lecture 6-pectins Flashcards
- describe the general structure of high methoxyl pectins
have a degree of methylation that is higher than 50 % so more than one half of the carobzyl groups have been methylated
describe the general structure of low-methoxyl pectins
have a DM lower than 50 % and the carboxyl groups that remain are a mixture of free acid (COOH) and salt form of the acid
describe the general structure of amidated pectins
these are pectins that have been treated with ammonia dissolved in methanol which will convert around 15-25% of methyl ester groups into carboxamide. By defintion these would also be a low-methoxyl pectin. And instead would be classified by degree of amidation (DA)
what do the degree of methylation and amidation values strongly influence?
- solubility
- gel-forming ability
- conditions required for gelation
- gelling temperature
- gel properties of pectin
what is gelation and what governs the mechanism of gelation for pectins?
is the formation of a gel that happens by chemical/physical cross-linking of polymers. It is governed by degree of esterfication
describe the process of gelation of high methoxyl pectin
this requires an acid and a sugar and is not thermoreviersble. The acid is used to remove the charge so that crosslinks can form. Th sugar is added to get rid of water which will promote hydrogen bonding so that a network can be created forming a gel. The heat for this process will depend (35-90) on the level of methylation the more means lower the temperature as it is more ready for gelation because of removal of charge.
in high methoxyl pectin gelation how is the gel structure stabilized?
- by the large number of hydrogen bonds
- and the hydrophobic interactions of methyoxyl groups connected after taking away water, because the orginal iconic groups would be hydrophilic
what is the cooling rate effect?
a slow cooling rate allows for larger junction zones to form which will make fimer and more elastic gels
what are the applications of high methoxyl pectins?
- jams jellies
- stabiliztion of dairy drinks
- in beverages
- confectionary uses
describe the gelation of low-methoxyl pectins
just need calcium not sugar or an acid. calcium ions act as cross-linking agents that bind to the carboxylate groups of two adjacent pectin chains. This interaction forms a three-dimensional network of pectin molecules, resulting in gel formation. This process is thermoreversiable and requires temperatures from 40-100 degrees celcius
what are applications of low methoxy pectin
- low calorie perserves as it doesnt require sugar to gel
- barbeque sauces
- dairy products as it can complex with protiens
- canned products
- pastrys
describe the gelation of amidated pectins
similar to low methoxyl pectins form a gel with the help of calcium but require less calcium. The junction zones are stabilized by hydrogen bondings. And it was altered to enhance gelling properties and forms a thermoreviersible gel.,
describe the relationship between calcium and gel strength
there is an ideal calcium concentration that will result in the max gel strength. If the calcium concentration is too high the gel will be less stable since there are more calcium ions than neeed which will disrupt the network by making too many cross links. On the other hand too low of a calcium concentration will mean there is not enough calcium to form junction zones that stabilize the gel. There is not enough crosslinks to form a firm gel
what is the chemical structure of native pectins?
it is derived from galactose and is an acidic sugar being made up of galactornonic acid. The galacturonic acid residues are methylated or acyleated
describe methylation vs aceylation
so methylation occurs by combining an acid (CH3COOH) and an alcohol which when they bind together will release water and will add an CH3 group (OCH3) this process can only happen where the acid is located. On the other hand aceylation can happen whever there is an OH. This process requires alchol and acetic acid and will form an ester
