A wide range of textures and technical functions can be achieved by hydrocolloids (gums) in food products. Hot and cold-water-soluble hydrocolloids are available, which can for example thicken and gel cold, whilst some thicken and gel on heating and cooling. Others dissolve cold and gel on heating (e.g. Hypromelose and cellulose gel – rather like egg white). Some of the more common hydrocolloids and their origins and applications are listed in Tables 1 and 2. Some hydrocolloids are useful in bake-fast products, preventing boil-out on cooking. Hydrocolloids are forms of soluble pre-biotic fibre; in particular gum acacia offers the possibility of ‘a source of fibre’ label in ‘healthy eating’ confectionery.
The shear-thinning, ‘melt-in-the-mouth’ characteristics of hydrocolloids are ideal for fat- and sugar-reduced products; producing a light texture and shiny finish with excellent flavour release and translucent appearance. The semi-gelled nature of xanthan gum solutions and certain carrageenan and Gellan-based systems is excellent for suspending insoluble materials such as cocoa powder or an oil emulsion – whilst maintaining an apparently low, pourable viscosity. Hydrocolloids are suitable for vegetarians and most are used at a 5-10 times lower concentration than a typical starch thickener – which produces a heavy, pasty texture by comparison, which is often opaque with poor flavour release and a matt finish . In addition, hydrocolloids are resistant to enzymes (present in salad dressings and dips for example) and usually have much better resistance to high shear mixing and high processing temperatures at low pH. Starch in contrast, cannot survive homogenisation once hydrated.
There is sometimes a case for using a combination of hydrocolloid and starch to produce a heavier texture when required – as long as the processing conditions are not too severe for the starch. Examples include sliceable custard for vanilla slices (cold process) and cheesecake (short-duration cook at neutral pH and without shear). In addition, the flavour- masking properties of starch can actually be an advantage in certain types of dressing with high levels of added vinegar (salad dressing).
Table 1: Cold Soluble Hydrocolloids
| Cold Soluble Hydrocolloid | Description |
|---|---|
| Gum Acacia | A tree exudate with emulsifier and gelling properties at higher use levels. Used in spray dried flavours, flavour emulsions, beverages and confectionery gels and coatings. |
| Guar Gum | Milled seed parts, thickener, slight beany flavour and slimy texture at high levels. Often used with xanthan gum in dressings and dairy systems. This combination can gel after heating and cooling. |
| Low Methoxy (LM), Pectin and Amidated Pectin | Chemically modified pectin producing a calcium-dependent gel. Amidated pectin is used for hot-prepared gelatine-free trifle jellies (buffer salts adjust the setting temperature). LM pectin is also used in starch-based dairy desserts and sauces – to improve texture. |
| Xantham Gum | A natural thickener manufactured by fermentation. Almost gel-like in solution, so well-suited to stabilising emulsions, batter coatings and coleslaw dressings. Synergy with guar, LBG and Konjac. Foam stabiliser and freeze/thaw stabiliser. Used in gluten-free bakery products and improves the texture of cakes. |
| Sodium Alginate | Brown seaweed extract, gelled by calcium. Use with buffer salts to control setting rate and produce bake-fast gels. Used in vanilla slices, restructured fruit and ice cream. Will dissolve hot in milk. |
| Lambsa Carrageenan | Soluble in cold milk, forming a soft gel (often used with phosphate). Present in commercial Carrageenan blends with iota and kappa types (all derived from red seaweed). Used in cold make-up dairy desserts and to modify the hot viscosity and final texture of kappa Carrageenan gels and dairy drinks. |
| Cellulose Gum | Chemically modified thickener forming creamy, transparent solutions. Stabiliser for foams, acid dairy drinks, fruit drinks and ice cream. Can also stabilise some acid dairy systems to avoid gelation. |
| Cellulose Gel (Hypromelose) | Gels on heating. Used vegetarian burgers, hot fillings, glazes and coatings. |
Table 2: Hot soluble hydrocolloids
(*variants with lower temperature solubility are also available)
| Hot Soluble Hydrocolloids | Description |
|---|---|
| Locust Bean Gum (LGB)* | Milled seed parts, thickener. Synergistic thickening/gelling with xanthan (gels on cooling). Synergistic gelling with kappa carrageenan. Used in dairy ice cream (often with guar). Also pet food. |
| Agar* | Red seaweed extract, gelling agent. Does not require low pH, high solids or added salts to gel. Good acid stability. Produces brittle, bake-fast gels on cooling (low setting temperature). Some types are synergistic with LBG for stronger, more elastic gels. Higher soluble solids improve gel clarity. |
| High Methoxy (HM) Pectin* | Fruit peel extract used in acidic systems also requires high solids for gelling. Excellent acid stability. Transparent gels. Widely used in jam (bake fast). Improves texture in starch systems like custard. Stabilises acid dairy drinks and also used in cold-prepared emulsions (especially dairy). |
| Kappa Carrageenan | Red seaweed extract, transparent, brittle gel on cooling (does not require high solids). Stronger, dryer elastic gels with LBG. All carrageenans have limited acid stability. Used in low sugar jams, gelatine-free trifle jellies, dairy drinks, ice cream and pet food. Medium setting temp (potassium dependent. |
| Iota Carrageenan | Red seaweed extract, soft, flexible gel on cooling. Used in dairy desserts confectionery (synergy with starch) and water jellies. High setting temperature (calcium dependent). |
| Gellan (High Acyl or Low Acyl) | Produced by fermentation. Thickens or gels on cooling (does not require high solids). Use with buffer salt. Better heat stability than carrageenan. Wide range of gel textures possible (sensitive to mineral salts). Gelled confectionery, dairy systems, fluid gels in drinks and herb dressings (with xanthan/LBG). |
| Konjac | Milled plant tuber, thickener and gelling agent. Similar synergism to LBG. Widely used as a gelling agent in Asia (high pH used). |
| Micro Crystalline Cellulose* | Thickener and stabiliser, requires high shear. UHT Dairy drinks, cocoa suspension. |
Shelf-life Improvement
Hydrocolloids can increase shelf-life in starch-thickened systems by inhibiting staling in baked goods and preventing gelling and syneresis in starch-thickened sauces. A heavy and pasty frozen cheesecake with poor flavour, a squeezable mustard sauce that goes solid in its pot before the end of its shelf-life, a dressing that separates into two layers – can all be indicators of starch systems lacking hydrocolloid addition.
Hydrocolloids can also control ice crystal growth in frozen products (CMC , LBG and xanthan are particularly effective). A synergistic combination of xanthan and LBG (often with guar) can improve texture and reduce syneresis in dairy systems such as cottage cheese dressings.
Xanthan gum is particularly effective at stabilising the oil droplets in non-dairy food emulsions to prevent creaming and separation. A coleslaw dressing thickened with guar alone will be a little slimy and ‘stringy’ and will have a limited shelf-life as the dressing runs off the vegetables. A synergistic combination of guar and xanthan gum will produce a creamier texture with improved ‘cling’ to the cut vegetable surfaces – extending the shelf-life. In UHT dairy drinks, carrageenan or microcrystalline cellulose (often with cellulose gum) can provide a creamy mouthfeel and suspend cocoa powder.
Gelatine, Egg and Gluten Replacement
Hydrocolloids are often used for gelatine replacement. There is no single hydrocolloid gelatine replacer – the best option being dependent on the particular food type and process. Even when carefully selecting the hydrocolloids for a gelatine-free system, some change in process will often be required (usually associated with a higher setting temperature). This is because the setting of gelatine gels can often be delayed by continual stirring – even at low temperature as in some dairy gels. However the setting of hydrocolloids cannot generally be delayed in this way and continued stirring at low temperature will result in a permanent loss of gel strength in a hydrocolloid system. If there is a production hold up with a gelatine system and it sets before depositing – the situation can often be rescued by re-mixing and melting the gelatine gel. Such product re-cycling is not usually possible in gelatine-free systems. Agar and Gellan are probably the most flexible with respect to low setting temperature and product re-cycling.
Amidated pectin in conjunction with calcium present in fruit (or added as a calcium salt) – is often used in gelatine-free trifle jellies. Agar and locust bean gum in combination are one of the best gelatine replacement systems in manufactured dairy desserts.
The hot gelling properties of gluten and egg in bakery products can be replaced by cellulose gel in conjunction with hot swell starches, whey protein, gluten-free flours or xanthan gum. Other systems which can reduce the level of egg as a cost-saving measure include xanthan/locust bean gum and carrageenan.
The foaming properties of egg white in meringue can be replaced by cellulose gel or a combination of microcrystalline cellulose with cellulose gum and xanthan gum.
How to use hydrocolloids
Solubility is one of the main challenges associated with hydrocolloids – resulting in reduced performance, with either lumping (due to poor dispersion) or graininess (due to insolubility).If a hydrocolloid is gelled by calcium ions for example, it will dissolve best in the absence of calcium ions. Adding a sequestrant such as sodium citrate is one way of temporarily removing the calcium ions from solution to encourage solubility. Fine mesh hydrocolloids will dissolve faster (but are prone to lumping) whilst coarse mesh ingredients disperse better but dissolves more slowly. There are certain tricks which can be used to improve dispersion – from simply mixing the hydrocolloid with other dry ingredients – to pre-dispersing the hydrocolloid in oil or liquid flavour – prior to mixing into the water phase. Fine mesh size may be required to achieve full solubility in milk, fruit juice, higher sugar solids etc. although high shear mixing may still be needed. Overall, hydrocolloids vary in the best conditions for dissolving them – some will dissolve more quickly if heated (locust bean gum and pectin) whilst others (HPMC and MC) will only dissolve cold. Whilst carrageenan and micro crystalline cellulose are widely used to stabilise RTD dairy drinks, some hydrocolloids can cause phase separation in chilled dairy drinks especially at higher use-levels. Certain types of pectin tend to be less prone to this effect. Hydrocolloids generally in combination with polymers such as maltodextrin or gelatine can result in phase separation to produce in effect a water-in-water dispersion.
Freeze/Thaw Stability of Hydrocolloids
As a general rule, un-gelled hydrocolloid solutions and weak, elastic hydrocolloid gels will have better freeze/thaw stability than hydrocolloid gels with a strong brittle texture. Most hydrocolloids can reduce retrogradation of starch gels, which tends to improve freeze/thaw stability. Cellulose gum and xanthan gum are particularly effective in imparting freeze/thaw stability. Obviously, increasing soluble solids improves freeze/thaw stability – so reduced-sugar products are harder to stabilise.