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Abstract

A newly developed shearing device was used to study shear-induced inactivation of thermostable alpha-amylase in a plain shear field, under conditions comparable to extrusion. The results show that the inactivation can be described well with a first-order process, in which the inactivation energy largely depends on the shear stress, instead of specific mechanical energy or strain history. The resulting dependency of the rate of inactivation on the shear stress is very strong and nonlinear, which leads to the conclusion that in many cases the maximally applied shear stress determines the inactivation. Quantification of the inactivation rates gives design criteria for the application of enzymes in more viscous systems than conventionally used, provided that the reactor is designed such that no peak shear stresses occur.

Bioextrusion of Broken Rice in the Presence of Divalent Metal Salts: Effects on Starch Microstructure and Phenolics Compounds

“…Jyothi et al reported that Fe­(II) increased PV of cassava starch treated in the absence of α-amylase, and similar results were obtained with Cu­(II). The influence of enzyme-Fe/Cu combination on pasting viscosity should be further studied to find more evidence that could explain the decrease of the enzyme activity in the presence of these cations . However, especially considering the shearing and pressure effects occurring during the extrusion process, some evidence and possible inactivation mechanisms are given below.…”

Effects of shear stress on the microalgae Chaetoceros muelleri

“…Dividing cells are probably more shear sensitive. Step responses to shear stress have previously been reported for enzymes [36] and starch molecules [37, 38], suggesting a more general role of shear stress in deactivation and breakage processes.…”

Hydrodynamic effects in proteins

“…Another possible way to increase the shear-induced forces is to use a solvent with a larger viscosity than water, as is the case in the study by van der Veen et al [35] on α-amylase deactivation in concentrated starch solution. Due to the very high viscosity of the medium, relatively large shear stresses of about 3×10 4 Pa were reached, which have partially deactivated the enzyme by deforming its tertiary structure.…”