Physical properties

The thickening and gelling properties of the different types of carrageenan are quite different. For example, kappa carrageenan forms a firm gel with potassium ions while iota and lambda are only slightly affected. Iota carrageenan interacts with calcium ions to give soft elastic gels but salts have no effect on the properties of lambda carrageenan. Application of these combinations requires experience and understanding of carrageenans but this expertise is available from the major suppliers of this material.

 

Solution properties

All carrageenans are soluble in hot water. However, only lambda and the sodium salts of kappa and iota are soluble in cold water. Lambda carrageenan gives viscous solutions which show pseudoplasticity or shear-thinning when pumped or stirred. These solutions are used for thickening, particularly in dairy products, to give a full body with a nongummy, creamy texture. The influence of temperature is an important factor in deciding which carrageenan should be used in a food system. All carrageenans hydrate at high temperatures and kappa and iota carrageenans in particular exhibit a low fluid viscosity. On cooling, these carrageenans set between 40–60ºC, depending on the cations present, to form a range of gel textures.

 

Acid stability

Carrageenan solutions will lose viscosity and gel strength in systems below pH values of about 4.3. This effect is due to autohydrolysis which occurs at low pH values as carrageenan in the acid form cleaves the molecule at the 3,6-anhydrogalactose linkage. The rate of autohydrolysis increases at elevated temperatures and at low cation levels. However, once it has been cooled below the gelling temperature, carrageenan retains the sulfate-bound potassium ions and this prevents autohydrolysis proceeding. Consequently, in acidic products, the carrageenan should be added at the last moment to avoid excessive acid degradation and, if possible, acid should be added to the food immediately before depositing and filling to minimise polymer breakdown.

Table shows approximate processing times at various pH values for a gel produced with 0.5% kappa carrageenan and 0.2% potassium chloride, such that no more than 20– 25% of the

 

 

gel strength is lost when the solution is cooled. In general, each 0.5 pH unit reduction will decrease the potential processing time by a factor of three. Times will vary somewhat depending on carrageenan concentrations or system ingredients such as salts and sugars. In a continuous process the processing time should be kept to a minimum. In systems above about pH 4.5 the process conditions become irrelevant as the carrageenan solution is stable to most food processing times.

 

Gel properties

Hot solutions of kappa and iota carrageenans set to form a range of gel textures when cooled to between 40 and 60ºC depending on the cations present. Carrageenan gels are thermally reversible and exhibit hysteresis or a difference between setting and melting temperatures. These gels are stable at room temperature but can be remelted by heating to 5–20ºC above the gelling temperature. On cooling the system will re-gel. The ionic composition of a food system is important for effective utilisation of the carrageenan. For example, kappa carrageenan selects for potassium ions to stabilise the junction zones within the characteristically firm, brittle gel. Iota carrageenan selects for calcium ions to bridge between adjacent chains to give typically soft elastic gels. The presence of these ions also has a dramatic effect on the hydration temperature of the carrageenan and on its subsequent setting and remelting temperatures. For example, iota carrageenan will hydrate at ambient temperature in water but the addition of salt raises the gel point so that the solution is converted into a gel with distinct yield point which is used for cold-prepared salad dressings. Sodium salts of kappa carrageenan will hydrate at 40ºC but the same carrageenan in a meat brine will only show full hydration at 55ºC or above.

 

Synergism with other gums

Hot solutions of kappa carrageenan-locust bean gum form strong elastic gels with low syneresis when cooled below 50–60ºC. Locust bean gum is a galactomannan with a level of substitution of one part mannose to four units of galactose. However, this substitution is not regular and regions of the locust bean gum are unsubstituted. The mannose-free regions of the locust bean gum are able to associate with the repeating helical structure of carrageenan dimers to form gels. The maximum interaction, and hence peak rupture gel strength, occurs at a ratios between 60:40 and 40:60 kappa carrageenan to locust bean gum as shown in Fig. 5.6. These polymer combinations are used in very large quantities in cooked meats and in gelled petfoods. Kappa carrageenan and clarified locust bean gum mixtures can be used for cake glaze and flan gels or formulated to give clear water dessert gels with an elastic cohesive gel texture like gelatin. Recent improvements in formulations of kappa and iota carrageenan blends are also able to give elastic cohesive gels similar to gelatin in texture. Konjac flour (E425i) interacts even more strongly than locust bean gum to form strong elastic gels with kappa carrageenan which are at least four times the rupture strength of kappa carrageenan alone. Probably the best known synergistic carrageenan interaction is that involving milk proteins. Some of the first uses of carrageenan were in milk gels and flans, and in the stabilisation of evaporated milk and ice cream mixes. In these applications the kappa carrageenan forms a weak gel in the aqueous phase and it also interacts with positively charged amino acids in the proteins in the surface of the casein micelles.

Applications

Dairy products: The main applications for carrageenan are in the food industry, especially in dairy products. Frequently, only very small additions are necessary, 0.01-0.05 percent. For example, kappa carrageenan (at 0.01-0.04 percent) added to cottage cheese will prevent separation of whey, and a similar amount added to ice cream also prevents whey separation that may be caused by other gums that were added to the ice cream to control texture and ice crystal growth. The cocoa in chocolate milk can be kept in suspension by addition of similar amounts of kappa; it builds a weak thixotropic gel that is stable as long as it is not shaken strongly. Dry instant chocolate mixes, to be mixed with water or milk, can have improved stability and mouth feel using lambda or a mixture of carrageenans.

Lambda or a mixture can also improve liquid coffee whiteners by preventing the separation of fat; these applications require 0.2-0.3 percent additions, but much smaller quantities will prevent fat separation in evaporated milks. Those small containers of UHT sterilized milk found in the refrigerators of some hotels may have kappa added to prevent fat and protein separation. Lambda or kappa may be added to natural cream to help maintain the lightness (incorporated air) if it is whipped. Many more uses in milk and dairy products can be found in the references below.

Water-based foods: With the appearance of bovine spongiform encephalopathy (BSE, or mad cow disease) and foot-and-mouth disease, efforts have been made to find suitable substitutes for gelatin. Gelatin jellies have long been favoured because they melt at body temperature, giving a smooth mouth feel and easy release of flavours. However, if they are stored for a day or two, they toughen and are less pleasant to eat. Gels made from iota carrageenan have the disadvantage of a high melting temperature, so they are not as smooth to eat as gelatin gels. They do not melt on hot days and do not require refrigeration to make them set, so these are advantages in hot or tropical climates, and a further advantage is that they do not toughen on storage. In the last two years there have been several claims by food ingredients companies for products, made from a mixture of hydrocolloids that imitate the properties of gelatin. Carrageenan producers find that by combining various carrageenans with locust bean gum, konjac flour and starch, they can provide a variety of melting and non-melting gels and gel textures to meet the requirements of most of their clients. Long-life refrigerated mousse desserts, based on carrageenan and pectin rather than gelatin, are suitable for vegetarians and some ethnic groups.

Conventional fruit jellies are based on pectin and a high sugar content to help set the jelly. In a low- or non-calorie jelly the pectin must be replaced, and mixtures of kappa and iota have proved to be suitable. Fruit drink mixes to be reconstituted in cold water contain sugar (or aspartame), acid and flavor. Addition of lambda carrageenan gives body and a pleasant mouth feel. Sorbet is a creamy alternative to ice cream with no fat; use of a mixed kappa and iota together with locust bean gum or pectin provides a smooth texture to the sorbet.

Low-oil or no-oil salad dressings use iota or kappa to help suspend herbs, etc., and to provide the mouth feel that is expected from a normal salad dressing. The low oil content of reduced-oil mayonnaise normally gives a thin product, rather like a hand lotion; additives are needed to thicken it and to stabilize the oil-in-water emulsion. A combination of carrageenan and xanthan gum is effective. Xanthan gum is made by a bacterial fermentation process; its development was pioneered in the early 1960s by the Kelco Company, then the largest producer of alginate; it is now an accepted and widely used food additive. The interaction of carrageenan and protein can be used in the clarification of beer, with the complex formed precipitating from the wort. More water-based applications of carrageenan are given in the references below.