Comparative study between the free and immobilized cells of Bacillus velezensis AMA2 P164707 and Bacillus atrophaeus AMA6 OP225343 for acidic β, α amylases production and applied experiment

Nowadays, acid-stable α-amylase demand is increasing in starch liquefaction processes. Four bacterial honey isolates, numbers 2 and 6 showed the highest amylase production on commercial starch as the sole medium component and were immobilized in alginate beads. The highest cell immobilization capacity was obtained by organisms' Bacillus velezensis AMA2 and Bacillus atrophaeus AMA6. Amylase production increases after the immobilization process from 78 to 232 U/mg and 71 to 216 U/mg for isolates numbers 2 and 6 respectively. The isolates were identified as Bacillus velezensis AMA2 and Bacillus atrophaeus AMA6, which produced β and α-amylases, respectively. They were able to retain 85 % and 53 % of their production after 7 cycles. The optimum temperature and pH for enzyme production shifted from 40 °C to 45 °C and the pHs 7 shifted to 6, after the immobilization. The immobilized cells for both isolates were more tolerant to the temperature elevation and the alkaline pHs than the free enzymes. Ca (NO3)₂ stimulated the free and immobilized Bacillus velezensis AMA2 amylase production, and all other tested metals had adverse effects on both. The activation energy decreased after the immobilization process to 41.60 and 22.2-fold, respectively, and the t_1/2 and D values increased. The enzymes showed high stability in the presence of different detergents.