Extraction of carrageenan from Eucheuma spinosum using ohmic heating: optimization of extraction conditions using response surface methodology

Seaweed is an important global commodity since it is the source of many important products such as carrageenans, agar, alginates, and bioactive compounds. Seaweed processing is an energy intensive process since it involves heating large volumes of seaweeds in alkali solutions at high temperatures for up to six hours. To increase energy efficiency, an ohmic based processing system has been developed but has not been tested thoroughly. Therefore, the objective of this study was to identify optimum processing conditions for extraction of carrageenan from Eucheuma spinosum using ohmic heating technology. The experiment was conducted using Central Composite Design with four variables, i.e. extraction temperature, extraction duration, KOH concentration, and solution to seaweed ratio. Following the extraction process, carrageenan was recovered through precipitation using 90% isoprophyl alcohol solution. Results of experiments indicate that extraction yields varied from 29.6-62.4% dry basis with viscosity and gel strength varied from 259-290 mPa.s and 42.54-70.41 g/cm2 respectively. Statistical analysis indicated that extraction yield can be adequately modeled using the four variables and optimum extraction yield (61.59%), gel strength (53.48 g/cm2 ), and viscosity (284.51 mPa.s) were achieved at 95 °C extraction temperature, 240 minutes of extraction time, 0.4M KOH concentration, and 45:1 solution to seaweed ratio.