Naked Science Forum

General Science => General Science => Topic started by: paul.fr on 24/07/2007 15:37:55

Title: what makes jelly, jelly?
Post by: paul.fr on 24/07/2007 15:37:55

Having just made some wonderful blackcurrant jelly (not for sharing), i wonder what makes it go all solid. Well, not actually solid as it still wobbles. But you know what i mean

Title: what makes jelly, jelly?
Post by: Karen W. on 24/07/2007 15:42:43

 Fruit Pectin !

Pectin
From Wikipedia, the free encyclopedia

   

Pectin, a white to light brown powder, is a heterosaccharide derived from the cell wall of higher terrestrial plants. It was first isolated and described in 1825 by Henri Braconnot[1].

It is mainly used in food as a gelling agent in jams and jellies. Today it is also used in fillings, sweets, as a stabiliser in fruit-juices and milk-drinks and as a source of dietary fiber in foods.

Title: what makes jelly, jelly?
Post by: daveshorts on 24/07/2007 16:26:54

Gels are all made from long polymer molecules that are attached together in a few places so they can't move too far past each other. They can straighten out and rearrange themselves within the the restriction of being tied together though so they are flexible.

If you heat them up they are strong enough to break the attachments and they often melt.

Pectin is one form of long molecule, gelatin is another. It is animal derived, you boil up all the connective tissue which is made out of collagen, and purify it a bit and you get gelatin.

There are lots of other polymers that can have a similar effect if suitabley crosslinked, PVA, polyacrylamide etc.

Title: what makes jelly, jelly?
Post by: eric l on 24/07/2007 17:18:51

Quote from: daveshorts on 24/07/2007 16:26:54

There are lots of other polymers that can have a similar effect if suitabley crosslinked, PVA, polyacrylamide etc.

... but few of them can be used in foodstuffs.

As stated by daveshorts, gelatin comes from animal sources.  Pectin and lignin come (mainly) from vegetable sources, but while pectin is found mainly in the fruit, lignin is found mainly in the stem.  As far as I know, lignin is not used in foodstuffs.

Gelatin is registered as E441, pectin as E440a.  There is also xanthan (E415), a polysacharide product from a fermentation process, and equally used as a viscosity modifier.

Title: what makes jelly, jelly?
Post by: that mad man on 24/07/2007 20:45:41

I believe Dr.Magnus Pike once proposed using pectin as a non calorific filler in foodstuffs, but then he was beautifully eccentric!

A biscuit or cake made up mainly of pectin or something like that.

I know it causes a bad haze, unless careful, when brewing home made fruit wine but you can include some pectic enzyme that breaks it down.

Bee