Thermal and pressure‐temperature denaturation kinetics ofbacillus subtilisα‐amylase: A study based on gel electrophoresis

A simple 2-step purification process of α-amylase from Bacillus subtilis: Optimization by response surface methodology

Purification of extracellular α-amylase from Bacillus subtilis was carried out via fractional precipitation by acetone and ion exchange chromatography. These steps provide fast precipitation as well as purification of α-amylase to improve enzyme purity, activity and stability. Compared with two-phase methods in which the yield was less than 1, this method resulted in a yield of more than 3. Moreover, 95% of acetone was recovered that enhanced the economy of the downstream process. Using the data provided by 2D electrophoresis, purification was done by a single step ion exchange chromatography. The enzyme exhibited a molecular mass (SDS-PAGE) of 50KD and the pI of 5. Maximum "yield" and "purification fold" were achieved through optimization of operation parameters such as volume and flowrate of loaded protein using response surface methodology (RSM). 0.5ml of loaded protein at a flow rate of 0.5 ml/min was purified as 48 folds and achieved a specific activity of 524 U/mg.

Effects of temperature and pressure on Rhizomucor miehei lipase stability

Both high temperature and high hydrostatic pressure induce irreversible deactivation of enzymes. They enable the enzyme's thermodynamic parameters to be determined and are used to study the mechanisms involved in biochemical systems. The effect of these two factors on the stability of Rhizomucor miehei lipase have been investigated. The stability criterion used was residual hydrolytic activity of the lipase. Experimental and theoretical parameters, obtained by linear regression analysis, were compared with theoretical kinetics in order to validate the series-type inactivation model. The lipase of R. miehei was deactivated by either thermal or pressure treatment. Moreover conformational studies made by fluorescence spectroscopy suggest that the conformational changes induced by pressure were different from those induced by temperature. In addition they show that after thermal deactivation there were less intermolecular hydrogen bonded structures formed than was the case for deactivation by high pressure.

Physiological and mathematical aspects in setting criteria for decontamination of foods by physical means

In heat processing, microbial inactivation is traditionally described as log-linear. As a general rule, the relation between rate of inactivation and temperature is also described as a log-linear relation. The model is also sometimes applied in pressure and in pulsed electric field (PEF) processing. The model has proven its value by the excellent safety record of the last 80 years, but there are many deviations from log-linearity. This could lead to either over-processing or under-processing resulting in safety problems or, more likely, spoilage problems. As there is a need for minimal processing, accurate information of the inactivation kinetics is badly needed. To predict inactivation more precisely, models have been developed that can cope with deviations of linearity. As extremely low probabilities of survival must be predicted, extrapolation is almost always necessary. However, extrapolation is hardly possible without knowledge of the nature of nonlinearity. Therefore, knowledge of the physiology of inactivation is necessary. This paper discusses the physiology of denaturation by heat, high pressure and pulse electric field. After discussion of the physiological aspects, the various aspects of the development of inactivation models will be addressed. Both general and more specific aspects are discussed such as choice of test strains, effect of the culture conditions, conditions during processing and recovery conditions and mathematical modelling of inactivation. In addition to lethal inactivation, attention will be paid to sublethal inactivation because of its relevance to food preservation. Finally, the principles of quantitative microbiological risk assessment are briefly mentioned to show how appropriate inactivation criteria can be set.