Harvest optimization of four Kappaphycus species from the Philippines

The booming seaweed industry in the Philippines has been recently challenged by several problems, including the degrading quality of carrageenan extracts from farmed Kappaphycus species. One emerging concern is the correctness of certain agronomic protocols, specifically the recommended duration of culture of farmed seaweeds. We determined in this study the effect of duration of culture on seaweed biomass and carrageenan quantity and quality of four commercially farmed Kappaphycus species. A mathematical formula was then employed to derive a weekly optimization index (a metric incorporating several parameters or product attributes, viz., biomass, carrageenan yield and gel strength) which was used to determine the appropriate time of harvest. The Kappaphycus species exhibited c. 300% increase in biomass within 4-7 weeks in culture (c. 150 g from an initial biomass of 50 g wet weight) and then a biomass plateau was observed. Carrageenan yield in all seaweeds fluctuated minimally (mean: 55-58%; s.d.: 2-4%), however, gel strength peaked at 8-9 weeks of culture. Highest optimization index was obtained during week 8 for Kappaphycus alvarezii var. alvarezii and week 9 for the rest of the cultured seaweeds (Kappaphycus striatum var. sacol, Kappaphycus sp. aring-aring and Kappaphycus sp. duyan); hence, the recommended harvest times for the respective seaweeds are during these weeks of culture. As several seaweed manuals recommend other culture durations, a revision of these is appealed in order to safeguard the quality of farmed Kappaphycus species. (C) 2010 Elsevier Ltd. All rights reserved.