Questions Flashcards
1
Q
Please define fruit quality?
A
- Degree to which a set of inherent characteristics (texture, sugar content, pH…) fulfil requiremnts (cosumer satisfaction).
2
Q
What factors are affecting fruit quality?
A
- Microorganisms (fungi, moulds, yeast)
- Enzymes (pectinase-hot brake, PPO-cold brake)
- Insects, rodents
- Volatiles
- Light
- Temperature
- Atmosphere
- Water activity/moisture
3
Q
What are pectins?
A
- Pectin is a structural element in plant tissue and themain the component of the middle lamella
- it provides cohesion and stability in tissues and cells
- Pectin is mainly formed with galacturonic acid molecules which are linked to each other by a 1-4 glycosidic bond to become polygalacturonic acid
- The carboxyl groups are partially esterified with methanol → Methoxyl
4
Q
What is the difference bewtween low methoxyl, high methoxyl and amidated pectins?
A
- Pectin types can be differentiated according to the number of ester groups (methoxyl groups
- High methoxyl pectins: > 70% esters
- Medium methoxyl pectins > 50% esters groups.
- Low methoxyl pectins < 50% esters groups.
- Amidated pectins are low methoxyl pectins which also contain up to 25% amide groups
5
Q
What are the intended purposes of pectins?
Examplify?
A
- Pectin is a thickener in many products.
- If there is sufficient sugar in the mixture, pectin forms a firm gel→Jams and jellies are thickened with pectin
- Pectin binds water, and thus keeps products from drying out
- It stabilizes emulsions
- It is also used in sweets, fruit juices, milk drinks, yogurt, milk desserts, baking industry, fruit fillings, cake glazings, confectionery industry (gums), etc
6
Q
Describe the production of a clear juice?
A
- Fruit (fresh or thawed)
- Cleaning/Washing
- Sorting/Culling
- Sanitizing
- Preperation for extraction (pitting, crushing, heating, enzymatic treatment)
- Juice extraction (pressing, decanting)
- Clarification (Depectinizing, centrifuging, filtering)
- Concentration ( evaporation, reverse osmosis, freeze concentration)
- Pasteurization (78 C for 15s)
- Filling and Storage (shelf-stable, refigerated, frozen)
7
Q
Describe the enzymatic browning process?
A
- Surface dicoloration- most common defect in fresh cut fruit and most limiting for shelf life
- Occurs during the peeling and cutting operations
- Cells are broken, and their contents include previously compartmentalized enzymes that are now in contact with their substrates
- A group of enzymes called polyphenol oxidases (PPO), which occur in particularly high amounts in fruits such as banana, apple, pear, avocado, and peach, are responsible for the discoloration referred to as enzymatic browning
8
Q
How can enzymatic browning process be slowed down/controlled?
Physical methods
A
Physical methods:
- reduction of temperature
- reduction of oxygen
- use of modified atmosphere packaging
- use of edible coatings
9
Q
How can enzymatic browning process be slowed down/controlled?
Chemical methods
A
Chemical methods depend on:
- compounds that inhibit polyphenol oxidase
- remove its substrates (oxygen and phenolics)
- or function as preferred substrates
Most common anti browning agents:
- Ascorbic acid (or Erythorbic acid it´s isomer)
- Acidulants (e.g., citric acid, malic acid)
- Chelators (e.g., EDTA)
- 4-hexylresorcinol (not allowed for fruits only shrimp)
10
Q
Discuss the biological hazard potentially present in transformed fruits?
A
- residues of pesticides
- presence of heavy metals
- mycotoxins produced by certain species of fungi
- microbial contamination
11
Q
Describe the most important thermal operations used in fruit processing?
A
Blanching
Pasteurization
12
Q
Describe the production of a single strength cloudy juice?
A
- Fruit (fresh or thawed)
- Cleaning/Washing
- Sorting/Culling
- Sanitizing
- Preperation for extraction (pitting, crushing, heating, enzymatic treatment)
- Juice extraction (pressing, decanting)
- Cloudy juice (further clarification not nesessary)
- Pasteurization (to achieve safe and stable juice)
- Filling and storage
13
Q
What are the goals and what are drawbacks of the heating process?
A
- Heating determine chemical, physical and organoleptic changes in food
- Food concentration with water removal
- Hydrolysis due to protein and polysaccharides;
- Odors and flavors improvement
- Distroying microorganisms
- Extension of the shelf-life
- Enzyme inactivation
DRAWBACKS
- Lower nutritional value
- Production of nocive chemical compounds
- Degradation of vitamins (in particular vitamina C e B) ;
- Loss of vitamins and mineral salts in water;
14
Q
Define the D-Value?
A
- The D value is a measure of the heat resistance of a microorganism.
- It is the time in minutes at a given temperature required to destroy 1 log cycle (90%) of the target microorganism.
- For example, a D value at 72°C of 1 minute means that for each minute of processing at 72°C the bacteria population of the target microorganism will be reduced by 90%.
Typical D-Values:
D value for microbial destruction is about 1-5 min; D value for enzyme inactivation is about 1-5 min; D value for vitamin loss is about 0.1-120 min; D value for pigment loss is about 15-30
15
Q
Define the z-Value?
A
- The Z value reflects the temperature dependence of the reaction
- It is defined as the temperature change required to change the D value by a factor of 10. In the illustration below the Z value is 10°C. Small Z values means high temperature dependence.
Typical z-Values:
- Z value for microbial destruction is about 5-10C
- Z value for enzyme inactivation is about 30-40C
- Z value for vitamin loss is about 20-25C
- Z value for pigment loss is about 40-70C
