Agar yield, gel strength and sulfate content in Gracilariopsis heteroclada farmed in brackishwater canals

Abstract

This paper aimed at determining the optimum NaOH pretreatment strength and duration and the monthly variations in gel strength, agar yield and sulfate content of agar from Gracilariopsis heteroclada (Zhang et Xia) farmed in brackishwater canals in Leganes, Iloilo, Philippines, during the dry season (October to March). The highest gel strength (641 g/cm²) and lowest sulfate content (7.66 µg/mg SO₄) were obtained following pretreatment with 5% NaOH for 30 min. The agar yield from this treatment was 32.4% and negatively correlated with percent alkali used (r = -0.92465, p<0.05) and gel strength (r = -0.72711, p<0.05). The sulfate content was also negatively correlated with gel strength (r = -0.40911, p<0.05). The gel strength (274-622 g/cm²), agar yield (18.1-38.1%) and sulfate content (11.4-22.9 µg/mg) showed monthly variations. Water temperature ranged 30-35°C, salinity 26-32 ppt, and rainfall 39.4-561 mm. The agar yield was negatively correlated with temperature (r = -0.57286, p<0.05) and rainfall (r = -0.66435, p<0.05). Results showed that agar from G. heteroclada has very good potential for use as a raw material in the production of food, drug and industrial grades of agar because of its superior gel strength.