Amylase Activity in Banana Fruit: Properties and Changes in Activity with Ripening

Following subcellular fractionation and centrifugation, the amylase activity was located in the cytosol fraction of banana fruit. Over 80% of the observed activity (15—20 units per mg of protein) was attributed to α‐amylase. The activity of β‐amylase was tenfold lower and starch phosphorylase activity was low (17 μg inorganic phosphorus released per mg protein per 24 hr.). The activity of amylase in crude preparations was stimulated 40% by calcium ions. The amylase preparation, which was very stable at 4°C, hydrolyzed soluble potato starch and banana starch at similar rates. Maximum activity was observed between pH 6—7. The energy of activation of hydrolysis was 9.74 Kcal/mole. Amylase was quite active up to 62°C but rapidly lost activity above this temperature. There was an approximate twofold increase in amylase during the initial phase of ripening.