Development of an Enzymic Time Temperature Integrator for Sterilization Processes Based on Bacillus licheniformis α-amylase at Reduced Water Content

ABSTRACT: The thermal stability of Bacillus licheniformis α-amylase at low moisture content was studied, based on isothermal experiments performed in a temperature range 113 to 125 °C. The thermal inactivation was monitored by measuring the decrease in thermal denaturation enthalpy and/or the decrease in enzymic activity on pnitrophenyl-α-D-maltoheptaoside, or on starch as a substrate. Based on enthalpy readings, an enzymic system with a z-value of 10.4 °C was observed when using a relative humidity of 81% at 4 °C. A theoretical study showed that this system could be used as a Time Temperature Integrator (TTI) to monitor the safety of sterilization processes of numerous food products.     

Carotene Degradation and Isomerization during Thermal Processing: A Review on the Kinetic Aspects

Kinetic models are important tools for process design and optimization to balance desired and undesired reactions taking place in complex food systems during food processing and preservation. This review covers the state of the art on kinetic models available to describe heat-induced conversion of carotenoids, in particular lycopene and β-carotene. First, relevant properties of these carotenoids are discussed. Second, some general aspects of kinetic modeling are introduced, including both empirical single-response modeling and mechanism-based multi-response modeling. The merits of multi-response modeling to simultaneously describe carotene degradation and isomerization are demonstrated. The future challenge in this research field lies in the extension of the current multi-response models to better approach the real reaction pathway and in the integration of kinetic models with mass transfer models in case of reaction in multi-phase food systems.     

Kinetics of alkaline phosphatase and lactoperoxidase inactivation,and of beta-lactoglobulin denaturation in milk with different fat content

In the context of identifying intrinsic time temperature integrators (TTIs) for evaluating heat processing of milk, the extent to which milk fat content has an effect on alkaline phosphatase (ALP) and lactoperoxidase (Lpo) inactivation and on beta-lactoglobulin (beta-Ig) denaturation kinetics was studied. Inactivation and denaturation kinetics were analysed in whole, semi-skimmed and skimmed milk. In previous experiments (isothermal and non-isothermal heating conditions), heat inactivation of ALP and Lpo and heat denaturation of beta-Ig were found to follow first order kinetics. This allowed experimental design to be simplified. Data analysis was performed by non-linear regression and results were evaluated by construction of joint confidence regions. The possible effect of milk fat was illustrated by temperature time tolerance (TTT-) diagrams. Although initial ALP activity was lower in skimmed milk compared with semi-skimmed or whole milk, kinetics were comparable and fat content did not seem to substantially affect the ALP test result for pasteurized milk. Unlike ALP, Lpo inactivation and beta-Ig denaturation kinetics differed significantly in milk with different fat content. Differences between Lpo inactivation kinetics were relatively small and acceptable in the context of quantifying the process impact. Denaturation of beta-Ig, on the other hand, seemed to be enhanced at higher milk fat content (> 72 degrees C).     

Extended study on the influence of z-value(s) of single and multicomponent time-temperature integrators on the accuracy of quantitative thermal process assessment

The possibilities and limitations of single- and multicomponent time-temperature integrators (TTIs) for evaluating the impact of thermal processes on a target food attribute with a Ztarget value different from the zTTI value(s) of the TTI is far from sufficiently documented. In this study, several thousand time-temperature profiles were generated by heat transfer simulations based on a wide range of product and process thermal parameters and considering a Ztarget value of 10 degrees C and a reference temperature of 121.1 degrees C, both currently used to assess the safety of food sterilization processes. These simulations included 15 different Ztarget=10 degrees CF121.1 degrees C values in the range 3 to 60 min. The integration of the time-temperature profiles with ZTTI values of 5.5 to 20.5 degrees C in steps of 1 degrees C allowed generation of a large database containing for each combination of product and process parameters the correction factor to apply to the process value FmultiTTI, which was derived from a single- or multicomponent TTI, to obtain the target process value 10 degrees CF121.1 degrees C. The table and the graph results clearly demonstrated that multicomponent TTIs with z-values close to 10 degrees C can be used as an extremely efficient approach when a single-component TTI with a z-value of 10 degrees C is not available. In particular, a two-component TTI with z1 and z2 values respectively above and below the Ztarget value (10 degrees C in this study) would be the best option for the development of a TTI to assess the safety of sterilized foods. Whatever process and product parameters are used, such a TTI allows proper evaluation of the process value 10 degrees CF121.1 degrees C.     

Temperature and pressure stability of l-ascorbic acid and/or [6s] 5-methyltetrahydrofolic acid: A kinetic study

Processing (i.e. pressure and temperature) stability of l-ascorbic acid (l-AA) and/or [6S]-5-methy-ltetrahydrofolate ([6S]-5-CH₃-H₄folate) was studied on a kinetic basis using different vitamin and initial oxygen concentrations. Stability of both folate and l-AA was enhanced by increasing the vitamin concentration or by decreasing the oxygen concentration. Based on this study, it was concluded that (i) l-AA increased the folate stability during processing; (ii) the molar ratio between l-AA or folate and the initial oxygen content was an important parameter to determine the proportion of aerobic degradation; and (iii) the minimum concentration of l-AA needed to prevent the oxidation of folate was at least 2 times as high as the molar concentration of the initial oxygen content when l-AA exists as a single antioxidant in the system.     

Solvent engineering as a tool in enzymatic indicator development for mild high pressure pasteurization processing

When developing an indicator to detect temperature heterogeneities in a high pressure (HP) vessel, the temperature sensitivity and the broadness of the application window have to be weighed against each other. In this study, the potential of a Bacillus amyloliquefaciens α-amylase (BAA)-based indicator for mild pasteurization conditions was evaluated. Solvent engineering was successfully used to reach two objectives: (i) to shift the pressure,temperature-stability of BAA in the HP pasteurization range; (ii) to differentiate the pressure,temperature-range of BAA inactivation from the pressure,temperature-range of inactivation of a previously developed Bacillus subtilis α-amylase (BSA)-based indicator system (1 g/L – 0.05 M MES pH 5.0), towards milder processing conditions. The BAA-system (0.1 g/L – 0.1 M MES pH 5.0) was kinetically calibrated and modeled under static conditions. As these model parameters were inadequate to predict the residual α-amylase activity of BAA under dynamic conditions correctly, parameters were determined under dynamic conditions and subsequently successfully validated on an independent dynamic data set. Based on the kinetic model and parameters valid under dynamic conditions, isorate contour plots for different inactivation levels were constructed, demonstrating clearly the different application windows of the BAA- and BSA-systems.     

Statistical Variability Of Heat Penetration Parameters in Relation to Process Design

ABSTRACT: This study was undertaken to develop statistical approaches that can deal with variations in heating parameters when designing processes. In this context, the statistical variability of heat penetration parameters of a large amount of both hand-filled and machine-filled containers was investigated in different case studies. Two new statistical approaches are presented: an univariate and a bivariate statistical method. Both approaches appear successful for statistically based determination of heating parameters for process design. The statistical approaches also enable estimating the minimum number of heat penetration measurements to give reliable values to use in calculating safe thermal processes.     

Towards a better understanding of the pectin structure-function relationship in broccoli during processing: Part I—macroscopic and molecular analyses

To investigate the structure-function relationship of pectin during (pre)processing, broccoli samples (Brassica oleracea L. cultivar italica) were subjected to one of the following pretreatments: (i) low-temperature blanching (LTB), (ii) LTB in combination with Ca²⁺ infusion, (iii) high-pressure pretreatment (HP), (iv) HP in combination with Ca²⁺ infusion, or (v) no pretreatment (control sample), whether or not in combination with a thermal treatment of 15 min at 90 °C. The macroscopic attributes of broccoli were linked to the chemical structure of broccoli pectin. By enhancing the cross-linking of pectic polymers, both LTB and HP reduced the texture loss that occurred during thermal processing of broccoli. During these pretreatments, homogalacturonan was de-esterified by pectin methylesterase, which led to changes in pectin solubility. When LTB or HP was combined with Ca²⁺ infusion, changes in the structure of pectin occurred, however not always reflected at the macroscopic level. The degree of esterification of pectin in Ca²⁺-soaked broccoli samples was lower compared to non-Ca²⁺-soaked samples and, in addition, a higher amount of ionically cross-linked pectin was retrieved.     

Mild-Heat and High-Pressure Inactivation of Carrot Pectin Methylesterase: A Kinetic Study

ABSTRACT: Pectin methylesterase (PME) was extracted from carrots and purified by affinity chromatography. The thermal high-pressure inactivation of the PME was investigated in a model system. Under these conditions, the (thermo) stable fraction is not inactivated and the isobaric-isothermal inactivation followed a fractional-conversion model. At lower pressures (< 300 MPa) and higher temperatures (> 50°C), an antagonistic effect of pressure and heat was observed. A 2nd- and 3rd-degree polynomial model (derived from available thermodynamic model) was successfully used to describe the heat pressure dependence of the inactivation rate constants. From the purified carrot PME sample, the thermostable PME fraction was isolated. The thermal inactivation of this fraction followed first-order kinetics.