In vitro approaches to estimate the effect of food processing on carotenoid bioavailability need thorough understanding of process induced microstructural changes

Carotenoids represent an example of micronutrients for which processing-induced food structure changes (e.g., matrix disruption) strongly influence their bioavailability. The available scientific information on this topic resulting from both in vivo and in vitro studies shows however the complexity of this problem. Although in vitro studies have been shown useful to better understand the relation between processing and carotenoid bioavailability, there is still conflicting information. To expand our current knowledge on this topic in order to allow rational design of food processing solutions resulting in products with maximal carotenoid accessibility and (bio)availability, it is suggested (i) to further evaluate and standardize in vitro models to be used as high throughput screening tools to determine the effect of extrinsic (process-related) and intrinsic (product-related) factors and (ii) to integrate food structure information as a useful approach for understanding and quantifying the bioavailability of carotenoids in foods. However, it will be necessary to validate the information obtained from these in vitro methods thoroughly against human studies (in vivo studies).     

Thermal and High-Pressure Inactivation of Tomato Polygalacturonase: A Kinetic Study

ABSTRACT: Polygalacturonase (PG) was extracted from tomato fruit. The inactivation kinetics of the PG crude extract was investigated under isothermal and isobaric-isothermal conditions. Thermal inactivation of tomato PG in the temperature range 58 to 65 °C could be described by a fractional conversion model, and in the temperature range from 70 to 90 °C by a biphasic model. Pressure-temperature inactivation (range 300 to 600 MPa/5 to 50 °C) of tomato PG could be described by a fractional conversion model, which points to first-order inactivation kinetics of a pressure-sensitive enzyme fraction and to the occurrence of a pressure-stable PG fraction. A mathematical model describing the influence of pressure and temperature on the inactivation rate constant was formulated.     

The Effects of Process-Induced Pectin Changes on the Viscosity of Carrot and Tomato Sera

The influence of process-induced pectin changes on the kinematic viscosity of the serum phases of carrot and tomato purées was investigated in this study. Variations in the amount of pectin present in the serum phase and pectin’s fine structure were induced by subjecting carrot and tomato to different thermal treatments, i.e. a mild and a strong heat treatment, followed by blending and high-pressure homogenisation at different pressure levels (0, 20 and 100 MPa). Changes in pectin structure were monitored by determination of the degree of methoxylation, analysing the molar mass distribution and immuno-dot blotting using anti-pectin antibodies. Characterisation of serum pectins revealed that a strong thermal treatment caused pectin thermosolubilisation and depolymerisation, especially in carrot sera, and high-pressure homogenisation provoked predominantly mechanical pectin solubilisation in carrot sera and pectin depolymerisation in tomato sera. It was observed that the kinematic viscosity of carrot sera was mainly affected by the amount of solubilised pectin, whereas in tomato sera, the kinematic viscosity could mainly be explained in terms of polysaccharide chain length. The degree of methoxylation of pectin, which has a broader distribution in tomato sera than in carrot sera, seemed to have a less pronounced role in determining the kinematic viscosity. In general, it could be concluded that serum viscosity is mainly determined by the amount and size of the solubilised pectin. The influence of serum viscosity on the rheology of the studied purées was limited as the rheology of this type of system is largely determined by the particle properties of the dispersed phase.     

The kinetics of heat-induced structural changes of beta-lactoglobulin

Heat-induced structural changes of beta-lactoglobulin were studied at temperatures ranging from 67.5 to 82.5 degrees C, and at pH 7.5. These changes were monitored by measurement of surface hydrophobicity, thiol availability, and protein solubility. Kinetic studies were conducted to quantitatively describe the contribution of hydrophobic and SH/SS interchange reactions to the thermal structural changes of beta-lactoglobulin. Results indicate that beta-lactoglobulin is sensitive to heat-induced interchange reactions with consequences for protein solubility. The extent of changes measured by the increase in surface hydrophobicity and the decrease in slow-reacting SH groups content could be described by a first-order fractional conversion model and were characterized by activation energy values of 233.9 +/- 8.6 and 148.2 +/- 6.7 kJ/mol, respectively. The break in the Arrhenius plot suggested in literature for beta-lactoglobulin denaturation was confirmed in this study only for the kinetics of exposed SH groups.     

Influence of pilot scale in pack pasteurization and sterilization treatments on nutritional and textural characteristics of carrot pieces

The current work presents a pilot scale study in which the effect of in pack thermal preservation processes in a retort system on particular carrot quality aspects, more specifically nutritional and textural characteristics, was investigated. Pasteurization as well as sterilization processes with different intensities were included. The carrot hardness, analyzed by a compression test, and the β-carotene bio-accessibility, analyzed by an in vitro digestion method, were the main quality markers. As a main conclusion, it can be stated that the results of this pilot scale study are a good validation of results obtained during previous laboratory scale experiments on carrot nutritional and textural characteristics. The processes applied in this study only resulted in limited conversion of all-trans-β-carotene to its cis-isomers. Furthermore, it was shown that intense thermal processing is required to observe a significant increase in the β-carotene bio-accessibility. However, this was accompanied with a clear degradation of the hardness. When thermal processing was preceded by low temperature blanching, a technique to improve texture retention of thermally processed plant-based foods, a lower β-carotene bio-accessibility was observed. Both observations clearly illustrated the inverse correlation between textural and nutritional characteristics of (processed) carrots. Statistical analyses confirmed the trends observed. For process design, the choice of the process intensity was identified to be crucial: the required product safety needs to be achieved, while still reaching an acceptable structural and nutritional quality. Exploring strategies to enhance the β-carotene bio-accessibility while ensuring an acceptable carrot texture can therefore be useful.     

Thermal and pressure‐temperature denaturation kinetics of bacillus subtilis α‐amylase: A study based on gel electrophoresis

Abstract

The commercially available enzyme Bacillus subtilis α‐amylase was characterized by a molecular weight of about 55 kDa and contained isozymes with pI values ranging in a narrow zone (4.6–5.3). Furthermore, the sample was confirmed to contain no disulfide bonds. Upon thermal denaturation in the presence of sodium dodecyl sulfate, a band at half molecular weight was noticed, indicating that the native enzyme might be a dimeric form. Thermal as well as pressure‐temperature denaturation kinetics were investigated using gel electrophoresis and both could accurately be described by a first order kinetic model. For thermal denaturation an activation energy of 283 kJ/mole was calculated. As far as pressure‐temperature denaturation is concerned, activation energy and activation volume at a constant pressure of 5500 bar and a constant temperature of 40°C were calculated respectively as 77.6 kJ/mole and ‐23.2 cm³/mole. These values were compared with those for thermal and pressure‐temperature inactivation of Bacillus subtilis α‐amylase, as determined from residual enzyme activity measurements. No significant differences between the activation energy and volume characterizing denaturation and inactivation of Bacillus subtilis ct‐amylase were observed.     

Use of pectinmethylesterase and calcium in osmotic dehydration and osmodehydrofreezing of strawberries

Strawberry samples of two varieties (Camarosa and Elsanta) were dehydrated using different osmotic solutions (60% glucose, fructose, sucrose and raftilose) and subsequently frozen by rapid and high-pressure shift freezing (HPSF). The effect of pectinmethylesterase (PME) and calcium (Ca⁺⁺) added to the osmotic solutions on several compositional parameters and the textural/structural quality of dehydrated and osmodehydrofrozen-then-thawed samples was studied. Due to the presence of PME and Ca⁺⁺ in the osmotic solutions, weight reduction upon dehydration was slightly decreased, which was correlated to a small positive effect on the net uptake of sugars and depression of the initial freezing point. Except for the Camarosa samples treated with sucrose, PME and Ca⁺⁺ in osmotic sugar solutions positively affected the relative hardness of dehydrated fruits, which was ascribed to the effect of PME and Ca⁺⁺ on the cell wall strength of the tissue. No cell wall damage and tissue particle alterations were observed upon dehydration. The effect of osmotic dehydration (OD) using different sugar solutions without PME and Ca⁺⁺ on the texture and structure of frozen-then-thawed samples was limited and sometimes negative. The added PME and Ca⁺⁺ however positively influenced the volume and shape of the thawed samples, which could be related to slightly higher relative hardness values and, for the Elsanta strawberry fruits, also to the reduced (up to 81%) drip loss upon thawing. Upon freezing the dehydrated fruits, no cell wall disruption was observed. Tissue distortion caused by freezing and indicated by a decrease in particle size, convexity and roundness, was compensated by the use of PME and Ca⁺⁺ during OD.     

High pressure thermal inactivation kinetics of a plasmin system

A crude plasmin extract was prepared from milk by ultracentrifugation and was partially purified using ammonium sulfate precipitation. Isothermal and high-pressure inactivation of this plasmin system at pH 6.7 could be described by a first-order kinetic model. As expected, the plasmin system displayed a high thermostability. High-pressure treatments were conducted in the 300- to 800-MPa pressure range, combined with temperatures from 25 to 65 degrees C. The plasmin system was very pressure stable at room temperature, but inactivation occurred with combined high-pressure/temperature-treatments. The influence of temperature at different constant pressures on the inactivation rate constant was quantified using the Arrhenius equation. At all temperatures studied, a synergistic effect of temperature and high pressure was observed in the 300- to 600-MPa pressure range. However, an antagonistic effect of temperature and pressure appeared at pressures above 600 MPa.