Autecology and identification of carrageenan type of Gracilaria manilaensis under different light intensities, salinities and pH

Abstract

The high demand of seaweed for their polysaccharide namely carrageenan leads to the commercial production of carrageenophytes through mariculture. Mariculture has also become the alternative way to meet the growing demand of seaweed as raw materials. Based on literatures, it is well documented that growth rate and carrageenan yield depend on environmental factors such as salinity, pH, temperature, light intensity and water movement. In this study, growth rate and carrageenan yield of Gracilaria manilaensis, a red seaweed, were determined at different conditions. G. manilaensis was cultured under laboratory conditions in a 500 mL flask of seawater at different light intensities (100, 500 and 1000 lux), salinities (15, 20, 25 and 30 psu) and pH (7.6, 7.8, and 8.0) for 21 days. At the end of experiment, the growth rate was determined followed by carrageenan analysis. Then, the ground seaweed samples were used for Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) to identify the carrageenan type of each treatment. From the analysis, the highest growth rate was observed at high light intensity, low salinity and slightly alkali pH (1000 lux, 15 psu and pH 7.6). Meanwhile, the carrageenan yield was highest at low light intensity, high salinity and more towards alkaline pH (500 lux, 25 psu and pH 8.0). Result also showed that carrageenan yields from G. manilaensis under laboratory conditions were higher compared to farmed G. manilaensis (50.2 ± 10.9 %). This indicates that the quality of G. manilaensis in term of carrageenan content can be optimized under certain growth conditions. Analysis of carrageenan types showed that different types of carrageenan; kappa, iota and lambda were observed under different conditions. Kappa carrageenan was the most dominant type identified in the samples followed by lambda and iota. This demonstrated carrageenan can change under specific conditions. Findings from this study are important as baseline information to culture Gracilaria for high biomass or for carrageenan production as both differed in growth requirement. The identification of different types of carrageenan from Gracilaria indicates that this species has high potential to be commercialized for pharmaceutical and food industries