lecture 8 Flashcards
Purpose of sorting and what the automatic equipment does?
To remove foreign bodies and sort material into uniform batches
Automatic equipment to detect and sort by:
Colour, Size, Weight, Density, Etc.
What does the mechanical sorter do?
distributes pieces according to smallest diameter
What does the electronic sorter do?
that weighs each piece and drops it into a corresponding crate
How do freezers work?
Gas from freezer is compressed to liquid, heating it up. The hot liquid is cooled to ambient (room) temperature, then evaporated via the expansion valve, resulting in very cold gas where it enters the freezer again.
What temperature is fruit and vegetables usually froze at?
-24 c
What is done to reduce ice crystals when freezing fruit and vegetables, but why will they change texture anyway?
Freezing process must be rapid, e.g. using liquid nitrogen, to minimise formation (size) of ice crystals.
Fresh fruit and vegetables change texture in any case, due to the vacuole and cell wall, which are easily damaged by ice crystals
Why is blanching often used before freezing fruit and veg?
Freezing does not inactivate enzymes (peroxidases and lipases), which cause browning and formation of rancid taste, respectively, mainly during thawing
So blanching is often used, to inactivate enzymes
What can you do to reduce time of freezing for fruit and veg?
Cutting to uniform pieces, because large pieces take longer to freeze.
What is blanching and why is it done?
Food is heated rapidly to a pre-determined temperature, held for a pre-set time then cooled quickly
Aims to achieve full denaturation of target enzymes with minimal change of texture and composition
What factors effect the blanching process?
Type of fruit or vegetable
Size of pieces (affects heat penetration)
Blanching temperature (70-100ºC) and duration (0.5-2 minutes)
Method of heating (e.g. steam or hot water)
With or without active cooling
Summarise the freezing of fruits and vegetables?
- Cut into uniform pieces
2a. Blanch at high temperature until enzymes are inactivated
2b. Cool rapidly to refrigerator temperature to minimise nutrient loss - Freeze rapidly to minimise ice crystal growth
- Store at approximately -24°C
What are stages of juice production?
Maceration - Pressing/filtering - Stabilisation
Key quality aspects of juice?
Safety
Appearance and taste
Nutrient value
What is maceration and its purpose?
Purpose: To release the juice from the solid fruit matrix
Processes involved:
Crushing: Breaks down cell walls and releases juice from brittle tissues, e.g. apples
Heating: Breaks down cell membranes and releases juice from pulpy tissues, e.g. berries
Enzyme treatment: Breaks down viscous polymers such as pectin and protein, to facilitate separation of juice and pulp
What is stabilisation?
It prevent loss of quality until the juice is consumed, caused by:
Enzymes (browning, flavour loss, off-flavours)
Microbes (yeast and bacteria)
