Technology Development Of Gracilaria Agar Extraction By Enzyme Process Replacing Alkali

Agar is a hydrophilic polysaccharide extracted from red algae.As a red algae,Gracilaria is rich in colloid and is recognized as a raw material for extracting agar.With the wide use and increasing demand,agar extraction technology is constantly exploring and improving.Firstly,the physicochemical and gel properties of agar from enzyme extraction and enzyme-assisted extraction were compared with those of alkali-extracted agar in this thesis.Then,the low-viscosity enzyme-extracted agar was prepared by assisting with H₂O₂,and its physicochemical and structural properties were analyzed.And finally,a production workshop with an annual output of 300 tons of low-viscosity enzyme-extracted agar was designed.Firstly of all,the physicochemical properties of enzyme-assisted extracted agar（EAA）and enzyme-extracted agar（EA）were evaluated and compared with those of the traditional alkali-extracted agar（AA）.Compared with EAA and EA,AA showed a significant advantage in the aspect of gel strength（1521±54.5 g/cm²）,sulfate content（0.84%±0.15%）,and 3,6-AG content（29.2%±0.3%）.EAA showed similar properties to AA with lower sewage discharge;therefore,the use of enzymatic assisted process replacing alkali process for agar extraction has great prospects.Moreover,Enzyme extraction technology is more consistent with sustainable development strategies in terms of energy consumption and waste emissions than the alkaline processes,and some of the physicochemical properties exhibited by EA,such as high viscosity,water retention and sulfate content,and low melting temperature,etc.,has a good application prospect in related fields.Secondly,the process of preparing low-viscosity enzyme-extracted agar（EHA）by assisting with H₂O₂ was explored.The optimum process conditions for low-viscosity enzyme-extracted agar were optimized by single factor test with viscosity and gel strength as evaluation parameters:in the 1 L reaction system,the amount of H₂O₂ addtion was 8 mL,initial pH of the reaction was 3.0-4.0,treatment time was 2 h,and treatment temperature was 25℃.Under the optimal condition,the extracted agar still had a significant viscosity reducing effect when H₂O₂ was reused 3 times.Compared with the filtration effect of agar gel solution and the dehydration effect of agar gel,the filtration rate of EHA was significantly expedited,and the gel dehydration rate was increased by 14%compared to EA.In addition,the physical and chemical properties of EHA were analyzed and compared with AA and EA.The results showed that EHA had the lowest viscosity（9.4±0.8 cP）,and lower sulfate content and higher gel strength than EA.TG and SEM results show that EHA had a slightly lower water retention capacity than EA.The production workshop with an annual output of 300 tons of low-viscosity enzyme-extracted agar was designed.The two-shift work system was adopted with 11 employees and three batches per shift.Through material balance,the demand for raw materials,auxiliary materials and water,electricity and steam in the workshop was determined.Through equipment selection,choose the main equipments including stainless steel reaction kettle,plate-and-frame filter press,pusher,oil press,conveyor dryer,ultrafine pulverizer,sewage treatment system,etc.In addition,a simple design description of the treatment process for industrial wastewater is provided.