Studies on Gracilaria gracilis (Stackhouse) Steentoft, Irvine and Farnham and Gracilaria aculeata (Hering) Papenfuss from southern Africa. II. Agar production

The production of agar by two southern African agarophytes, Gracilaria gracilis and G. aculeata was studied. Wild collected (field populations) and laboratory cultured (22°C, 100μmolm−2 s−1, 35%±330μmolN) material were compared. Pre-treatment with alkali reduced agar yields from both species but did not significantlys influence gel strength, gelling temperature and melting temperature. Yields, gel strengths, gelling temperatures and melting temperatures of agar extracted from wild and cultured material of both species were not significantly different. Agar yields of G. gracilis ranged from 41.6 – 49.1% dry weight, without alkali pre-treatment, which was reduced to 11.1 – 17.7% with alkali pre-treatment. Gel strength was between 427–507gcm−2, with ranges of agar melting and gelling temperatures of 82° – 89.5°C and 32° – 42.3°C respectively. Agar yields of G. aculeata ranged from 26.1 – 29.0% dry weight without alkali pre-treatment, which was reduced to 8.4 – 13.0% with alkali pre-treatment. The range of gel strength was 424–632gcm−2, with ranges of agar melting and gelling temperatures of 81.7° – 90.5°C and 42.7° – 50.3°C respectively. Based on their gel strengths (generally