3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures
3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures
3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures
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Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology<br />
P93 INFLuENCE OF Ph ON ThE RhEOLOGy<br />
PROPERTIES OF TOMATO KETChuPS<br />
JARMILA LEHKOŽIVOVá, JOLAnA KAROVIČOVá,<br />
JARMILA HOJEROVá, ZLATICA KOHAJDOVá and<br />
IVAnA ŠIMOnOVá<br />
Institute of Biotechnology and Food Science, Faculty of Chemical<br />
and Food Technology, Slovak University of Technology,<br />
Radlinského 9, 812 37 Bratislava, Slovak Republic,<br />
jarmila.lehkozivova@stuba.sk<br />
Introduction<br />
A large part of the world tomato crop is processed into<br />
tomato paste, which is subsequently used as an ingredient<br />
in many food products, mainly soups, sauces and ketchup 1 .<br />
Tomato ketchup is concentrated dispersion of insoluble matter<br />
in aqueous medium 2 .<br />
By definition, rheology is the study of the deformation<br />
and flow of matter. So, rheological properties are based on<br />
flow and deformation responses of foods when subjected to<br />
stress 3 . The flow properties of food products significantly<br />
influence not only technology processes during the production,<br />
but the texture of final products, too 4 . Tomato ketchup<br />
viscosity is very important from both engineering and consumer<br />
viewpoints 5 .<br />
The aim of this work was investigated the influence of<br />
pH on the rheological properties of 3 samples of the formulated<br />
tomato ketchups at pH levels <strong>3.</strong>5, 4.0 and 4.5. This pH<br />
range is most common for tomato ketchups. In recent years<br />
rheological properties of food products have become increasingly<br />
important in the formulation of food and the optimization<br />
of food processing.<br />
Experimental<br />
Three samples of tomato ketchup were prepared in laboratory<br />
conditions. The tomato paste with tomato soluble solids<br />
30 % and guar gum cames from the company Kolagrex Int.,<br />
s.r.o., Kolárovo, Slovak Republic. Some ingredients such as<br />
Fig. 1. Flow curves of the studied ketchup samples at shear<br />
rate 0–1,000 s –1 and temperature 25 ± 1 °C<br />
s787<br />
Isosweet and Resistamyl 348 were from Amylum Slovakia,<br />
s.r.o., Boleráz, Slovak Republic and other were purchased<br />
from local market.<br />
T o m a t o K e t c h u p P r e p a r a t i o n<br />
The 100 g of tomato ketchup samples were prepared<br />
following the recipe: 35 g of tomato paste (TSS 30 %)<br />
mixed with ingredients typically used in ketchup preparation<br />
(15 g of isosweet, 11.5 g of vinegar, 1.5 g of salt, 2 g<br />
of resistamyl 348, 0.1 g of guar gum and 34.9 g of water).<br />
The pH level of the mixture was modified at level <strong>3.</strong>5 (A1),<br />
4.0 (A2) or 4.5 (A3) and followed by stirring for 5 min. The<br />
mixture was heated and stirred constantly until temperature<br />
between 80–85 °C reached. Ketchup samples were then stored<br />
at ambient temperature (25 °C) for 24 h before analyses.<br />
R h e o l o g i c a l M e a s u r e m e n t<br />
The rheological measurements of this study were carried<br />
out using the rotational viscometer (controlled rate mode)<br />
HAAKE Viscotester VT 550 (Haake, Karlsruhe, Germany)<br />
with coaxial cylinder measuring sensor systems MV DIn<br />
53019. The Viscotester VT 550 was computer-operated with<br />
the application software RheoWin Job Manager and data<br />
evaluation software RheoWin Data Manager (ThermoHaake,<br />
Karlsruhe, Germany).<br />
Flow curves (the graphical correlation between shear<br />
stress τ and shear rate D) were measured at a continuously<br />
increasing shear rate ramp over 3 min from 0 to 1000 s –1 . The<br />
apparent viscosity:<br />
η a = τ/D (1)<br />
The thermal stability of the studied samples was measured<br />
at the low shear rate of 10 s –1 after 3 min of shearing.<br />
Results<br />
From the shape of the flow curves, which are demonstrated<br />
on the Fig. 1., it is possible to get the important information<br />
about rheological character of each ketchup sample.<br />
All 3 samples behave as non-newtonian fluids, of which<br />
shear stress and apparent viscosity was changed with rate of<br />
dynamic strain. Rheograms confirmed their pseudoplastic<br />
characters too.<br />
Viscosity curves (Fig. 2.) were constructed by conversion<br />
of values of flow curves. From their shape it is possible<br />
to set viscosity of the product at specific shear rates to which<br />
will be product exposed during dispersion, mixing, pumping,<br />
and filling to container as well as during application<br />
with consumer. The highest apparent viscosity during shear<br />
rate range 10–1,000 s –1 was determined in ketchup sample<br />
A1 with pH <strong>3.</strong>5. Decreasing in the apparent viscosity was<br />
followed by sample A2 with pH 4.0 and then by sample A3<br />
with pH 4.5.The requirement putting on some food products<br />
exposed to the specified temperature range is that its viscosity<br />
changed minimally. The effect of temperature on viscosity of<br />
ketchup samples is showed in Fig. <strong>3.</strong> Ketchups should have