Agar from Gracilariopsis heteroclada from Panay Island, Philippines
This paper aims to determine the optimum NaOH pretreatment strength and duration and also the monthly variations in gel strength, agar yield and sulfate content of agar from Gracilariopsis heteroclada (Zhang et Xia) Zhang et Xia. Samples collected from Leganes, Iloilo, Philippines were pretreated with NaOH at different strengths (1,3 and 5%) and duration (30 min and 60 min) at 85-90°C. Agar extractions were done by the method of Nelson et al. (1983) Agar yield was calculated based on Santos (1980). Gel strength and sulfate content were determined using the methods of Aguilar-Santos and Doty (1978) and Jackson and McCandless (1978), respectively. Agar gelling and melting temperatures were analyzed in triplicate (Whyte and Englar, 1976). Viscosity in cps, moisture and ash contents in per percent, were determined using standard methods. Analysis of variance and Duncan’s multiple range test were used to compare the gel strength for the NaOH pretreatment experiment and the different monthly samples. Correlation analysis was carried out to determine the relationship between the different parameters analyzed. Highest gel strength (641 gm cm-2 ) and lowest sulfate content (7.66 gm/mg SO4) were obtained following alkaline pre-treatment with 5% NaOH for 30 min with agar yield of 32.4 per cent. Gelling and melting temperatures of agar with the highest gel strength were 40°C and 80°C, respectively, while specific viscosity, moisture and ash contents were 7.5 cps, 12.2% and 4.32%, respectively. Agar yield was negatively correlated with NaOH pre-treatment (P<0.05). Sulfate content was negatively correlated with gel strength (P<0.05). Gel strength, agar yield and sulfate content showed monthly variation. Sulfate was highly correlated with gel strength (P<0.05). Agar yield was positively correlated with month, while it is negatively correlated with gel strength (P<0.05). The results showed that agar from Gracilariopsis heteroclada has a very good potential for use as raw material for the production of food, drug and industrial grades of agar because of its superior gel strength.