. Air pressure** – partial vacuum reduces water molecules in air, increases VPD (lower RH) and is thus the driving force of transpiration VPD : (amount of water in saturated air - actual amount of water in air) x 100% If actual amount of water in air decreases, the difference increases **4. Air movement** Strong air current near produce surface (e.g. fan blowing only at a particular fruit) takes away water from air, reducing RH and increasing transpiration Air circulation in an enclosure promotes uniform temperature distribution, reducing VPD

Answer 39

Superficial wound caused by mechanical forces during harvest and post-harvest handling

Answer 40

1. Discolouration of wounded area Loss of water in tuber → loss of turgor 2. Increased susceptibility to pressure bruising and blackspot development 3. Pressure from machinery → bruise (like blueblack) → when bruise is healing it turns black 4. Creation of areas open to infection

Answer 41

Artifically induce maturation by killing potato (tuber) plants 7-21 days prior to harvest - when plant dies, growth stops and activity of the phellogen stops (phellogen adds skin to potato) - thus, the skin wont continue expanding. Since the skin cells are dead, they adhere to tuber flesh in a process called skin-set, making it more resistant to damage ## Footnote VS if skin cells (phellogen) still alive when harvesting, tuber will get injured more easily

Answer 42

Curing. Rationale : promotes skin thickening, thus tuber less likely to: 1. Loose water via transpiration 2. Greater resistance to post harvest diseases (thicker skin limits microbes accessibility to moisture and substrates within tubers) Thus, curing extends shelf life

Answer 43

False. Curing should begin as soon after harvest as possible, preferably within 12h of harvest

Answer 44

1. Warm temperatures Warm temperatures (30-40℃) 2. High relative humidity (>85% RH) + good ventilation to remove CO2 and replenish O2 3. Tubers should not be washed prior to curing → washing introduces pressure, forming more injuries, surface for curing becomes more uneven and making it harder to heal

Answer 45

Starch is broken down into sugars, increasing the concentration of solutes. This lowers the freezing temperature of water in sap and thus the plant won't freeze in the winter.

Answer 46

For cold-growing vegetables, cold-induced sweetening is desirable for their sweet flavour For potato tubers, accumulation of reducing sugars lowers its processing quality - if tubers are fried (e.g. potato chips), more reducing sugars result in darker fry colour due to Maillard reaction → if very dark brown, not nice - Risk of acrylamide production (which may cause cancer in humans, not sufficient human studies to prove this yet)

Answer 47

Modification of the gas composition **within the storage room** where produce is stored - *Continuous monitoring and precise adjustment of gases* within storage space to a predetermined level are carried out

Answer 48

Involves reduction of O2 and increasing CO2 as compared to ambient temperature (may involve removal of ethylene) - to reduce respiration rate so less ethylene produced (for climacteric fruits) + slow rate of senescence

Answer 49

1. Changes in gas composition in the room is dynamic and always changing due to commodities respiring and producing ethylene, but controlled atmosphere storage conditions are predetermined and fixed → thus requires very intensive monitoring and controlling of parameters 2. A few over-ripe/diseased/damaged fruits can impair effectiveness of the controlled atmospheric environment → a lot of ethylene produced → leads to accelerated ripening of other fruits and CA storage conditions becomes ineffective.

Answer 50

Controlling the gas composition within the packaging of the produce itself. - The gas composition is not actively controlled and the atmosphere within package is created by the respiratory activity of the fresh produce.

Answer 51

- Involves using of a film. Its permeability to gases and water vapour should match respiration rate of produce → atmosphere reaches an equilibrium over a few days - The desired atmosphere develops naturally due to the products' respiration and the diffusion of gasses through the film.

Answer 52

CO2 permeability 3-5 times more than O2 permeability to avoid excessive build up of CO2 (which may lead to anaerobic resp and off-flavour)

Answer 53

MAP is a method that establishes a modified atmosphere in a package by creating a light vacuum and replacing the atmosphere with a desired gas mixture.

Answer 54

1. Film that has desired permeability for gases and water vapour 2. Scavengers / scrubbers packed in sachets to actively adjust atmosphere within packaging.

Answer 55

Packaging system that can carry out intelligent functions like detecting, containment, convenience, tracing, communicating and applying scientific logic

Answer 56

- putting a small sensor to the packaging of produce → ability to **track and trace the exact location** of a product in the supply chain using unique barcodes, QR codes, or RFID technology. Also involves usage of time-**temperature indicators (TTIs), ripeness indicators, chemical sensors** etc

Answer 57

Purpose : to decrease movement of water vapour out of cells due to the wax serving as a physical barrier, reducing transpiration - Applied mostly on whole and cut fruits

Answer 58

Hydrocolloids (water-soluble polymers) - protein / polysaccharide films

Answer 59

Acting as gas barriers for O2 and CO2 - more hydrophilic =also permeable to water vapour and less permeable to gas

Answer 60

True. 1. Water leads to swelling of coating, creating gaps and making easier for gases to pass through 2. water disrupts the structure of hydrophilic network as hydrocolloids start to react with water 3. Water may weaken mechanical properties of coating, leading to cracks or tears

Answer 61

Petroleum based waxes and oils - E.g. paraffin wax, polyethylene wax, mineral oils

Answer 62

Calcium treatments provides stability and rigidity to cell wall as they cause cross-linking of pectin

Answer 63

calcium lactate, calcium propionate,calcium gluconate

Answer 64

1. Pectin methylesterase : breaks down the ester bond in the --COOCH3 bonds to give carboxy groups (COO-) 2. Polygalacturonase (PG) : breaks down pectin into its monomer, galacturonic acid

Answer 65

- Pectin methylesterase (PME) break up methoxygroups (COOCH3) in the pectin molecules which creates free carboxyl groups - Polygalacturonase then can access the glycosidic bonds which breaks up the pectin chain, leading to a less rigid cell wall

Answer 66

1. Calcium impregnation 2. Calcium dipping

Answer 67

Calcium impregnantion involves placing the produce in a vacuum to draw out air. This reduces the pressure, thus causing the calcium treatment solution to flow into the lenticels and penetrate deep into the fruit (effective penetration of calcium treatment rather than just applying on surface) - Used on whole and cut fruits and vegetables which are not so soft (e.g. apple/tomato/brocolli)

Answer 68

Calcium dipping involves soaking of product, applying mechanical agitation (or may not) and removal of excess solution - it is a more gentle treatment used on more perishable fresh products like leafy vegetables

Answer 69

1. Reduces microbial load 2. Enhances PME activity: - This provides more carboxylate groups for interaction with calcium ions. 3. Reduces PG activity: Reduces pectic acid cleavage

Answer 70

PAs reduce production of ethylene by restricting transcriptional synthesis of **aminocyclopropane-1-carboxylic acid synthase (ACS).** - ACS : enzyme that converts methionine to 1-aminocyclopropane-1-carboxylic acid (ACC), which is the direct precursor of ethylene.

Answer 71

1. Delays fruit ripening and softening - Polyamines are positively charged at physiological pH (NH3+), causing cross-linking of COO- in pectin chains 2. Polyamine treatments can reduce chill injury as positively charged amino grooups associate with negatively charged phosphate groups in lipid bilayer. - polyamine embed in lipid bilayer, increasing membrane fluidity so that membranes will not be so rigid and prone to damage (chill injury)