Table 6.

Gelling agents used in culture media [60,63,67]

Origin	Type	Gel texture	Necessary ions	Gelling temperature	Melting temperature
Red seaweed extracts	Agar	Firm, brittle, transparent Acid-resistant (up to pH 3.5)		<35°C	>80°C
Red seaweed extracts	Carrageenans (kappa, iota)	Kappa Elastic or firm (depending on concentration), transparent, glossy. Very fast gel setting	K+	<40°C	>65°C
		Iota Elastic, transparent, reformable	Na+ or K+
Brown seaweed extracts	Sodium alginate	Flexible gel	Ca2+	Whatever the temperature	Thermo-irreversible
Extracts of vegetable by-products	HM Pectin	Gels in an acidic environment (pH < 3) and in the presence of sugar Slow gel setting ‘Spreadable’ gel		<65°C	Thermo-irreversible
Extracts of vegetable by-products	LM Pectine	Brittle, transparent	Ca2+		Thermo-reversible
Biosynthetics	Gellan gum	Transparent, shiny, firm Stable up to pH 3		<90°C	>90°C
Animal	Gelatin	Elastic gel, transparent		<20°C	>40°C
Xanthomonas campestris bacteria	Xanthan gum (+carob bean gum)	Stable over a wide temperature and pH range Soft elastic gel in combination with carob bean gum and in the presence of salts			270°C thermo-reversible
Plant exudates	Arabic gum	Soft gel (>10% of final volume) Stable in acidic medium Heating must be limited in time as there is a risk of loss of the gum's gelification capacity
Animal	Egg			Thermo-irreversible