3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
P63 FATTy ACIDS LIKE MARKERS OF
PROCESSED ChEESE ChANGES DuRING
STORAGE
BLAnKA LOUPAnCOVá, EVA VíTOVá, HAnA
ŠTOUDKOVá and FRAnTIŠEK BUňKA
Institute of Food Science and Biotechnology, Faculty of
Chemistry, Brno University of Technology, Purkyňova 118,
612 00 Brno
blankaloupancova@seznam.cz
Introduction
Pasteurized processed cheese products are cheese-based
food produced by comminuting, blending and melting one or
more natural cheeses and optional ingredients into a smooth
homogenous blend with the aid of heat, mechanical shear and
usually emulsifying salts.
Optional ingredients which are determined by the product
type include dairy ingredients, vegetables, meats, stabilizers,
emulsifying salts, flavours, colours, preservatives
and water 1,2 . Dairy ingredients means butter, cottage cheese,
milk concentrates (e.g. skimmed milk powder, whey powder,
caseinates).
Chemical composition of processed cheese depends
on a processed cheese type and raw materials used 3 .
Although the dairy products fall into the class of so
called non-acid foodstuffs and suitable methods must be used
to prolong their durability, the processed cheese was proposed
as a part of Combat Ratio. The Combat Ratio serves
for nutrition of soldiers in specific combat situations such as
separation from a unit, battle, etc. 3 . There are special requirements
for a minimum durability of individual components of
Combat Ration which has been set as 24 months depending
on an ambient temperature 4 .
Practically the only method of achieving the 24 month
durability of processed cheese is the thermo-sterilization. In
the article the effect of a defined sterilization heating and
storage conditions, such as temperature and time, on changes
of fatty acids contents in sterilized processed cheese was
investigated.
Experimental
Processed cheese (40 % dry matter, 45 % fat in dry matter)
was manufactured following the traditional technology
process in a selected dairy. The processing temperature was
91 °C, total time of heating was 5 minutes. Cheeses were than
sterilized at 117 °C for 20 minutes and then cooled down to
10 °C in 2 hours.
Cheese samples were stored at 6 ± 2 °C, 23 ± 2 °C and
40 ± 2 °C during 24 month.
E x t r a c t i o n o f F a t
The cheese sample (5.0 g) was heated with 15 ml of
hydrochloric acid in boiling water bath until it dissolves and
then still 20 minutes.
s714
Ethanol (15 ml), diethyl ether and petrol ether (both
30 ml), were added into stirred mixture after cooling down.
Closed flask was shaken and then allowed to separate the
water and organic phases. The upper (organic) phase was displaced
by the pipette to dried weighed flask. next the water
phase was reextracted with 15 ml of diethyl ether and 15 ml
of petrol ether two times.
The rest of organic solvent was evaporated in 60 °C
water bath (to dispose smell). Flask with fat sample was dried
at 105 °C for one hour 1 .
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
The fat sample (5.0 g) was saponified with 50 ml methanolic
solution of potassium hydroxide (c = 0.5 mol dm –3 ) for
30 minutes in distilling flask with condenser and was esterified
after neutralization by sulphuric acid on methyl orange
for 30 minutes again.
After cooling methyl esters were shaken with 10 ml
of heptane three times. The extract was dried by anhydrous
sodium sulphate and filtered to a 50 ml volumetric flask
again. Both heptane portions were rinsed with 20 ml of water
twice. The extract was dried by anhydrous sodium sulphate
and filtered to a 50 ml volumetric flask and filled up to the
mark with heptane 5 .
G C A n a l y s i s
Prepared heptane methyl esters solutions were injected
to gas chromatograph using autosampler.
GC conditions: gas chromatograph TRACE GC (ThermoQuest
Italia S. p. A., I) equipped with flame ionization detector,
split/splitless injector and capillary column SPTM 2560
(100 m × 0.25 mm × 0.2 μm) with the temperature programme
60 °C held for 2 min, ramp 10 °C min –1 up to 220 °C, held for
20 min. The injector temperature was 250 °C and the detector
temperature was 220 °C. The flow rate of the carrier gas n 2
was 1.2 ml min –1 .
Results
This work deals with the fatty acids included in processed
cheese. The most abundant fatty acids such as lauric,
Fig. 1. Influence of the storage time on the amount of fatty
acids (cheeses stored at 6 ± 2 °C) (mg g –1 of cheese)