Recovery Of Poly γ-glutamic Acid And Preparation Of Poly γ-glutamic Acid Resin

Poly y-glutamic acid (y-PGA) is a homopolyer synthesized by microorganisms. It is a kind of high molecular compound polymerized with a-amino and y-carboxyl on glutamic acid monomer (type D or L) in the form of amide bond. It has a lot of excellent properties such as great water-soluble, biocompatibility, biodegraded, nontoxic effects, which make y-PGA broad application prospects in fields of agricultural, medicine, cosmetics, food, and environmental protection.In this paper, three aspects were researched including:the bacteria liquid separation with flocculation method from high viscosity of y-PGA fermentation broth; the determination of y-PGA average molecular weight by Chemical method; the crosslinking technology of y-PGA water-absorbent resin with y-PGA as raw materials.For the separation process of y-PGA fermentation broth it was determined that flocculant was chitosan through a series of single-factor experiment and orthogonal test design. The other flocculation conditions as follows:The fermentation broth was adjusted in pH4.0, then hydrolyzed in 80℃ for 30 min, chitosan dosage was 400 mg/L, pH was about 4.0, stirring speed was 200 r/min, stirring temperature and time were respectively 70 ℃C and 15 min. Compared with diatomite filtration method, the ratio of bacterium removing and recovery were beyond to 99.8% and 94.3%, increased by 5.1% and 2.7%, respectively.2,4-dinitrofluorobenzene was chosen for the derivatization reagent of y-PGA. The four factors including FDNB dosage, pH, reaction temperature and time were investigated. The derivatization condition was studied by orthogonal test design, which obtained as follows:the amount of 50 mM FDNB solution was 80 μL/mL, pH value was about 8.5,the reaction temperature was 65℃,and the reaction lasted for 50 min in dark condition. The mole number of free y-carboxyl of y-PGA was determined with GC, and then the average molecular weight of y-PGA can be calculated. The result was consistent with that by GPC.The preparation of y-PGA water-absorbent resin was studied. With polyethylene glycol diglycidyl ether (PEGGE) as crosslinking agent, the influence of y-PGA concentration, amounts of PEGGE, pH value, reaction time and temperature, NaCl concentration, y-PGA molecular weight on the crosslinking reaction of y-PGA water-absorbent resin were have been investigated. The optimum crosslinking conditions of y-PGA water-absorbent resin were have been determined by orthogonal test design that γ-PGA concentration was 18%, the amount of PEGGE was 8%of γ-PGA monomer moles, pH5.0, the reaction temperature and time were 65℃ and 50 h.Meanwhile,the concentration of NaCl and γ-PGA molecular weight was about 0.6% and 1000 KD, respectively. The absorbency of γ-PGA water-absorbent resin preparede under this condition can be as high as 1271 g/g, and 78g/g in 0.9% NaCl solution. Through the absorbency of γ-PGA water-absorbent resin in the monovalent, divalent and trivalent salt ions solutions,it was discovered that the higher salt ions charges was,the smaller the absorbency of γ-PGA water-absorbent resin was.And when pH value of deionized water was between 4.0～10.0,γ-PGA water-absorbent resin had greater water absorption effect.