Veg and fruit, storage, freezing and processing

Question 1

Defining characteristics of fruit and veg:

Answer 1

• high water content
• dry matter is mostly carbohydrate
• tissues are alive (respiration and enzymes)

Question 2

Sorting:

Answer 2

To remove foreign bodies and sort material into uniform batches. Sort by: colour size, weight, density etc

• conveyer belt
• colour detector
• send products in different directions depending on colour

Question 3

Methods for transport and storage of fresh produce:

Answer 3

• slow down senescence processes (these processes will cause the product to decay)
• prevent rot or mould development
• minimise loss of quality compared with fresh material
• provide material outside of reason

Question 4

refrigeration

Answer 4

• cooling down one thing while you heat something else
• compressor until gas becomes a liquid
• as gas becomes a liquid, it gives off heat
• remove heat as quickly as possible
• after condensing to liquid, cool it down to room temperature
• expansion valve allows pressure to drop and gas will evaporate
• evaporation requires energy so temp goes down

Question 5

Modified atmosphere packaging

Answer 5

• fresh produce, living respiring organism
• cooling produce reduces metabolic rate
• lowering oxygen level reduces metabolic rate
• normal air: 78% nitrogen, 21% oxygen, 0.04% C02
• respiration in closed containers - reduces oxygen, increases CO2 content
• therefore inhibit/slow down respiration
• carbohydrate stores in plant tissue are extended, insects and fungi inhibited
• CO2 dissolved in water - H2C03 (carbonic acid). this lowers pH, which can inhibit bacterial growth

Question 6

Ethylene

Answer 6

• 2C and 4H atoms
• Generated by ripening fruit and rotten/mouldy produce
• Exposure induces synthesis of more ethylene

1. Unripened fruit: acid, starch, amylase, hydrolase, pectinate, hydrolyses

When ethylene is produced it activates many enzymes: kinase, amylase, hydrolase, pectinate, hydrolases

2. Ripened fruit: neutral, sugar, anthocyanin, less pectin (soft), aromatic

Question 7

effects of ethylene

Answer 7

• leaf green veg, flower buds and shoots will wilt turn yellow and drop leaves, become less sweet more bitter
• dormant veg (onions, potatoes, beetroot) sprouting inhibited, storage time extended
• nono-climacteric fruit (oranges, strawberries), improved resistance to disease, improved shelf life

Question 8

Managing ethylene

Answer 8

1. Minimise unintentional ethylene generation and exposure
   - delay ripening
   - ethylene scrubbers absorb gas from room
   - packaging can help to prevent exposure
2. Treat sensitive produce with ethylene inhibitor 1-MCP
3. Add ethylene gas where it is beneficial
4. Control the concentration

Question 9

Freezing

Answer 9

• cooling to -24C
• must be rapid e.g liquid nitrogen to minimise formation of ice crystals
• doesn’t inactivate peroxides and lipase, enzymes that cause browning and formation of rancid taste during frozen storage or thawing
• fresh fruit and veg change texture in any case, due to vacuole and cell wall, which are easily damaged by ice crystals

Question 10

Freezing process key steps

Answer 10

1. cutting - minimise time for freezing

2. Blanching, used to destroy enzyme activity before freezing, food is heated, hold for pre-set time then cooled quickly, minimal change of texture and composition
Factors affecting process:
-type of fruit and veg
-size of pieces
-blanching temp
-method of heating
-with or without active cooling

3. Cool rapidly to refrigerator temperature
4. Rapid freezing by direct contact with liquid nitrogen or other coolant
5. Store at approx -24C

Question 11

Juicing

Answer 11

1. Maceration
2. Pressing/filtering
3. Stabilisation

Question 12

Maceration

Answer 12

• Purpose: to release juice from the soil fruit matrix
• crushing: break down cell wall and release juices from brittle tissues
• heating: breaks down cell membranes and releases juice from pulpy tissues
• enzymes treatment: break down viscous polymers such as pectin and protein, to facilitate separation of juice and pulp

Question 13

Stabilisation

Answer 13

purpose: to prevent loss of quality until the juice is consumed
-enzymes, oxidation (rapid, browning, flavour loss)
-Microbes (yeast and bacteria)
Processing options
-rapid consumption
-refrigeration or freezing
-pasteurisation: removes most microbes at ph below 4.6
-concentration: reduces cost of transport and storage
-additives (so2, acids): prevent browning and microbes
-packaging/bottling: practical handing, storage and presentation

Question 14

Peeling

Answer 14

1. Flash steam peeling - rapid heating of skin, steam peeler
2. Knife peeling - cutting away of outer layer
   - carrot knife peeling
   - onion peeler
3. Abrasion peeling - carborundum and water
   - potato abrasion peeling

Question 15

Canning

Answer 15

• container closed before heat hutment and kept closed until use
• high temp particular important for non-acid foods (ph>4.6) to ensure killing of spores of Clostridium botulinum
• high temp is achieved using high pressure steam
• high temp treatment destroys taste compounds and vitamins, the longer and hotter the worse
• water and steam promote heat transfer
• speed of movement through equipment determines rate of heating and cooling
• Heating and cooling require longer time for larger cans