AcknowledgementsThanks to Mark Wingfield, Malvern Instruments GmbH, Germany, for giving valuable introduction and advice into practical rheology.

Funding for this research was provided by the fFORTE WIT - Women in Technology Program of the Vienna University of Technology. This program is co-financed by the Vienna University of Technology, the Ministry for Science and Research and the fFORTE Initiative of the Austrian Government.

AERC 2010

Göteborg, Sweden

Kathrin Scharnhorst, Ingrid SteinerVienna University of Technology, Institute of Chemical Engineering

Research Area of Natural Products and Food Chemistry

References[1] Saravacos, G. D.: Transport properties of foods, New York, Dekker, 2001[2] Aguilera, J.M.: Why food microstructure, Journal of Food Engineering, 2005, 67, p 3-11[3] Steiner, I., Volansky, P.: Determination of diphenylphthalate and benzophenone in foodstuffs; in: "Compilation of analytical methods for model migrants in foodstuffs", P. Paseiro Losada, C. Simoneau, R. Franz (Hrg.); European Commission, Directorate General, Joint Research Center, Ispra, 2006, EUR 22232 EN, p. 51 - 66.

Contact: Kathrin.Scharnhorst@tuwien.ac.at

Introduction and ObjectivesSince plastic packaging has being used more commonly for food during the last decades and complex solutions of material are developed, the issue of migration of any compound from the packaging into the food needs more attention as well. It is not only a question of migration rates but also which other parameters influence the transport process of the components migrating from food contact materials into the food. As migration is known as a transport process controlled by diffusion it is all the same structure dependent as Zaravacos pointed out in his studies [1].

Structure (of food) itself depends on the composition which of course causes the macrostrucure. But as Aguilera has shown microstructure seems to have an impact on transport processes as well [2].

In order to describe structure properties of liquid and semisolid matters rheological characteristics like viscosity, shearthinning and thixotropic effects have been proved to be useful. These effects are also important for the product design and processability.

The objective of this study is whether there is a correlation between structure properties of the non-Newtonian liquid foodstuff ketchup (rheologically determinable and others) and migration rates of 2 model contaminants out of a LDPE plastic film.

Results and Discussion

Materials and MethodsSeveral ketchups were purchased at local supermarkets to be analysed. They were selected for differernt contents of carbohydrates and protein as indicated on the packaging.

Further characteristics were determined as water content, pH, electric conductivity and refractive index of the centrifugal supernatant.

For migration tests a LDPE film of 164 µm thickness was applied in single side contact containing 450 mg benzophenone and 561 mg diphenylphthalate/kg film.

Migration tests: were carried out at 25 °C for 22 days and at 70°C for 25 h both in a static way (kept in an oven) and a dynamic way (shaken in a waterbath at a frequency of 80/min. The dynamic tests were carried out in order to simulate transport processes. Analysis of benzophenone and diphenylphthalate was conducted as described by Steiner et Volansky [3].

Rheological investigations were performed using a Rheomat RM 180 Rotational Viscosimeter using a bob and tube geometry No 3 (gap width: 0,59 mm). To examine thixotropy samples were pre sheared for 120 s at 50 s-1, after a settling time of 30 min shearing from 6.5 to 300 s-1 in 45 s forth and backwards was conducted.

Shearthinning and flow behaviour were investigated performing a step test with ramps at 10 – 20 – 40 – 80 – 200 – 300 – 500 – 750 – 1000 s-1

also after pre shearing for 120 s at 50 s -1 and a 30 min settling time.

Food PropertyKetschup A

Ketchup B

Ketchup C

% Protein 1,5 2,2 1,5

% Carbohydrates 29 35 20

% Water 67 69 73

pH 3,7 3,9 3,9

Refractive index (22°C)

1,3879 1,3859 1,3757

Electric conductivity 16,5 mS/cm

8,2 mS/cm

9,6 mS/cm

ConclusionsMigration of additive compounds into various ketchups differs slightly, but cannot linked directly to the rheological and physico-chemical properties of the analysed ketchups. It cannot be concluded unambiguously that hydrocolloids like the carbohydrates used as thickening agents prevent migrating of contaminants though they might have a hindering influence at higher temperatures for bigger molecules as could be detected for DPP.

Rheological characteristics are clearly a good means to describe structure properties of liquid and semisolid foodstuffs. Additional data have to be collected to relate food structure properties to migration rates of additive compounds out of plastics.

Flow behaviour at 25 and 40 °C

0,10

1,00

10,00

0 200 400 600 800 1000 1200

Shear rate [s-1]

lg V

isco

sity

[P

as] Ketchup A 25°C

Ketchup A 40°C

Ketchup B 25°C

Ketchup B 40°C

Ketchup C 25°C

Ketchup C 40°C

Thixotropy at 25 and 40°C

20

40

60

80

100

120

140

160

0 50 100 150 200 250 300 350

Shear rate [s-1]

Sh

ear

stre

ss [

Pa] Ketchup C 25°C

Ketchup A 25°C

Ketchup B 25°C

Ketchup C 40°C

Ketchup A 40°C

Ketchup B 40°C

Table 1: physico-chemical properties of the analysed ketchups