Carbohydrates / Polysaccharides - Cell wall polysaccharides - Pectin
16 important questions on Carbohydrates / Polysaccharides - Cell wall polysaccharides - Pectin
What are the properties of homogalacturonan?
- Consists of an alfa-(1-u) linked linear chan of D-galacturonic acid.
- Varying proportion of methyl esters at the carboxyl function at C-6 (30-80%).
- Varying proportion of O-acetyl groups (20-30%) substituted at O2 and or O3 of the galacturionic acid residues.
What are the properties of rhamnogalacturonan II (RG-II)?
- highly branced polysaccharide.
- Consists of a backbone of about 9 afla-(1-4) linked galacturonosyl residues carrying four side chains containg a number of rare sugars.
- The rare sugars can be apios, aceric acid, KDO and DHA.
What are the properties of rhamnogalacturonan I (RG-I)?
- Consists of aletering alfa-(1-2) linked rhamnosyl and alfa-(1-4) linked galacuronosyluronic acid residues.
- The galacturonic acids residues are highly substituted with acetyl groups.
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What determines the function of pectins?
What are the two ideas of structure for pectin?
What are the 3 different structure elements of a pectin?
- Homogalacturonan
- rhamnogalacturonan
- neutral sugar side chains
How can pectins molecules be interconnected?
- Eather troug calcium ions (eg box structure)
- Di-rhamnogalacturonan II - boran comples. (enzymes can influance this process to ditermen when it is needed and when not)
- Di-ferulic acid cross linking
- Hydrogen bonding in celluose
What is the role of pectins in plants?
- Porosity of cell wall
- Water holding capacity
- Rigidity of cell wall and tissue
What is the role of food products?
- Ripening and texture of fruit and vegetables
- Texture of canned vegetables, pickles, tomato products (beta-elimination)
- Cloud stability in e.g. fruit juices
- Processability of by-products of the agro-industry
● Beet pulp, potato fibre
What happens with the pectins during ripening?
What happens to pectin if treated with hot water, buffer solution, and alkali?
Treatment of the cell wall material with alkali results in the removal of ester linkages and disruption of Van der Waals forces, resulting in the extraction of another population of pectins.
For what are pectins used in food products?
- Gelling agents
- Stabilising agents
- important untritional role as soluble or insoluble components of dietary fiber rich diet.
How can you classify pectins by degree of methylation?
- High methyl (HM) pectins: >50% methyl ester
Sugar Acid gel
● Sugar lowers water activity and increase chain-chain interaction (= gel)
● Low pH reduces acidity – less interaction – more chain-chain interaction - Low methyl (LM) pectins: <50% methyl ester
● Calcium-pectate gel
● Low sugar jams
What are the health aspects of pectin/plant cell wall polysaccharides?
- Dietary fibre:
● cholesterol lowering, glycemic index, faecal bulk and transit time - Anti-diarrhoea
- Detoxicant – metal binder
- Regulation & protection gastrointestinal tract
- Regulation satiation & satiety
- Immuno-modulating
- Anti-metastasis activity
- Anti-ulcer activity
- Anti-nephrosis activity
- Drug delivery
What enzyme do you need to cut a pectin?
How can a fruit or vegetable become soft if the enzyme is not active anymore?
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