Todd Becker

Failure mechanism determination for industrial granules using a repeated compression test

This work describes the development of a particle compression test that allows direct and repeated application of the stress. The test is designed to quickly reduce the load on a granule during its incipient failure. By so doing, the breakage can be arrested and thus the process can be studied in detail. Experimental tests have been made on samples of industrial enzyme granules, which have a complex layered structure, and reproducible results have been obtained. The contribution of the various layers to the strength of the granule has been investigated, showing that the use of coating materials results in improved granule strength. The microstructure of the granule determines the failure mode of the granule. It is concluded that the failure mechanisms can be defined from tests on only a few granules as can assessment of the relative contribution of the layers and of the granule core to its strength. A measurement of the distribution of strength requires a larger, statistically representative, sample.

Ca2+–Surfactant Interactions Affect Enzyme Stability in Detergent Solutions

Detergent proteases and amylases generally bind Ca2+ ions. These bound ions enhance enzyme stability, reducing the rates of degradative reactions such as unfolding and proteolysis. Thus, surfactant aggregates, such as micelles, affect protease and amylase stability indirectly, by competing with the enzymes for Ca2+ ions. Dissociation constants for Ca2+ interactions with anionic surfactant micelles are in the 10−3 to 10−2 M range. These interactions are weak relative to enzyme‐Ca2+ interactions (Kd of order 10−6 M). However, surfactant is typically present at much higher concentration than enzyme, and it is the Ca2+–micelle equilibrium that largely determines the amount of free Ca2+ available for binding to enzymes. The problem of surfactant‐mediated Ca2+ removal from enzymes can be avoided by adding calcium to a detergent formulation in an amount such that the concentration of free Ca2+ is around 10−5M.

Surfactant-induced unfolding of cellulase: kinetic studies.

Surfactant‐induced unfolding is a significant degradation pathway for detergent enzymes. This study examines the kinetics of surfactant‐induced unfolding for endoglucanase III, a detergent cellulase, under conditions of varying pH, temperature, ionic strength, surfactant type, and surfactant concentration. Interactions between protein and surfactant monomer are shown to play a key role in determining the kinetics of the unfolding process. We demonstrate that the unfolding rate can be slowed by (1) modifying protein charge and/or pH conditions to create electrostatic repulsion of ionic surfactants and (2) reducing the amount of monomeric ionic surfactant available for interaction with the enzyme (i.e., by lowering the critical micelle concentration). Additionally, our results illustrate that there is a poor correlation between thermodynamic stability in buffer (ΔGunfolding) and resistance to surfactant‐induced unfolding.

Measurement of Granule Attrition and Fatigue in a Vibrating Box

This paper describes a new test machine that has been designed to measure the strength of single particles in the size range of 102–103 μm. The device is a vibrating box that subjects each particle in the sample to a large number of impacts of known but variable strength. By tracking the size and shape of the particles as a function of the number of impacts, their strength characteristics against the mechanisms of fracture, fatigue and attrition can be differentiated. The number of particles tested in one sample is restricted in order to make any particle-particle interaction negligible but is sufficiently large that the distribution of these characteristics can be determined.

Spherical Alginate Granules Formulated for Quick-Release Active Subtilisin

Novel attrition‐resistant and spherical enzyme granules encapsulating active subtilisin were formed by emulsification of 2% alginate sol loaded with active enzyme, instantaneous gelation triggered through in situ release of Ca2+ (internal gelation), particle separation, and finally acetone extractive drying. Granular subtilisin was highly active, readily dispersible, and mechanically robust. This technique serves as a new and attractive alternative to established enzyme granulation processes, such as fluid bed coating, extrusion followed by marumerization, drum granulation, or prilling, for use in industrial enzyme applications such as detergents, textile manufacturing, and food processing. The formulation and encapsulation conditions were optimized to maximize the resistance of the granule to compression and impact forces, consistent with enzyme release and particle dispersion in detergent solutions. Well characterized alginates, with specified guluronic/mannuronic acid (G/M) content and molecular weight, were used in the formulation. The characteristics of the resulting microspheres, including their size and distribution, morphology, shrinkage, compression resistance, impact strength, solubility and encapsulation yield, were examined. Spherical dry granules were formulated with a mean diameter of 500 μm with particle sizes ranging from 300 to 800 μm. Dry alginate granules were discrete, spherical, and glossy white and exhibited impact strength, compression resistance, and solubility difference dependent on composition. Reduced starch levels, high alginate concentration, low alginate molecular weight, and use of high guluronate alginates resulted in the lowest dust level and highest compression resistance. Subtilisin mass yields were approximately 50%, and specific activity yields ranged from 60% to 100%. A formulation consisting of 3% SG150 alginate, 10% starch, 10% TiO2, and 1% CaCO3 provided granules appropriate for use in detergent application.