FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

Gracilaria sp., a red alga, was used as the material to produce bio ethanol. The hydrolytic processes for sugar conversion and yeast fermentation conditions were tested. The process of the highest amount of fermentable sugars obtained was that 10.0% Gracilaria (w/w, dry base) was prepared in a 0.5 NH₂SO₄ solution and then autoclaved for 60 min at 121 ℃. High performance liquid chromatography (HPLC) analysis showed that most hydrolysate were galactose 20-27 mg/mL, glucose 2-5 mg/mL, and 5-hydoxymethyl furaldehyde (HMF, an ethanol fermentation inhibitor) 4-6 mg/mL, and there was no fufural (also an ethanol fermentation inhibitor) found in the HPLC profile. The hydrolysate was further treated with overliming by adding sodium hydroxide, calcium hydroxide, or calcium oxide. Results showed that the HMF in the hydrolysate reduced to less than 50% with each of the treatments. The overlimed hydrolysate was then prepared as media for the test of 38 different yeast strains to produce ethanol. It was found that the competent strains were B4 and B10, which could produce about 10 and 8 g ethanol per liter, respectively. Futher observation of the fermentation time, a highest yield of ethanol (8.7 g/L) was achieved in a batch culture at the 7th day. The ethanol producing ratio of Gracilaria hydrolysate was around 13-16%, while converted and calculated based on the dry base (w/w).