On the interaction of α-amylase with crosslinked starch: Evaluation of process conditions

Abstract

The interaction of α-amylase with crosslinked starch is described. The adsorption characteristics are influenced especially by pH and temperature. Adsorption preferentially takes place at 4°C. The adsorption behavior corresponds with the catalytic activity of the enzymes studied. α-Amylase of Bacillus licheniformis, which has a broad pH optimum, adsorbs over a larger range (pH 5.0–9.0) than the α-amylase from Bacillus subtilis (pH 5.0–7.0). Capacities and Langmuir constants were determined in the relevant pH range. At pH values of 9.0–11.0 the catalytic activity and the adsorption levels drop, but the enzyme activity is not irreversibly lost. These conditions are used to recover the enzyme from the matrix. The crosslinked starch matrix is a competitive inhibitor for the enzyme in the enzyme assay. The K_i was determined to be 6–8 g ml⁻¹ for the inhibition of B. licheniformis α-amylase. The affinity for soluble starch appears to be approximately 30 times higher than for the matrix. As a result, limit dextrin solutions can be used as competitive eluents for the recovery of the enzyme from the adsorbent. A temperature shift from 4°C to 70°C can be used to recover the enzyme from the adsorbent, although this makes the matrix susceptible to biodegradation and enzyme activity is lost. The latter effect can be reduced by adding Ca²⁺ to the system. Sodium chloride and glycerol have an influence on the interaction between α-amylase and the adsorbent. V_max of the enzyme and the adsorption levels of α-amylase decrease among others as the water activity of the system is lowered. The matrix adsorbs a variety of α-amylases from bacterial and mammalian origin.