Jesus Maria Frias

Modelling respiration rate of shredded Galega kale for development of modified atmosphere packaging

Abstract The design of modified atmosphere packaging (MAP) for fresh-cut produce requires an adequate model for prediction of respiration rate as a function of both temperature and gas composition. In this work, the O2 consumption and CO2 production rates of shredded Galega kale were studied. The storage temperatures used were 1, 5, 10, 15 and 20 °C. The atmospheres tested were all combinations of 1, 5 and 10% v/v O2 plus 0, 10 and 20% v/v CO2 with the balance being N2, as well as ambient air. Temperature was the variable with the greatest influence on respiration rate and the effect of gas composition increased with temperature. The dependence of respiration rate on gas composition was well described by a Michaelis–Menten type equation with uncompetitive CO2 inhibition. The respiratory quotient (RQ) was found to be constant for the range of temperatures and gas compositions tested and was equal to 0.93±0.01. The constants of the Michaelis–Menten equation increased exponentially with temperature. The change over time of respiration rate of leaves exposed to air at 20 °C was also analysed. It was observed that respiration rate decreased with time and that the ratio between the respiration rate of shredded and intact leaves was approximately constant in the period tested and equal to 2.8.

Inactivation of Escherichia coli by ozone treatment of apple juice at different pH levels.

This research investigated the efficacy of gaseous ozone on the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in apple juice of a range of pH levels, using an ozone bubble column. The pH levels investigated were 3.0, 3.5, 4.0, 4.5 and 5.0. Apple juice inoculated with E. coli strains (10(6)CFU/mL) was treated with ozone gas at a flow rate of 0.12L/min and ozone concentration of 0.048 mg/min/mL for up to 18 min. Results show that inactivation kinetics of E. coli by ozone were affected by pH of the juice. The ozone treatment duration required for achieving a 5-log reduction was faster (4 min) at the lowest pH than at the highest pH (18 min) studied. The relationship between time required to achieve 5log reduction (t(5d)) and pH for both strains was described mathematically by two exponential equations. Ozone treatment appears to be an effective process for reducing bacteria in apple juice and the required applied treatment for producing a safe apple juice is dependant on its acidity level.

Purification and properties of Amycolatopsis mediterranei DSM 43304 lipase and its potential in flavour ester synthesis

An extracellular thermostable lipase from Amycolatopsis mediterranei DSM 43304 has been purified to homogeneity using ammonium sulphate precipitation followed by anion exchange chromatography and hydrophobic interaction chromatography. This protocol resulted in a 398-fold purification with 36% final recovery. The purified A. mediterranei DSM 43304 lipase (AML) has an apparent molecular mass of 33 kDa. The N-terminal sequence, AANPYERGPDPTTASIEATR, showed highest similarity to a lipase from Streptomyces exfoliatus. The values of K(m)(app) and V(max)(app) for p-nitrophenyl palmitate (p-NPP) at the optimal temperature (60°C) and pH (8.0) were 0.099±0.010 mM and 2.53±0.06 mmol/min mg, respectively. The purified AML displayed significant activity towards a range of short and long chain triglyceride substrates and p-nitrophenyl esters. Hydrolysis of glycerol ester bonds occurred non-specifically. The purified AML displayed significant stability in the presence of organic solvents (40%, v/v) and catalyzed the synthesis of the flavour ester isoamyl acetate in free and immobilized states.

Postharvest Hardness and Color Evolution of White Button Mushrooms (Agaricus bisporus).

UNLABELLED The quality evaluation of mushrooms was studied by storing fresh white button mushrooms (Agaricus bisporus) for 6 to 8 d, at various controlled temperature conditions (3.5 to 15 degrees C) and measuring the instrumental textural hardness and color of the mushroom cap for different product batches. A nonlinear mixed effect Weibull model was used to describe mushroom cap texture and color kinetics during storage considering the batch variability into account. Storage temperature was found to play a significant role in controlling texture and color degradation. On lowering storage temperature (i) the extent of the final browning extent in the mushroom after storage was reduced and (ii) the rate textural hardness losses was slowed down. A linear dependence of the final browning index with temperature was found. An Arrhenius type relationship was found to exist between the temperature of storage and storage time with respect to textural hardness. The average batch energy of activation was calculated to be 207 +/- 42 kJ/mol in a temperature range of 3.5 to 20 degrees C. PRACTICAL APPLICATION This article evaluates how temperature abuse affects mushroom texture and color, applying methods that allow for the consideration of the natural product variability that is inherent in mushrooms. Its results apply to mushroom producers, retail distribution, and supermarkets for effective storage management.

Effect of Heat Shock on Browning-Related Enzymes in Minimally Processed Iceberg Lettuce and Crude Extracts

The effects of heat shock on PPO and POD activity in minimally processed Iceberg lettuce was examined during storage (10 days). The results were compared with the effect of temperature on crude extracts of these enzymes (in vitro analysis). Fresh-cut lettuce washed at 50 °C showed significantly lower PPO and POD activity throughout storage than lettuce washed at 4 °C and 25 °C. These results were consistent with a sensory analysis in which the panellists found the lowest browning scores in those samples treated at 50 °C. When PPO and POD were analysed in vitro, the samples treated at 50 °C showed a rapid loss of POD activity and a similar but slower loss of PPO activity in all tissues, while incubation at 4 °C and 25 °C showed no significant loss of activity. While heat shock did not lead to significant loss of activity it did repress the synthesis of PPO and POD during storage.

Modelling of stress due to shrinkage during drying of spaghetti

Abstract The aim of this study is to model the stress building in a solid product which shrinks during drying, in order to choose the best drying parameters to avoid cracks formation. For this, a simulation model has been developed to predict the evolution of temperature and moisture content in the product, and consequently the shrinkage and the induced strain and stress. The studied case is an infinite cylinder of pasta, representing the case of spaghetti. For this, we need to know the mechanical behaviour of the studied product, which varies both with moisture X and temperature T. The experimental results are presented as an effective Young’s modulus Eeff=f(X,T). The simulation results evaluate the mechanical stress path followed at each location in the material, during all the drying process, and according to the chosen external drying conditions.

Characterization of cinnamyl alcohol dehydrogenase of Helicobacter pylori. An aldehyde dismutating enzyme.

Cinnamyl alcohol dehydrogenases (CAD; 1.1.1.195) catalyse the reversible conversion of p‐hydroxycinnamaldehydes to their corresponding alcohols, leading to the biosynthesis of lignin in plants. Outside of plants their role is less defined. The gene for cinnamyl alcohol dehydrogenase from Helicobacter pylori (HpCAD) was cloned in Escherichia coli and the recombinant enzyme characterized for substrate specificity. The enzyme is a monomer of 42.5 kDa found predominantly in the cytosol of the bacterium. It is specific for NADP(H) as cofactor and has a broad substrate specificity for alcohol and aldehyde substrates. Its substrate specificity is similar to the well‐characterized plant enzymes. High substrate inhibition was observed and a mechanism of competitive inhibition proposed. The enzyme was found to be capable of catalysing the dismutation of benzaldehyde to benzyl alcohol and benzoic acid. This dismutation reaction has not been shown previously for this class of alcohol dehydrogenase and provides the bacterium with a means of reducing aldehyde concentration within the cell.

Prediction of Polyphenol Oxidase Activity Using Visible Near-Infrared Hyperspectral Imaging on Mushroom (Agaricus bisporus) Caps.

Physical stress (i.e., bruising) during harvesting, handling, and transportation triggers enzymatic discoloration of mushrooms, a common and detrimental phenomenon largely mediated by polyphenol oxidase (PPO) enzymes. Hyperspectral imaging (HSI) is a nondestructive technique that combines imaging and spectroscopy to obtain information from a sample. The objective of this study was to assess the ability of HSI to predict the activity of PPO on mushroom caps. Hyperspectral images of mushrooms subjected to various damage treatments were taken, followed by enzyme extraction and PPO activity measurement. Principal component regression (PCR) models (each with three PCs) built on raw reflectance and multiple scatter-corrected (MSC) reflectance data were found to be the best modeling approach. Prediction maps showed that the MSC model allowed for compensation of spectral differences due to sample curvature and surface irregularities. Results reveal the possibility of developing a sensor that could rapidly identify mushrooms with a higher likelihood to develop enzymatic browning, hence aiding produce management decision makers in the industry.

Kinetic models of ascorbic acid thermal degradation during hot air drying of maltodextrin solutions

Abstract The kinetic parameters of models that describe the joint influence of water content and temperature on the thermal degradation of ascorbic acid were estimated from drying experiments using maltodextrin DE 12 as a base material. Two models were used: a first-order decay model with (1) a TDT temperature dependency and a polynomial dependency of the Dr and z values with water content, and (2) a WLF dependency of the D value on glass transition temperature, with the Gordon–Taylor equation describing the influence of water content on Tg. Experiments were performed in a drying oven with dry bulb temperatures between 100°C and 160°C, with most of the drying occurring with the sample temperature below the oven temperature. Both models provided good fits of the experimental data. Other data from literature for a very different temperature range (4°C–68°C) and for maltodextrin DE 25 were handled in the same way and while the polynomial/TDT model yielded a different moisture dependence structure, the WLF/Gordon–Taylor model yielded similar parameters, thus showing a better predictive power.

PK/PD modelling of comb-shaped PEGylated salmon calcitonin conjugates of differing molecular weights

Salmon calcitonin (sCT) was conjugated via cysteine-1 to novel comb-shaped end-functionalised (poly(PEG) methyl ether methacrylate) (sCT-P) polymers, to yield conjugates of total molecular weights (MW) inclusive of sCT: 6.5, 9.5, 23 and 40kDa. The conjugates were characterised by HPLC and their in vitro and in vivo bioactivity was measured by cAMP assay on human T47D cells and following intravenous (i.v.) injection to rats, respectively. Stability against endopeptidases, rat serum and liver homogenates was assessed. There were linear and exponential relationships between conjugate MW with potency and efficacy respectively, however the largest MW conjugate still retained 70% of E(max) and an EC(50) of 3.7nM. In vivo, while free sCT and the conjugates reduced serum [calcium] to a maximum of 15-30% over 240 min, the half-life (T(1/2)) was increased and the area under the curve (AUC) was extended in proportion to conjugate MW. Likewise, the polymer conferred protection on sCT against attack by trypsin, chymotrypsin, elastase, rat serum and liver homogenates, with the best protection afforded by sCT-P (40kDa). Mathematical modelling accurately predicted the MW relationships to in vitro efficacy, potency, in vivo PK and enzymatic stability. With a significant increase in T(1/2) for sCT, the 40kDa MW comb-shaped PEG conjugate of sCT may have potential as a long-acting injectable formulation.