Agar agar is a thermos-reversible gel and is considered to be the strongest natural gelling agent. It is odor and colorless. It gels even at low concentrations. It is completely soluble in boiling water but also can be dissolved even at low temperatures. It gels at a temperature from 35 to 45C and melts at temperatures from 80 to 95C making it the only hydrocolloid that can gel at sterilization temperatures. Agar Agar has good synergies with sugar and with different hydrocolloids.
| E-No. | E 406 |
|---|---|
| Origin | Seaweed extract |
| Chemical composition |
Galactose and anhydro-galactose; low sulfate content (<4.5%, mostly 1.5–2.5%) |
| Nutritional value (in 100 g) – metabolism |
1425 kJ (340 kcal); slow resorption |
| Fiber content | 2.2% (42% protein, 36% carbohydrates) |
| Toxicology |
No health concerns, consumption generally 1–2 g per day (mild laxative effect at 6 g per day); no ADI value defined; considered as food in Asia, not as an additive |
| Solubility at low temperature (H2O) | Insoluble |
| Appearance of an aqueous solution | Opaque, yellowish |
| Viscosity of solution in water | Low, insoluble in cold water |
| Impact of heat on viscosity in water (pH 7) | Soluble at T>80 °C (176 °F) |
|
Viscosity development in water at pH 7 (T=0–100 °C) |
Forms a thermoreversible gel after the dissolution and cooling to 35 °C (95 °F) (gel melts at T>85 °C (185 °F)) |
| Shear stability | High |
| Thickening effect | High (gel formation) |
| pH stability | Medium, hydrolysis by cooking in an acidic system |
| Decomposition | Combination of heat+low pH (below pH 4) |
| Film formation | High |
| Emulsion stabilization | No |
| Gelation |
Thermoreversible gelation after heating to T>80 °C (176 °F) and cooling to 35 °C (95 °F); also gels in saturated sugar solutions; gelation temperature is independent of sugar concentration |
| Gel strength and gel stability | High gel strength, gels are highly heat-stable |
| Gel transparency | Low |
| Tendency for gel synaeresis | High |
| Impact of electrolytes (cations +, 2+, 3+) | No |
| Reaction with Ca2+ ions | No |
| Protein activity | Low/no |
| Crystallization control | No |
| Synergistic effects with other hydrocolloids |
+ LBG or guar: less syneresis, more elasticity; + 10% LBG: maximum gel strength (+8%); + 10% konjac: maximum gel strength |
| Other synergistic effects | Enhanced gel strength with high sugar concentrations (>60%) for some agar types |
| Negative interactions |
Tannic acid can inhibit the gelling process; gum karaya reduces the gel strength of agar gels; Proton scavengers like potassium iodide, urea, Guanidine, sodium thiocyanate, and so on block the gelling process and prevent agarose gel formation |
| Dosage level in foods | Low, typical 0.5-2%, gelation already at 0.2% |
