Fig. 4
The effects of pH value (a), temperature (b), incubation time (c) and metal ion (d) on the activity of glucoamylase. The pH optimum of proteinase was studied from 3 to 11. The temperature optimum was studied from 30 to 60 °C. Temperature stability was determined by holding the enzyme at 40–55 °C for 120 min. Metal ions included Mn2+, Mg2+, Ca2+, Cu2+, Zn2+, Fe2+ and Fe3+. Values represent the mean ± SD of three replicates. Values with different letters indicate significant differences (p < 0.05)