Distortion of Norway spruce timber Part 2. Modelling twist

Picea abies ). Several material parameters were also measured, such as spiral grain angle, shrinkage in all three directions, annual ring width and density. Twist in the studs was measured at four different times at different moisture contents. The amount of twist correlated well with the moisture content and was reversible throughout several moisture changes. When the moisture content decreased, the twist increased and vice versa. About 50% of the variation in twist could be explained by a single parameter, i.e. the average growth ring curvature. All studs with severe twist were cut with its centroid within a radius of 75 mm from the pith. A statistical analysis of the data shows that growth ring curvature and spiral grain angle together explained about 70% of the variation in twist. Other parameters, such as shrinkage strains, density and ring width, did not increase predictability. When using a model developed by Stevens and Johnston (1960), about 66% of the variation in twist could be explained. The model also explained twist quantitatively well. The model included curvature of the growth ring, spiral grain angle and the tangential shrinkage strain.

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Picea abies ). Mehrere Materialeigenschaften wurden ebenfalls gemessen, und zwar: Faserwinkel, Schwinden in drei Richtungen, Jahrringbreite und Dichte. Die Verdrehung der Kanth?lzer wurde zu vier verschiedenen Zeitpunkten bei unterschiedlichen Feuchtegraden gemessen. Das Ausma? der Verdrehung war gut korreliert mit der Feuchte. Mit abnehmender Feuchte stieg die Verdrehung und umgekehrt. Rund 50% der Verdrehungswerte sind durch einen einzigen Parameter erkl?rt, n?mlich die Jahrringkrümmung. Bei allen Kanth?lzern mit starker Verdrehung lag die Mittelachse innerhalb eines Abstandes von 75 mm von der Markr?hre. Die statistische Analyse ergab, da? Jahrringkrümmung und Faserwinkel zusammen ca. 70% der Variation der Verdrehung erkl?ren. Andere Parameter wie Schwindspannungen, Dichte und Jahrringbreite erh?hten die Vorhersagbarkeit nicht. Mit Hilfe des Modells von Stevens und Johnson (1960) konnten rund 66% der Verdrehung erkl?rt werden. Dieses Modell lieferte auch zufriedenstellende quantitative Ergebnisse. Berücksichtigt werden dabei Jahrringkrümmung, Faserwinkel und tangentiale Schwindspannung.

     

Modelling natamycin release from alginate/chitosan active films

In antimicrobial active films, the active agent is incorporated in the polymeric matrix and is released from the film to the product surface where most deterioration processes take place. In this study, films structured solely by alginate and by blends of alginate:chitosan (82.5:17.5 and 65:35) were obtained by casting. The film formulations received natamycin (4 and 8 g/100 g biopolymer) as antimicrobial agent. Films were characterised according to their thickness and morphology. Diffusion experiments in water indicated very slow release kinetics of the antimicrobial, being markedly hindered in the alginate and chitosan composite films, probably due to electrostatic interactions between chitosan and natamycin. Fickian diffusion prevailed and the diffusion coefficients found for the films varied from 2.6 × 10^?11 to 2.5 × 10^?12 cm² s^?1.     

Modelling the effect of oil/fat content in food systems on flavour absorption by LLDPE.

One of the phenomena in food-packaging interactions is flavour absorption. Absorption of flavour compounds from food products into food-packaging materials can result in loss of flavour compounds or an unbalance in the flavour profile changing a product's quality. The food matrix influences the amounts of absorbed flavour compounds; the presence of oil or fat especially determines the ability to absorb flavour compounds from the food to the package. On the other hand, the polarity of the flavour compound itself is a characteristic that also influences the level of absorption into synthetic polymers. A model based on the effect of the polarity (logP) of flavour compounds and on their partitioning coefficients between the food (matrix) and the packaging material is described. The model can be used for predicting absorption of flavour compounds from foods into LLDPE. However, an attempt to apply the proposed model on real foods shows serious limitations of the model for (very) low fat products. Predictive values deviate from the measured values, probably due to other interaction phenomena, e.g. with proteins. Predictive and measured values from a product with a substantial amount of fat match much better, suggesting that the model is valid for products having a substantial amount of (free) fat.     

Modelling to predict thermophysiological properties of hollow/microporous yarn fabrics

Hollow/microporous yarn spinning is a technique used to increase the bulk of yarn without increasing its weight. Hollowness in the cotton yarns has been introduced by various methods and techniques. Empirical models have been developed to predict the thermophysiological properties through structural parameters. Based on standardized multiple linear regression models, fabric’s structural parameters are related with thermophysiological properties of hollow yarn fabrics. Three basic parameters i.e. yarns packing density, inter-yarn porosity and fabric thickness have been found to relate strongly with fabric thermophysiological properties except water vapour permeability.     

Modelling of dehydration-rehydration of orange slices in combined microwave/air drying

The development of new citrus products, such as dry products for direct use or for rehydration, is interesting to promote their consumption. Combined microwaves (MW)–air (2 m/s, 60 °C) drying of orange slices has been studied in terms of process kinetics and of the rehydration capability as affected by the applied MW power (0, 0.17, 0.36, 0.69 and 0.88 W/g). Drying curves were modelled considering two periods, with different kinetic constants, related with the effective water diffusivity. These constants increased linearly with the applied MW power and, despite the low levels of MW power used, a sharp reduction in drying time of orange slices was obtained. Rehydration behaviour of orange slices was modelled through Peleg's and Weibull's equations. No differences in rehydrating behaviour were observed as a function of the applied MW power. So, the highest level, which was limited to avoid sample browning, will be recommended to reduce the drying time.     

Modelling the influence of temperature on the recovery ofListeria monocytogenesfrom heat injury

The ability ofListeria monocytogenesScott A to recover from heat injury, as monitored by repair of salt-tolerance, was modelled as a function of temperature and extent of cell injury. A modification to the equation of Hills and Mackey ((1995) Food Microbiology, 12, 333-346), which included parameters for the maximum rate of recovery (R_r), and the decreasing rate of recovery (a_r), and eliminated the parameter describing the increasing rate of recovery (b_r), was used to model the recovery from injury. Lag phase duration (LPD) and R_rwere well predicted by models including both temperature and extent of injury (R²=0.99 and 0.92 for LPD and R_rrespectively), while the growth rate (R_g) was influenced by temperature alone (R²=0.96). The degree to which cells had recovered salt-tolerance at the end of the lag phase (i.e. proportion of cells capable of growth on agar containing 5% ((w/v) NaCl) was found to be related to the initial extent of injury. The results suggest that loss of salt-tolerance may not be the most important site of injury, and that alternative models are needed to adequately account for the contribution of sub-populations of cells to growth after repair of heat injury.     

Modelling the bacterial survival/death interface induced by high pressure processing

The survival/death interface model was developed for prediction of inactivation of Listeria monocytogenes by high pressure processing (HPP). The model was derived from data sets comprising 360 combinations of environmental factors such as pressure (200, 300 400, and 500 MPa), pressure-holding time (1, 3, 5, 10, 20, 30 min), pH (3, 4, 5, 6, 7), and inoculum level (3, 5, 7 log(10) CFU/ml). The determination of survival/death of L. monocytogenes after HPP was confirmed by the presence/absence of colony forming ability on non-selective agar plates after 30 days of incubation at 20 degrees C in broth to take into account recovery of HPP-induced injured cells. The developed linear logistic model with time logarithmically transformed gave a degree of agreement between probabilities predicted by the fitted model and all observations as 99.3% concordant. The model provided a good fit to the data as shown by performance statistics. The developed interface model in the present study provided requisite process conditions for the target effect of HPP on L. monocytogenes. In addition to using the simple linear logistic model, a polynomial logistic model was also fitted to the data where pressure-holding time was not logarithmically transformed. That model did not produce a better fit to the data and resulted in some potentially misleading predictions. Optimization of HPP could be accomplished using the model developed in this study. Furthermore, choice in processing factors allows for processing flexibility in HPP and specifies the process criteria that are incorporated into the HACCP plan.     

Modelling of the carding process for spunlace nonwovens with particular regard to selected mechanical parameters in a double-drum card. Part 2: Modelling of delay times in the longitudinal mixing process

Abstract

The production of Spunlace nonwoven fabric is a complex process and includes, among other things, several important stages, such as carding, needling and drying. One of the most important stages is the carding process, which has a significant impact on the shaping of the physico-mechanical and qualitative characteristics of the nonwoven fabric. The article presents the modelling of the carding process in a two-drum system. A mathematical model, determining the expected number of drum and carding card cycles was proposed. Based on this model, delays were determined, due to longitudinal shifts of fibre in the carding process. Numerical simulations have been made and discussed in relation to fibre collection factors, at different production speeds and the number of carding rollers in the worker-stripper system.     

Modelling the variability of lag times and the first generation times of single cells of E. coli

A mathematical model combining deterministic and stochastic elements describes the growth and division of single cells. Its deterministic part is based on the model of Baranyi and Roberts [International Journal of Food Microbiology 23 (1994) 277] modelling the gradual adjustment of the cells to a new environment. The stochastic part assumes a random threshold size for the division of a single cell, which accounts for the variability of the individual generation times. Experimental results of the first division times of thousands of single cells using a microscopic flow system could be reproduced with this model, and it has the potential to be used to study the effects of different stress and environmental factors on the distribution of the lag and generation times of individual cells.     

Reducing salt level in food: Part 2. Modelling salt diffusion in model cheese systems with regards to their composition

In the first part of the paper (Floury, J., Camier, B. Rousseau, F., Lopez, C., Tissier, J. P., & Famelart, M. H. (2009) Reducing salt level in food: Part 1. controlled manufacture of model cheese systems and their structure-texture relationships. LWT – Food Science and Technology 49(10), 1611–1620), a model cheese matrix presenting different textural properties was developed in order to further study the factors implied in the salt release in mouth during food chewing. The present work consists in physical and modelling approaches to better understand the mass transfer phenomena occurring in the product during its consumption in the mouth. Concentration profiles of several ionic species were measured during the release of salt from the different model matrices into artificial saliva. Apparent diffusion coefficients of the sodium chloride were determined by fitting the experimental data to the second Fick's law. Apparent diffusion coefficients were included between 2.81 and 3.43 × 10⁻¹⁰ m² s⁻¹ at 15 °C and 75% HR. D-value decreased strongly when the dry matter content decreased. Microstructure of the matrices with the lower protein concentration was coarser and fluffier, facilitating the diffusion of the solutes. The D-value increased with the pH at renneting, probably because of the chemical changes of the structure of the casein micelles and significant differences in textural characteristics of cheeses. The diffusion coefficient also significantly decreased with the initial salt concentration, due to the tightening of the matrix microstructure.