This study investigated the optimal sequential hydrolysis conditions by comparing with reducing sugar yield ofsequential hydrolysis of Laminaria japonica processing residue. After acid-catalyzed hydrothermal hydrolysis, sequentialenzymatic hydrolysis was performed with single enzymes such as Celluclast® 1.5L, Saczyme, and Alginate Lyase, andtheir mixture. As a result, the yield of reducing sugar by sequential hydrolysis with the mixed enzymes was the highest,but there would be an economical problem with excessive enzyme loading. Therefore, considering the reducing sugaryield and economics, it is thought that hydrolysis by the mixed enzymes has no advantage, thus, using the Celluclast®1.5L in the sequential hydrolysis was practically more appropriate. The optimal sequential hydrolysis conditions ofLaminaria japonica processing residue were determined to be 8% v/w of enzyme injection, 42.6oC of reaction temperature,pH 4.1, and 26 hours of reaction time after acid-catalyzed hydrothermal hydrolysis (0.108 N-HCl, 144oC of reactiontemperature, and 22 minute of reaction time).

To investigate optimal condition of acid-catalyzed hydrothermal hydrolysis of Laminaria japonica, the main constituentsof Laminaria japonica such as cellulose, alginic acid and mannitol were hydrolyzed using acid-catalyzed hydrothermalreaction. Then, we proposed the re-designed experimental method including the predicted optimal conditions of the mainconstituents and performed acid-catalyzed hydrothermal hydrolysis of Laminaria japonica. The coefficients ofdetermination (R2) of Y5 (yield of reducing sugar from Laminaria japonica) were 0.877. P values of Y5 were 0.002,indicating significance, within 1% (p<0.01). The optimum reaction condition for acid-catalyzed hydrothermal hydrolysisof Laminaria japonica determined by the response surface methodology is 143.65oC of reaction temperature, 22min ofreaction time, hydrochloric acid concentration 0.108N, resulting in a production rate of 115.62mg/g-Laminaria japonica.

Acid hydrolysis of cellulose using hydrothermal reaction was conducted to maximize reducing sugar concentration and the response surface methodology (RSM) was applied to study the effects of independent variables, such as reaction temperature (116 ~ 184oC), reaction time (12 ~ 28 min) and hydrochloric acid concentration (HCl, 0.0159 ~ 0.1841 N) on reducing sugar concentration and production yield from the cellulose. With the optimum conditions of the acid-catalyzed hydrothermal hydrolysis, the reducing sugar (RS) was obtained as 369.14 mg-RS/g-cellulose in 172.77oC of the reaction temperature, 28.41 min of the reaction time and 0.067 N of the hydrochloric acid concentration. The glucose (Glu) was obtained as 281.94 mg-Glu/g-cellulose in 154.70oC of the reaction temperature, 11.59 min of the reaction time and 0.184 N of the hydrochloric acid concentration.