Tween (Polysorbates) (Nonionic Surfactant)

Tween (Polysorbates)

(Nonionic Surfactant)

Overview:

Tween (also known as Polysorbates) is a nonionic surfactant with a characteristic odor and a warm, slightly bitter taste. It consists of a series of partial fatty acid esters of polyoxyethylene sorbitan. Tween is widely used as an emulsifier and solubilizer for oils. Polysorbates are generally considered non-toxic and non-irritating. According to WHO, the acceptable daily intake (ADI) of total polysorbates can be up to 25 mg/kg body weight.

Names:

• Generic Name: Polysorbates (Polyoxyethylene sorbitan fatty acid esters)

• English Name: Polyoxyethylene Sorbitan Fatty Acid Esters

• Other Names: Tween, Polysorbates, Polysorbatum

Categories:

• Emulsifier

• Nonionic surfactant

• Solubilizer

• Wetting agent

• Dispersant/Suspending agent

Properties:

• Appearance: Viscous liquid ranging from pale yellow to amber (varies depending on molecular weight)

• Odor/Taste: Characteristic odor, warm and slightly bitter

• pH: Approx. 6–8 (5% w/v aqueous solution)

• Flash Point: 149°C

• Stability:

  • Stable in presence of electrolytes, weak acids, and weak bases

  • Gradually saponifies under strong acids or strong alkalis

  • Sensitive to oxidation and hygroscopic

  • May form peroxides upon long storage; drying may be necessary if required

Mechanism:

Due to the presence of hydrophilic polyoxyethylene groups in its molecular structure, polysorbates are strongly hydrophilic and act as nonionic surfactants.

Applications:

1. Biological Research:

   • Used to emulsify proteins without denaturing them, unlike ionic detergents such as SDS.

   • Nonionic surfactants like Tween and Triton X-100 preserve protein structure and minimize disruption of protein–protein interactions.

2. Blocking Agent in Immunoassays:

   • Used in techniques like Western blotting to block non-specific binding sites on membranes without displacing target proteins.

   • Tween-20 helps renature antigens and enhance specificity.

   • Common blocking agents include BSA, non-fat milk, casein, gelatin, and Tween-20 (typically 0.05–0.1% solutions).

3. Emulsification in Formulations:

   • Commonly used as O/W (oil-in-water) emulsifiers in pesticides, food, and cosmetics.

   • Enhance stability when used with other emulsifiers like sodium lauryl sulfate or Span-type emulsifiers.

   • Efficient at solubilizing essential oils in aqueous solutions.

   • Tween-20 is milder, while Tween-80 has stronger emulsifying properties.

4. Pharmaceutical Use:

   • (1) Used as solubilizers for certain drugs.

   • (2) Exhibits hemolytic activity; Tween-80 has the weakest hemolytic effect.

   • (3) Aqueous solutions may appear cloudy when heated and become clear upon cooling — this does not affect quality.

   • (4) May interfere with the activity of preservatives in solutions.