Question

Which of the following is an extract from red algae?

• A. Carrageenan
• B. Algin
• C. Agar
• D. Xanthan

Hint:

Red algae → Carrageenan; used in gels and food products for thickening.

Answer 1

The Correct Option is A

Red Algae

Red algae (Rhodophyta) are marine organisms that produce several important hydrocolloids used in food, pharmaceuticals, and biotechnology. These extracts are valued for their gelling, thickening, and stabilizing properties.

Let's examine each option:

1. Carrageenan

Carrageenan is a natural polysaccharide extracted from certain species of red seaweed. It comes in three main forms (kappa, iota, and lambda) with different gelling properties.

• Used as a thickener/stabilizer in dairy products, toothpaste, and processed foods
• Forms thermo-reversible gels
• Derived from species like Chondrus crispus (Irish moss) and Kappaphycus alvarezii

2. Algin

Algin (or alginate) is extracted from brown seaweed (Phaeophyceae), not red algae.

• Forms strong gels with calcium ions
• Used in wound dressings, food thickeners, and dental impressions
• Comes from species like Macrocystis pyrifera (giant kelp)

3. Agar

Agar is indeed extracted from red algae, particularly species of Gelidium and Gracilaria.

• Forms strong gels at low concentrations
• Widely used in microbiology as a culture medium
• Common in Asian desserts and vegetarian gelatin substitutes

4. Xanthan

Xanthan gum is a bacterial polysaccharide produced by Xanthomonas campestris, completely unrelated to algae.

• Produced through fermentation
• Used as a food additive and rheology modifier
• Common in gluten-free products

Why Both Carrageenan and Agar Are Correct

The question asks which extracts come from red algae. Both carrageenan and agar are correct answers as they are both derived from different species of red algae. However, they have different applications:

Extract	Source Algae	Main Uses
Carrageenan	Chondrus, Eucheuma, Kappaphycus	Dairy stabilization, meat products
Agar	Gelidium, Gracilaria	Microbiology, food gels

Why Not the Other Options?

• Algin: Comes from brown algae, not red algae
• Xanthan: Bacterial product, not algal at all

Final Answer

The extracts from red algae are Carrageenan and Agar.