Activity of pectin methyl esterase during blanching of peaches

Microwave Food Processing

Consumers prefer food products with enlarged shelf life, which are quick to prepare, healthy and fresh like. Traditional food processing methods are based on intensive heating and as a result cause quality loss. Minimal processing techniques such as microwaves approach consumer's demands to create fresh like products with enlarged shelf life. Microwave technology can be very useful for food processing, because products are heated directly instead of conventional heating by convection and conduction. This means a reduction of the total processing time, no overheating on the outside of the product, and preservation of the fresh product quality. This chapter presents a complete picture of current knowledge on application of microwave in food processing which has been used for different processes like blanching, sterilisation, thawing, drying and extraction of various products. In many cases combinations with microwaves gave the best results.

Noncovalent immobilization of Pectinesterase (Prunus armeniaca L.) onto bentonite

In this work, pectinesterase isolated from Malatya apricot was immobilized onto acid-treated bentonite surface by simple adsorption at pH 9.0. The properties of free and immobilized enzyme were defined. The effect of various factors such as pH, temperature, heat, and storage stability on immobilized enzyme were investigated. Optimum pH and temperature were determined to be 9.0 and 50 degrees C, respectively. Kinetic parameters of the immobilized enzyme (Km and Vmax values) were also determined as 0.51 mM of the Km and 14.6 micromol min(-1) mg(-1) of the Vmax. No drastic change was observed in the Km value after immobilization. The Vmax value of immobilized enzyme was 8.4-fold bigger than those of free enzyme. Thermal and storage stability experiments were carried out. The patterns of heat stability indicated that the immobilization process tends to stabilize the enzyme. The properties of the immobilized enzyme were compared to those of the free enzyme.

Study on the thermal stability of green fluorescent protein (GFP) in glucose parenteral formulations

Large volume parenteral solutions (LVPS) that are widely used in the healthcare system must be processed by moist-heat treatment to an assured sterility level in which the efficacy is measured by a bioindicator (BI) that provides fast, accurate and reliable results. This study evaluated the thermal stability of green fluorescent protein (GFP) into glucose-based LVPS (1.5-50%) solutions to determine its utility as a BI for thermal processes. GFP, expressed by Escherichia coli, isolated/purified by TPP/HIC, was diluted in buffered (each 10mM: Tris-EDTA, pH 8; phosphate, pH 6 and 7; acetate, pH 5) and in water for injection (WFI; pH 6.70+/-0.40) glucose solutions (1.5-50%) and exposed to constant temperatures from 80 degrees C to 95 degrees C. The thermal stability was expressed in decimal reduction time (D-value, time required to reduce 90% of the GFP fluorescence intensity). At 95 degrees C, the D-values for GFP in 1.5-50% glucose were: (i) 1.63+/-0.23 min (pH 5); (ii) 2.64+/-0.26 min (WFI); (iii) 2.50+/-0.18 min (pH 6); (iv) 3.24+/-0.28 min (pH 7); (v) 2.89+/-0.44 min (pH 8). By the convenient measure of fluorescence intensity and its thermal stability, GFP has the potential as a BI to assay the efficacy of moist-heat processing of LVPS at temperatures < or =100 degrees C.

Affinity-tagged green fluorescent protein (GFP) extraction from a clarifiedE. coli cell lysate using a two-phase aqueous micellar system

Green fluorescent protein (GFP) has been proposed as an ideal choice for a protein-based biological indicator for use in the validation of decontamination or disinfection treatments. In this article, we present a potentially scalable and cost-effective way to purify recombinant GFP, produced by fermentation in Escherichia coli, by affinity-enhanced extraction in a two-phase aqueous micellar system. Affinity-enhanced partitioning, which improves the specificity and yield of the target protein by specific bioaffinity interactions, has been demonstrated. A novel affinity tag, family 9 carbohydrate-binding module (CBM9) is fused to GFP, and the resulting fusion protein is affinity-extracted in a decyl beta-D-glucopyranoside (C10G1) two-phase aqueous micellar system. In this system, C10G1 acts as phase forming and as affinity surfactant. We will further demonstrate the implementation of this concept to attain partial recovery of affinity-tagged GFP from a clarified E. coli cell lysate, including the simultaneous removal of other contaminating proteins. The cell lysate was partitioned at three levels of dilution (5x, 10x, and 40x). Irrespective of the dilution level, CBM9-GFP was found to partition preferentially to the micelle-rich phase, with the same partition coefficient value as that found in the absence of the cell lysate. The host cell proteins from the cell lysate were found to partition preferentially to the micelle-poor phase, where they experience less excluded-volume interactions. The demonstration of proof-of-principle of the direct affinity-enhanced extraction of CBM9-GFP from the cell lysate represents an important first step towards developing a cost-effective separation method for GFP, and more generally, for other proteins of interest.

Thermal characteristics of recombinant green fluorescent protein (GFPuv) extracted from Escherichia coli

AIMS

The thermal stability of isolated and extracted recombinant green fluorescent protein (GFPuv) was evaluated by analysing the loss of fluorescence intensity.

METHODS AND RESULTS

GFPuv was expressed by Escherichia coli, extracted by the three-phase partitioning method and purified by elution through an hydrophobic interaction column. The collected fractions were further diluted in Tris-HCl-EDTA (pH 8.0) and subjected to continuous heating at set temperatures (45-95 degrees C). From a standard curve relating fluorescence intensity to GFPuv concentration, the loss of fluorescence intensity was converted to denatured GFPuv concentration (microg ml-1). To determine the extent of the thermal stability of GFPuv, decimal reduction times (D-values), z-value and energy of activation (Ea) were calculated.

CONCLUSIONS

For temperatures between 45 and 70 degrees C, extracted native GFPuv activity decreased from 11 to 75% relative to initial native protein concentration above 70 degrees C, the average decrease in GFPuv fluorescence was between 72 to 83%.

SIGNIFICANCE AND IMPACT OF THE STUDY

The thermal stability of GFPuv provides the basis for its potential utility as a fluorescent biological indicator to assess the efficacy of the treatment of liquids and materials exposed to steam.

Modeling the effect of temperature and pH on activity of enzymes: the case of phytases

In this study, the behavior of enzyme activity as a function of pH and temperature is modeled on the basis of fundamental considerations. A formulation is developed that includes the activation of enzymes with increasing temperatures and the deactivation of enzymes at higher temperature, together with the effect of protonation and hydroxylation on activity at various constant pH levels. The model is calibrated and validated against an extensive set of experimental data on phytases from seven different origins. The percentage variance accounted for (R(2)(adj)), obtained by statistical nonlinear regression analysis on all data sets, was shown to range from 97.6% to 99.5%. The equilibrium constant of protonation and hydroxylation proved to be independent of temperature.

Kinetics of thermal deactivation of enzymes: a simple three parameters phenomenological model can describe the decay of enzyme activity, irrespectively of the mechanism

Heat induced enzyme inactivation or protein denaturation is now well documented, due to progresses in methods, instruments and computation resources. Complex mechanisms, rather than the classic simple "one step - two states" model (still in use) are recognized in many cases, leading investigators to manipulate more or less complicated kinetic expressions describing the heat induced decay of enzyme activity.We show that the different kinetic expressions related to different mechanisms among the most frequently encountered can be arranged in a common simple three-parameters biexponential equation.This unifying simplification is of interest for people focusing attention to phenomenological rather than mechanistic description of the kinetics of heat induced enzyme deactivation. Moreover, the reduction in the number of parameters reduces the risk of cross-correlation and allows a better estimation of the apparent rate constants (which are in many cases the pertinent required information). It also illustrates the difficulty to make inference of mechanism from kinetics, since the same equation applies for a variety of mechanisms ("kinetic homeomorphism") - in particular, it stresses out the need of caution when reporting on existence of isoenzymes from deactivation kinetics.Application of this simple 3-parameters biexponential kinetic expression has been validated with a number of results in the Literature and current investigations in our laboratory. Two examples are given.