FOOD CHEMISTRY: GELLING AGENTS
Diagram
Two ways to set a jelly
Gelatin
A protein from animal collagen. Sets soft, melts in the mouth, needs no sugar or acid.
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Pectin
A plant fibre from fruit. Sets with sugar and acid, or with calcium, and stays set when warm.
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Use
Gelatin suits soft desserts. Pectin suits jams and jellies that must keep their set on the shelf.
Figure 1: Gelatin is a protein that melts in the mouth; pectin is a plant fibre that sets with sugar and acid. Drawn in our own style from the gelling agents covered in Edwards, The Science of Sugar Confectionery, and the pectin discussion in Coultate, Food: The Chemistry of Its Components.
Introduction
Gelatin and pectin both set jams and jellies, but they work in different ways. Gelatin is a protein made from animal collagen, and it sets on cooling alone. Pectin is a plant fibre found in fruit, and it sets only when sugar and acid are present, or, for low methoxyl pectin, when calcium is present. That difference decides which one is used in a soft dessert and which one is used in a jam.
Edwards covers gelatine and pectin together as gelling agents, and Coultate covers pectins as food polysaccharides. This article follows those two books.
Quick comparison
Table 1: Gelatin compared with pectin
| Aspect | Gelatin | Pectin |
|---|---|---|
| Source | Animal collagen | Fruit, especially citrus peel and apple pomace |
| Chemical type | Protein | Polysaccharide, a plant fibre |
| What it needs to set | Cooling only | Sugar and acid, or calcium for low methoxyl pectin |
| Setting | Sets into a soft, elastic gel | Sets into a firm, spreadable gel |
| Melting | Melts at mouth temperature | Stays set when warm; does not melt in the mouth |
| Texture | Soft, wobbly, melts as eaten | Firm, short, spreads cleanly |
| Heat stability | Melts in hot food | Holds its set in hot food and on the shelf |
| Use in acid food | Works in acid food, but strong acid and long boiling weaken it | Needs acid to set, so it suits acid fruit |
| Suitable for vegetarians | No, it comes from animals | Yes, it comes from plants |
| Typical foods | Jellies, marshmallows, gummy sweets, mousses | Jams, jellies, marmalades, fruit preserves |
Scientific explanation
Definition
Gelatin is a protein gelling agent made from animal collagen. It dissolves in warm water, sets into a soft gel on cooling, and melts again at mouth temperature. Pectin is a polysaccharide found in the cell walls of fruit. High methoxyl pectin sets when sugar and acid are present; low methoxyl pectin sets with calcium. The pectin gel stays set when warm.
Working principle
Gelatin chains form a network on cooling that traps water, and the network breaks again at mouth temperature because its links are weak. Pectin chains form a network only when sugar draws water away and acid lowers the charge on the chains, so the chains can join; low methoxyl pectin instead joins through calcium bridges between chains. Once formed, the pectin network is stable at room temperature and in warm food, which is why a jam keeps its set on the shelf.
Apparatus
The books used here name no laboratory apparatus for telling the two apart, so no apparatus list is given.
Measurement procedure
The books used here name no single standard laboratory procedure for telling the two apart. The distinction is made from the definitions and properties given above, not from one test.
Factors affecting readings
For gelatin, concentration and cooling decide firmness, and long boiling or strong acid weakens the set. For pectin, sugar content, acidity and the type of pectin decide the set: high methoxyl pectin needs sugar and acid, low methoxyl pectin needs calcium and sets with little or no sugar. Fruit ripeness changes the natural pectin content of the fruit.
Formulas and calculations
The books used here give no formula for this comparison, so no formula or worked calculation is given.
Industrial applications
- Gelatin is used in soft jellies, marshmallows, gummy sweets and mousses.
- Pectin is used in jams, jellies and marmalades, where the set must survive storage.
- Pectin is used in low sugar spreads, using low methoxyl pectin with calcium.
- Gelatin is used to clarify and to stabilise foams in confectionery.
- Both are used to give body to fruit desserts.
Advantages and limitations
- Gelatin: advantage: melts in the mouth, giving a smooth, soft eating quality. Limitation: melts in hot food and cannot hold a set on a warm shelf.
- Pectin: advantage: gives a firm set that survives storage and warm serving. Limitation: needs sugar and acid, or calcium, so it cannot set a plain liquid alone.
- Pectin: advantage: plant based and suitable for vegetarian food. Limitation: the set is sensitive to the exact sugar and acid levels.
FAQ
Why does jam use pectin and not gelatin?
Jam must keep its set on the shelf at room temperature, and pectin gives a firm set that survives storage, while gelatin would melt.
Can pectin set without sugar?
High methoxyl pectin needs sugar and acid. Low methoxyl pectin sets with calcium and little or no sugar.
Is pectin vegetarian?
Yes. Pectin comes from fruit, while gelatin comes from animals.
Why does my jelly not set?
For pectin, the sugar or acid level may be wrong; for gelatin, the liquid may be too hot or too acid, or too little gelatin may have been used.
