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 />
P63 FATTy ACIDS LIKE MARKERS OF<br />
PROCESSED ChEESE ChANGES DuRING<br />
STORAGE<br />
BLAnKA LOUPAnCOVá, EVA VíTOVá, HAnA<br />
ŠTOUDKOVá and FRAnTIŠEK BUňKA<br />
Institute of Food Science and Biotechnology, Faculty of<br />
Chemistry, Brno University of Technology, Purkyňova 118,<br />
612 00 Brno<br />
blankaloupancova@seznam.cz<br />
Introduction<br />
Pasteurized processed cheese products are cheese-based<br />
food produced by comminuting, blending and melting one or<br />
more natural cheeses and optional ingredients into a smooth<br />
homogenous blend with the aid of heat, mechanical shear and<br />
usually emulsifying salts.<br />
Optional ingredients which are determined by the product<br />
type include dairy ingredients, vegetables, meats, stabilizers,<br />
emulsifying salts, flavours, colours, preservatives<br />
and water 1,2 . Dairy ingredients means butter, cottage cheese,<br />
milk concentrates (e.g. skimmed milk powder, whey powder,<br />
caseinates).<br />
Chemical composition of processed cheese depends<br />
on a processed cheese type and raw materials used 3 .<br />
Although the dairy products fall into the class of so<br />
called non-acid foodstuffs and suitable methods must be used<br />
to prolong their durability, the processed cheese was proposed<br />
as a part of Combat Ratio. The Combat Ratio serves<br />
for nutrition of soldiers in specific combat situations such as<br />
separation from a unit, battle, etc. 3 . There are special requirements<br />
for a minimum durability of individual components of<br />
Combat Ration which has been set as 24 months depending<br />
on an ambient temperature 4 .<br />
Practically the only method of achieving the 24 month<br />
durability of processed cheese is the thermo-sterilization. In<br />
the article the effect of a defined sterilization heating and<br />
storage conditions, such as temperature and time, on changes<br />
of fatty acids contents in sterilized processed cheese was<br />
investigated.<br />
Experimental<br />
Processed cheese (40 % dry matter, 45 % fat in dry matter)<br />
was manufactured following the traditional technology<br />
process in a selected dairy. The processing temperature was<br />
91 °C, total time of heating was 5 minutes. Cheeses were than<br />
sterilized at 117 °C for 20 minutes and then cooled down to<br />
10 °C in 2 hours.<br />
Cheese samples were stored at 6 ± 2 °C, 23 ± 2 °C and<br />
40 ± 2 °C during 24 month.<br />
E x t r a c t i o n o f F a t<br />
The cheese sample (5.0 g) was heated with 15 ml of<br />
hydrochloric acid in boiling water bath until it dissolves and<br />
then still 20 minutes.<br />
s714<br />
Ethanol (15 ml), diethyl ether and petrol ether (both<br />
30 ml), were added into stirred mixture after cooling down.<br />
Closed flask was shaken and then allowed to separate the<br />
water and organic phases. The upper (organic) phase was displaced<br />
by the pipette to dried weighed flask. next the water<br />
phase was reextracted with 15 ml of diethyl ether and 15 ml<br />
of petrol ether two times.<br />
The rest of organic solvent was evaporated in 60 °C<br />
water bath (to dispose smell). Flask with fat sample was dried<br />
at 105 °C for one hour 1 .<br />
M e t h a n o l E s t e r i f i c a t i o n M e t h o d<br />
The fat sample (5.0 g) was saponified with 50 ml methanolic<br />
solution of potassium hydroxide (c = 0.5 mol dm –3 ) for<br />
30 minutes in distilling flask with condenser and was esterified<br />
after neutralization by sulphuric acid on methyl orange<br />
for 30 minutes again.<br />
After cooling methyl esters were shaken with 10 ml<br />
of heptane three times. The extract was dried by anhydrous<br />
sodium sulphate and filtered to a 50 ml volumetric flask<br />
again. Both heptane portions were rinsed with 20 ml of water<br />
twice. The extract was dried by anhydrous sodium sulphate<br />
and filtered to a 50 ml volumetric flask and filled up to the<br />
mark with heptane 5 .<br />
G C A n a l y s i s<br />
Prepared heptane methyl esters solutions were injected<br />
to gas chromatograph using autosampler.<br />
GC conditions: gas chromatograph TRACE GC (ThermoQuest<br />
Italia S. p. A., I) equipped with flame ionization detector,<br />
split/splitless injector and capillary column SPTM 2560<br />
(100 m × 0.25 mm × 0.2 μm) with the temperature programme<br />
60 °C held for 2 min, ramp 10 °C min –1 up to 220 °C, held for<br />
20 min. The injector temperature was 250 °C and the detector<br />
temperature was 220 °C. The flow rate of the carrier gas n 2<br />
was 1.2 ml min –1 .<br />
Results<br />
This work deals with the fatty acids included in processed<br />
cheese. The most abundant fatty acids such as lauric,<br />
Fig. 1. Influence of the storage time on the amount of fatty<br />
acids (cheeses stored at 6 ± 2 °C) (mg g –1 of cheese)