Christoph Hartmann

Christoph Hartmann
Nestlé S.A. · Nestlé Research Center

Prof. Dr.-Ing.

About

86
Publications
11,425
Reads
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1,581
Citations
Introduction
What I like most about research is diversity. It is challenging to deliver excellent research in an unknown area of science instead of doing incremental research over decades. But this is all the fun. Mechanical Engineering, Numerical Simulation, Food Science, Flavor Science, Food Safety.... that is an uncommon but rewarding professional experience. I hope there is more to come.
Additional affiliations
November 2019 - present
Technische Universität Berlin
Position
  • Professor
September 2018 - present
Nestlé S.A.
Position
  • Academic Alliances
August 2016 - August 2018
Nestlé S.A.
Position
  • Head of Department

Publications

Publications (86)
Article
Thermal properties, such as thermal conductivity, specific heat capacity and latent heat, influence the melting and solidification of chocolate. The accurate prediction of these properties for micro-aerated chocolate products with varying levels of porosity ranging from 0% to 15% is beneficial for understanding and control of heat transfer mechanis...
Article
Micro-aeration has been employed by the chocolate industry as a texture and flavour modifier. However, the impact of micro-aeration on oral processing is still not well understood. This study quantifies the mechanical, thermal and tribological behaviour of chocolate materials of different porosity levels. These material properties were then linked...
Article
Aeration in foods has been widely utilised in the food industry to develop novel foods with enhanced sensorial characteristics. Specifically, aeration at the micron-sized scale has a significant impact on the microstructure where micro-bubbles interact with the other microstructural features in chocolates. This study aims to determine the effect of...
Article
Full-text available
We illustrate how scientific understanding of Food Oral Processing enables food product development with specific benefits for several target populations. in vivo, in vitro , and in silico approaches are discussed in the context of their ability to quantify oral processing from the molecular to the macroscopic scale. Based on this understanding, fo...
Article
Full-text available
The perception of some food attributes is related to mechanical stimulation and friction experienced in the tongue-palate contact during mastication. This paper reports a new bench test to measure friction in the simulated tongue-palate contact. The test consists of a flat PDMS disk, representing the tongue loaded and reciprocating against a statio...
Article
This work was carried out to study the airflow and heat transfer above a cup of hot drink. The experiment was undertaken in a device in which the air temperature and velocity were controlled representing a room condition. The influence of heat exchange by convection and evaporation between the hot drink (at different temperatures) and air on the ve...
Article
Full-text available
Synthetic and natural steroid hormones have attracted some attention in recent years as endocrine active substances (EAS) that interact or interfere with the endocrine system. Endogenous hormones occur naturally in food of animal origin, among which bovine milk represents an important source. This study was conducted to determine the occurrence of...
Article
We propose a mechanistic modelling approach for studying the indoor dispersion of aroma compounds which are released from, for instance, food products. The approach combines the indoor velocity field with a release model for aroma compounds. The release mass flux is expressed as a function of key variables such as mass transfer and gas–liquid parti...
Patent
Methods for evaluating and treating patients for dysphagia are provided. In a general embodiment, the method comprises screening the patient for dysphagia symptoms, diagnosing and categorizing the dysphagia if the patient exceeds a threshold of dysphagia symptoms, choosing the proper dysphagia treatment product based the patient's dysphagia, and gi...
Article
Full-text available
The human diet contains a large variety of aromas, tastes and textures. The latter is particularly important since it determines whether foods are difficult to process orally and thus can be one source of food avoidance. It has also been reported in recent literature that food texture was a main driver for satiation processes and thus it is of inte...
Article
The sensory characteristics of dark chocolate have been studied for many years and to date, its oral perception has been modulated only by playing on conventional factors (e.g. processing, particles size, ingredients or recipe). This study aims at enhancing the in-mouth perception of chocolate based on the shape of the chocolate piece introduced in...
Article
Full-text available
A set of six espresso coffees with different foam characteristics and similar above cup and in-mouth flavour sensory profiles was produced by combination of two varying parameters, the extraction pressure and the filtration of the coffee beverage. The coffees were subsequently evaluated in a comparative manner by a set of analytical (headspace, nos...
Article
The relationship between the physical structure of espresso coffee foam, called crema, and the above-the-cup aroma release was studied. Espresso coffee samples were produced using the Nespresso extraction system. The samples were extracted with water with different levels of mineral content, which resulted in liquid phases with similar volatile pro...
Article
Full-text available
Swallowing is triggered when a food bolus being prepared by mastication has reached a defined state. However, although this view is consensual and well supported, the physical properties of the swallowable bolus have been under-researched. We tested the hypothesis that measuring bolus physical changes during the masticatory sequence to deglutition...
Article
To study food disruption and bolus formation, a simulator of mastication (AM2) was developed to mimic masticatory behaviour and allow collection of a bolus at any stage in the masticatory sequence. Here we set out to validate the AM2 by comparing boluses obtained in vitro and in vivo.Boluses were obtained from the AM2 and 30 young dentate subjects...
Article
Rheology and water content properties of cereal boluses collected just before swallowing were investigated. No specific physical markers for swallowing were found between subjects. Each subject had his own mastication strategy leading to food boluses with different rheological and water content properties. However, for most of the subjects, similar...
Article
Full-text available
The present study aimed to compare the accuracy and reliability of four standard methods used for classification of people as taster or non-tasters based on their sensitivity to PROP (6-n-propylthiouracil). A panel consisting of 21 subjects was tested for threshold and suprathreshold sensitivity of sodium chloride, PROP, and genotyped for TAS2R38....
Article
P>The role of fat content and type of surfactant for oral friction processes and texture perception of oil-in-water emulsions was assessed. Emulsions at 22% and 33% fat content containing either sodium caseinate or a sucrose ester as emulsifier were compared with viscosity-adapted aqueous solutions of dextran using both sensory evaluation and frict...
Article
Texture perceived in mouth largely depends on the behaviour of the food when it is broken down and transformed by the mouth elements. Texture results from a dynamic process in which texture attributes are continuously analysed by the oral sensory systems during mastication. However, the particular sequence of perceptual events that occur during ora...
Article
Perception of sour, sweet, bitter, and salty taste can be related to specialized sensors (taste buds), however, this is not possible for texture perception. Although different types of oral mechanoreceptors are known, it remains unclear how texture perception relates to these structures. The aim of this work is to better understand textural attribu...
Article
Full-text available
We discuss the perception of grittiness in the human mouth from the perspective of continuum mechanics and draw some conclusions about the likely interactions between hydrodynamically arising stress fluctuations and stimulation of biological mechanoreceptor structures. Two classes of mechanoreceptors exist, responding to either static or dynamic st...
Article
In the present contribution experimental and numerical investigations of multiphase flow in a sequencing batch reactor (SBR) are presented. In the bioreactor the formation and growth of granular activated sludge (GAS) with diameter up to 5 mm occurs. In order to experimentally analyse multiphase flow patterns in a mixture of water, air and granules...
Article
A mathematical model to predict lethal and sublethal pressure effects on Lactococcus lactic was established through combined use of Principal Component Analysis (PCA) and Fuzzy Logic. The model was based on data comprising pressure inactivation kinetics with 64 combinations of the parameters pressure, temperature, pH, and buffer composition, sample...
Article
Full-text available
The objective of this work is to gain more insight into the processes of oral perception of food texture. Particularly, the limits for detectable thickness differences of objects, which are evaluated in the human mouth, are investigated. In a sensory study small, flexible circular disks (diameter in mm range) of varying thickness (in microm range)...
Article
The feeding mechanism of the sessile protozoon Opercularia asymmetrica (Oligohymenophorea, Peritrichia) relies on the cilia beat generating a flow field that convectively transports suspended particles and dissolved substances to the oral cavity of the organism. By use of optical micro-flow measurement and theoretical methods the flow environment o...
Article
This work is aimed at investigating phase change processes of water under high pressure by help of an in situ visualization technique. High Pressure Digital Particle Image Velocimetry and Thermography (HP-DPIV and HP-DPIT) techniques are applied to a phase change process for the first time and temperature-convective fields are analysed. Peculiar lo...
Article
The heat inactivation of Lactococcus lactis was studied by determination of cell counts, and by FT-IR spectroscopy recording the average structure of cell proteins. Cell counts were measured after incubation milk buffer or milk buffer with 1. 5 M sucrose, and FT-IR spectra were recorded in (2)H(2)O or (2)H(2)O with 1. 5 M sucrose in the range of 6-...
Article
The present contribution is dedicated to experimental and theoretical assessment of microbiological process heterogeneities of the high-pressure (HP) inactivation of Lactococcus lactis ssp. cremoris MG 1363. The inactivation kinetics are determined in dependence of pressure, process time, temperature and absence or presence of co-solutes in the buf...
Article
Mechanical stresses and deformation of cellular structures due to the application of high hydrostatic pressure (HHP) is analysed for two cases. In the first case, a liquid-filled spherical shell with linear elastic material properties is considered as first approximation of a biological cell. The theoretical analysis reveals the existence of severe...
Article
It was the aim of this work to determine the combined effects of pressure, temperature, and co-solutes on Lactococcus lactis, and to detect correlations between culture-dependent and culture-independent methods for assessment of cellular viability and sublethal injury. Therefore, the pressure induced inactivation of L. lactis MG 1363 was investigat...
Article
During the compression phase of high pressure treatment of aqueous food, the temperature locally increases approx. 2-3 K per 100 MPa in the isentropic case as a result of the external work done by the volume change of the fluid. It could be concluded in the authors' previous contributions that heat transfer induces undesired process non-uniformitie...
Article
This work is aimed at investigating phase change processes of water under high pressure by help of an in situ visualization technique. High Pressure Digital Particle Image Velocimetry and Thermography (HP-DPIV and HP-DPIT) techniques are applied to a phase change process for the first time and temperature-convective fields are analysed. Peculiar lo...
Article
In present contribution a study is presented, where fluid dynamic measurements are used to observe multiphase flow pattern in a bioreactor. It can be shown that hydrodynamic effects have a major influence on the formation, shape and size of Granular Activated Sludge (GAS) in a Sequencing Batch Reactor (SBR) under aerobic condition. In order to anal...
Article
It was the aim of this work to determine the combined effects of pressure, temperature, and co-solvents on Lactococcus lactis , and to detect correlations between culture-dependent and culture-independent methods for assessment of cellular viability and sublethal injury. Therefore, the pressure induced inactivation of L. lactis MG 1363 was investig...
Article
The inactivation by 200–400 MPa and post-pressure survival at acid conditions of E. coli TMW 2.497 was characterized by the measurement of intracellular pH (pHin), viable cell counts, glutamate (Glu) and arginine (Arg) consumption, and the influence of mild adaptation to mild acid stress prior to pressure treatment. Glutamate and arginine did not a...
Article
In the present contribution high pressure phase change of food in a 3.4 ml high pressure chamber is investigated by means of numerical simulation and experimental techniques. The researches of freezing and thawing in samples of potato, pork and cod at atmospheric pressure and two high pressure levels up to 200 MPa are carried out. In order to enabl...
Article
The current paper deals with the effects of convective transport and heterogeneous heat transfer on high pressure induced inactivation. While the pressure within a high pressure chamber can be considered as spatially constant, the temperature, in general, is a heterogeneously distributed field quantity. The present paper shows up to which extend th...
Article
The high-pressure inactivation (200 to 600 MPa) of Lactococcus lactis ssp. cremoris MG 1363 suspended in milk buffer was investigated with both experimental and theoretical methods. The inactivation kinetics were characterised by the determination of the viable cell counts, cell counts of undamaged cells, LmrP activity, membrane integrity, and meta...
Article
The mechanical effects of the compression of a yeast cell (Saccharomyces cerevisiae) under high hydrostatic pressure (HHP) are modeled and simulated numerically. The deformation of the cell under pressure deviates strongly from isotropic volume reduction. In the cell wall, von-Mises stress reaches the critical value upon failure at a pressure load...
Article
Thermofluiddynamics and process uniformity of high-pressure processing in a laboratory-scale autoclave (3.3 l volume) is assessed by use of experimental and numerical simulation techniques. Direct treatment of water at pressure levels of 500 and 300 MPa and with a pressure holding phase of 820 s is considered. Multiple thermocouple measurements are...
Article
Die durch Temperaturunterschiede induzierten Prozessheterogenitäten bei der Hochdruckbehandlung von Lebensmitteln werden sowohl experimentell als auch numerisch untersucht. Hierbei werden Prozesse bei bis zu 500 MPa während einer 20-minütigen Hochdruckbehandlung in einem 3-Liter-Hochdruckautoklaven betrachtet. Als Maß für die Heterogenitäten der Pr...
Article
Im vorliegenden Beitrag wird die Deformation von Belebtschlammflocken (BSF) in einer Dehnströmung betrachtet. Dazu werden BSF aus einer kommunalen Kläranlage in einem entsprechend geformten Kanal einer laminaren, dehnungsbehafteten Strömung ausgesetzt. Eine Dehnung der Flocken sowie Desintegration größerer Flockenaggregate durch diese mechanische B...
Article
The mechanical effects of the compression of a yeast cell (Saccharomyces cerevisiae) under high hydrostatic pressure used for the processing of food and food ingredients are modelled and simulated with the finite-element method. The cell model consists of a cell wall, cytoplasm a lipid filled vacuole and the nucleus. Material parameters have been t...
Article
The mechanical effects of the compression of a yeast cell (Saccharomyces cerevisiae) under high hydrostatic pressure used for the processing of food and food ingredients are modelled and simulated with the finite-element method. The cell model consists of a cell wall, cytoplasm a lipid filled vacuole and the nucleus. Material parameters have been t...
Conference Paper
Full-text available
Im vorliegenden Beitrag wird die Deformation von Belebtschlammflocken (BSF) in einer Dehnströmung betrachtet. Dazu werden BSF aus einer kommunalen Kläranlage in einem entsprechend geformten Kanal einer laminaren, dehnungsbehafteten Strömung ausgesetzt. Eine Dehnung der Flocken sowie Desintegration größerer Flockenaggregate durch diese mechanische B...
Article
High pressure induced freezing and thawing processes are investigated by means of modelling and numerical simulation. The enthalpy–porosity model is reformulated in terms of conservation equations of mass, momentum and heat for a compressible medium. It can be shown that convective fluid motion has a major influence on the formation of the ice fron...
Article
Recognition of representative damages on returnable crates of beverages is carried out by an artificial neural network (ANN) trained exclusively with frequency response spectra from finite-element simulations. Finite-element mode shape analysis implies that two sensors are sufficient for successful damage recognition. Amongst three topologies, a lo...
Article
Full-text available
vсокого гидростатического давления (ВГД) приводит к нарушению рав-новесия образования химических связей в биохимических реакциях, фазовых пере-ходах и процессах переноса. Tаким образом, ВГД, как новый метод в науке о про-дуктах питания и биотехнологии, предлагает широкий спектр приложений. Данная работа на двух примерах иллюстрирует влияние механич...
Article
High pressure technology opens new possibilities for freezing and thawing of liquid and solid substances. In the present contribution modelling and numerical simulation of high pressure induced freezing and thawing processes of a fluid food system is presented. Phase transitions between water and ice I under pressure in the range 0.1-200 MPa are si...
Article
This numerical study evaluates the momentum and mass transfer in an immobilized enzyme reactor. The simulation gives detailed information of the local substrate and product concentrations with respect to external and internal transport limitations. The flow field characterization of the system makes it possible to understand fluid mechanical proper...
Article
In this paper the modelling and numerical simulation of the freezing and thawing processes of water under high hydrostatic pressure up to 200 MPa is presented. The system of equation consists of the conservation laws of mass, momentum and energy. Moreover, it contains also the equation of phase change and the equations of state for water and ice. I...
Article
This numerical study evaluates the momentum and mass transfer in an immobilized enzyme reactor. The simulation is based on the solution of the three-dimensional Navier-Stokes equation and a scalar transport equation with a sink term for the transport and the conversion of substrate to product. The reactor consists of a container filled with 20 sphe...
Article
The present contribution investigates the influence of heat and mass transport effects on the uniformity of a high-pressure induced inactivation. It is based on mathematical modelling and numerical simulation. The inactivation of E. coli suspended in packed UHT-milk carried out in a batch process with water as pressure medium is taken as a model pr...
Article
Here we deal with the influence of heat-transport effects on a high-pressure-induced enzyme inactivation in packed substances. Special attention is given to the influence of the geometrical scale and to the heat-transfer characteristics of the packaging material. The investigation is based on mathematical modeling and numerical simulation. The meth...
Article
Subject of the present contribution is the numerical simulation of the effect of a elongational flow field on a suspended particle-aggregate. The particle-aggregate consists of seven rigid spherical particles and is suspended in the flow field at low Re-numbers (Re=0.01–0.1). The ratio of particle and fluid densities varies between 1 and 15. The ve...
Article
The main purpose of the present contribution is to demonstrate that the high pressure effect on biotechnological materials and food components can be considered as instantaneous but not homogeneous. In contradiction to this, the homogeneity of the pressure effect and, consequently, the independence on geometrical parameters is often declared in lit...
Chapter
In the present contribution modelling and numerical simulation of high pressure induced freezing and thawing processes of a fluid food system is presented. Phase transitions between water and ice I under pressure in the range 0.1 – 200 MPa are simulated accounting for convective motion of the liquid phase. The results of the simulation are presente...
Chapter
The contribution deals with the influence of high pressure on viscosity and phase transition of edible oils. For both cases the effect of pressure is reverse to that of temperature. A kinetic relation which demands a pressure dependent activation energy and prognoses an exponential increase of viscosity in absolute agreement with experiments has be...
Article
In the present contribution a high hydrostatic pressure (HHP) treatment of a fluid food system is analysed by means of numerical simulation. The considered process is subdivided into a phase of pressure increase from ambient pressure to 500 MPa and a phase of constant pressure application. For both phases temperature and fluid velocity distribution...
Article
High-pressure-induced conversions, such as the inactivation of enzymes or of microorganisms, are dependent on the applied pressure and the temperature of the process. The former can be considered to be a spatially homogeneous quantity, while the latter, being a transport quantity, varies over space and time. Here we question whether the uniformity...
Conference Paper
A new method to detect damages on crates of beverages is investigated. It is based on a pattern-recognition-system by an artificial neural network (ANN) with a feedforward multilayer-perceptron topology. The sorting criterion is obtained by mechanical vibration analysis which provides characteristic frequency spectra for all possible damage cases a...
Article
In the present contribution, thermodynamic and fluid-dynamic effects of high-pressure treatment are analyzed by means of numerical simulation. The following process is considered: pure water is compressed up to 500 MPa in a 4-ml chamber at different compression rates by enforced mass inflow. After the compression phase, the inflow is stopped for 20...
Article
A new method to detect damages on crates of beverages is investigated. It is based on a pattern-recognition-system by an artificial neural network (ANN) with a feedforward multilayer-perceptron topology. The sorting criterion is obtained by mechanical vibration analysis which provides characteristic frequency spectra for all possible damage cases a...
Article
Full-text available
This paper describes the development of a new method to detect damages on crates of beverages. Therefore, a pattern-recognition-system based on an artificial neural network (ANN) is applied on frequency spectra obtained by mechanical vibration response analysis. To support the network training a large number of numerical data-sets is calculated by...
Article
The deformation of a drop in a surrounding uni,form flow field including surface tension effects is investigated. The full Navier-Stokes equations are solved numerically with a finite volume method for the flow inside and around the drop. The shape of the drop is determined on the basis of a variational principle. A Galerkin method is employed risi...
Article
In the present paper, we investigate the influence of the initial condition of a three-dimensional (3D) shock focusing problem on its solution. We search for an optimum combination of initial values to produce a maximum pressure amplification under the condition that the total energy input in the system is constant for each parameter combination. T...
Chapter
Based on Cabannes’ [1] analytic investigation on nonstationary attached shock waves around accelerated or decelerated bodies at supersonic velocities, the unsteady supersonic flow around wedge-like and conical bodies is analysed analytically and numerically with respect to the relationship between the curvature of the body contour at the pointed no...