Effect of drying temperature on carrageenan yield and quality of Kappaphycus alvarezii (Rhodophyta, Solieriaceae) cultivated in Brazil

This study evaluates the effect of different drying temperatures on the properties of semi-refined (SR) and refined (R) carrageenan extracted from Kappaphycus alvarezii cultivated in Brazil. Drying kinetics was studied in seaweeds under the following treatments: sun drying (control) and drying at 40, 60, and 90 °C in convective air dryer. Drying was carried out until the moisture content of seaweeds reached values below of 30 % on wet basis. Significant reductions in drying time were observed with the increase of temperature. At 90 °C, 30 % moisture content was reached in 100 min, as compared with the 1,440 min required by the sun-drying treatment. SR yields showed no significant differences when compared to the control, varying from 40 to 44 %, while R had a significantly higher yield (30 %) at 90 °C in relation to control (26 %). Gel strength of SR was significantly higher in the sun-dried samples (1,685.1 g cm⁻²) and 60 °C samples (1,727.2 g cm⁻²), but no significant differences were observed in R gel strengths. Lowest syneresis was observed in both SR (9.8 %) and R (10.3 %) after the treatment at 90 °C. Significantly lower viscosity values were observed for SR at 60 °C (233 mPa s) and at 90 °C (175 mPa s), as for R, the lowest value was observed at 90 °C (205 mPa s). Based on these results, it was concluded that best results for both types of carrageenan are obtained drying at 60 °C.