Researching On The Production Of Sodium Gluconate By Immobilized Enzyme

Sodium gluconate has a wide range of applications in the food, construction industrial and texture dyeing sectors. Currently there is an increasing demand for sodium gluconate in the markets. Production of sodium gluconate by enzyme biocatalysis has attracted great attention due to its relatively low cost and perceived environmental benefits. To further cut the cost, it is important to reuse the enzyme catalyst. In this study, the effect of different enzyme immobilization methods on the GOD and CAT and the parameters affecting sodium gluconate production efficiency were investigated.Effects of different methods including cross-linking of glutaraldehyde. sodium alginate entrapment and covalently linked with epoxy resins on the efficiency of immbilization were investigated. The method of covalently linked with epoxy resins showed excellent enzyme activity and activity recovery was chosen for further immobilization study. The optimum conditions for the immobilization of GOD and CAT were as follows:ES-4 1g, amounts of GOD and CAT,1.0 ml and 0.8 ml; pH 6.5 and 6.0; sodium phosphate buffer, both are 1.0 M; temperature,20℃ and 30℃; fixed time,24 h and 32 h.Enzymatic property studies show that the optimal temperature and pH for immobilized GOD were 38℃ and 6.5, respectively, whereas for free enzyme the optimal conditions were 32℃ and 6.0, respectively. When the enzyme was incubated at 60℃ for 1 h, more than 80% and 12% residual activity of immobilized GOD and free enzyme remained, respectively. Zn2+ enhanced the immobilized GOD activity, while Cu2+、Ag+、Hg+ strongly inhibited the activity. Storage stability tests showed that 90.4% enzymatic activity of immobilized GOD was retained when stored for seven weeks. The optimum temperature of both free and immobilized CAT were shown to be 30℃. The optimum pH of free and immobilized CAT were 6.8 and 7.0. respectively. Zn2+、Ca2+、Cu2+、 Cr3+ exhibit inhibitory effects on the immobilized CAT, and Cu2+ has the greatest effect. Immobilized CAT still remained 88.5% activity after it was stored for seven weeks.One-factor experiment was carried out to optimize sodium gluconate production The optimum conditions were:mass ratio of immobilized GOD and CAT is 1:3, substrate concentration 250 g/L, temperature 36℃, pH 6.8, ventilation 0.8 vvm. reaction time 14 h. It was found that 70% and 62% of the initial activity of immobilized GOD and CAT remained even after continuous bioconversion for 15 batches.Our results facilitate the applications of immobilized enzymes for gluconate production.